ELECTRIC POWER STEERING APPARATUS

Abstract

A vector-control type electric power steering apparatus that applies an assist torque to a steering mechanism of a vehicle, including: a temperature coefficient calculating section to calculate a temperature coefficient depending on a temperature of a control section including the inverter, wherein a dead time compensation of the inverter is performed by estimating compensation signs of 3-phase current model command values in which the dq-phase current command values are converted into a 3-phase current command value model, calculating a first dead time compensation amount based on an inverter applying voltage, calculating a second dead time compensation amount by multiplying the first dead time compensation amount by the temperature coefficient, and adding 2-phase dead time compensation values in which values multiplied the second dead time compensation amount by the compensation signs are converted into 2-phase values, to dq-phase voltage command values.

Claims

1.-6. (canceled)

7. A vector-control type electric power steering apparatus that converts dq-phase current command values calculated based on at least a steering torque into 3-phase duty command values, drives and controls a 3-phase brushless motor by a pulse width modulation (PWM) controlled inverter, and applies an assist torque to a steering mechanism of a vehicle, comprising: a temperature coefficient calculating section to calculate a temperature coefficient depending on a temperature of a control section including said inverter, wherein said temperature coefficient calculating section measures required dead time compensation amounts at three points that are a compensation amount setting temperature, a performance guarantee temperature upper-limit and a performance guarantee temperature lower-limit, by setting a value of said compensation amount setting temperature as a reference value, calculates a ratio of said dead time compensation amount at said performance guarantee temperature upper-limit to said reference value and a ratio of said dead time compensation amount at said performance guarantee temperature lower-limit to said reference value, respectively, and calculates said temperature coefficient, and wherein a dead time compensation of said inverter is performed by estimating compensation signs of 3-phase current model command values in which said dq-phase current command values are converted into a 3-phase current command value model, calculating a first dead time compensation amount based on an inverter applying voltage, calculating a second dead time compensation amount by multiplying said first dead time compensation amount by said temperature coefficient, and adding dead time compensation values in which values multiplied said second dead time compensation amount by said compensation signs are converted into 2-phase values, to dq-phase voltage command values.

8. A vector-control type electric power steering apparatus that converts dq-phase current command values calculated based on at least a steering torque into 3-phase voltage command values, calculates duty command values based on said 3-phase voltage command values, drives and controls a 3-phase brushless motor by a pulse width modulation (PWM) controlled inverter, and applies an assist torque to a steering mechanism of a vehicle, comprising: a temperature coefficient calculating section to calculate a temperature coefficient depending on temperature of a control section including said inverter, wherein said temperature coefficient calculating section measures required dead time compensation amounts at three points that are a compensation amount setting temperature, a performance guarantee temperature upper-limit and a performance guarantee temperature lower-limit, by setting a value of said compensation amount setting temperature as a reference value, calculates a ratio of said dead time compensation amount at said performance guarantee temperature upper-limit to said reference value and a ratio of said dead time compensation amount at said performance guarantee temperature lower-limit to said reference value, respectively, and calculates said temperature coefficient, and wherein a dead time compensation of said inverter is performed by estimating compensation signs of 3-phase current model command values in which said dq-phase current command values are converted into a 3-phase current command value model, calculating a first dead time compensation amount based on an inverter applying voltage, calculating a second dead time compensation amount by multiplying said first dead time compensation amount by said temperature coefficient, and adding dead time compensation values in which said second dead time compensation amount is multiplied by said compensation signs, to 3-phase voltage command values.

9. The vector-control type electric power steering apparatus according to claim 7, wherein said inverter is constituted by a bridge circuit of field-effect transistors (FETs) and said temperature is a temperature of said FETs or a temperature in the neighborhood of said FETs.

10. The vector-control type electric power steering apparatus according to claim 8, wherein said inverter is constituted by a bridge circuit of field-effect transistors (FETs) and said temperature is a temperature of said FETs or a temperature in the neighborhood of said FETs.

11. The vector-control type electric power steering apparatus according to claim 7, wherein limit values of said temperature coefficients at said performance guarantee temperature upper-limit and said performance guarantee temperature lower-limit are set.

12. The vector-control type electric power steering apparatus according to claim 8, wherein limit values of said temperature coefficients at said performance guarantee temperature upper-limit and said performance guarantee temperature lower-limit are set.

13. The vector-control type electric power steering apparatus according to claim 9, wherein limit values of said temperature coefficients at said performance guarantee temperature upper-limit and said performance guarantee temperature lower-limit are set.

14. The vector-control type electric power steering apparatus according to claim 10, wherein limit values of said temperature coefficients at said performance guarantee temperature upper-limit and said performance guarantee temperature lower-limit are set.

15. The vector-control type electric power steering apparatus according to claim 11, wherein said temperature coefficient among said three points is obtained by linear interpolation calculation or a data table to said temperature.

16. The vector-control type electric power steering apparatus according to claim 12, wherein said temperature coefficient among said three points is obtained by linear interpolation calculation or a data table to said temperature.

17. The vector-control type electric power steering apparatus according to claim 13, wherein said temperature coefficient among said three points is obtained by linear interpolation calculation or a data table to said temperature.

18. The vector-control type electric power steering apparatus according to claim 14, wherein said temperature coefficient among said three points is obtained by linear interpolation calculation or a data table to said temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In the accompanying drawings:

[0029] FIG. 1 is a configuration diagram showing a general outline of an electric power steering apparatus;

[0030] FIG. 2 is a block diagram showing a configuration example of a control system of the electric power steering apparatus;

[0031] FIG. 3 is a block diagram showing a configuration example of a vector control system;

[0032] FIG. 4 is a wiring diagram showing a configuration example of a general inverter;

[0033] FIG. 5 is a block diagram showing a configuration example (the first embodiment) of the present invention;

[0034] FIG. 6 is a characteristic diagram showing one example of a characteristic of a phase adjusting section;

[0035] FIG. 7 is a block diagram showing a configuration example of an inverter applying voltage-sensitive compensation-amount calculating section;

[0036] FIG. 8 is a characteristic diagram showing a characteristic example of the inverter applying voltage-sensitive compensation-amount calculating section;

[0037] FIG. 9 is a characteristic diagram showing a characteristic example of a temperature coefficient calculating section;

[0038] FIG. 10 is a characteristic diagram showing a setting example of the temperature coefficient;

[0039] FIG. 11 is a waveform chart showing one example of an output waveform of a 3-phase current command value model;

[0040] FIGS. 12A and 12B are waveform charts showing an operation example of a phase current compensation sign estimating section;

[0041] FIG. 13 is a block diagram showing a configuration example of a space vector modulating section;

[0042] FIG. 14 is a diagram showing an operation example of the space vector modulating section;

[0043] FIG. 15 is a diagram showing an operation example of the space vector modulating section;

[0044] FIG. 16 is a timing chart showing an operation example of the space vector modulating section;

[0045] FIG. 17 is a waveform chart showing an effect of the space vector modulating section;

[0046] FIGS. 18A, 18B and 18C are waveform charts showing an effect of the present invention (the first embodiment);

[0047] FIGS. 19A, 19B and 19C are waveform charts showing an effect of the present invention (the first embodiment);

[0048] FIGS. 20A, 20B and 20C are waveform charts showing an effect of the present invention (the first embodiment);

[0049] FIGS. 21A, 21B and 21C are waveform charts showing an effect of the present invention (the first embodiment);

[0050] FIGS. 22A, 22B and 22C are waveform charts showing an effect of the present invention (the first embodiment);

[0051] FIGS. 23A, 23B and 23C are waveform charts showing an effect of the present invention (the first embodiment);

[0052] FIG. 24 is a block diagram showing a configuration example (the second embodiment) of the present invention;

[0053] FIG. 25 is a waveform chart showing an effect of the present invention (the second embodiment); and

[0054] FIG. 26 is a waveform chart showing an effect of the present invention (the second embodiment).

MODE FOR CARRYING OUT THE INVENTION

[0055] In order to resolve problems that a current distortion and a torque ripple occur and a steering sound becomes louder due to an influence of a dead time of an inverter in a control section (ECU), the present invention performs a dead time compensation by converting dq-phase current command values into 3-phase current model command values, estimating compensation signs, calculating a dead time compensation amount which is calculated from an inverter applying voltage and is corrected depending on a temperature of the ECU, calculating dead time compensation values based on the dead time compensation amount and the estimated compensation signs, and converting the dead time compensation values into 2-phase values and adding (feed-forwarding) the 2-phase values to dq-phase voltage command values (the first embodiment), or adding (feed-forwarding) the dead time compensation values to 3-phase voltage command values (the second embodiment). Thereby, the electric power steering apparatus compensates the dead time of the inverter on the dq-phase or on the 3-phase without a tuning operation, and improves the distortion of the current waveform and the responsibility of the current control.

[0056] Embodiments of the present invention will be described with reference to the accompanying drawings as follows.

[0057] FIG. 5 shows an overall configuration of the present invention (the first embodiment) corresponding to FIG. 3, and there is provided a dead time compensating section 200 to calculate dq-phase dead time compensation values v.sub.d* and v.sub.q*. A d-phase current command value i.sub.d* and a q-phase current command value i.sub.q*, a motor rotational angle and a motor angular velocity are inputted into the dead time compensating section 200. The inverter applying voltage VR applied to the inverter 161 is also inputted into the dead time compensating section 200. In the present invention, there is provided a temperature detecting section 400 to detect (or estimate) a temperature of a power device such as FETs of the control section (ECU) or a temperature neighborhood of the power device of the control section (ECU), and the temperature Tm detected at the temperature detecting section 400 is inputted into the dead time compensating section 200.

[0058] The d-phase current command value i.sub.d* and the q-phase current command value i.sub.q* in which the maximum values of the steering assist command values calculated at a steering assist command value calculating section (not shown) are limited are respectively inputted into subtracting sections 131d and 131q, and a current deviation i.sub.d* between the d-phase current command value i.sub.d* and the feed-back current i.sub.d and a current deviation i.sub.q* between the q-phase current command value i.sub.q* and the feed-back current i.sub.q are respectively calculated at the subtracting sections 131d and 131q. The calculated current deviation i.sub.d* is inputted into a PI-control section 120d, and the calculated current deviation i.sub.q* is inputted into a PI-control section 120q. The PI-controlled d-phase voltage command value v.sub.d and the PI-controlled q-phase voltage command value v.sub.q are respectively inputted into adding sections 121d and 121q, and are compensated by respectively adding to the dead time compensation values v.sub.d* and v.sub.q* from the dead time compensating section 200 described below. The compensated voltage values are inputted into a subtracting section 141d and an adding section 141q, respectively. The voltage v.sub.d1* from a d-q decoupling control section 140 is inputted into the subtracting section 141d and a d-phase voltage command value v.sub.d** which is the difference is obtained at the subtracting section 141d. The voltage v.sub.q1* from the d-q decoupling control section 140 is inputted into the adding section 141q and a q-phase voltage command value v.sub.q** which is the added result is obtained at the adding section 141q. The voltage command values v.sub.d** and v.sub.q** whose dead time is compensated are inputted into a space vector modulating section 300, and converted from 2-phase values on the dq-phase into 3-phase values constituted by U-phase, V-phase and W-phase, in which the third-harmonic is superimposed. The 3-phase voltage command values Vu*, Vv* and Vw* which are vector-modulated at the space vector modulating section 300 are inputted into a PWM-control section 160, and the motor 100 is driven and controlled via the PWM-control section 160 and the inverter 161 as described above.

[0059] Next, the dead time compensating section 200 will be described.

[0060] The dead time compensating section 200 comprises an adding section 201, multiplying sections 202 and 281, an inverter applying voltage-sensitive compensation-amount calculating section 210, a 3-phase current command value model 220, a phase current compensation sign estimating section 221, a phase adjusting section 230, a 3-phase to dq-phase converting section 240, and a temperature coefficient calculating section 280. As well, a dead time compensation value outputting section comprises the multiplying section 202 and the 3-phase to dq-phase converting section 240. A motor rotational angle is inputted into an adding section 201 and a motor angular velocity is inputted into a phase adjusting section 230. An inverter applying voltage VR is inputted into the inverter applying voltage-sensitive compensation-amount calculating section 210, and a phase-adjusted motor rotational angle .sub.m calculated at the adding section 201 is inputted into the 3-phase current command value model 220.

[0061] In a case that the dead time compensation timing is hastened or is delayed in response to the motor angular velocity , there is provided the phase adjusting section 230 which has a function for calculating the adjustment angle depending on the motor angular velocity . The phase adjusting section 230 has a characteristic as shown in FIG. 6 in a case of a lead angle control. The calculated phase adjustment angle is inputted into the adding section 201 and is added to the detected motor rotational angle . The phase-adjusted motor rotational angle .sub.m (=+) that is an added result of the adding section 201 is inputted into the 3-phase current command value model 220 and the 3-phase to dq-phase converting section 240.

[0062] 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 correcting the PWM-signals. Since the motor is rotating during the delay time, a phase deviation between the motor electric angle in the calculation and the motor electric angle in the correction is generated. In order to compensate this phase deviation, the lead angle is performed depending on the motor angular velocity and the phase is adjusted.

[0063] Since the optimal dead time compensation amount varies depending on the inverter applying voltage VR, the present invention calculates the dead time compensation amount DTC depending on the inverter applying voltage VR and makes the dead time compensation amount DTC be changeable. The configuration of the inverter applying voltage-sensitive compensation-amount calculating section 210 to output the dead time compensation amount DTC by inputting the inverter applying voltage VR is shown in FIG. 7. The positive maximum value and the negative maximum value of the inverter applying voltage VR are limited in an input limiting section 211 and the inverter applying voltage VR.sub.I whose maximum value is limited is inputted into an inverter applying voltage/dead time compensation-amount conversion table 212.

[0064] The characteristic of the inverter applying voltage/dead time compensation-amount conversion table 212 is shown, for example, in FIG. 8. That is, the outputted 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) increases when the inverter applying voltage VR is equal to or higher than the predetermined inverter applying voltage VR1 and is lower than a predetermined inverter applying voltage VR2 (>VR1), and is 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. The dead time compensation amount DTC from the inverter applying voltage sensitive compensation amount calculating section 210 is inputted into the multiplying section 281.

[0065] The temperature detecting section 400 detects (or estimates) the temperature of the control section (ECU), for example the temperature of the power device such as the FETs or the temperature in the neighborhood of the power device, and the detected temperature Tm is inputted into the temperature coefficient calculating section 280 in the dead time compensating section 200. As shown in FIG. 9, the temperature coefficient calculating section 280 measures the required dead time compensation amounts at the three points that are a compensation amount setting temperature, a performance guarantee temperature upper-limit and a performance guarantee temperature lower-limit. By setting the value at the compensation amount setting temperature as a reference value 1.00, the ratio of the dead time compensation amount at the performance guarantee temperature upper-limit to that at the compensation amount setting temperature and the ratio of the dead time compensation amount at the performance guarantee temperature lower-limit to that at the compensation amount setting temperature are respectively calculated, and the temperature coefficient Tc is obtained. The temperature coefficient (the ratio) between the three points is obtained by a linear interpolation calculation or the table to the temperature Tm. The limit values of the temperature coefficients at the performance guarantee temperature upper-limit and the performance guarantee temperature lower-limit may be set. When the temperature characteristic of the control section 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 coefficient Tc 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 dead time compensation amount at 40 degrees Celsius increases 10% to the dead time compensation amount at +20 degrees Celsius and the required dead time compensation amount at +80 degrees Celsius decreases 10% to the dead time compensation amount at +20 degrees Celsius, is set, the characteristic table of the temperature coefficient Tc is shown in FIG. 10.

[0066] The temperature coefficient Tc from the temperature coefficient calculating section 280 is inputted into the multiplying section 281 and is multiplied by the dead time compensation amount DTC. The dead time compensation amount DTCb which is corrected by the temperature coefficient Tc is inputted into the multiplying section 202.

[0067] The d-phase current command value i.sub.d*, the q-phase current command value i.sub.q* and the motor rotational angle .sub.m are inputted into the 3-phase current command value model 220. The 3-phase current command value model 220 calculates the sinusoidal 3-phase current model command values I.sub.cm whose phases are shifted each other by 120 [deg] as shown in FIG. 11, from the dq-phase current command values i.sub.d* and i.sub.q* and the motor rotational angle .sub.m by the calculation or using the table (refer to the following Expressions 1 and 2). The 3-phase current model command values I.sub.cm are different depending on the motor type. The d-phase current command value I.sub.ref_d and the q-phase current command value i.sub.ref_q are converted into the 3-phase current command values (U-phase, V-phase and W-phase) using the motor electric angle .sub.e. The above conversion relationship is represented by the following Expression 1.

[00001]$\begin{array}{cc}\left[\begin{array}{c}{i}_{\mathrm{ref\_u}}\\ i_{\mathrm{ref\_v}}\\ i_{\mathrm{ref\_w}}\end{array}\right]=\left[\begin{array}{cc}\cos \left({}_e\right)& \sin \left({}_e\right)\\ \cos \left({}_e-\frac{2}{3}.Math.\right)& \sin \left({}_e-\frac{2}{3}.Math.\right)\\ \cos \left({}_e+\frac{2}{3}.Math.\right)& \sin \left({}_e+\frac{2}{3}.Math.\right)\end{array}\right]\left[\begin{array}{c}{i}_{\mathrm{ref\_d}}\\ i_{\mathrm{ref\_q}}\end{array}\right]& \left[\mathrm{Expression}.Math..Math.1\right]\end{array}$

[0068] The respective phase current command values are calculated from the above Expression 1, and the U-phase current command value model i.sub.ref_u, the V-phase current command value model i.sub.ref_v and the W-phase current command value model i.sub.ref_w are represented by the following Expression 2.

i.sub.ref_u=i.sub.ref_d.Math.cos(.sub.e)+i.sub.ref_q.Math.sin(.sub.e)

i.sub.ref_v=i.sub.ref_d.Math.cos(.sub.e)+i.sub.ref_q.Math.sin(.sub.e)

i.sub.ref_w=i.sub.ref_d.Math.cos(.sub.e+)+i.sub.ref_q.Math.sin(.sub.e+) [Expression 2]

[0069] The table may be stored in an electrically erasable and programmable read-only memory (EEPROM) or may be loaded to a random access memory (RAM). In using the Expression 2, only the values of sin .sub.e are stored in the table. The values of cos .sub.e may be calculated by offsetting the input .sub.e to 90 and other sine function terms may be calculated by offsetting the input .sub.e to 120. In a case that the capacity of the ROM is sufficiently large or the command value model, for example, a model with respect to a pseudo rectangular wave motor or the like, is complicated, all the values in the Expression 2 are stored in the table.

[0070] The 3-phase current model command values I.sub.cm are inputted into the phase current compensation sign estimating section 221. The phase current compensation sign estimating section 221 outputs compensation signs SN, which have a positive value +1 or a negative value 1 and indicate a hysteresis characteristic shown in FIGS. 12A and 12B, against the inputted 3-phase current model command values I.sub.cm. The compensation signs SN are estimated based on zero cross points of the 3-phase current model command values I.sub.cm as a reference. In order to suppress the chattering, the compensation signs SN have the hysteresis characteristic. The estimated compensation signs SN are inputted into the multiplying section 202. Positive and negative thresholds in the hysteresis characteristic are appropriately changeable.

[0071] In a case that the signs of the dead time compensation values are simply determined from the current signs of the phase current command value model, the chattering is occurred in the low load. For example, 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 (0.25 [A] in FIGS. 12A and 12B). In each of the 3-phase currents, the present compensation sign is held except for a case that the current is changed beyond the set current value and the current sign is changed, and the chattering is suppressed.

[0072] The dead time compensation amount DTCb from the multiplying section 281 is inputted into the multiplying section 202. The multiplying section 202 outputs the dead time compensation amounts DTCa (=DTCbSN) that the dead time compensation amount DTCb is multiplied by the compensation signs SN. The dead time compensation amounts DTCa are inputted into the 3-phase to dq-phase converting section 240. The 3-phase to dq-phase converting section 240 outputs the 2-phase dead time compensation values v.sub.d* and v.sub.q* synchronized with the motor rotational angle .sub.m. The dead time compensation value v.sub.d* and v.sub.q* are added to the voltage command values v.sub.d and v.sub.q at the adding sections 121d and 121q, respectively, and the dead time compensation of the inverter 161 is performed.

[0073] In the present invention, the dead time of the inverter is compensated by converting the dq-phase current command values into the 3-phase current model command values, estimating the compensation signs, correcting the dead time compensation amount of the inverter obtained from the inverter applying voltage depending on the temperature of the control section, calculating the dead time compensation values based on the temperature-corrected dead time compensation amount and the compensation signs, and converting the dead time compensation values into 2-phase values and adding (feed-forwarding) the 2-phase values to the dq-phase voltage command values. The 3-phase current model command values are used for determining the compensation signs of the dead time, the dead time compensation amount is calculated from the inverter applying voltage VR and the compensation values are variable so that the magnitudes and directions of the compensation values are optimal depending on the magnitude of the current command values (i.sub.d* and i.sub.q*) and the magnitude of the inverter applying voltage VR.

[0074] Next, the space vector modulation will be described. As shown in FIG. 13, the space vector modulating section 300 may have a function that converts the 2-phase voltages v.sub.d** and v.sub.q** on the dq-phase space into the 3-phase voltages Vua, Vva and Vwa, superimposes the third-harmonic on the 3-phase voltages Vua, Vva and Vwa, and outputs the modulated 3-phase voltages V.sub.u*, V.sub.v* and V.sub.w*. 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.

[0075] That is, the space vector modulation has a function that controls the rotation of the motor by performing a following coordinate transformation based on the voltage command values v.sub.d** and v.sub.q** on the dq-phase space, the motor rotational angle and a sector number n (#1 to #6), and supplying switching patterns S1 to S6, which control turning-ON/turning-OFF of the FETs (the upper-arm Q1, Q3 and Q5, and the lower-arm Q2, Q4 and Q6) of the inverter with the bridge configuration and are corresponding to the sectors #1 to #6, to the motor. With respect to the coordinate transformation, in the space vector modulation, the voltage command values v.sub.d** and v.sub.q** are coordinate-transformed into the voltage vectors V and V in the - coordinate system based on an Expression 3. A relationship between the coordinate axes (the phases) that are used in this coordinate transformation and the motor rotational angle are shown in FIG. 14.

[00002]$\begin{array}{cc}\left[\begin{array}{c}V.Math.\\ V.Math.\end{array}\right]=\left[\begin{array}{cc}\cos .Math..Math.& -\sin .Math..Math.\\ \sin .Math..Math.& \cos .Math..Math.\end{array}\right]\left[\begin{array}{c}{v}_d^{**}\\ v_q^{**}\end{array}\right]& \left[\mathrm{Expression}.Math..Math.3\right]\end{array}$

[0076] A relationship shown in an Expression 4 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 V 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 4]

[0077] In the switching patterns of the space vector control, the output voltage of the inverter 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. 15, depending on the switching patterns S1 to S6 of the FETs (Q1 to Q6). The selection of these reference output voltage vectors V0 to V7 and the occurring time of the selected reference output voltage vector are controlled by the switching patterns. By using six regions sandwiched between adjacent reference output voltage vectors, the space vector can be divided into the six sectors #1 to #6, the target voltage vector V is belong to any one of the sectors #1 to #6, and the sector number can be assigned to the target voltage vector V. The target voltage vector V is a synthetic vector of V and V and there are six sectors in a regular hexagon of the - space, as shown in FIG. 15. Which sector that the target voltage vector V exists can be determined based on the rotational angle of the target voltage vector V in the - coordinate system. 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 (=+).

[0078] FIG. 16 shows a basic timing chart that determines the switching pulse width and the timing in the turning-ON/turning-OFF signals S1 to S6 (switching patterns) to the FETs in order to output the target voltage vector V 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, transforms the calculation result into the respective pulse widths and the timings in the switching patterns S1 to S6 and outputs the transformed result in the next sampling period Ts.

[0079] 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. 16, in a case of the sector number #1 (n=1), one example of the FET switching patterns S1 to S6 of the inverter is shown. The signals S1, S3 and S5 show the gate signals of the FETs 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 .

[0080] In a case that the space vector modulation is not performed, the dead time compensation of the present invention is applied on the dq-phase, and the dead time compensation value waveform (the U-phase waveform) that the dq-phase to 3-phase conversion is performed to only the dead time compensation value is shown in a waveform represented by a dashed line of FIG. 17 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-phase to 3-phase conversion, the third-harmonic can be superimposed on the 3-phase signals, the third-order component that is removed by the 3-phase conversion can be compensated, and the ideal dead time compensation waveform that is shown by a solid line of FIG. 17 can be generated.

[0081] FIGS. 18A to 23C show a simulation validation result performed in a testing apparatus of the present invention (the first embodiment) . In the low load and the low speed steering condition (the motor applying voltage=12 [V], Iq=8 [A], Id=0 [A] and the motor rotational number=120 [rpm]), simulations of with the temperature correction and without the temperature correction are performed. The temperature coefficient Tc in FIG. 10 is used in the temperature characteristic of the control section.

[0082] FIGS. 18A to 20C show the current forms of without the temperature correction. FIG. 18A shows the U-phase current form of without the temperature correction at +20 degrees Celsius, FIG. 18B shows the q-phase current form of without the temperature correction at +20 degrees Celsius, and FIG. 18C shows the d-phase current form of without the temperature correction at +20 degrees Celsius. As shown in FIGS. 18A, 18B and 18C, because the compensation amount is appropriate in the +20 degrees Celsius temperature condition, the distortion of the U-phase current waveform due to the dead time is hardly recognized. FIG. 19A shows the U-phase current form of without the temperature correction at 40 degrees Celsius, FIG. 19B shows the q-phase current form of without the temperature correction at 40 degrees Celsius, and FIG. 19C shows the d-phase current form of without the temperature correction at 40 degrees Celsius. As shown in FIGS. 19A, 19B and 19C, because of the shortage of the compensation amount in the 40 degrees Celsius temperature condition, the concave distortion is existed near 0 [A] in the U-phase current, the wave-shape distortion is occurred in the q-phase current, and the sawtooth-shape distortion is occurred in the d-phase current. FIG. 20A shows the U-phase current form of without the temperature correction at +80 degrees Celsius, FIG. 20B shows the q-phase current form of without the temperature correction at +80 degrees Celsius, and FIG. 20C shows the d-phase current form of without the temperature correction at +80 degrees Celsius. As shown in FIGS. 20A, 20B and 20C, because of too large compensation amount in the +80 degrees Celsius temperature condition, the convex distortion is existed near 0 [A] in the U-phase current, the wave-shape distortion is occurred in the q-phase current, and the sawtooth-shape distortion is occurred in the d-phase current.

[0083] In contrast, FIGS. 21A to 23C show the current forms of with the temperature correction. FIG. 21A shows the U-phase current form of with the temperature correction at +20 degrees Celsius, FIG. 21B shows the q-phase current form of with the temperature correction at +20 degrees Celsius, and FIG. 18C shows the d-phase current form of with the temperature correction at +20 degrees Celsius. As shown in FIGS. 21A, 21B and 21C, because of applying the temperature correction and correcting the compensation amount depending on the temperature, the distortion due to the dead time is hardly recognized in the +20 degrees Celsius temperature condition as well as a case of not applying the temperature correction in the +20 degrees Celsius temperature condition. An adverse influence due to applying the temperature correction is not shown. FIG. 22A shows the U-phase current form of with the temperature correction at 40 degrees Celsius, FIG. 22B shows the q-phase current form of with the temperature correction at 40 degrees Celsius, and FIG. 22C shows the d-phase current form of with the temperature correction at40 degrees Celsius. As shown in FIGS. 22A, 22B and 22C, because of applying the temperature correction of the present invention and correcting the compensation amount depending on the temperature, improvements in the waveform distortions in the U-phase current, the d-phase current and the q-phase current (the ripples in the d-phase current waveform and the q-phase current waveform are reduced and the 3-phase current waveforms are almost sinusoidal) can be confirmed and the torque ripple is also improved in the 40 degrees Celsius temperature condition. FIG. 23A shows the U-phase current form of with the temperature correction at +80 degrees Celsius, FIG. 23B shows the q-phase current form of with the temperature correction at +80 degrees Celsius, and FIG. 23C shows the d-phase current form of with the temperature correction at +80 degrees Celsius. As shown in FIGS. 23A, 23B and 23C, because of applying the temperature correction of the present invention and correcting the compensation amount depending on the temperature, improvements in the waveform distortions in the U-phase current, the d-phase current and the q-phase current (the ripples in the d-phase current waveform and the q-phase current waveform are reduced and the 3-phase current waveforms are almost sinusoidal) can be confirmed and the torque ripple is also improved in the +80 degrees Celsius temperature condition.

[0084] In FIGS. 18A, 19A, 20A, 21A, 22A and 23A, only the U-phase current waveform is typically shown, and the same phenomena are confirmed in the V-phase and W-phase current waveforms.

[0085] Next, the second embodiment which compensate the dead time by adding (feed-forwarding) the dead time compensation values based on the estimated compensation signs to the 3-phase voltage command values will be described with reference to FIG. 24 corresponding to FIG. 5.

[0086] In the second embodiment shown in FIG. 24, the dead time compensating section 200A does not include the 3-phase to dq-phase converting section 240, and thus the adding sections 121d and 121q on the dq-phase are not existed. In the second embodiment, to add (feed-forward) the dead time compensation values based on the estimated compensation signs to the 3-phase voltage command values, there are provided adding sections 163U, 163V and 163W between the space vector modulating section 300 and the PWM-control section 160. The 3-phase dead time compensation values DTC.sub.a (DTC.sub.au, DTC.sub.av and DTC.sub.aw) which are multiplied the dead time compensation amount DTCb by the compensation signs SN at the multiplying section 202 are respectively inputted into the adding sections 163U, 163V and 163W, and the added voltage command values V.sub.u**, V.sub.v** and V.sub.w** in which the dead time compensation is performed are inputted into the PWM-control section 160. The following control operations are the same as those of the first embodiment.

[0087] The characteristics and the operations of the inverter applying voltage-sensitive compensation-amount calculating section 210, the 3-phase current command value model 220, the phase current compensation sign estimating section 221, the phase adjusting section 230 and the temperature coefficient calculating section 280 are similar to those of the first embodiment. The effects of the second embodiment are shown in FIGS. 25 and 26. In FIGS. 25 and 26, only the U-phase current is typically shown.

[0088] In the above-described embodiments, the column type electric power steering apparatus is described. The present invention can similarly be applied to the downstream type electric power steering apparatus.

EXPLANATION OF REFERENCE NUMERALS

[0089] 1 handle (steering wheel) [0090] 2 column shaft (steering shaft, handle shaft) [0091] 10 torque sensor [0092] 12 vehicle speed sensor [0093] 13 battery [0094] 20, 100 motor [0095] 30 control unit (ECU) [0096] 31 steering assist command value calculating section [0097] 35, 203, 204 PI-control section [0098] 36, 160 PWM-control section [0099] 37, 161 inverter [0100] 110 angle detecting section [0101] 130 3-phase to dq-phase converting section [0102] 140 d-q decoupling control section [0103] 200, 200A dead time compensating section [0104] 210 inverter applying voltage-sensitive compensation-amount calculating section [0105] 220 3-phase current command value model [0106] 221 phase current compensation sign estimating section [0107] 230 phase adjusting section [0108] 240 3-phase to dq-phase converting section [0109] 280 temperature coefficient calculating section [0110] 300 space vector modulating section [0111] 301 2-phase to 3-phase converting section [0112] 302 third-harmonic superimposition section [0113] 400 temperature detecting section