Electric power steering apparatus

Abstract

An electric power steering apparatus compensates a dead time of an inverter without tuning operation, improves distortion of a current waveform and responsibility of a current control, and suppresses sound, vibration and ripple. The apparatus calculates dq-axes steering-assist command values based on at least a steering torque, calculates dq-axes current command values from the dq-axes steering-assist command values, converts the dq-axes current command values into 3-phase duty command values, driving-controls a 3-phase brushless motor by an inverter of a PWM control, and applies an assist torque to a steering system of a vehicle. Dead time reference compensation values are calculated based on a motor rotational angle. Dead time compensation of the inverter adds dead time compensation values in which the dead time reference compensation values are processed by using a gain, a sign and the like, to dq-axes voltage command values or to 3-phase voltage command values.

Claims

1. An electric power steering apparatus of a vector control system, the electric power steering apparatus comprising: at least one hardware processor configured to implement: calculating dq-axes steering-assist command values based on at least a steering torque, calculating dq-axes voltage command values from said dq-axes steering-assist command values; converting said dq-axes voltage command values into three-phase duty command values; driving-controlling a 3-phase brushless motor by an inverter of a pulse width modulation (PWM) control; and controlling application of an assist torque to a steering system of a vehicle, wherein a dead time compensation of said inverter is performed by adding dq-axes dead time compensation values obtained by multiplying dq-axes dead time reference compensation values, which are obtained from an angle-dead time compensation-value reference table having a characteristic that 3-phase dead time compensation values based on a motor rotational angle are converted into 2-phase values, by a voltage sensitive-gain sensitive to an inverter-applying voltage, to said dq-axes voltage command values.

2. The electric power steering apparatus according to claim 1, wherein a phase of said motor rotational angle is changeable depending on motor rotational number.

3. The electric power steering apparatus according to claim 2, wherein said dq-axes dead time compensation values are changeable based on at least one of said dq-axes steering-assist command values.

4. The electric power steering apparatus according to claim 1, wherein the at least one hardware processor is further configured to implement calculating a current command value sensitive-gain that makes a compensation amount of said dq-axes dead time compensation values be changeable depending on at least one of said dq-axes steering-assist command values.

5. An electric power steering apparatus of a vector control system, the electric power steering apparatus comprising: at least one hardware processor configured to implement: calculating dq-axes steering-assist command values based on at least a steering torque; calculating dq-axes current command values from said dq-axes steering-assist command values; converting said dq-axes current command values into 3-phase duty command values; driving-controlling a 3-phase brushless motor by an inverter of a pulse width modulation (PWM) control; controlling application of an assist torque to a steering system of a vehicle; an angle-dead time compensation-value functional section to calculate 3-phase dead time reference compensation values based on a motor rotational angle; an inverter-applying voltage sensitive-gain calculating section to calculate a voltage sensitive-gain based on an inverter-applying voltage; and a dead time compensation-value outputting section to add dq-axes dead time compensation values that are obtained by multiplying said 3-phase dead time reference compensation values with said voltage sensitive-gain and converting 3-phase multiplied values into dq-axes values, to dq-axes voltage command values that are obtained by processing said dq-axes current command values.

6. The electric power steering apparatus according to claim 5, wherein said dead time compensation-value outputting section comprises: multiplying sections to multiply said 3-phase dead time reference compensation values with said voltage sensitive-gain; and a 3-phase alternating current (AC) to dq-axes converting section to convert 3-phase outputs of said multiplying sections into said dq-axes dead time compensation values.

7. The electric power steering apparatus according to claim 5, wherein the at least one hardware processor is further configured to implement a current command value sensitive-gain calculating section to calculate a current command value sensitive-gain that makes a compensation amount of said dq-axes dead time compensation values be changeable depending on at least one of said dq-axes steering-assist command values.

8. An electric power steering apparatus of a vector control system, the electric power steering apparatus comprising: at least one hardware processor configured to implement: calculating dq-axes steering-assist command values based on at least a steering torque; calculating dq-axes voltage command values from said dq-axes steering-assist command values; converting said dq-axes voltage command values into 3-phase duty command values; driving-controlling a 3-phase brushless motor by an inverter of a pulse width modulation (PWM) control; controlling application of an assist torque to a steering system of a vehicle; an angle-dead time compensation-value reference table having a characteristic that 3-phase dead time compensation values based on a motor rotational angle are converted into 2-phase values; an inverter-applying voltage sensitive-gain calculating section to calculate a voltage sensitive-gain based on an inverter-applying voltage; a first multiplying section to multiply dq-axes dead time reference compensation values from said angle-dead time compensation-value reference table with said voltage sensitive-gain; a current command value sensitive-gain calculating section to calculate a current command value sensitive-gain in order that a compensation amount is changeable depending on said dq-axes steering-assist command values; and a second multiplying section to multiply outputs of said first multiplying section with said current command value sensitive-gain, wherein a dead time compensation is performed by adding outputs of said second multiplying section to said dq-axes voltage command values.

9. The electric power steering apparatus according to claim 8, wherein said current command value sensitive-gain calculating section comprises: a current control delay model to compensate a delay of a current by inputting at least one of said dq-axes steering-assist command values; a compensation sign estimating section to estimate a sign of an output of said current control delay model; a current command value sensitive-gain section to output a sensitive gain based on an output of said current control delay model; and a third multiplying section to multiply said sensitive gain with said sign.

10. An electric power steering apparatus of a vector control system, the electric power steering apparatus comrising: at least one hardware processor configured to implement: calculating dq-axes steering-assist command values based on at least a steering torque; calculating dq-axes current command values from said dq-axes steering-assist command value; converting said dq-axes current command values into 3-phase duty command values; driving-controlling a 3-phase brushless motor by an inverter of a pulse width modulation (PWM) control; applying an assist torque to a steering system of a vehicle; a spatial vector modulating section to obtain 3-phase voltage command values by spatial-vector-modulating said dq-axes current command values; an angle-dead time compensation-value functional section to calculate 3-phase dead time reference compensation values based on a motor rotational angle; an inverter-applying voltage sensitive-gain calculating section to calculate a voltage sensitive-gain based on an inverter-applying voltage; a first multiplying section to obtain first 3-phase dead time compensation values by multiplying said 3-phase dead time reference compensation values with said voltage sensitive-gain; a current command value sensitive-gain calculating section to calculate a current command value sensitive-gain in which a compensation amount of said first 3-phase dead time compensation values is changeable depending on said dq-axes steering-assist command values; and a dead time compensation-value outputting section to output second dead time compensation values by multiplying said first 3-phase dead time compensation values with said current command value sensitive-gain, wherein a dead time compensation of said inverter is performed by adding said second dead time compensation values to said 3-phase voltage command values.

11. The electric power steering apparatus according to claim 10, wherein said current command value sensitive-gain calculating section comprises: a current control delay model to compensate a delay of a current by inputting at least one of said dq-axes steering-assist command values; a compensation sign estimating section to estimate a sign of an output of said current control delay model; a current command value sensitive-gain section to output said current command value sensitive-gain based on an output of said current control delay model; and a second multiplying section to multiply said current command value sensitive-gain with said sign.

12. The electric power steering apparatus according to claim 1, wherein controlling application of the assist torque comprises controlling the steering system to implement physically outputting the assist torque.

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 detail configuration example of a dead time compensating section according to the present invention;

(8) FIG. 7 is a block diagram showing a configuration example of a current command value sensitive-gain section;

(9) FIG. 8 is a characteristic diagram showing a gain section in the current command value sensitive-gain section;

(10) FIG. 9 is a characteristic diagram showing a characteristic example of the current command value sensitive-gain section;

(11) FIG. 10A and FIG. 10B are waveform charts showing an operation example of a compensation sign estimating section;

(12) FIG. 11 is a block diagram showing a configuration example of an inverter-applying voltage sensitive-gain section;

(13) FIG. 12 is a characteristic diagram showing a characteristic example of the inverter-applying voltage sensitive-gain section;

(14) FIG. 13 is a characteristic diagram showing a characteristic example of a phase adjusting section;

(15) FIG. 14 is a diagram showing an operation example of a respective angle-dead time compensation-value functional section;

(16) FIG. 15 is a block diagram showing a configuration example of a spatial vector modulating section;

(17) FIG. 16 is a diagram showing an operation example of the spatial vector modulating section;

(18) FIG. 17 is a diagram showing an operation example of the spatial vector modulating section;

(19) FIG. 18 is a timing chart showing an operation example of the spatial vector modulating section;

(20) FIG. 19 is a waveform chart showing an effect of the spatial vector modulation;

(21) FIG. 20 is a waveform chart showing an effect of the present invention (the first embodiment);

(22) FIG. 21 is a waveform chart showing an effect of the present invention (the first embodiment);

(23) FIG. 22 is a block diagram showing a configuration example (the second embodiment) of the present invention;

(24) FIG. 23 is a block diagram showing a detail configuration example of the dead time compensating section according to the present invention;

(25) FIG. 24 is a diagram showing an operation example of the respective angle-dead time compensation-value functional section;

(26) FIG. 25A and FIG. 25B are characteristic diagrams showing an output voltage characteristic of a dq-axes angle-dead time compensation-value reference table;

(27) FIG. 26 is a waveform chart showing an effect of the present invention (the second embodiment);

(28) FIG. 27 is a waveform chart showing an effect of the present invention (the second embodiment);

(29) FIG. 28 is a block diagram showing a configuration example (the third embodiment) of the present invention;

(30) FIG. 29 is a block diagram showing a detail configuration example of the dead time compensating section according to the present invention;

(31) FIG. 30 is a waveform chart showing an effect of the present invention (the third embodiment); and

(32) FIG. 31 is a waveform chart showing an effect of the present invention (the third embodiment).

MODE FOR CARRYING OUT THE INVENTION

(33) 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, the present invention treats dead time compensation values as a function of a motor rotational angle (an electric angle), and performs a feed-forward compensation to 3-phase voltage command values after a dq-axes modulation or a spatial vector modulation. The dq-axes dead time compensation values or the 3-phase dead time compensation values are previously obtained by using the function depending on the motor rotational angle (the electric angle) in offline. A dq-axes angle (a 3-phase angle)-dead time compensation-value reference table is created based on the output waveforms of the above compensation values. The feed-forward dead time compensation is performed to the dq-axes voltage command values or the 3-phase voltage command values by using the dq-axes angle (the 3-phase angle)-dead time compensation-value reference table.

(34) Adjustment of an appropriate dead time compensation amount and an estimation of a compensation direction can be performed by using steering-assist command values of a dq-axes command section or a 3-phase command section. The dead time compensation amount is adjusted by an inverter-applying voltage, appropriately. The dead time compensation values due to the motor rotational angle can be calculated on a real time, and the dead time compensation values depending on the motor rotational angle can be compensated on the dq-axes voltage values or the 3-phase voltage values.

(35) In a low speed steering region and a middle speed steering region, there are problems (the steering sound is louder, and the uncomfortable steering feeling increases) that a compensation shift on an amplitude of a particular phase current and a compensation shift in particular rotational number are caused in conventional 3-phase dead time compensation. To adjust a timing in the conventional 3-phase dead time compensation, it is necessary to consider the magnitudes of the rotational number and the amplitude of the phase currents. The optimal adjustment that the both magnitudes are considered is difficult. In the conventional 3-phase dead time compensation, in a case that the 3-phase compensation waveforms are not a rectangular wave, there is a problem that the precise compensation cannot be performed. In order to resolve such a problem, the present invention that has a great effect in the low speed and middle speed steering states, is proposed.

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

(37) 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 200 to calculate dead time compensation values v.sub.d* and v.sub.q* on the dq-axes. The q-axis steering-assist command value I.sub.qref corresponding to the steering-assist command values Iref2 in FIG. 2, a motor rotational angle and a motor rotational number are inputted into the dead time compensating section 200. An inverter-applying voltage VR applied to the inverter 161 is also inputted into the dead time compensating section 200. PWM-signals (U.sub.PWM, V.sub.PWM and W.sub.PWM) from a PWM-control circuit (not shown) in a PWM-control section 160 are inputted into the inverter 161.

(38) A d-axis current command value i.sub.d* and a q-axis current command value i.sub.q* whose maximum values of the steering-assist command values i.sub.dref and i.sub.qref are limited are respectively inputted into subtracting sections 131d and 131q, and current deviations i.sub.d* and i.sub.q* for the feed-back currents i.sub.d and i.sub.q are respectively calculated at the subtracting sections 131d and 131q. The calculated current deviation i.sub.d* is inputted into the PI-control section 120d, and the calculated current deviation i.sub.q* is inputted into the PI-control section 120q. The PI-controlled d-axis voltage command value v.sub.d and q-axis voltage command value v.sub.q are inputted into the adding sections 121d and 121q, the dead time compensation values v.sub.d* and v.sub.q* from the dead time compensating section 200 described below are added and compensated at the adding section 121d and 121q, and the compensated voltage values are respectively inputted into the subtracting section 141d and the adding section 141q. The voltage v.sub.d1* from the d-q non-interference control section 140 is inputted into the subtracting section 141d, and the voltage command value v.sub.d** being the difference is obtained. The voltage v.sub.q1* from the d-q non-interference control section 140 is inputted into the adding section 141q, and the voltage command value v.sub.q** being the addition result is obtained. The voltage command values v.sub.d** and v.sub.q** which are dead time-compensated are inputted into a spatial vector modulating section 300 that converts 2-phase values on the dq-axes into 3-phase values of a U-phase, a V-phase and a W-phase and superimposes a third-harmonic. 3-phase voltage command values V.sub.u*, V.sub.v* and V.sub.w* vector-modulated at the spatial vector modulating section 300 are inputted into the PWM-control section 160, and the motor 100 is driving-controlled via the PWM-control section 160 and the inverter 161 as described above.

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

(40) The dead time compensating section 200 comprises a current control delay model 201, a compensation sign estimating section 202, multiplying sections 203, 204d and 204q, an adding section 221, a phase adjusting section 210, an inverter-applying voltage sensitive-gain section 220, angle-dead time compensation-value functional sections 230U, 230V and 230W, multiplying sections 231U, 231V and 231W, a 3-phase alternating current (AC)/dq-axes converting section 240, and a current command value sensitive-gain section 250.

(41) As well, the multiplying sections 231U, 231V and 231W and the 3-phase AC/dq-axes converting section 240A constitute a dead time compensation-value outputting section. The current control delay model 201, the compensation sign estimating section 202, the current command value sensitive-gain section 250 and the multiplying section 203 constitute a current command value sensitive-gain calculating section.

(42) The detail configuration of the dead time compensating section 200 is shown in FIG. 6, and will be described with reference to FIG. 6.

(43) The q-axis steering-assist command value i.sub.qref is inputted into the current control delay model 201. A delay due to a noise filter or the like in the ECU is occurred until the dq-axes current command values i.sub.d* and i.sub.q* are reflected for the actual currents. 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 embodiment approximates the delay of the overall current control as a first order filter model and improves the phase difference. The current control delay model 201 of the first embodiment is a primary filter of the below Expression 1 and T denotes a filter time constant. The current control delay model 201 may be a model of a secondary filter or higher order filter.

(44) $\begin{matrix} \frac{1}{Ts + 1} & [Expression 1] \end{matrix}$

(45) The current command value I.sub.cm outputted from the current control delay model 201 is inputted into the current command value sensitive-gain section 250 and the compensation sign estimating section 202. In a low current region, a case that the dead time compensation amount is overcompensated is occurred. The current command value sensitive-gain section 250 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 i.sub.qref), 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 i.sub.qref), or the like, a noise reduction process is performed by using a weighted average filter.

(46) The current command value sensitive-gain 250 has a configuration shown in FIG. 7. An absolute value of the current command value I.sub.cm is calculated at an absolute value section 251. The absolute value of the current command value I.sub.cm whose maximum value is limited is inputted into a weighted average filter 254 via a scale converting section 253. The current command value I.sub.am that the noise is reduced at the weighted average filter 254 is addition-inputted into a subtracting section 255, and a predetermined offset OS is subtracted from the current command value I.sub.am at the subtracting section 255. The reason for subtracting the offset OS 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 offset OS is a constant value. The current command value I.sub.as that the offset OS is subtracted at the subtracting section 255 is inputted into a gain section 256, and the current command value sensitive-gain G.sub.c is outputted in accordance with a gain characteristic as shown in FIG. 8.

(47) The current command value sensitive-gain G.sub.c outputted from the current command value sensitive-gain section 250 has a characteristic, for example, as shown in FIG. 9, for 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 zero.

(48) The compensation sign estimating section 202 outputs a compensation sign SN, which has a positive value (+1) or a negative value (1) and indicates a hysteresis characteristic shown in FIGS. 10A and 10B, against the inputted current command value I.sub.cm. The compensation sign SN 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 SN has the hysteresis characteristic. The estimated compensation sign SN is inputted into the multiplying section 203. The positive and negative thresholds of the hysteresis characteristic are appropriately changeable.

(49) In a case that the sign of the dead time compensation value is simply determined from the current sign of the phase-current command value model, the chattering is occurred in the low load. When the handle is slightly steered to the left or the right near the on-center, the torque ripple is occurred. In order to improve this problem, the hysteresis is adopted in the sign judgement. The current sign is held except for a case that the sign is changed beyond the set current value, and the chattering is suppressed.

(50) The current command value sensitive-gain G.sub.c from the current command value sensitive-gain section 250 is inputted into the multiplying section 203. The multiplying section 203 outputs the current command value sensitive-gain G.sub.cs (=G.sub.cSN) that the compensation sign SN is multiplied with the current command value sensitive-gain G.sub.c. The current command value sensitive-gain G.sub.cs is inputted into the multiplying sections 204d and 204q.

(51) Further, since the optimal dead time compensation amount varies depending on the inverter-applying voltage VR, the present embodiment (the first embodiment) calculates the voltage sensitive-gain G.sub.v 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 220 to output the voltage sensitive-gain G.sub.v by inputting the inverter-applying voltage VR is shown in FIG. 11. An absolute value of the maximum value of the inverter-applying voltage VR is limited in an input limiting section 221 and the limited inverter-applying voltage VR.sub.I is inputted into an inverter-applying voltage/dead time compensation-gain converting table 222. The characteristic of the inverter-applying voltage/dead time compensation-gain converting table 222 is shown, for example, in FIG. 12. 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 voltage sensitive-gain G.sub.v is inputted into the multiplying sections 231U, 231V and 231W.

(52) In a case that the dead time compensation timing is hastened or is delayed in response to the motor rotational number w, the phase adjusting section 210 has a function to calculate the adjustment angle depending on the motor rotational number w. The phase adjusting section 210 has a characteristic as shown in FIG. 13 in a case of a lead angle control. The calculated phase adjustment angle is inputted into the adding section 221 and is added to the detected motor rotational angle . The motor rotational angle .sub.m (=+G) that is an added result of the adding section 421 is inputted into the angle-dead time compensation-value functional sections 230U, 230V and 230W and the 3-phase AC/dq-axes converting section 240.

(53) After detecting a motor electric angle and calculating the duty command values, a time delay whose time is several tens of microseconds to one hundred microseconds is existed until actually reflecting for the PWM-signals. Since the motor is rotating during the delay time, a phase shift between the motor electric angle in the calculation and the motor electric angle in the reflection is generated. In order to compensate this phase shift, the lead angle is performed depending on the motor rotational number and the phase is adjusted.

(54) The angle-dead time compensation-value functional sections 230U, 230V and 230W, as shown in FIG. 14 in detail, respectively output respective 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 to 359 [deg] in the electric angle, to the phase-adjusted motor rotational angle .sub.m. The angle-dead time compensation-value functional sections 230U, 230V and 230W treat the dead time compensation values, which are needed in the 3-phases, as functions depending on the angle, calculates the dead time compensation values in the real time of the ECU, and outputs the 3-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.

(55) The dead time compensation values U.sub.dt, V.sub.dt and W.sub.dt are respectively inputted into multiplying sections 231U, 231V and 231W, and are multiplied with the voltage sensitive-gain G.sub.v. The 3-phase dead time compensation values U.sub.dtc (=G.sub.v.Math.U.sub.dt), V.sub.dtc (=G.sub.v.Math.V.sub.dt) and W.sub.dtc (=G.sub.v.Math.W.sub.dt) which are multiplied with the voltage sensitive-gain G.sub.v are inputted into the 3-phase AC/dq-axes converting section 240. The 3-phase AC/dq-axes converting section 240 converts the 3-phase dead time compensation values U.sub.dtc, V.sub.dtc, and W.sub.dtc into the 2-phase dq-axes dead time compensation values v.sub.da* and v.sub.qa*, in synchronization with the motor rotational angle m. The 2-phase dq-axes dead time compensation values v.sub.da* and v.sub.qa* are respectively inputted into the multiplying sections 204d and 204q, and are multiplied with the current command value sensitive-gain G.sub.cs. The multiplied results at the multiplying sections 204d and 204q are the dead time compensation value v.sub.d* and v.sub.q*. The dead time compensation value v.sub.d* and v.sub.q are respectively added to the voltage command values v.sub.d and v.sub.q at the adding sections 121d and 121q. The voltage command values v.sub.d** and v.sub.q**, which are the added results, are inputted into the spatial vector modulation section 300 via the adding section 141d and the subtracting section 141q.

(56) In the first embodiment, the dead time compensation values are 3-phase functions depending on the motor rotational angle (the electric angle), and the control unit (ECU) has a configuration that the 3-phase dead time compensation values are converted into the dq-axes dead time compensation values by the 3-phase/dq-axes conversion, and the voltage command values on the dq-axes are compensated by feed-forwarding the dq-axes dead time compensation values. The dq-axes steering-assist command values are used in the compensation sign of the dead time. The compensation amount is changeable so that the magnitude of the compensation amount is optimal depending on the magnitude of the steering-assist command value i.sub.qref and the magnitude of the inverter-applying voltage VR.

(57) Next, the spatial vector modulation will be described.

(58) As shown in FIG. 15, the spatial vector modulating section 300 may have a function that converts the 2-phase voltages v.sub.d** and v.sub.q** on the d-q space into the 3-phase voltages V.sub.ua, V.sub.va and V.sub.wa, and superimposes the third harmonic on the 3-phase voltages V.sub.ua, V.sub.va and V.sub.wa. For example, the method of the spatial vector modulation that the applicant proposes in Japanese Unexamined Patent Publication No. 2017-70066, WO2017/098840 (Japanese Patent Application No. 2015-239898) and the like may be used.

(59) That is, the spatial vector modulation has a function that performs a following coordinate transformation based on the voltage command values v.sub.d** and v.sub.q** on 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 reference to the coordinate transformation, in the spatial 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 2. A relationship between the coordinate axes that are used in this coordinate transformation and the motor rotational angle is shown in FIG. 16.

(60) $\begin{matrix} [\begin{matrix} V \\ V \end{matrix}] = [\begin{matrix} \cos & - \sin \\ \sin & \cos \end{matrix}] [\begin{matrix} v_{d}^{**} \\ v_{q}^{**} \end{matrix}] & [Expression 2] \end{matrix}$

(61) A relationship shown in an Expression 3 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 3]

(62) In the switching pattern of the spatial 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 spatial vector diagram of FIG. 17, 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 spatial 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. 17, 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 (=+).

(63) FIG. 18 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 spatial vector control. The spatial 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.

(64) The spatial 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. 18, in a case of the sector number #1 (n=1), one example of the switching patterns S1 to S6 of 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 .

(65) In a case that the spatial vector modulation is not performed, the dead time compensation of the present invention is applied on the dq-axes, and the dead time compensation value waveform (the U-phase waveform) that the dq-axes/3-phase converting is performed to only the dead time compensation value is shown in a waveform represented by a dashed line of FIG. 19 that the third-order component is removed. The same phenomena are exhibited in the V-phase and the W-phase. By applying the spatial vector modulation instead of the dq-axes/3-phase converting, the third-harmonic can be superimposed on the 3-phase signals, the third-order component that is removed by the 3-phase converting can be compensated, and the ideal dead time compensation waveform that is shown in a solid line of FIG. 19 can be generated.

(66) FIGS. 20 and 21 are simulation results showing an effect of the present invention (the first embodiment). FIG. 20 shows the U-phase current, the d-axis current and the q-axis current in a case that the dead time compensation is not performed. By applying the dead time compensation of the present invention (the first embodiment), in the low speed and middle speed steering states, the improvements in the waveform distortion of the phase currents and the dq-axes currents as shown in FIG. 21 (the ripple is reduced in the dq-axes current waveforms and the phase currents whose waveforms are almost sinusoidal are obtained) can be confirmed. The torque ripple in steering and the steering sound are improved.

(67) FIGS. 20 and 21 typically show the U-phase current.

(68) Next, a second embodiment according to the present invention will be described.

(69) FIG. 22 shows an overall configuration of the present invention (the second embodiment), corresponding to FIG. 5. The dead time compensation section 200A that calculates the dead time compensation value V.sub.d* and V.sub.q* on the dq-axes is disposed, and the detail configuration of the dead time compensation section 200A is shown in FIG. 23. In the following, the explanation is performed with reference to FIG. 23.

(70) The dead time compensation section 200A comprises the current control delay model 201, which has the same configuration as that of the first embodiment and performs the same operation as that of the first embodiment, the compensation sign estimating section 202, the phase adjusting section 210, the inverter applying voltage sensitive gain calculating section 220, the adding section 221 and the multiplying sections 203, 204d and 204q. In the second embodiment, ad-axis angle-dead time compensation-value reference table 260d that inputs the motor rotational angle .sub.m and outputs a d-axis dead time reference compensation value v.sub.da, and a q-axis angle-dead time compensation-value reference table 260q that inputs the motor rotational angle .sub.m and outputs a q-axis dead time reference compensation value v.sub.qa are provided. The dead time reference compensation values v.sub.da and v.sub.qa are respectively inputted into the multiplying sections 205d and 205q, and are multiplied with the voltage sensitive-gain G.sub.v from the inverter-applying voltage sensitive-gain section 220. The dead time compensation values v.sub.db and v.sub.qb, which the dead time reference compensation values v.sub.da and v.sub.qa are multiplied with the voltage sensitive-gain G.sub.v, are respectively inputted into the multiplying sections 204d and 204q. The current command value sensitive-gain G.sub.cs is inputted into the multiplying sections 204d and 204q. The dead time compensation values v.sub.d* and v.sub.q*, which are the results that the dead time compensation values v.sub.db and v.sub.qb are multiplied with the current command value sensitive-gain G.sub.cs, are outputted from the multiplying sections 204d and 204q.

(71) The dq-axes angle-dead time compensation-value reference tables 260d and 260q, as shown in FIG. 24 in detail, calculate 3-phase dead time compensation values, which are the angle functions and are needed in the three phases, in an offline, and convert the 3-phase dead time compensation values into dead time compensation values on the dq-axes. That is, as described in the first embodiment, the 3-phase angle-dead time compensation value functional sections 230U, 230V and 230W 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 to 359 [deg] in the electric angle, to the phase-adjusted motor rotational angle .sub.m. The dead time compensation-value functional sections 230U, 230V and 230W calculate the dead time compensation values, which are needed in the three phases, as the function depending on the angle in the offline, and output the 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 U.sub.dt, V.sub.dt and W.sub.dt are different depending on the characteristic of the dead time in the ECU.

(72) The dead time reference compensation values U.sub.dt, V.sub.dt and W.sub.dt are inputted into the 3-phase AC/dq-axes converting section 261, and are converted into the dq-axes dead time compensation values v.sub.da and v.sub.qa whose output waveforms are shown in FIG. 24. The angle-dead time compensation-value reference tables 260d and 260q whose input is the angle .sub.m are generated based on the dq-axes output waveforms of FIG. 24. As shown in FIG. 25A, the dead time compensation-value reference table 260d has a saw teeth shape output voltage characteristic (a d-axis dead time reference compensation value) for the motor rotational angle .sub.m. As shown in FIG. 25B, the dead time compensation-value reference table 260q is added with the offset voltage, and has a wave shape output voltage characteristic (a q-axis dead time reference compensation value).

(73) The dead time reference compensation values v.sub.da and v.sub.qa from the angle-dead time compensation-value reference tables 260d and 260q are respectively inputted into the multiplying sections 205d and 205q, and are multiplied with the voltage sensitive-gain G.sub.v. The dq-axes dead time compensation values v.sub.db and v.sub.qb, which are multiplied with the voltage sensitive-gain G.sub.v, are respectively inputted into the multiplying sections 204d and 204q, and are multiplied with the current command value sensitive-gain G.sub.cs. The dead time compensation values v.sub.d* and v.sub.q* from the multiplying sections 204d and 204q are respectively added to the voltage command values v.sub.d and v.sub.q at the adding sections 121d and 121q. The added values are inputted into the spatial vector modulation section 300 as the voltage command values v.sub.d** and v.sub.q**.

(74) In the present invention (the second embodiment), the dead time compensation values are calculated from the angle-dead time compensation-value reference table which uses the function depending on the motor rotational angle (the electric angle). The second embodiment has a configuration that the dead time compensation values are compensated by directly feed-forwarding (adding) to the voltage command values on the dq-axes. The steering-assist command value (i.sub.qref) is used in the compensation sign of the dead time. The compensation amount is changeable so that the magnitude of the compensation amount is optimal depending on the magnitude of the steering-assist command value i.sub.qref and the magnitude of the inverter-applying voltage.

(75) FIGS. 26 and 27 show the effect of the second embodiment, and also show the U-phase results by a bench test apparatus to which the actual vehicle is simulated. FIG. 26 shows the U-phase current, the d-axis current and the q-axis current in a case that the dead time compensation is not performed. By applying the dead time compensation of the present invention (the second embodiment), in the low speed and middle speed steering states, the improvements in the waveform distortion of the phase currents and the dq-axes currents as shown in FIG. 27 (the ripple is reduced in the dq-axes current waveforms and the phase currents whose waveforms are almost sinusoidal are obtained) can be confirmed. The torque ripple in the steering and the steering sound are improved.

(76) Next, a third embodiment of the present invention is shown in FIG. 28, corresponding to FIG. 5. A detail of the dead time compensation section 200B is shown in FIG. 29. In the third embodiment, the dead time compensating section 200B calculates the 3-phase dead time compensation values V.sub.um, V.sub.vm and V.sub.wm, and the dead time compensation is performed by adding the 3-phase dead time compensation values V.sub.um, V.sub.vm and V.sub.wm to the 3-phase voltage command values V.sub.u*, V.sub.v* and V.sub.w* from the spatial vector modulation section 300.

(77) In the third embodiment, the compensation value adjusting section 270 comprising the multiplying sections 271U, 271V and 271W is provided. The dead time compensation values U.sub.dtc, V.sub.dtc and W.sub.dtc from the multiplying sections 231U, 231V and 231W are respectively inputted into the multiplying sections 271U, 271V and 271W, and are multiplied with the current command value sensitive-gain G.sub.cs. The multiplied results using the current command value sensitive-gain G.sub.cs are outputted as the dead time compensation values V.sub.um, V.sub.vm and V.sub.wm, and the dead time compensation values V.sub.um, V.sub.vm and V.sub.wm are respectively added to the voltage command values V.sub.u*, V.sub.v* and V.sub.w* after the spatial vector modulation at the adding sections 310U, 310V and 310W. The voltage command values V.sub.uc*, V.sub.vc* and V.sub.wc* that are the added results are inputted into the PWM-control section 160.

(78) In the present invention (the third embodiment), the dead time compensation values are 3-phase functions depending on the motor rotational angle (the electric angle), and the control unit (ECU) has a configuration that the dead time compensation values are compensated by directly feed-forwarding to the 3-phase voltage command values. The dq-axes steering-assist command values are used in the compensation sign of the dead time. The compensation amount is changeable so that the magnitude of the compensation amount is optimal depending on the magnitude of the steering-assist command value and the magnitude of the inverter applying voltage.

(79) FIGS. 30 and 31 are simulation results showing an effect of the present invention (the third embodiment). FIG. 30 shows the U-phase current, the d-axis current and the q-axis current in a case that the dead time compensation is not performed. By applying the dead time compensation of the present invention (the third embodiment), in the low speed and middle speed steering states, the improvements in the waveform distortion of the phase currents and the dq-axes currents as shown in FIG. 31 (the ripple is reduced in the dq-axes current waveforms and the phase currents whose waveforms are almost sinusoidal are obtained) can be confirmed. The torque ripple in steering and the steering sound are improved.

EXPLANATION OF REFERENCE NUMERALS

(80) 1 handle (steering wheel) 2 column shaft (steering shaft, handle shaft) 10 torque sensor 12 vehicle speed sensor 13 battery 20, 100 motor 30 control unit (ECU) 31 steering-assist command value calculating section 35, 203, 204 PI-control section 36, 160 PWM-control section 37, 161 inverter 110 angle detecting section 130 3-phase/dq-axes converting section 140 d-q non-interference control section 200, 200A, 200B dead time compensating section 201 current control delay model 202 compensation sign estimating section 210 phase adjusting section 220 inverter-applying voltage sensitive-gain section 230U, 230V, 230W angle-dead time compensation-value functional section 240 3-phase AC/dq-axes converting section 250 current command value sensitive-gain section 300 spatial vector modulating section 301 2-phase/3-phase converting section 302 third-harmonic superimposition section

Electric power steering apparatus

Assignee

Inventors

Cpc classification

Classification Explorer

H02P21/50

ELECTRICITY

Classification Explorer

H02M7/48

ELECTRICITY

Classification Explorer

B62D6/00

PERFORMING OPERATIONS; TRANSPORTING

Classification Explorer

B62D5/04

PERFORMING OPERATIONS; TRANSPORTING

Classification Explorer

H02P27/00

ELECTRICITY

International classification

Classification Explorer

B62D5/00

PERFORMING OPERATIONS; TRANSPORTING

Classification Explorer

B62D6/00

PERFORMING OPERATIONS; TRANSPORTING

Classification Explorer

H02P27/00

ELECTRICITY

Classification Explorer

H02M7/48

ELECTRICITY

Classification Explorer

H02P21/00

ELECTRICITY

Classification Explorer

B62D5/04

PERFORMING OPERATIONS; TRANSPORTING

Abstract

Claims

Description