Electric power steering apparatus

Abstract

An electric power steering apparatus of a vector control system that drives and controls a motor by an inverter and applies an assist torque to a steering system of a vehicle, including the first compensation function to perform a dead time (DT) compensation based on respective phase motor terminal voltages and respective phase duty command values, the second compensation function to perform a DT compensation based on steering assist command values, the third compensation function to perform the DT compensation based on dq-axis current command values, and a temperature detecting section to detect temperature of ECU, wherein the correction of the DT compensation is performed based on the temperature, wherein switches of the compensation functions are performed by using a conditional branch due to software and a gradual-changing switch, wherein the dq-axis DT compensation values after the conditional branch and the gradual-changing switch are performed are calculated, and wherein the dq-axis voltage command values are compensated by the dq-axis DT compensation values.

Claims

1. An electric power steering apparatus of a vector control system that calculates dq-axis steering assist command values based on at least a steering torque, calculates dq-axis current command values from said dq-axis steering assist command values, converts dq-axis voltage command values calculated from said dq-axis current command values into duty command values of three phases, drives and controls a three-phase brushless motor by an inverter of a pulse width modulation (PWM) control, and applies an assist torque to a steering system of a vehicle, comprising: a first compensation function to perform a dead time compensation A based on respective phase motor terminal voltages and said duty command values; a second compensation function to perform a dead time compensation B based on said dq-axis steering assist command values; and a third compensation function to perform a dead time compensation C based on said dq-axis current command values, wherein switches of said first compensation function, said second compensation function and said third compensation function are performed by using a conditional branch due to software and a gradual-changing switch, wherein dq-axis dead time compensation values are calculated, and wherein said dq-axis voltage command values are compensated by said dq-axis dead time compensation values.

2. The electric power steering apparatus according to claim 1, wherein said gradual-changing switch is used in a case that a switch difference of a compensation amount in a switching time is small and said conditional branch is used in a case that a quickness of switch timing is needed.

3. The electric power steering apparatus according to claim 1, wherein a motor rotational angle, a motor rotational velocity and an inverter applying voltage are further used in calculations of said first compensation function, said second compensation function and said third compensation function.

4. The electric power steering apparatus according to claim 1, further comprising: a temperature detecting section to detect a temperature of said inverter or a temperature near said inverter, wherein said temperature detecting section performs dead time corrections of said dead time compensation B and said dead time compensation C based on said temperature.

5. An electric power steering apparatus of a vector control system that calculates dq-axis steering assist command values based on at least a steering torque, calculates dq-axis current command values from said dq-axis steering assist command values, converts dq-axis voltage command values calculated from said dq-axis current command values into duty command values of three phases, drives and controls a three-phase brushless motor by an inverter of a pulse width modulation (PWM) control, and applies an assist torque to a steering system of a vehicle, comprising: a dead time compensating section A to calculate a compensation value CA based on respective phase motor terminal voltages, said duty command values, a motor rotational angle, a motor rotational velocity and an inverter applying voltage; a dead time compensating section B to calculate a compensation value CB based on said dq-axis steering assist command values, said motor rotational angle, said motor rotational velocity and said inverter applying voltage; a dead time compensating section C to calculate a compensation value CC based on said dq-axis current command values, said motor rotational angle, said motor rotational velocity and said inverter applying voltage; and a compensation value switching section to input said compensation value CA, said compensation value CB, said compensation value CC, and a switch condition which is determined by said dq-axis steering assist command values, said dq-axis current command values and said motor rotational velocity, to perform a switching of said compensation value CA, said compensation value CB and said compensation value CC using a conditional branch due to software and a gradual-changing switch depending on a judged condition, and to calculate dq-axis dead time compensation values, wherein said dq-axis voltage command values are compensated by said dq-axis dead time compensation values.

6. The electric power steering apparatus according to claim 5, wherein said compensation value switching section comprises: a switch judging section to input said dq-axis current command values and said motor rotational velocity, perform a switch judgment and output a switch judgment flag; a conditional branch section to input said compensation values CB and CC and output dq-axis compensation values CD using said conditional branch based on said switch judgment flag; a gradual-changing section to judge said gradual-changing switch based on said dq-axis steering assist command values and calculate gradual-changing ratios; and a gradual-changing switching section to input said compensation value CA and said dq-axis compensation values CD and calculate and output said dq-axis dead time compensation values using said gradual-changing ratios.

7. The electric power steering apparatus according to claim 6, wherein said gradual-changing section comprises: a gradual-changing switch judging section to judge said gradual-changing switch based on said dq-axis steering assist command values and output an UP-DOWN judgment flag; and a gradual-changing ratio calculating section to calculate said gradual-changing ratios based on said UP-DOWN judgment flag.

8. The electric power steering apparatus according to claim 7, wherein said gradual-changing ratios are a gradual-changing ratio RA for said compensation value CA and a gradual-changing ratio RBC for said compensation values CB and CC, and wherein said gradual-changing switching section comprises: a first multiplying section to multiply said compensation value CA with said gradual-changing ratio RA; a second multiplying section to multiply said dq-axis command CD with said gradual-changing ratio RBC; and an adding section to add with a multiplied result of said first multiplying section and a multiplied result of said second multiplying section and output said dq-axis dead time compensation values.

9. An electric power steering apparatus of a vector control system that calculates dq-axis steering assist command values based on at least a steering torque, calculates dq-axis current command values from said dq-axis steering assist command values, converts dq-axis voltage command values calculated from said dq-axis current command values into duty command values of three phases, drives and controls a three-phase brushless motor by an inverter of a pulse width modulation (PWM) control, and applies an assist torque to a steering system of a vehicle, comprising: a temperature detecting section to detect a temperature of said inverter or a temperature near said inverter; a dead time compensating section A to calculate a compensation value CA based on respective phase motor terminal voltages, said duty command values, a motor rotational angle, a motor rotational velocity and an inverter applying voltage; a dead time compensating section B to calculate a compensation value CB based on said dq-axis steering assist command values, said motor rotational angle, said motor rotational velocity, said inverter applying voltage and said temperature; a dead time compensating section C to calculate a compensation value CC based on said dq-axis current command values, said motor rotational angle, said motor rotational velocity, said inverter applying voltage and said temperature; and a compensation value switching section to input said compensation value CA, said temperature-corrected compensation value CB, said temperature-corrected compensation value CC, and a switch condition which is determined by said dq-axis steering assist command values, said dq-axis current command values and said motor rotational velocity, to perform a switching of said compensation value CA, said compensation value CB and said compensation value CC using a conditional branch due to software and a gradual-changing switch based on said steering assist command values and a motor rotational number, and to calculate dq-axis dead time compensation values, wherein said dq-axis voltage command values are compensated by temperature-corrected dq-axis dead time compensation values.

10. The electric power steering apparatus according to claim 9, wherein said gradual-changing switch comprises: a gradual-changing switch judging section to input said steering assist command value and said motor rotational number and output a switch counting value; and a gradual-changing ratio calculating section to input said switch counting value and calculate a gradual-changing switch ratio.

11. The electric power steering apparatus according to claim 10, wherein said gradual-changing switch judging section comprises: a current factor section to output a q-axis current-factor switch COUNT-UP value or a q-axis current-factor switch COUNT-DOWN value based on said dq-axis steering assist command values; a rotational number factor section to output a rotational number-factor switch COUNT-UP value or a rotational number-factor switch COUNT-DOWN value based on said motor rotational number; and an adding section to output a switch counting value by adding with said q-axis current-factor switch COUNT-UP value or said q-axis current-factor switch COUNT-DOWN value and said rotational number-factor switch COUNT-UP value or said rotational number-factor switch COUNT-DOWN value.

12. The electric power steering apparatus according to claim 10, wherein said gradual-changing ratio calculating section comprises: a counting-value limiting section to input an added value which is added with said switch counting value and a previous value of a second gradual-changing ratio; and a subtracting section to output a first gradual-changing ratio which is calculated by subtracting said second gradual-changing ratio from a fixed value 100%.

13. An electric power steering apparatus of a vector control system that calculates dq-axis steering assist command values based on at least a steering torque, calculates dq-axis current command values from said dq-axis steering assist command values, converts dq-axis voltage command values calculated from said dq-axis current command values into duty command values of three phases, drives and controls a three-phase brushless motor by an inverter of a pulse width modulation (PWM) control, and applies an assist torque to a steering system of a vehicle, comprising: a first compensation function to perform a dead time compensation A based on respective phase motor terminal voltages and said duty command values; a second compensation function to perform a dead time compensation B based on said dq-axis steering assist command values; and a third compensation function to perform a dead time compensation C based on said dq-axis current command values, wherein switches of said first compensation function, said second compensation function and said third compensation function are performed by using a conditional branch due to software and a gradual-changing switch based on said dq-axis steering assist command values and a motor rotational number, wherein said gradual-changing switch is performed by a nonlinear function, wherein dq-axis dead time compensation values after said conditional branch and said gradual-changing switch are performed are calculated, and wherein said dq-axis voltage command values are compensated by said dq-axis dead time compensation values.

14. The electric power steering apparatus according to claim 13, wherein said nonlinear function comprises a gradual-changing ratio characteristic conversion table having a nonlinear characteristic which is disposed at a subsequent stage of a counting-value limiting section after switching to a COUNT-UP value or a COUNT-DOWN value.

15. The electric power steering apparatus according to claim 13, wherein said nonlinear function comprises: a COUNT-UP value calculation processing section which is sensitive to a motor rotational number and has a nonlinear characteristic; and a COUNT-DOWN value calculation processing section which is sensitive to a motor rotational number and has a nonlinear characteristic, and serves as an output switch between said COUNT-UP value calculation processing section and said COUNT-DOWN value calculation processing section.

16. The electric power steering apparatus according to claim 13, further comprising a temperature detecting section to detect a temperature of said inverter or a temperature near said inverter, wherein said temperature detecting section corrects said second compensation function and said third compensation function based on said temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the accompanying drawings:

(2) FIG. 1 is a configuration diagram showing a general outline of an electric power steering apparatus;

(3) FIG. 2 is a block diagram showing a configuration example of a control unit (ECU) of the electric power steering apparatus;

(4) FIG. 3 is a block diagram showing a configuration example of a vector control system;

(5) FIG. 4 is a wiring diagram showing a configuration example of a general inverter;

(6) FIG. 5 is a block diagram showing a configuration example (the first embodiment) of the present invention;

(7) FIG. 6 is a block diagram showing a configuration example of a dead time compensating section (A);

(8) FIG. 7 is a block diagram showing a configuration example of a midpoint voltage estimating section;

(9) FIG. 8 is a block diagram showing a detail configuration example of the correction timing judging section and the correction value holding section;

(10) FIG. 9 is a block diagram showing a detail configuration example of the correction-amount limiting section;

(11) FIG. 10 is a characteristic chart showing an example of an upper limit value of the compensation amount;

(12) FIG. 11 is a block diagram showing a configuration example (the first example) of a dead time compensating section (B);

(13) FIG. 12 is a block diagram showing a configuration example of a current command value-sensitive gain section;

(14) FIG. 13 is a characteristic diagram showing a gain section in the current command value-sensitive gain section;

(15) FIG. 14 is a characteristic diagram showing a characteristic example of the current command value-sensitive gain section;

(16) FIGS. 15A and 15B are waveform charts showing an operation example of a compensation sign estimating section;

(17) FIG. 16 is a block diagram showing a configuration example of an inverter applying voltage-sensitive gain calculating section;

(18) FIG. 17 is a characteristic diagram showing a characteristic example of the inverter applying voltage-sensitive gain calculating section;

(19) FIG. 18 is a characteristic diagram showing a characteristic example of a phase adjusting section;

(20) FIG. 19 is a diagram showing an operation example of a respective phase angle-dead time compensation value function section;

(21) FIG. 20 is a block diagram showing a configuration example (the first example) of a dead time compensating section (C);

(22) FIG. 21 is a block diagram showing a configuration example of an inverter applying voltage-sensitive compensation-amount calculating section;

(23) FIG. 22 is a characteristic diagram showing a characteristic example of the inverter applying voltage-sensitive compensation-amount calculating section;

(24) FIG. 23 is a waveform chart showing an example of an output waveform of a three-phase current command value model;

(25) FIGS. 24A and 24B are waveform charts showing an operation example of a phase current compensation sign estimating section;

(26) FIG. 25 is a block diagram showing a configuration example of a switch judging section;

(27) FIG. 26 is a block diagram showing a detail configuration example of a gradual-changing switch judging section (the first example);

(28) FIG. 27 is a block diagram showing a detail configuration example of a gradual-changing ratio calculating section (the first example);

(29) FIG. 28 is a characteristic diagram showing a characteristic example of the gradual-changing ratio;

(30) FIG. 29 is a flowchart showing an operation example of dead time compensation;

(31) FIG. 30 is a flowchart showing another operation example of the dead time compensation;

(32) FIG. 31 is a block diagram showing a detail configuration example of the gradual-changing ratio calculating section (the second example);

(33) FIG. 32 is a block diagram showing a detail configuration example of the gradual-changing ratio calculating section (the third example);

(34) FIG. 33 is a block diagram showing a detail configuration example of the gradual-changing ratio calculating section (the fourth example);

(35) FIG. 34 is a block diagram showing a configuration example of a space vector modulating section;

(36) FIG. 35 is a diagram showing an operation example of the space vector modulating section;

(37) FIG. 36 is a diagram showing an operation example of the space vector modulating section;

(38) FIG. 37 is a timing chart showing an operation example of the space vector modulating section;

(39) FIG. 38 is a waveform chart showing an effect of the space vector modulation;

(40) FIG. 39 is a waveform chart showing an example of a switch operation in the dead time compensation value of the present invention;

(41) FIG. 40 is a waveform chart showing an effect of the present invention (the first embodiment);

(42) FIG. 41 is a waveform chart showing an effect of the present invention (the first embodiment);

(43) FIG. 42 is a waveform chart showing an effect of the present invention (the first embodiment);

(44) FIG. 43 is a block diagram showing a configuration example (the second embodiment) of the present invention;

(45) FIG. 44 is a block diagram showing a configuration example (the second example) of a dead time compensating section (B);

(46) FIG. 45 is a characteristic diagram showing a characteristic example of a temperature-sensitive gain calculating section;

(47) FIG. 46 is a characteristic diagram showing a characteristic example of the temperature-sensitive gain calculating section;

(48) FIG. 47 is a block diagram showing a configuration example (the second example) of a dead time compensating section (C);

(49) FIG. 48 is a characteristic diagram showing a characteristic example of the temperature-sensitive gain calculating section;

(50) FIG. 49 is a characteristic diagram showing a characteristic example of the temperature-sensitive gain calculating section;

(51) FIG. 50 is a block diagram showing a configuration example of the gradual-changing switch judging section (the second example);

(52) FIG. 51 is a block diagram showing a configuration example of the gradual-changing ratio calculating section (the second example);

(53) FIGS. 52A, 52B and 52C are waveform charts showing current waveform examples in a case that temperature compensation is not performed;

(54) FIGS. 53A, 53B and 53C are waveform charts showing current waveform examples in a case that the temperature compensation is not performed;

(55) FIGS. 54A, 54B and 54C are waveform charts showing current waveform examples in a case that the temperature compensation is not performed;

(56) FIGS. 55A, 55B and 55C are waveform charts showing an effect of the present invention (the second embodiment);

(57) FIGS. 56A, 56B and 56C are waveform charts showing an effect of the present invention (the second embodiment); and

(58) FIGS. 57A, 57B and 57C are waveform charts showing an effect of the present invention (the second embodiment).

MODE FOR CARRYING OUT THE INVENTION

(59) In order to resolve a problem that a current distortion and a torque ripple occur due to an influence of a dead time of an inverter in a control unit (ECU) and a steering sound is louder, in calculating a dead time compensation value of the inverter, the present invention switches a dead time compensation function to the dead time compensation function (A) of the inverter based on respective phase motor terminal voltages and respective phase duty command values, the dead time compensation function (B) based on functions depending on a motor rotational angle (an electrical angle) or the dead time compensation function (C) based on a current command value model, under the predetermined conditions. That is, the present invention calculates the dead time compensation value by using the gradual-changing switch for the accuracy-weight when a difference between the switching compensation amounts is large, and by using a conditional branch due to software (a switch type) for a speed-weight when the speed of the switch timing is required, and compensates the dead time compensation value on the dq-axis by using a feed-forward control.

(60) In the dead time compensation function with a single function and a single algorithm, the dead time compensation value is accurately compensated during the low speed steering. However, the compensation accuracy decreases during the high speed steering. Conversely, the dead time compensation value can be accurately compensated during the high speed steering, and the compensation accuracy can decrease during the low speed steering. In the low load and the low speed steering state, in a case that the switch is instantaneously switched, since the dead time compensation values are changed in a step shape or discontinuously from the differences among the compensation values of the respective functions, the torque ripple can be occurred. In the high speed steering state, when the dead time compensation functions are switched by the gradual-changing, the phase of the compensation values can be deviated during the period of the gradual-changing switch. Therefore, in the dead time compensation function with a single function and a single algorithm, it is difficult to accurately compensate the compensation value in a whole steering region. In a case that the switch of the compensation value is performed by the single function (the single switch), the performance can be deteriorated. However, the present invention prepares the plural dead time compensation functions having the high compensation accuracy depending on the steering conditions, switches to the optimal dead time compensation function depending on the steering state, and separately uses the switch means of the instantaneous conditional branch due to the software and that of the gradual-changing switch. Thereby, the present invention can perform the dead time compensation having the high compensation accuracy over all steering regions.

(61) The present invention performs the dead time compensation based on the plural compensation functions for the d-axis and q-axis voltage command values of the dq-axis vector control system independently and respectively, and switches the plural dead time compensation functions depending on the predetermined conditions which are determined by the d-axis current command value, the q-axis current command value and the motor rotational velocity. Thereby, the optimal dead time compensation value can be selected over all steering regions which include the low speed steering region, the medium speed steering region and the high speed steering region.

(62) In embodiments of the present invention, the dead time compensation function (A) based on the respective phase motor terminal voltages, the respective phase duty command values, the motor rotational angle, the motor rotational velocity and the inverter applying voltage, the dead time compensation function (B) based on steering assist command values, the motor rotational angle, the motor rotational velocity and the inverter applying voltage, and the dead time compensation function (C) based on the dq-axis current command values, the motor rotational angle, the motor rotational velocity and the inverter applying voltage are used, the switch judgment by using the dq-axis current command values and the motor rotational velocity is performed, the dead time compensation functions (B) and (C) are switched by the conditional branch due to the software, and the switch between the dead time compensation function (A) and the dead time compensation (B) or (C) is performed by the gradual-changing using the steering assist command value. In the switch between the dead time compensation functions (B) and (C), the conditional branch due to the software (the switch type) which can instantaneously be switched for the speed-weight is used. In the switch between the dead time compensation function (A) and the dead time compensation function (B) or (C), the gradual-changing which is for an accuracy-weight and is required for the constant time in switching is used.

(63) In the present invention, since the dead time compensation functions (B) and (C) are corrected depending on the temperature of the ECU (the temperature of the inverter or the temperature near the inverter), and the motor rotational velocity (the motor rotational number) and the steering assist command value (iqref) are considered in the gradual-changing switch operation, the finer and more accurate dead time compensation can be realized.

(64) Typical motor rotational numbers are depending on the kind of the motor and the reduction ratio of the reduction gears 3 of the EPS. For example, the motor rotational number of the low speed steering region is in a range of 0 [rpm] to 300 [rpm], the motor rotational number of the middle speed steering region is in a range of 300 [rpm] to 1800 [rpm], and the motor rotational number of the high speed steering region is in a range of 1800 [rpm] to 4000 [rpm]. The above high motor rotational number is equal to or more than the rated rotational number of the motor and is a rotational number region that a weak-field control is required.

(65) Embodiments according to the present invention will be described with reference to the accompanying drawings.

(66) FIG. 5 shows a whole configuration example (the first embodiment) of the present invention corresponding to FIG. 3, and there is provided a dead time compensating section (A) 200 to calculate compensation values CdA and CqA on the dq-axes, a dead time compensating section (B) 400 to calculate compensation values CdB and CqB on the dq-axis, a dead time compensating section (C) 600 to calculate compensation values CdC and CqC on the dq-axes, and a compensation value switching section 500 to switch the compensation values CdA and CqA, the compensation values CdB and CqB and the compensation values CdC and CqC depending on the predetermined conditions and the functions, calculate the dead time compensation values v.sub.d* and v.sub.q* on the dq-axes and output the dead time compensation values v.sub.d* and v.sub.q* on the dq-axes. The compensation function of the dead time compensating section (A) 200 enables to compensate without chattering in the low load and low speed steering state near the on-center position of the handle, the compensation function of the dead time compensating section (B) 400 has the high compensation accuracy in the low speed steering region and the middle speed steering region, and the compensation function of the dead time compensating section (C) 600 has the high compensation accuracy characteristic in the high speed steering region.

(67) Motor terminal voltages V.sub.u, V.sub.v and V.sub.w are inputted into the dead time compensating section 200 (the detail is described as below) via lowpass filters (LPFs) 163U, 163V and 163W for removing the noise. Duty command values Duty.sub.u, Duty.sub.v and Duty.sub.w from the duty command value calculating section 160A in the PWM-control section 160 are also inputted into the dead time compensating section (A) 200. Further, the motor rotational angle , the motor rotational velocity and the inverter applying voltage VR which is applied to the inverter 161 are inputted into the dead time compensating section (A) 200. The q-axis steering assist command value iqref corresponding to the steering assist command value Iref2, the inverter applying voltage VR, the motor rotational angle and the motor rotational velocity are inputted into the dead time compensating section (B) 400 (the detail is described as below). The d-axis current command value i.sub.d*, the q-axis current command value i.sub.q*, the motor rotational angle , the inverter applying voltage VR and the motor rotational velocity are inputted into the dead time compensating section (C) 600 (the detail is described as below).

(68) The compensation value switching section 500 comprises a switch judging section 510 to judge the switch (the switch of a conditional branch section) and output a switch judgment flag SF1, a conditional branch section 540 due to software (switch sections 541 and 542) to switch the compensation values CdB and CqB from the dead time compensating section (B) 400 or the compensation values CdC and CqC from the dead time compensating section (C) 600 and output the switched compensation values, and a gradual-changing switching section 550 which includes a gradual-changing switch judging section 520 to judge the gradual-changing switch based on the steering assist command value iqref and output an UP/DOWN judgment flag SF2, a gradual-changing ratio calculating section 530 to calculate the compensation values Cd and Cq from the conditional branch section 540 by the UP/DOWN judgment flag SF2, a gradual-changing ratio RtA (for example, 0 [%] to 100 [%]) of the compensation values CdA and CqA from the dead time compensating section (A) 200 and a gradual-changing ratio RtBC (for example, 100 [%] to 0 [%]), multiplying sections 551 to 554 and adding sections 555 and 556. A gradual-changing section comprises the gradual-changing switch judging section 520 and the gradual-changing ratio calculating section 530.

(69) The switch sections 541 and 542 of the conditional branch section 540 functionally have the contact points a1 and b1 and the contact points a2 and b2. The compensation value CdB is inputted into the contact point a1, the compensation value CdC is inputted into the contact point b1, the compensation value CqB is inputted into the contact point a2, and the compensation value CqC is inputted into the contact point b2. The contact points a1 and b1 of the switch section 541 and the contact points a2 and b2 of the switch section 542 are synchronously switched by the switch judgment flag SF1 from the switch judging section 510. That is, when the switch judgment flag SF1 is not inputted (for example, the logic is L), the contact points a1 and a2 are connected. When the switch judgment flag SF1 is inputted (for example, the logic is H), the contact points b1 and b2 are connected. The compensation values Cd and Cq are outputted from the conditional branch section 540, and are inputted into the multiplying section 552 and 554 in the gradual-changing switching section 550, respectively.

(70) Next, the dead time compensating section (A) 200 will be described.

(71) As shown in FIG. 6, the dead time compensating section (A) 200 comprises subtracting sections 201 (201u, 201v and 201w) and 202, a midpoint voltage estimating section 210, a respective phase applying voltage calculating section 220, a voltage detection delay model 230, a gain section 240, a compensation-amount limiting section 250 and a three-phase AC/dq-axes converting section 260. The motor rotational angle is inputted into the midpoint voltage estimating section 210 and the three-phase AC/dq-axes converting section 260, and the motor rotational velocity is inputted into the midpoint voltage estimating section 210. The motor terminal voltages V.sub.u, V.sub.v and V.sub.w are inputted into the midpoint voltage estimating section 210 and the subtracting sections 201u, 201v and 201w via the LPFs 163U, 163V and 163W. Further, the duties Duty.sub.u, Duty.sub.v and Duty.sub.w from the duty command value calculating section 160A in the PWM-control section 160 are inputted into the three-phase command voltage calculating section 220, and the inverter applying voltage VR is inputted into the midpoint voltage estimating section 210, the respective phase applying voltage calculating section 220 and the compensation amount limiting section 250.

(72) The midpoint voltage estimating section 210 calculates a reference voltage of midpoint voltages by using the inverter applying voltage VR. The detail configuration is shown in FIG. 7, since the midpoint voltages vary depending on the influence of a hardware configuration, a detection error and so on, the correction is performed based on the differences between the inverter applying voltage VR and the motor terminal voltages V.sub.u, V.sub.v and V.sub.w. The correction timing is adjusted under conditions of a specific motor rotational angle and a specific motor rotational velocity . Namely, the inverter applying voltage VR is reduced by half (VR/2) in a half reducing section 211 and the half-reduced value (VR/2) is addition-inputted into subtracting sections 217 and 218. The motor terminal voltages V.sub.u, V.sub.v and V.sub.w are inputted into the adding section 216 and are added, the added result V.sub.u+V.sub.v+V.sub.w is -multiplied at a dividing section () 212, and a -multiplied voltage (V.sub.u+V.sub.v+V.sub.w)/3 is subtraction-inputted into the subtracting section 217. The subtracting section 217 subtracts the voltage (V.sub.u+V.sub.v+V.sub.w)/3 from the half-reduced value VR/2, and the subtracted result VR.sub.na, is inputted into a correction value holding section 214. A correction timing judging section 213 judges a correction timing based on the motor rotational angle and the motor rotational velocity and inputs a correction signal CT to the correction value holding section 214. The correction-amount limiting section 215 calculates a voltage correction value V.sub.m based on a voltage VR.sub.nb held in the correction value holding section 214.

(73) The details of the correction timing judging section 213 and the correction value holding section 214 are shown in FIG. 8, the correction timing judging section 213 comprises an angle judging section 213-1, an effective rotational velocity judging section 213-2 and an AND-circuit 213-3, and the correction value holding section 214 comprises a switching section 214-1 and a holding unit (Z.sup.1) 214-2. That is, the motor rotational angle is inputted into the angle judging section 213-1 and the judgment is performed by using the below Expression 1. When the Expression 1 is established, the angle judging section 213-1 outputs a judging signal JD1.
179[deg]<<180[deg][Expression 1]

(74) Since the calculation at the point where the phase voltage is zero-crossed as the midpoint correction value has a high accuracy, the angle near 180 [deg] of the motor rotational angle where the U-phase voltage is zero-crossed is set as the correction condition. Further, when the motor rotational velocity is high, since the influence of the back-EMF increases, it is impossible to perform the accurate correction calculation. Thus, the effective rotational velocity judging section 213-2 judges whether the motor rotational velocity is equal to or less than an effective rotational velocity .sub.0 being capable of correction-calculating, or not. When the motor rotational velocity is equal to or less than the effective rotational velocity .sub.0, the effective rotational velocity judging section 213-2 outputs the judging signal JD2.
.sub.0[Expression 2]

(75) The judging signals JD1 and JD2 are inputted into the AND-circuit 213-3, and the correction signal CT is outputted in accordance with the AND-condition that the judging signals JD1 and JD2 are inputted. The correction signal CT is inputted into the switching section 214-1 in the correction value holding section 214 as a switching signal and switches contact points a and b. The subtracted result VR.sub.na is inputted into the contact point a, and the output voltage VR.sub.nb is inputted into the contact point b via the holding unit (Z.sup.1) 214-2. The correction value holding section 214 holds a value in order to output a stable correction value till a next timing. Further, in a case that the correction amount is clearly greater than a normal value due to the noise, the back-EMF, the correction timing miss-judgment and so on, the correction-amount limiting section 215 judges that the present correction amount is not right and limits the maximum correction value. The voltage correction value V.sub.m which is limited by the maximum correction value is inputted into the subtracting section 218, and the midpoint voltage estimation value V.sub.m calculated in accordance with the below Expression 3 at the subtracting section 218 is outputted. The midpoint voltage estimation value V.sub.m is subtraction-inputted into the subtracting sections 201u, 201v and 201w.

(76) $\begin{array}{cc}{V}_m=\frac{\mathrm{VR}}{2}-V_m& \left[\mathrm{Expression}3\right]\end{array}$

(77) Furthermore, the respective phase duty command values Duty.sub.u, Duty.sub.v and Duty.sub.w and the inverter applying voltage VR are inputted into the respective phase applying voltage calculating section 220, and the respective phase applying voltage calculating section 220 calculates the respective phase applying voltages V.sub.in by using the below Expression 4 in accordance with the respective phase duty command values Duty.sub.u, Duty.sub.v and Duty.sub.w and the inverter applying voltage VR. The respective phase applying voltages V.sub.in are inputted into the voltage detection delay model 230. As well, Duty.sub.ref in the Expression 4 denotes Duty.sub.u, Duty.sub.v and Duty.sub.w.

(78) $\begin{array}{cc}{V}_{in}=\mathrm{VR}\frac{\left({\mathrm{Duty}}_{\mathrm{ref}}-{\mathrm{Duty}}_{50\%}\right)}{{\mathrm{Duty}}_{100\%}}& \left[\mathrm{Expression}4\right]\end{array}$

(79) The midpoint voltage estimation value V.sub.m is subtraction-inputted into the subtracting section 201 (201u, 201v and 201w), and further the terminal voltages V.sub.u, V.sub.v and V.sub.w passed the LPFs 163U, 163V and 163W are addition-inputted into the subtracting section 201 (201u, 201v and 201w). The subtracting sections 201u, 201v and 201w subtract the midpoint voltage estimation value V.sub.m from the respective phase terminal voltages V.sub.u, V.sub.v and V.sub.w in accordance with the below Expression 5. Thereby, respective phase detection voltages V.sub.dn (V.sub.du, V.sub.dv and V.sub.dw) are calculated. The respective phase detection voltages V.sub.dn (V.sub.du, V.sub.dv and V.sub.dw) are inputted into the subtracting section 202 serving as a respective phase loss voltage calculating section.
V.sub.du=V.sub.uV.sub.m
V.sub.dv=V.sub.vV.sub.m
V.sub.dw=V.sub.wV.sub.m[Expression 5]

(80) The detection of the terminal voltages V.sub.u, V.sub.v and V.sub.w has a delay due to a noise filter or the like in the ECU. Consequently, in a case that the loss voltages are directly calculated by obtaining the differences between the respective phase applying voltages V.sub.in and the respective phase detection voltages V.sub.dn the error occurs due to the phase difference. In order to resolve this problem, the present embodiment approximates the detection delay of the hardware such as a filter circuit as a first order filter model and improves the phase difference. The voltage detection delay model 230 of the present embodiment is a primary filter of the below Expression 6 and T denotes a filter time constant. The voltage detection delay model 230 may be a model of a secondary filter or higher order filter.

(81) $\begin{array}{cc}\frac{1}{\mathrm{Ts}+1}& \left[\mathrm{Expression}6\right]\end{array}$

(82) The respective phase applying voltages V.sub.in are addition-inputted to the subtracting section 202, and the respective phase detection voltages V.sub.dn are subtraction-inputted into the subtracting section 202. The respective phase loss voltages PLA (V.sub.loss_n) are calculated by subtracting the respective phase detection voltages V.sub.dn from the respective phase applying voltages V.sub.in. Namely, the below Expression 7 is performed in the subtracting section 202.
V.sub.loss_n=V.sub.inuV.sub.du
V.sub.loss_v=V.sub.invV.sub.dv
V.sub.loss_w=V.sub.inwV.sub.dw[Expression 7]

(83) The respective phase loss voltages PLA (V.sub.loss_n) are multiplied with a gain P.sub.G (for example, P.sub.G=0.8) at the gain section 240, and the respective phase loss voltages PLA multiplied with the gain P.sub.G are inputted into the compensation-amount limiting section 250. Although the gain P.sub.G is not basically needed to adjust, the gain P.sub.G is changed in a case that an output adjustment is needed when the adjustment for another compensator is performed, actual vehicle tuning is performed, or parts of the ECU are changed.

(84) The compensation-amount limiting section 250 is sensitive to the inverter applying voltage VR, and the detail configuration is shown in FIG. 9. The inverter applying voltage VR is inputted into a compensation-amount upper limit value calculating section 251 in the compensation-amount limiting section 250, and a compensation-amount upper limit value DTCa is calculated with a characteristic as shown in FIG. 10. The compensation-amount upper limit value DTCa is a constant limit value DTCa1 when the inverter applying voltage VR is lower than a predetermined voltage VR1, linearly (or non-linearly) increases when the inverter applying voltage VR is equal to or higher than the predetermined voltage VR1 and is lower than a predetermined voltage VR2 (>VR1), and holds a constant limit value DTCa2 when the inverter applying voltage VR is equal to or higher than the predetermined voltage VR2. The compensation-amount upper limit value DTCa is inputted into a contact point a1A of the switching section 252, a comparing section 255 and an inverting section 254. Further, the respective phase loss voltages PLB (V.sub.loss_u, V.sub.loss_v, V.sub.loss_w) are inputted into the comparing sections 255 and 256, and a contact point b1A of the switching section 252. An output DTCa of the inverting section 254 is inputted into a contact point a2A of the switching section 253. The contact points a1A and b1A are switched based on a compared result CP1 of the comparing section 255, and the contact points a2 and b2 are switched based on a compared result CP2 of the comparing section 256.

(85) The comparing section 255 compares the compensation-amount upper limit value DTCa with the respective phase loss voltages PLB and switches the contact points a1A and b1A of the switching section 252 in accordance with the below Expression 8. Further, the comparing section 256 compares the compensation-amount upper limit value DTCa with the respective phase loss voltages PLB and switches the contact points a2A and b2A of the switching section 253 in accordance with the below Expression 9.
When the respective phase loss voltages PLBthe compensation-amount upper limit value DTCa, the contact point a1A of the switching section 252 is ON.
When the respective phase loss voltages PLB<the compensation-amount upper limit value DTCa, the contact point b1A of the switching section 252 is ON.[Expression 8]
When the respective phase loss voltages PLBthe compensation-amount upper limit value DTCa, the contact point a2A of the switching section 253 is ON (the dead time compensation value DTC=DTCa).
When the respective phase loss voltages PLB<the compensation-amount lower-limit value DTCa, the contact point b2A of the switching section 253 is ON (the dead time compensation value DTC=the output of the switching section 252).[Expression 9]

(86) Next, the dead time compensating section (B) 400 (the first example) will be described.

(87) As shown in FIG. 11, the dead time compensating section (B) 400 comprises a current control delay model 401, a compensation sign estimating section 402, multiplying sections 403, 404d and 404q, an adding section 421, a phase adjusting section 410, an inverter applying voltage-sensitive gain section 420, angle-dead time compensation value function sections 430U, 430V and 430W, multiplying sections 431U, 431V and 431W, a three-phase alternating current (AC)/dq-axes converting section 440 and a current command value-sensitive gain calculating section 450.

(88) The q-axis steering assist command value iqref is inputted into the current control delay model 401. A delay due to a noise filter or the like in the ECU is occurred until the dq-axis current command values i.sub.d and i.sub.q* are corrected in the actual currents.

(89) When the sign is directly judged from the current command value i.sub.q*, the timing deviation can be occurred. In order to resolve this problem, the first example approximates the delay of the overall current control as a first order filter model and improves the phase difference. The current control delay model 401 is a primary filter of the above Expression 6 and T denotes a filter time constant. The current control delay model 401 may be a model of a secondary filter or higher order filter.

(90) The current command value I.sub.cm outputted from the current control delay model 401 is inputted into the current command value-sensitive gain section 450 and the compensation sign estimating section 402. In a low current region, a case that the dead time compensation amount is overcompensated is occurred. The current command value-sensitive gain section 450 has a function that a gain, which the compensation amount is reduced depending on the magnitude of the current command value I.sub.cm (the steering assist command value iqref), is calculated. In order that the gain, which the compensation amount is reduced, is not largely changed due to a noise from the current command value I.sub.cm (the steering assist command value iqref) or the like, a noise reduction process is performed by using a weighted average filter.

(91) The current command value-sensitive gain section 450 has a configuration shown in FIG. 12. An absolute value of the current command value I.sub.cm is calculated at an absolute value section 451. The absolute value of the current command value I.sub.cm whose maximum value is limited is inputted into a weighted average filter 454 via a scale converting section 453. The current command value I.sub.am that the noise is reduced at the weighted average filter 454 is addition-inputted into a subtracting section 455, and an offset OS having a constant value is subtracted from the current command value I.sub.am at the subtracting section 455. The reason for subtracting the offset OS having the constant value is to prevent a chattering due to a minute current command value, and the input value that is equal to or smaller than the offset OS is fixed to the minimum gain. The current command value I.sub.as that the offset OS is subtracted at the subtracting section 455 is inputted into a gain section 456, and the current command value-sensitive gain G.sub.c is outputted in accordance with a gain characteristic as shown in FIG. 13.

(92) The current command value-sensitive gain G.sub.c outputted from the current command value-sensitive gain section 450 has a characteristic, for example, as shown in FIG. 14, to the inputted current command value I.sub.cm. That is, the current command value-sensitive gain G.sub.c is a constant gain G.sub.cc1 when the current command value I.sub.cm is smaller than a predetermined current I.sub.cm1, linearly (or nonlinearly) increases when the current command value I.sub.cm is equal to or larger than the predetermined current I.sub.cm1 and is smaller than a predetermined current I.sub.cm2 (>I.sub.cm1), and holds a constant gain G.sub.cc2 when the current command value I.sub.cm is equal to or larger than the predetermined current I.sub.cm2. The predetermined current I.sub.cm1 may be 0 [A].

(93) The compensation sign estimating section 402 outputs a compensation sign SN1, which has a positive value (+1) or a negative value (1) and indicates a hysteresis characteristic shown in FIGS. 15A and 15B, against the inputted current command value I.sub.cm. The compensation sign SN1 is estimated based on zero-cross points of the current command value I.sub.cm as a reference. In order to suppress the chattering, the compensation sign SN1 has the hysteresis characteristic. The estimated compensation sign SN1 is inputted into the multiplying section 403.

(94) The current command value-sensitive gain G.sub.o from the current command value-sensitive gain section 450 is inputted into the multiplying section 403. The multiplying section 403 outputs the current command value-sensitive gain G.sub.cs (=G.sub.cSN1) that the compensation sign SN1 is multiplied with the current command value-sensitive gain G.sub.c. The current command value-sensitive gain G.sub.c, is inputted into the multiplying sections 404d and 404q.

(95) Since the optimal dead time compensation amount varies depending on the inverter applying voltage VR, the present example (the first example) calculates the dead time compensation amount depending on the inverter applying voltage VR and changes the dead time compensation amount. The configuration of the inverter applying voltage-sensitive gain calculating section 420 to output the voltage-sensitive gain G.sub.v by inputting the inverter applying voltage VR is shown in FIG. 16. The positive maximum value and the negative maximum value of the inverter applying voltage VR are limited in an input limiting section 421 and the inverter applying voltage VRI whose maximum value is limited is inputted into an inverter applying voltage/dead time compensation gain conversion table 422. The characteristic of the inverter applying voltage/dead time compensation gain conversion table 422 is shown, for example, in FIG. 17. The inverter applying voltages 9.0[V] and 15.0 [V] of inflection points and the voltage-sensitive gains 0.7 and 1.2 are presented as examples and are appropriately changeable. The calculated voltage-sensitive gain G.sub.v is inputted into the multiplying sections 431U, 431V and 431W.

(96) In a case that the dead time compensation timing is hastened or is delayed in response to the motor rotational velocity co, the phase adjusting section 410 has a function to calculate the adjustment angle depending on the motor rotational velocity co. The phase adjusting section 410 has a characteristic as shown in FIG. 18 in a case of a lead angle control. The calculated phase adjustment angle is inputted into the adding section 421 and is added to the detected motor rotational angle . The motor rotational angle .sub.m (=+) that is an added result at the adding section 421 is inputted into the angle-dead time compensation value function sections 430U, 430V and 430W, and the three-phase AC/dq-axes converting section 440.

(97) The angle-dead time compensation value function sections 430U, 430V and 430W, as shown in FIG. 19 in detail, respectively output respective phase rectangular wave dead time reference compensation values U.sub.dt, V.sub.dt and W.sub.dt whose phases are shifted each other by 120 [deg] in a range of 0 [deg] to 359 [deg] in the electric angle, to the phase-adjusted motor rotational angle .sub.m. The angle-dead time compensation value function sections 430U, 430V and 430W treat the dead time compensation values, which are needed in the three-phases, as functions depending on the angle, calculates the dead time compensation values in the actual time of the ECU, and outputs the three-phase dead time reference compensation values U.sub.dt, V.sub.dt and W.sub.dt. The angle functions of the dead time reference compensation values are different depending on the characteristic of the dead time in the ECU.

(98) The dead time reference compensation values U.sub.dt, V.sub.dt and W.sub.dt are respectively inputted into multiplying sections 431U, 431V and 431W, and are multiplied with the voltage-sensitive gain G.sub.c. The three-phase dead time compensation values U.sub.dtc (=G.sub.c.Math.U.sub.dt), V.sub.dtc (=G.sub.c.Math.V.sub.dt) and W.sub.dtc (=G.sub.c.Math.W.sub.dt) which are multiplied with the voltage-sensitive gain G.sub.c are inputted into the three-phase AC/dq-axis converting section 440. The three-phase AC/dq-axes converting section 440 converts the three-phase dead time compensation values U.sub.dtc, V.sub.dtc, and W.sub.dtc into the two-phase dq-axis compensation values v.sub.da* and v.sub.qa*, synchronized with the motor rotational angle .sub.m. The compensation values v.sub.da* and v.sub.qa* are respectively inputted into the multiplying sections 404d and 404q, and are multiplied with the current command value-sensitive gain G.sub.cs. The multiplied results in the multiplying sections 404d and 404q are the dq-axis compensation values CdB and CqB, and the compensation values CdB and CqB are respectively inputted into the switch sections 541 and 542 in the compensation value switching section 500.

(99) Next, the dead time compensating section (C) 600 (the first example) will be described.

(100) As shown in FIG. 20, the dead time compensating section (C) 600 comprises an adding section 601, a multiplying section 602, an inverter applying voltage-sensitive compensation-amount calculating section 610, a three-phase current command value model 620, a phase current compensation sign estimating section 621, a phase adjusting section 630 and a three-phase AC/dq-axes converting section 640. The motor rotational angle is inputted into the adding section 601, and the motor rotational velocity is inputted into the phase adjusting section 630. The inverter applying voltage VR is inputted into the inverter applying voltage-sensitive compensation-amount calculating section 610, and the phase-adjusted motor rotational angle .sub.m calculated at the adding section 601 is inputted into the three-phase current command value model 620.

(101) In a case that the dead time compensation timing is hastened or is delayed in response to the motor rotational velocity , the phase adjusting section 630 has a function to calculate the adjustment angle depending on the motor rotational velocity . The phase adjusting section 630 has a characteristic as shown in FIG. 18 in a case of a lead angle control. The calculated phase adjustment angle is inputted into the adding section 601 and is added with the detected motor rotational angle . The phase-adjusted motor rotational angle .sub.m (=+) that is an added result at the adding section 601 is inputted into the three-phase current command value model 620 and the three-phase AC/dq-axes converting section 640.

(102) Since the optimal dead time compensation amount varies depending on the inverter applying voltage VR, the present example (the first example) calculates the dead time compensation amount DTC depending on the inverter applying voltage VR and changes the dead time compensation amount DTC. The configuration of the inverter applying voltage-sensitive compensation-amount calculating section 610 to output the dead time compensation amount DTC by inputting the inverter applying voltage VR is shown in FIG. 21. The positive maximum value and the negative maximum value of the inverter applying voltage VR are limited at an input limiting section 611 and the inverter applying voltage VRI whose maximum value is limited is inputted into an inverter applying voltage/dead time compensation-amount conversion table 612. The characteristic of the inverter applying voltage/dead time compensation-amount conversion table 612 is shown, for example, in FIG. 22. That is, the dead time compensation amount DTC is a constant dead time compensation amount DTC1 when the inverter applying voltage VR is lower than a predetermined inverter applying voltage VR1, linearly (or nonlinearly) increase when the inverter applying voltage VR is equal to or higher than a predetermined inverter applying voltage VR2 (>VR1), and holds a constant dead time compensation amount DTC2 when the inverter applying voltage VR is equal to or higher than the predetermined inverter applying voltage VR2.

(103) The d-axis current command value i.sub.d*, the q-axis current command value i.sub.q* and the motor rotational angle .sub.m are inputted into the three-phase current command value model 620. The three-phase current command value model 620 calculates the sinusoidal three-phase current model command values I.sub.cm whose phases are shifted each other by 120 [deg] as shown in FIG. 23 or obtains the three-phase current model command values I.sub.cm by using a table, from the dq-axis current command values i.sub.d* and i.sub.q* and the motor rotational angle .sub.m. The three-phase current model command values I.sub.cm are different depending on the motor type.

(104) The three-phase current model command values I.sub.cm are inputted into a phase current compensation sign estimating section 621. The phase current compensation sign estimating section 621 outputs compensation signs SN2, which have a positive value (+1) or a negative value (1) and indicate a hysteresis characteristic shown in FIGS. 24A and 24B, against the inputted three-phase current model command values I.sub.cm. The compensation signs SN2 are estimated based on zero-cross points of the three-phase current model command values I.sub.cm as a reference. In order to suppress the chattering, the compensation signs SN2 have the hysteresis characteristic. The estimated compensation signs SN2 are inputted into the multiplying section 602.

(105) The dead time compensation amount DTC from the inverter applying voltage-sensitive compensation-amount calculating section 610 is inputted into the multiplying section 602, and the multiplying section 602 outputs the dead time compensation amounts DTCa (=DTCSN2) that the compensation signs SN2 are multiplied with the dead time compensation amount DTC. The dead time compensation amounts DTCa are inputted into the three-phase AC/dq-axis converting section 640, and the three-phase AC/dq-axes converting section 640 outputs the dq-axes compensation values CdC and CqC, synchronized with the motor rotational angle .sub.m. The compensation values CdC and CqC are respectively inputted into the switch sections 541 and 542 in the compensation value switching section 500.

(106) The switch judging section 510 in the compensation value switching section 500 has a configuration shown in FIG. 25, and comprises a zero judging section 511 to output a judgment flag DF1 when the d-axis current command value i.sub.d* is near zero (for example, the d-axis current command value i.sub.d* is equal to or smaller than 0.1 [A]), an absolute value section 512 to obtain the absolute value |i.sub.q*| of the q-axis current command value i.sub.q*, a threshold section 513 to have the hysteresis characteristic and output a judgment flag DF2 when the absolute value |i.sub.q*| is equal to or larger than a predetermined threshold TH1, an absolute value section 514 to obtain the absolute value || of the motor rotational velocity co, and a threshold section 515 to have the hysteresis characteristic and output a judgment flag DF3 when the absolute value || is equal to or larger than a predetermined threshold TH2. The judgment flags DF1 to DF3 are inputted into a switch condition judging section 516, and the switch condition judging section 516 outputs a switch judgment flag SF1 when all the judgment flags DF1 to DF3 were inputted. For example, in a case that the judgment flag DF1 is L, the judgment flag DF2 is H and the judgment flag DF3 is H, the switch condition judging section 516 outputs the switch judgment flag SF1 that indicates H. Here, H and L indicate an example of the logical value, and the logical values H and L may be inverted.

(107) When the switch judgment flag SF1 is not outputted (is OFF) (for example, SF1 is L), as shown in FIG. 5, the contact points of the switch sections 541 and 542 of the conditional branch section 540 are respectively connected to a1 and a2, and the compensation values CdB and CqB from the dead time compensating section (B) 400 are respectively outputted as the compensation values Cd and Cq. When the switch judgment flag SF1 is outputted (is ON) (for example, SF1 is H), the contact points of the switch sections 541 and 542 are respectively switched from a1 and a2 to b1 and b2. As a result, the compensation values CdC and CqC from the dead time compensating section (C) 600 are respectively outputted as the compensation values Cd and Cq. The compensation values Cd and Cq from the conditional branch section 540 are inputted into the multiplying sections 552 and 554 in the gradual-changing switching section 550.

(108) The gradual-changing switch judging section 520 serves the steering assist command value iqref as the switch condition, has a dead band region to the input signal, and outputs the UP/DOWN judgment flag SF2 under the judgment condition having a hysteresis. The configuration example of the gradual-changing switch judging section 520 is shown in FIG. 26. The steering assist command value iqref is inputted into the dead band section 521 and is performed by the dead band process (for example, 0.5 [A]). The dead-band-processed steering assist command value iqref-d is inputted into the absolute value section 522. The upper limit value and the lower limit value of the absolute value |iqref-d| from the absolute value section 522 are limited at the limiter 523. The steering assist command value iqref-t whose upper limit value and lower limit value are limited is inputted into the threshold section 524 having a hysteresis characteristic, and the threshold section 524 outputs the UP/DOWN judgment flag SF2 based on a magnitude relationship to the predetermined threshold. The UP/DOWN judgment flag SF2 is inputted into the gradual-changing ratio calculating section 530.

(109) Since the signal is fluctuated due to the external factors (such as the road surface state (a gravel road, a slop or the like) and vibration of the vehicle body) near the on-center position of the handle, the dead band section 521 is disposed for avoid these external factors. The dead band section 521 removes the vibration component of the inputted steering assist command value iqref. The hysteresis characteristic of the threshold section 524 has functions that the chattering after the dead band process is prevented and the stabilization of the output is realized.

(110) The gradual-changing ratio calculating section 530 has a configuration shown in, for example, FIG. 27, and comprises a switch 531 that is switched to the contact point am or the contact point bm depending on ON (e.g., H) or OFF (e.g., L) of the UP/DOWN judgment flag SF2. For example, when the UP/DOWN judgment flag SF2 is inputted (SF2 is ON), the switch 531 is connected to the contact point am and outputs the COUNT-UP value 532 (e.g., +0.5%). When the UP/DOWN judgment flag SF2 is not inputted (SF2 is OFF), the switch 531 is switched to the contact point bm and outputs the COUNT-DOWN value 533 (e.g., 0.5%). The output of the switch 531 is inputted into an adding section 534, the maximum value of the added value is limited at a count value limiting section (0 to 100%) 535, and the limited added value is outputted as the gradual-changing ratio RtBC (%), is subtraction-inputted into a subtracting section 537 and is inputted into the adding section 534 via a holding unit (Z.sup.1) 536. The gradual-changing ratio RtBC is inputted into the subtracting section 537, and the subtracting section 537 outputs the gradual-changing ratio RtA (%) obtained by subtracting the gradual-changing ratio RtBC from a fixed value 100%. As a result, the gradual-changing ratio RtA linearly changes from 100% to 0%, the gradual-changing ratio RtBC linearly changes from 0% to 100% and the gradual-changing ratios RtA and RtBC can be obtained as shown in FIG. 28 by solid lines. The relationship which is represented by the below Expression 10 is always satisfied between the gradual-changing ratios RtA and RtBC. The gradual-changing ratios RtA and RtBC are inputted into the gradual-changing switching section 550.
RtA (%)+RtBC (%)=100%[Expression 10]

(111) The switch term by the gradual-changing switch is from a time point t.sub.0 to a time point t.sub.1 in FIG. 28. The switch term is changeable by varying the magnitude of the counting value. For example, by respectively setting the COUNT-UP value 532 and the COUNT-DOWN value 533 to +0.5% and 2%, the switch from the dead time compensation A to the dead time compensation B can be slow, the switch from the dead time compensation B to the dead time compensation A can be fast and the switch term can nonlinearly be changed. By setting the COUNT-UP value 532 and the COUNT-DOWN value 533 to be larger or smaller, the switching speed can be adjusted.

(112) As show in FIG. 28 by broken lines, the COUNT-UP value 532 and the COUNT-DOWN value 533 are nonlinearly changeable. The above nonlinearly changeable example is described below.

(113) As shown in FIG. 5, the gradual-changing switching section 550 comprises the multiplying sections 551 to 554 and the adding sections 555 and 556. The compensation values CdA and CqA from the dead time compensating section (A) 200 are respectively inputted into the multiplying sections 551 and 553, and the gradual-changing ratio RtA from the gradual-changing ratio calculating section 530 is inputted into the multiplying sections 551 and 553. The compensation values Cd and Cq from the conditional branch section 540 are respectively inputted into the multiplying sections 552 and 554, and the gradual-changing ratio RtBC from the gradual-changing ratio calculating section 530 is inputted into the multiplying sections 552 and 554. The compensation value RtA.Math.CdA that the compensation value CdA is multiplied with the gradual-changing ratio RtA is inputted into the adding section 555, and the compensation value RtBC Cd that the compensation value Cd is multiplied with the gradual-changing ratio RtBC is inputted into the adding section 555. The d-axis dead time compensation value v.sub.d* that is added with the compensation values RtA.Math.CdA and RtBC. Cd at the adding section 555 is inputted into the adding section 121d. The compensation value RtA.Math.CqA that compensation value CqA is multiplied with the gradual-changing ratio RtA is inputted into the adding section 556, and the compensation value RtBC.Math.Cq that the compensation value Cq is multiplied with the gradual-changing ratio RtBC is inputted into the adding section 556. The q-axis dead time compensation value v.sub.q* that is added with the compensation values RtA.Math.CqA and RtBC.Math.Cq at the adding section 556 is inputted into the adding section 121q.

(114) In such a configuration, the operation example of the dead time compensation will be described with reference to a flowchart of FIG. 29.

(115) In such a configuration, the operation example of the dead time compensation will be described with reference to a flowchart of FIG. 29. The dead time compensation is performed only once a control period (for example, 250 [s]) at the same timing of the current control.

(116) When the operation of the dead time compensation is started, the compensation values CdA and CqA are calculated at the dead time compensating section (A) 200 (Step S1), the compensation values CdB and CqB are calculated at the dead time compensating section (B) 400 (Step S2) and the compensation values CdC and CqC are calculated at the dead time compensating section (C) 600 (Step S3). These calculation orders are appropriately changeable.

(117) The switch judging section 510 judges the switch based on the d-axis current command value i.sub.d*, the q-axis current command value i.sub.q* and the motor rotational velocity co (Step S10), and judges whether the switch judgment flag SF1 is not outputted (is OFF) or not (Step S11). When the switch judgment flag SF1 is OFF, the compensation values CdB and CqB of the dead time compensating section (B) 400 are outputted from the conditional branch section 540 (Step S12). When the switch judgment flag SF1 is ON, the compensation values CdC and CqC of the dead time compensating section (C) 600 are outputted from the conditional branch section 540 (Step S13). Under the middle speed or high speed steering condition that the compensation value B (CdB and CqB) or the compensation value C (CdC and CqC) is outputted, the gradual-changing ratio becomes RtA=0% and RtBC=100%, the compensation value A0%+the compensation value B or C100% is calculated, and the switch compensation value B or C is outputted.

(118) The steering assist command value iqref is inputted into the gradual-changing switch judging section 520, and the gradual-changing switch judging section 520 calculates the judgement of the gradual-changing switch based on the steering assist command value iqref (Step S14) and judges whether the UP/DOWN judgment flag SF2 is ON or not (Step S15). In a case that the UP/DOWN judgment flag SF2 is ON, the COUNT-UP value 532 is outputted (Step 16), and in a case that the UP/DOWN judgment flag SF2 is OFF, the COUNT-DOWN value 533 is outputted (Step S17). The output value is added to the previous counting value stored in the memory (the holding unit 536) at the adding section 534 (Step S20). The counting value which is added at the adding section 534 is limited at the counting value limiting section 535 (Step S21), and the limited counting value is stored in the memory (the holding unit 536) (Step S22). The UP/DOWN count process is performed only once a control period (e.g., 250 [s]), the counting value is stored in the memory, and the UP process or the DOWN process to the stored counting value is performed once at the next control period.

(119) The gradual-changing ratio calculating section 530 calculates the gradual-changing ratios RtA and RtBC based on the outputted counting value (Step S23). The gradual-changing ratio RtA is inputted into the multiplying sections 551 and 553 in the gradual-changing switching section 550, the gradual-changing ratio RtBC is inputted into the multiplying sections 552 and 554 in the gradual-changing switching section 550, and the gradual-changing switch is performed (Step S24). The respective multiplied results at the multiplying sections 551 and 552 are added at the adding section 555, and the added result is outputted as the dead time compensation value v.sub.d*. The respective multiplied results at the multiplying sections 553 and 554 are added at the adding section 556, and the added result is outputted as the dead time compensation value v.sub.q* (Step S25).

(120) With respect to the calculation of the gradual-changing ratio, as shown in FIG. 30 corresponding to FIG. 29, the counting value from the counting value limiting section 535 is inputted into the characteristic conversion table, the gradual-changing ratios are calculated (Step S23-1), and the gradual-changing ratios RtA and RtBC may be calculated from the gradual-changing ratios after the characteristic conversion is performed (Step S23-2).

(121) In order to achieve the excellent grip feeling and the appropriate switching speed, the gradual-changing ratios can be changed nonlinearly. That is, in a case that the grip feeling is important, the change of the gradual-changing ratios may be slow, and in a case that the grip feeling is not important, the change of the gradual-changing ratios may be fast. As shown in FIG. 28 by the broken line, in a case that the gradual-changing ratios at the gradual-changing ratio calculating section 530 change nonlinearly, the configuration of FIG. 31 can be served as the nonlinear function (the second example). In the second example of FIG. 31, a gradual-changing ratio characteristic converting section 538 which is configured as the nonlinear element is disposed at a subsequent stage of the counting value limiting section 535, the gradual-changing ratio RtBC is outputted from the gradual-changing ratio characteristic converting section 538 and is subtraction-inputted into the subtracting section 537. The gradual-changing ratio characteristic converting section 538 may have a characteristic that the ratios change nonlinearly over the all regions as shown in FIG. 31, or may have a characteristic that the ratios saturate in a part of the regions as shown in FIG. 32 (the third example).

(122) As shown in FIG. 33, with respect to the dead time compensation value switch, the increase or the decrease of the UP/DOWN counting value can be adjusted by the conditions such as the motor rotational number rpm, the switch speed can also be adjusted by increasing or decreasing the counting value, and then the time point t1 can be changed along the arrow AR. In a case of the region of the motor rotational number rpm where the grip feeling is important, the changes of the gradual-changing ratios become slow. In a case of the region of the motor rotational number rpm where the grip feeling is not important, the changes of the gradual-changing ratios become fast. FIG. 33 shows a configuration example (the fourth example) of the above case, and the fourth example includes a COUNT-UP value calculation processing section 532A to input the motor rotational number rpm and output the rotational number-sensitive COUNT-UP value, a COUNT-DOWN value calculation processing section 533A to input the motor rotational number rpm and output the rotational number-sensitive COUNT-DOWN value. The rotational number-sensitive COUNT-UP value is inputted into the contact point a and the rotational number COUNT-DOWN value is inputted into the contact point b. As shown in FIG. 33, the COUNT-UP value calculation processing section 532A has a characteristic that the COUNT-UP value is a constant value until the motor rotational number rpm becomes a predetermined value, and increases when the motor rotational number rpm is equal to or higher than the predetermined value. As shown in FIG. 33, the COUNT-DOWN value calculation processing section 533A has a characteristic that the COUNT-DOWN value is a constant value until the motor rotational number rpm becomes a predetermined value, and decreases when the motor rotational number rpm is equal to or higher than the predetermined value.

(123) Next, the space vector modulation will be described. As shown in FIG. 34, the space vector modulating section 300 may have a function that converts the two-phase voltages v.sub.d** and v.sub.q** in the d-q space into the three-phase voltages V.sub.ua, V.sub.va and V.sub.wa, and superimposes the third-harmonic on the three-phase voltages V.sub.ua, V.sub.va and V.sub.wa. For example, the method of the space vector modulation that the applicant proposes in Japanese Unexamined Patent Publication No. 2017-70066, WO/2017/098840 and the like may be used.

(124) That is, the space vector modulation has a function that performs a following coordinate transformation based on the voltage command values v.sub.d** and v.sub.q** in the d-q space, the motor rotational angle and sector number n (#1 to #6), and controls the rotation of the motor by supplying switching patterns S1 to S6 to the motor. The switching patterns S1 to S6 are corresponding to the sectors #1 to #6, and control turning-ON/turning-OFF of the switching devices (the upper arm Q1, Q3 and Q5, and the lower arm Q2, Q4 and Q6) of the inverter with the bridge configuration. With respect to the coordinate transformation, in the space vector modulation, the voltage command values v.sub.d** and v.sub.q** perform the coordinate transformation to the voltage vectors V and V in the - coordinate system based on an Expression 11. A relationship between the coordinate axes that are used in this coordinate transformation and the motor rotational angle is shown in FIG. 35.

(125) $\begin{array}{cc}\left[\begin{array}{c}V\\ V\end{array}\right]=\left[\begin{array}{cc}\cos & -\sin \\ \sin & \cos \end{array}\right]\left[\begin{array}{c}{v}_d^{**}\\ v_q^{**}\end{array}\right]& \left[\mathrm{Expression}11\right]\end{array}$

(126) A relationship shown in an Expression 12 between a target voltage vector in the d-q coordinate system and a target voltage vector in the - coordinate system is existed. The absolute value of the target voltage vector is conserved.
|V|={square root over ((v.sub.d**).sup.2+(v.sub.q**).sup.2)}={square root over (V.sup.2+V.sup.2)}[Expression 12]

(127) In the switching pattern of the space vector control, the output voltage is defined by using eight discrete reference voltage vectors V0 to V7 (non-zero voltage vectors V1 to V6 that the phase differs every /3 [rad] and zero voltage vectors V0 and V7) that are shown in the space vector diagram of FIG. 36, depending on the switching patterns S1 to S6 of the switching devices (the FETs) (Q1 to Q6). The selection of these reference output voltage vectors V0 to V7 and the occurring time are controlled. By using six regions sandwiched between adjacent reference output voltage vectors, the space vector can be divided into the six sectors #1 to #6, and the target voltage vector V is belong to any one of the sectors #1 to #6, and can be assigned to the sector number. The rotational angle in the - coordinate system of the target voltage vector V can determine which sector that is separated into a regular hexagon in the - space, as shown in FIG. 36, is existed in the target voltage vector V that is a synthetic vector of V and V. The rotational angle is determined by a sum of the rotational angle of the motor and a phase obtained from the relationship of the voltage command values v.sub.d** and v.sub.q** in the d-q coordinate system (=+).

(128) FIG. 37 shows a basic timing chart that the switching pulse width and the timing in the turning-ON/turning-OFF signals S1 to S6 to the switching devices (the FETs) are determined in order to output the target voltage vector from the inverter by a digital control by means of the switching patterns S1, S3 and S5 of the inverter in the space vector control. The space vector modulation performs the calculation and the like in every defined sampling period Ts, and outputs the respective pulse widths and the timings in the switching patterns S1 to S6 to which the calculation result is transformed in the next sampling period Ts.

(129) The space vector modulation generates the switching patterns S1 to S6 depending on the sector number that is obtained based on the target voltage vector V. In FIG. 37, in a case of the sector number #1 (n=1), one example of the switching patterns S1 to S6 of the switching devices (the FETs) in the inverter is shown. The signals S1, S3 and S5 show the gate signals of the switching devices Q1, Q3 and Q5 that are corresponding to the upper arm. The horizontal axis denotes a time, and Ts is corresponding to the switching period and is divided into eight periods, T0/4, T1/2, T2/2, T0/4, T0/4, T2/2, T1/2 and T0/4. The periods T1 and T2 are the time depending on the sector number n and the rotational angle .

(130) In a case that the space vector modulation is not performed, the dead time compensation of the present invention is applied on the dq-axis, and the dead time compensation value waveform (the U-phase waveform) that the dq-axis/three-phase converting is performed to only the dead time compensation value is shown in a waveform represented by a broken line of FIG. 38 that the third-order component is removed. The same phenomena are exhibited in the V-phase and the W-phase. By applying the space vector modulation instead of the dq-axes/three-phase converting, the third-harmonic can be superimposed on the three-phase signals, the third-order component that is removed by the three-phase converting can be compensated, and the ideal dead time compensation waveform that is shown in a solid line of FIG. 38 can be generated.

(131) FIG. 39 shows the switch behaviors of the dead time compensation functions (A), (B) and (C) according to the first embodiment of the present invention. The electric power steering apparatus operates the dead time compensation function (A) until the time point t.sub.0. The switch by the gradual-changing is occurred at the time point t.sub.0. The electric power steering apparatus operates the dead time compensation function (A)+(B) from the time point t.sub.0 to the time point t.sub.1, and the operation is completely switched to the dead time compensation function (B) at the time point t.sub.1, and is instantaneously switched to the dead time compensation function (C) by the conditional branch at the time point t.sub.2.

(132) When the operation is switched to the dead time compensation having a different characteristic (from the time point t.sub.0 to the time point t.sub.1), the differences of the compensation amount and the phase are existed. In a case that the operation is simply switched from the dead time compensation function (A) to the dead time compensation function (B), the deviation in a step form is occurred in the compensation value due to the difference of the characteristic and then the torque ripple is occurred. For example, in a case that the compensation amount of the dead time compensation function (B) in switching is set to 1.00, the compensation amount of the dead time compensation function (A) is in a range of 0.92 to 0.95, and both are different. Particularly, in the low load and low speed steering in which the current amount flowing to the motor is small, the influence of the dead time compensation amount is large (this is because the dead time compensation voltage is higher than the command voltage such as the PI-control). Even in a case that the deviation in a small step form is occurred, the deviation makes the torque ripple be occurred. In the first embodiment, the two dead time compensation values are switched using the gradual-changing. By setting the transition period and making the deviation be a sweeping shape, the torque ripple is not occurred and the driver who steers the handle does not perceive when the compensation function is switched.

(133) For example, the dead time compensation function (A) is a terminal voltage feedback-type dead time compensation function, and can perform the accurate compensation for automatically calculating the optimal compensation sign and the optimal compensation amount in the low load and low speed steering state that the estimation of the compensation sign and the adjustment of the compensation amount are difficult (in a state that the handle is slowly steered to the left or to the right near the on-center position). The dead time compensation function (B) is an angle feedforward-type dead time compensation function, and can perform the accurate compensation because the ideal dead time compensation value is incorporated into the compensation value in feedforward in the low speed and middle speed steering state that the d-axis current is not needed (in a state that the handle is steered at the constant velocity, is gradually steered forward or the like). Since the dead time compensation value is calculated depending on the angle, in the steering load regions except for the low load steering region (for example, the region that the current command value is 0 [A] to 4 [A]), even in a case that the noise or the small ripple is existed in the detection current, the stable compensation can be performed without being affected to the calculation of the compensation value.

(134) FIGS. 40 to 42 show validation results of the present invention in a bench test apparatus that the actual vehicle is simulated. FIG. 40 shows the d-axis current and the d-axis dead time compensation value, and FIG. 41 shows the q-axis current and the q-axis dead time compensation value. In the low speed and low load steering state, since the dead time compensation of the present invention shown in FIGS. 40 and 41 is performed, even when the dead time compensation value is switched from A to B, it is confirmed that the distortion in a step form is not occurred in the d-axis and q-axis dead time compensation values and the distortion is not occurred in the waveforms of the d-axis and q-axis currents. It is also understood that the torque ripple in switching is not occurred in steering the handle. In a state that steering forward is performed from the middle speed to the high speed, as shown in FIG. 42, when the dead time compensation of the present invention is adapted and the dead time compensation value is switched, it is confirmed that the waveform distortions of the d-axis and q-axis currents due to the influence of the dead time are not occurred even in a case that the current control characteristic is changed when the d-axis current begins to flow to the motor.

(135) Next, the second embodiment of the present invention will be described with reference to FIG. 43. FIG. 43 is corresponding to FIG. 5, the same reference numerals are assigned to the same elements and the detailed explanation is omitted.

(136) In the second embodiment, a temperature detecting section 700 which detects the temperature of the power device of the control unit (the ECU), the temperature of the inverter or the temperature near the inverter by the known method is disposed. The dead time compensating section (B) 400 and the dead time compensating section (C) 600 are replaced with the dead time compensating section (B) 400S and the dead time compensating section (C) 600S, respectively. The temperature TM detected at the temperature detecting section 700 is inputted into the dead time compensating section (B) 400S and the dead time compensating section (C) 600S. The gradual-changing switch judging section 520 and the gradual-changing ratio calculating section 530 of the first embodiment by which the gradual-changing section is constituted, are replaced with the gradual-changing switch judging section 520S and the gradual-changing ratio calculating section 530S, respectively. The motor rotational number rpm is inputted into the gradual-changing switch judging section 520S, and can easily be calculated by the motor rotational velocity co in an internal calculation.

(137) The configuration example (the second example) of the dead time compensating section (B) 400S is shown in FIG. 44, the temperature TM from the temperature detecting section 700 is inputted into a temperature-sensitive gain calculating section 460 and the calculated temperature-sensitive gain Gtm is inputted into the multiplying section 461. As shown in FIG. 45, the temperature-sensitive gain calculating section 460 calculates the temperature-sensitive gain Gtm at the three points that are a compensation-amount setting temperature, a performance guarantee temperature upper limit and a performance guarantee temperature lower limit. Setting the value of the compensation-amount setting temperature as a reference value 1.00, the ratio to the performance guarantee temperature upper limit and the ratio to the performance guarantee temperature lower limit are respectively calculated, and the temperature-sensitive gain Gtm is obtained. The ratio among the three points is generated by linear interpolation calculation or the table to the temperature TM. The limits to the performance guarantee temperature upper limit and the performance guarantee temperature lower limit may be set. In a case that the temperature characteristic of the control unit (the inverter) is complicated, the contact points may increase and the curve interpolation table may be used. In a case that the characteristic example of the temperature-sensitive gain Gtm that the compensation-amount setting temperature is set to +20 degrees Celsius, the performance guarantee temperature lower limit is set to 40 degrees Celsius, the performance guarantee temperature upper limit is set to +80 degrees Celsius, the required gain at 40 degrees Celsius increases 10% to the gain at +20 degrees Celsius and the required gain at +80 degrees Celsius decreases 10% to the gain at +20 degrees Celsius, is set, the characteristic table of the temperature-sensitive gain Gtm is shown in FIG. 46.

(138) The temperature-sensitive gain Gtm from the temperature-sensitive gain calculating section 460 is inputted into the multiplying section 461 and is multiplied with the inverter applying voltage-sensitive gain Gva from the inverter applying voltage-sensitive gain calculating section 420 and the voltage-sensitive gain G.sub.v which is a multiplied result is inputted into the multiplying sections 431U, 431V and 431W. The following operations of the compensation value calculation which are the same as those of the first embodiment are performed.

(139) FIG. 47 shows the configuration example (the second example) of the dead time compensating section (C) 600S, the temperature TM from the temperature detecting section 700 is inputted into the temperature-sensitive gain calculating section 650 and the calculated temperature-sensitive gain Gtn is inputted into the multiplying section 651. The characteristic of the temperature-sensitive gain calculating section 650 is almost the same as that of the temperature-sensitive gain calculating section 460, is shown by the characteristic of FIG. 48 and the characteristic table of FIG. 49.

(140) The temperature-sensitive gain Gtn from the temperature-sensitive gain calculating section 650 is inputted into the multiplying section 651 and is multiplied with the dead time compensation amount DTCb from the inverter applying voltage-sensitive gain calculating 610 and the dead time compensation amount DTC which is a multiplied result is inputted into the multiplying section 602. The following operations of the compensation value calculation which are the same as those of the first embodiment are performed.

(141) The configuration example (the second example) of the gradual-changing switch judging section 520S is shown in FIG. 50 corresponding to FIG. 26 which shows the first example. The q-axis current command value iqref and the motor rotational number rpm are inputted into the gradual-changing switch judging section 520S of the second example, and the gradual-changing switch judging section 520S is divided into the system of the q-axis current command value iqref and the system of the motor rotational number rpm. In the system of the q-axis current command value iqref, as well as FIG. 26, the q-axis current command value iqref is processed at the dead band section 521, the absolute value section 522 and the limiter 523, the steering assist command value iqref-t from the limiter 523 is inputted into the threshold section 524 having the hysteresis characteristic for stabilizing the output, and the threshold section 524 outputs the UP/DOWN judgment flag SFc based on the magnitude relationship to the predetermined threshold. The UP/DOWN judgment flag SFc is inputted into the switch section 525, and switches to the COUNT-UP value 525A which is inputted into the contact point 525a or the COUNT-DOWN value 525B which is inputted into the contact point 525b. The switch section 525 outputs the switch count UP/DOWN value SCI due to the q-axis current factor. In the system of the motor rotational number rpm, the absolute value |rpm| of the motor rotational number rpm is calculated at the absolute section 526 and is inputted into the threshold section 527 having the hysteresis characteristic for stabilizing the output, and the threshold section 527 outputs the UP/DOWN judgment flag SFm based on the magnitude relationship to the predetermined threshold. The UP/DOWN judgment flag SFm is inputted into the switch section 528, and switches to the COUNT-UP value 528A which is inputted into the contact point 528a or the COUNT-DOWN value 528B which is inputted into the contact point 528b. The switch section 528 outputs the switch count UP/DOWN value SCM due to the rotational number factor. The switch count UP/DOWN value SCI and the switch count UP/DOWN value SCM are added at the adding section 529, and the switch count value SFC is outputted from the adding section 529 and is inputted into the gradual-changing ratio calculating section 530S.

(142) FIG. 51 shows a configuration example of the gradual-changing ratio calculating section 530S. The UP/DOWN judgment flag SF2 is inputted into the adding section 534 and is added to the previous value of the gradual-changing ratio RtBC from the holding unit (Z.sup.1) 536, the maximum value of the added value is limited at the counting value limiting section (0% to 100%) 535, and the limited added value is outputted as the gradual-changing ratio RtBC (%), is subtraction-inputted into subtraction-inputted into the subtracting section 537 and is inputted into the adding section 534 via the holding unit (Z.sup.1) 536. The gradual-changing ratio RtBC is inputted into the subtracting section 537, and the subtracting section 537 outputs the gradual-changing ratio RtA (%) obtained by subtracting the gradual-changing ratio RtBC from the fixed value 100%.

(143) The operation examples of the second embodiment are the same as those of the first embodiment in FIG. 29 except for a part of the temperature correction. Namely, the temperature detecting section 700 detects the temperature of the inverter or the like, the temperature TM is inputted into the dead time compensating section (B) 400S and the dead time compensating section (C) 600S, and the temperature-corrected compensation values (B) and (C) are outputted (Steps S12 and S13).

(144) The effects of the second embodiment will be described by using the validation results in the bench test apparatus that the actual vehicle is simulated as follows.

(145) FIGS. 52A, 52B and 52C are the results in a case that the temperature is +20 degrees Celsius and the temperature correction is not performed. FIG. 52A shows the U-phase current waveform, FIG. 52B shows the q-axis current waveform and FIG. 52C shows the d-axis current waveform. As shown in FIGS. 52A, 52B and 52C, since the compensation amount is appropriate in a case that the temperature condition is +20 degrees Celsius, the distortion of the current waveforms due to the dead time is not almost existed. FIGS. 53A, 53B and 53C are the results in a case that the temperature is 40 degrees Celsius and the temperature correction is not performed. FIG. 53A shows the U-phase current waveform, FIG. 53B shows the q-axis current waveform and FIG. 53C shows the d-axis current waveform. As shown in FIGS. 53A, 53B and 53C, since the compensation amount is inadequate in a case that the temperature condition is 40 degrees Celsius, the U-phase current has the recess-form distortion near 0 [A], and the wave-form distortion in the q-axis current and the sawtooth-form distort ion in the d-axis current are occurred. FIGS. 54A, 54B and 54C are the results in a case that the temperature is +80 degrees Celsius and the temperature correction is not performed. FIG. 54A shows the U-phase current waveform, FIG. 54B shows the q-axis current waveform and FIG. 54C shows the d-axis current waveform. As shown in FIGS. 54A, 54B and 54C, since the compensation amount is overcompensated, the U-phase current has the projection-form distortion near 0 [A], and the wave-form distortion in the q-axis current and the sawtooth-form distortion in the d-axis current are occurred.

(146) In contrast with the above results in a case that the temperature compensation is not performed, FIGS. 55A to 57C show the validation results in a case that the temperature correction of the second embodiment is performed.

(147) FIGS. 55A, 55B and 55C are the results in a case that the temperature is +20 degrees Celsius and the temperature correction is performed. FIG. 55A shows the U-phase current waveform, FIG. 55B shows the q-axis current waveform and FIG. 55C shows the d-axis current waveform. As shown in FIGS. 55A, 55B and 55C, since the temperature correction is adapted and the compensation amount is corrected depending on the temperature, in a case that the temperature condition is +20 degrees Celsius, the distortion of the waveforms due to the dead time is not almost existed as well as a case that the temperature correction is not performed. That is, contradiction against the temperature correction adaptation is not existed. FIGS. 56A, 56B and 56C are the results in a case that the temperature is 40 degrees Celsius and the temperature correction is performed. FIG. 56A shows the U-phase current waveform, FIG. 56B shows the q-axis current waveform and FIG. 56C shows the d-axis current waveform. As shown in FIGS. 56A, 56B and 56C, since the temperature correction is adapted and the compensation amount is corrected depending on the temperature, in a case that the temperature is 40 degrees Celsius, it can be confirmed that the waveform distortion of the U-phase current, the d-axis current and the q-axis current is improved and the torque ripple is also improved (the ripple is reduced in the d-axis current and the q-axis current and the phase currents are almost the sinusoidal waveform). FIGS. 57A, 57B and 57C are the results in a case that the temperature is +80 degrees Celsius and the temperature correction is performed. FIG. 57A shows the U-phase current waveform, FIG. 57B shows the q-axis current waveform and FIG. 57C shows the d-axis current waveform. As shown in FIGS. 57A, 57B and 57C, since the temperature correction is adapted and the compensation amount is corrected depending on the temperature, in a case that the temperature is +80 degrees Celsius, it can be confirmed that the waveform distortion of the U-phase current, the d-axis current and the q-axis current is improved and the torque ripple is also improved (the ripple is reduced in the d-axis current and the q-axis current and the phase currents are almost the sinusoidal waveform).

EXPLANATION OF REFERENCE NUMERALS

(148) 1 handle 2 column shaft (steering shaft, handle shaft) 10 torque sensor 12 vehicle speed sensor 20, 100 motor 30 control unit (ECU) 31 steering assist command value calculating section 35 PI-control section 36, 160 PWM-control section 37, 161 inverter 110 angle detecting section 130, 260, 440, 640 three-phase AC/dq-axes converting section 140 d-q non-interference control section 200 dead time compensating section (A) 210 midpoint voltage estimating section 220 respective phase applying voltage calculating section 230 voltage detection delay model 250 compensation-amount limiting section 300 space vector modulating section 301 two-phase/three-phase converting section 302 third-harmonic superimposition section 400, 400S dead time compensating section (B) 401 current control delay model 410, 630 phase adjusting section 460, 650 temperature-sensitive gain calculating section 500 compensation value switching section 510 switch judging section 520, 520S gradual-changing switch judging section 530, 530S gradual-changing ratio calculating section 540 conditional branch section 550 gradual-changing switching section 600, 600S dead time compensating section (C) 620 three-phase current command value model 621 phase current compensation sign estimating section 700 temperature detecting section