JP2009022074A - Motor controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor controller which increases the output while suppressing variation in motor current. <P>SOLUTION: A motor 3 for applying a steering auxiliary power to a steering mechanism 2 is controlled by a motor controller 5. The motor controller 5 controls the motor 3 by controlling a d-axis current and a q-axis current on dq coordinates. A dq-axis current command value operating section 26 sets a q-axis current command value i<SB>qa</SB><SP>*</SP>based on the steering torque and the vehicle speed, compares it with a q-axis current upper limit and a q-axis current lower limit, and then limits the q-axis current command value i<SB>qa</SB><SP>*</SP>depending on the comparison result. Furthermore, the dq-axis current command value operating section 26 determines a d-axis current command value i<SB>da</SB><SP>*</SP>based on the q-axis current command value i<SB>qa</SB><SP>*</SP>thus limited. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a motor control device for determining a command value of a two-phase current in dq coordinates of a motor and controlling the motor based on the command value.

2. Description of the Related Art There is known an electric power steering device that assists steering by transmitting a driving force generated by a motor to a steering mechanism. Specifically, the electric power steering device includes a torque sensor that detects a steering torque applied to the steering wheel, and a motor control device that drives the motor based on the steering torque detected by the torque sensor. .
For example, a three-phase DC brushless motor is applied to the motor. The motor control device performs sinusoidal driving that applies a voltage that changes in a sinusoidal manner to each phase of the stator based on the electrical angle of the rotor. More specifically, for example, the motor control device sets the command value of the two-phase current in the dq coordinate, that is, the d-axis current command value and the q-axis current command value, based on the steering torque detected by the torque sensor. To do. Furthermore, the motor control device detects the d-axis current value and the q-axis current value that are actually flowing through the motor, determines the deviation of the d-axis current value and the q-axis current value with respect to each command value, and responds to these deviations. The d-axis voltage command value and the q-axis voltage command value are calculated. The motor control device converts the d-axis voltage command value and the q-axis voltage command value into three-phase (U-phase, V-phase, W-phase) voltage values, and applies the voltages of these values to each phase of the motor. To do.
WO2006 / 109809

  In the low / medium speed rotation range, the d-axis current command value is set to zero, while the q-axis current command value is set to a value corresponding to the steering torque, whereby the necessary torque can be generated from the motor. However, in the high-speed rotation range, the output (torque) is insufficient due to the counter electromotive force of the motor. Therefore, in order to increase the output of the motor, the d-axis current command value is set to a significant value other than zero, and flux-weakening control is performed to flow current in the direction of weakening the field.

On the other hand, in order for the voltage of each phase to be a sine wave, the amplitude of each phase voltage must be ½ or less of the power supply voltage E _d , and the d-axis voltage V _d and the q-axis voltage V _q The following formula (P1) needs to be established (Patent Document 1).
√ (V _d ² + V _q ² ) ≦ E _d √3 / 2√2 (P1)
Therefore, depending on the d-axis current command value and the q-axis current command value, the d-axis voltage V _d and the q-axis voltage V _q do not satisfy the condition of the expression (P1), and the sine wave drive cannot be performed. Therefore, vibration is generated in the motor, and this vibration is transmitted to the steering wheel via the steering mechanism, resulting in deterioration of the steering feeling.

The prior art of Patent Document 1 restricts the q-axis voltage command value so that the condition of the formula (P1) is satisfied. However, in this prior art, since the q-axis voltage command value set based on the d-axis current command value and the q-axis current command value is limited afterwards, the q-axis current i _q becomes variable. The torque generated by the motor may fluctuate and vibration may occur in the motor. That is, when the q-axis voltage command value is limited in a high-speed rotation region and a high current value region that limit the q-axis voltage command value, the q-axis current i _q is forcibly made smaller than the target value. On the other hand, the d-axis voltage, because it includes also terms (see below formula (7)) including the q-axis current i _q with terms including the d-axis current i _d, by q-axis current i _q is reduced The d-axis current i _d (≦ 0) takes an absolute value larger than the target value. Then, since the absolute value of the d-axis current i _q is increased, there is a margin in the q-axis voltage (see formula (8) below), and an element that can increase the q-axis current i _q is generated. Therefore, the motor control device tries to increase the q-axis current i _q .

Thus, in a situation where the q-axis voltage command value is limited, the d-axis current _id and the q-axis current _iq are determined while interfering with each other on the dq axis. Then, the feedback loop sets a voltage command value for correcting the d-axis current i _d and the q-axis current i _q determined by the process to the d-axis current command value and the q-axis current command value. In this way, the q-axis current i _q becomes fluctuating, causing slight vibrations in the motor, resulting in an uncomfortable feeling of steering.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a motor control device capable of increasing an output while suppressing vibration of the motor.

  The invention according to claim 1 for achieving the above object is a motor control device (5) for controlling a motor (3) by controlling a d-axis current and a q-axis current on a dq coordinate. Q-axis current command value setting means (S2) for setting a q-axis current command value, upper / lower limit value setting means (S1) for setting an upper limit value and a lower limit value of the q-axis current, and the q-axis current command value Comparing means (S3, S5) for comparing the q-axis current command value set by the setting means with the upper limit value and the lower limit value set by the upper limit / lower limit value setting means, and according to the comparison result by the comparing means Based on the q-axis current command value limiting means (S4, S6) for limiting the q-axis current command value and the q-axis current command value after the limit by the q-axis current command value limiting means, D-axis current command value setting means (S ) And a, a motor control device. The alphanumeric characters in parentheses indicate corresponding components in the embodiments described later. The same applies hereinafter.

  According to this configuration, the q-axis current command value is compared with the upper limit value and lower limit value of the q-axis current, and the q-axis current command value is limited according to the comparison result. Then, a d-axis current command value corresponding to the q-axis current command value to which this restriction is added is set. Thus, the q-axis current command value is preliminarily limited and the d-axis current command value is set accordingly, so that the conditions that the d-axis voltage and the q-axis voltage should satisfy can be surely satisfied. Moreover, since the q-axis current command value is limited in advance, there is no possibility that the q-axis current becomes variable as in the case where the voltage command value is limited afterwards. As a result, it is possible to control the magnetic flux weakening by the d-axis current while suppressing or preventing the vibration from occurring in the motor, and to increase the output particularly in the high-speed rotation range.

The invention according to claim 2 is the motor control device according to claim 1, wherein the upper limit / lower limit value setting means sets an upper limit value and a lower limit value according to the rotational angular velocity of the motor.
According to this configuration, an appropriate upper limit value and lower limit value are set according to the rotational angular velocity of the motor, and thus the q-axis current command value can be appropriately limited according to the rotational angular velocity of the motor. Thereby, it can suppress that an excessive restriction | limiting is added to q-axis electric current command value, and can increase the output more effectively in the range which does not produce a vibration of a motor.

ｉ_{qa_uplim}はｑ軸電流上限値
ｉ_{qa_downlim}はｑ軸電流下限値
Ｒはモータの固定子巻線抵抗
φは界磁による固定子鎖交磁束から計算されるｄｑ座標上の磁束
ωはモータの電気角における回転角速度
Ｌ_dはｄ軸インダクタンス
Ｌ_qはｑ軸インダクタンス
Ｖ_limは正弦波駆動が可能なｄｑ座標での制限電圧
この構成によれば、ｄ軸電圧およびｑ軸電圧が正弦波駆動のための条件を満たすように予めｑ軸電流指令値に制限が加えられ、この制限されたｑ軸電流指令値に応じてｄ軸電流指令値が設定される。これにより、モータの振動をより確実に抑制または防止できる。 According to a third aspect of the present invention, the upper limit / lower limit value setting means determines the upper limit value to satisfy the following expression (A), and determines the lower limit value to satisfy the following expression (B): It is a motor control apparatus of description.

i _{qa_uplim} is the q-axis current upper limit value i _{qa_downlim} is the q-axis current lower limit value R is the stator winding resistance of the motor φ is the magnetic flux on the dq coordinate calculated from the stator linkage flux by the field ω is the motor electrical angle Rotational angular velocity L _d is d-axis inductance L _q is q-axis inductance V _lim is a limit voltage in dq coordinates that can be driven by sine wave According to this configuration, d-axis voltage and q-axis voltage are used for sine wave drive. The q-axis current command value is limited in advance so as to satisfy the condition, and the d-axis current command value is set according to the limited q-axis current command value. Thereby, the vibration of the motor can be more reliably suppressed or prevented.

この構成によれば、ｄ軸電圧およびｑ軸電圧が正弦波駆動のための条件を満たす範囲で最大のｑ軸電流指令値が予め求められ、このｑ軸電流指令値に応じてｄ軸電流指令値が設定される。これにより、モータの振動を確実に抑制または防止しつつ、モータの出力を最大限に増加させることができる。 According to a fourth aspect of the present invention, in the motor according to the third aspect, the upper limit / lower limit value setting means determines the upper limit value according to the following equation (A1) and determines the lower limit value according to the following equation (B1): It is a control device.

According to this configuration, the maximum q-axis current command value is obtained in advance within a range where the d-axis voltage and the q-axis voltage satisfy the conditions for sine wave driving, and the d-axis current command is determined according to the q-axis current command value. Value is set. Thereby, the output of the motor can be increased to the maximum while reliably suppressing or preventing the vibration of the motor.

  According to a fifth aspect of the present invention, the upper limit / lower limit value setting means determines the upper limit value to be smaller than a value obtained according to the equation (A1) in a rotational angular velocity range where the absolute value of the rotational angular velocity exceeds a predetermined value. The motor control device according to claim 4, wherein the lower limit value is determined to be larger than a value obtained according to the equation (B1). In this configuration, the q-axis current command value is greatly restricted in the high speed rotation range. As a result, it is possible to suppress or prevent the motor rotation speed from becoming excessive, so that it is possible to effectively avoid problems such as overflow of control variables.

ｉ_da ^*はｄ軸電流指令値
ｉ_qa ^*はｑ軸電流指令値
この構成によれば、正弦波駆動が可能な範囲でｄ軸電流指令値を設定することができるので、モータの振動を抑制しつつ、その出力を増加させることができる。 A sixth aspect of the present invention is the motor control apparatus according to the fourth or fifth aspect, wherein the d-axis current command value setting means sets a d-axis current command value according to the following equation (C).

i _da ^* is the d-axis current command value i _qa ^* is the q-axis current command value According to this configuration, the d-axis current command value can be set within a range in which sine wave drive is possible, so motor vibration is suppressed. However, the output can be increased.

この構成により、正弦波駆動が可能な範囲で、ｄ軸電流指令値の絶対値を可能な限り小さな値に設定することができる。これにより、モータの振動を抑制しつつ、効果的にその出力を増加させることができる。 A seventh aspect of the present invention is the motor control apparatus according to the sixth aspect, wherein the d-axis current command value setting means sets a d-axis current command value according to the following equation (C1).

With this configuration, the absolute value of the d-axis current command value can be set as small as possible within a range in which sine wave driving is possible. Thereby, the output can be effectively increased while suppressing the vibration of the motor.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram for explaining an electrical configuration of an electric power steering apparatus according to an embodiment of the present invention. The electric power steering apparatus includes a torque sensor 1 that detects a steering torque applied to a steering wheel of a vehicle, an electric motor 3 that applies a steering assist force to a steering mechanism 2 of the vehicle, and a motor control that drives and controls the electric motor 3. A device (ECU: electronic control unit) 5 is provided. The motor control device 5 realizes appropriate steering assistance according to the steering situation by driving the electric motor 3 according to the steering torque detected by the torque sensor 1 and the vehicle speed information given through the in-vehicle LAN (CAN bus). To do. In this embodiment, the electric motor 3 is a three-phase brushless DC motor.

The motor control device 5 includes a microcomputer 6 including a CPU, a RAM, and a ROM, motor current detection circuits 7U and 7V for detecting a U-phase current i _ua and a V-phase current i _va flowing in the electric motor 3, respectively, And a resolver amplifier 8 that amplifies an output signal of the resolver 4 as a rotor position sensor attached to the motor, and a motor driver 9 that supplies electric power to the electric motor 3. The resolver amplifier 8 constitutes signal output means together with the resolver 4, processes a signal from the resolver 4, and outputs a sine signal sin θ and a cosine signal cos θ relating to the rotor rotation angle θ of the electric motor 3. The rotor rotation angle θ is an angle (electrical angle) of the rotor (field) with respect to the position of the U-phase armature winding of the electric motor 3.

  The microcomputer 6 captures the output signal of the torque sensor 1 as a steering torque represented by digital data via the A / D conversion port 11 and captures vehicle speed information from the in-vehicle LAN via the communication port 12. The microcomputer 6 sets the current command value of the electric motor 3 based on the steering torque and the vehicle speed, and further determines the voltage command value based on the current command value and the output signals of the motor current detection circuits 7U and 7V. The voltage command value is set and given to the motor driver 9. As a result, an appropriate voltage is applied from the motor driver 9 to the electric motor 3, and a necessary and sufficient torque for assisting steering is generated from the electric motor 3.

  The microcomputer 6 includes a plurality of function processing means realized by executing a predetermined program. The plurality of function processing means includes a target current calculation unit 21 that calculates a target current value based on the steering torque and the vehicle speed. The target current value output by the target current calculation unit 21 is input to the addition unit 22. The addition unit 22 is given correction values from the compensation control unit 23 that performs various types of compensation control, and this correction value is added to the target current value to obtain a corrected target current value. Yes.

The compensation control unit 23 includes, for example, a convergence correction unit that calculates a convergence correction value for improving the convergence of the steering wheel, and adjusts the vehicle speed from the communication port 12 and the rotational angular velocity ω of the rotor of the electric motor 3. Based on this, a correction value for correcting the target current value is calculated.
The microcomputer 6 includes an angular velocity calculation unit 25 for calculating the rotational angular velocity ω (rotational angular velocity in electrical angle) of the rotor of the electric motor 3. The angular velocity calculation unit 25 is supplied with data from the A / D conversion port 13 which converts the output signal of the resolver amplifier 8 into digital data and takes it in. The A / D conversion port 13 samples the output signal of the resolver amplifier 8 at a predetermined sampling period and converts it into digital data, and generates a digitized sine signal sinθ and cosine signal cosθ.

The angular velocity calculation unit 25 may be configured to obtain the rotational angular velocity ω according to the following equation, for example.
ω = Δθ ≒ sinΔθ = sinθ _i cosθ _{i -1} −cosθ _i sinθ _i-1
Where θ _i is the rotor rotation angle at the sampling period,
θ _i-1 is the rotor rotation angle in the previous sampling period
Δθ = θ _i −θ _i−1 .

The microcomputer 6 further includes a dq-axis current command value calculation unit 26. The dq-axis current command value calculator 26 obtains a d-axis current command value i _da ^* and a q-axis current command value i _qa ^* in the dq coordinate system based on the corrected target current value. The dq coordinate system is a rotation orthogonal coordinate system including a d-axis and a q-axis that rotate in synchronization with the rotor of the electric motor 3. The d-axis is an axis along the direction of the magnetic flux formed by the rotor, and the q-axis is an axis that is in a phase advanced by π / 2 with respect to the d-axis. However, in this embodiment, the direction from the south pole to the north pole of the field (rotor) is taken as the positive direction of the d-axis.

The dq-axis current command value calculation unit 26 sets the d-axis current command value i _da ^* ≠ 0 in a high-speed rotation range (for example, a rotation speed range exceeding 800 rpm), and performs so-called weakening magnetic flux control to increase the output. Let
The q-axis current command value i _qa ^* calculated by the dq-axis current command value calculation unit 26 is input to the subtraction unit 27q. The subtractor 27q is obtained by performing three-phase AC / dq coordinate conversion on the U-phase current i _ua and the V-phase current i _va detected by the U-phase motor current detection circuit 7U and the V-phase motor current detection circuit 7V, respectively. The shaft current i _qa is input. The output signals of the U-phase motor current detection circuit 7U and the V-phase motor current detection circuit 7V are converted into digital data by the A / D conversion ports 14 and 15 and taken into the microcomputer 6, and detected by the current detection units 16 and 17. Then, it is input to the three-phase AC / dq coordinate conversion unit 28. The three-phase AC / dq coordinate conversion unit 28 converts the U-phase current i _ua and the V-phase current i _va into values in the dq coordinate system according to the following equation (1).

三相交流／ｄｑ座標変換部２８には、Ａ／Ｄ変換ポート１３からの正弦信号sinθおよび余弦信号cosθが与えられており、これらを用いて前記（１）式に従う演算が行われるようになっている。

The three-phase AC / dq coordinate conversion unit 28 is supplied with the sine signal sinθ and the cosine signal cosθ from the A / D conversion port 13, and the calculation according to the above equation (1) is performed using these signals. ing.

The three-phase AC / dq coordinate conversion unit 28 gives the q-axis current i _qa obtained by the three-phase AC / dq coordinate conversion to the subtraction unit 27q. Accordingly, the subtraction unit 27q outputs a deviation of the q-axis current i _qa from the q-axis current command value i _qa ^* .
On the other hand, the d-axis current command value i _da ^* is input to the subtraction unit 27d. The subtractor 27d has a three-phase AC / dq coordinate conversion unit 28 that performs a three-phase AC / dq coordinate conversion of the U-phase current i _ua and the V-phase current i _va according to the equation (1). The current i _da is input. As a result, the subtraction unit 27d outputs a deviation of the d-axis current i _{da from} the d-axis current command value i _da ^* .

Deviations output from the subtracting units 27d and 27q are given to a d-axis current PI (proportional integration) control unit 29d and a q-axis current PI control unit 29q, respectively. The PI control units 29d and 29q perform the PI calculation based on the deviations input from the subtraction units 27d and 27q, respectively, thereby obtaining the d-axis voltage command value V _da ^* and the q-axis voltage command value V _qa ^* .
The d-axis voltage command value V _da ^* and the q-axis voltage command value V _qa ^* are input to the dq / three-phase AC coordinate conversion unit 31. The dq / three-phase alternating current coordinate conversion unit 31 also receives a sine signal sinθ and a cosine signal cosθ taken from the resolver amplifier 8 via the A / D conversion port 13. Using these, the dq / three-phase AC coordinate conversion unit 31 converts the d-axis voltage command value V _da ^* and the q-axis voltage command value V _qa ^* into the command value V _ua of the three-phase AC coordinate system according to the following equation (2). ^* , V _va ^* , and V _wa ^* are converted. Then, the obtained U-phase voltage command value V _ua ^* , V-phase voltage command value V _va ^*, and W-phase voltage command value V _wa ^* are input to the three-phase PWM forming unit 32.

なお、Ｗ相電圧指令値Ｖ_wa ^*は、上記（２）式の演算によるのではなく、零からＵ相電圧指令値Ｖ_ua ^*およびＶ相電圧指令値Ｖ_va ^*を減算することにより求めることができる。このようにすれば、ＣＰＵへの負担を軽減できる。むろん、ＣＰＵの演算速度が十分である場合には、上記（２）式に従う演算によってＷ相電圧指令値Ｖ_wa ^*を算出するようにしてもよい。

The W-phase voltage command value V _wa ^* is obtained by subtracting the U-phase voltage command value V _ua ^* and the V-phase voltage command value V _va ^* from zero, not by the calculation of the above equation (2). Can do. In this way, the burden on the CPU can be reduced. Of course, if the calculation speed of the CPU is sufficient, the W-phase voltage command value V _wa ^* may be calculated by calculation according to the above equation (2).

The three-phase PWM forming unit 32 generates PWM signals S _u , S _v , and S _w corresponding to the U-phase voltage command value V _ua ^* , the V-phase voltage command value V _va ^*, and the W-phase voltage command value V _wa ^* , respectively. Then, the generated PWM signals S _u , S _v , S _w are output to the motor driver 9. As a result, voltages V _ua , V _va , V _wa corresponding to the PWM signals S _u , S _v , S _w are applied from the motor driver 9 to the U phase, V phase, and W phase of the electric motor 3, respectively. Torque necessary for assisting steering is generated from the motor 3.

Figure 2 is a diagram for explaining the operation of the dq-axis current command value calculating section 26, q-axis current command value corresponding to the motor rotational angular velocity omega i _qa ^* upper limit value i _{Qa_uplim} and lower limit i _{Qa_downlim} is shown Has been. A sine wave that applies a sine wave voltage to the U-phase, V-phase, and W-phase of the electric motor 3 by setting the q-axis current command value i _qa ^* between the upper limit value i _{qa_uplim} and the lower limit value i _{qa_downlim.} Drive becomes possible.

When the flux-weakening control is not performed, that is, when the d-axis current command value i _da ^* = 0, the q-axis current command value i _qa ^* is limited according to the characteristics L1 ⁺ and L1 ⁻ indicated by broken _lines . Characteristic L1 ⁺ indicates an upper limit value when positive q-axis current command value i _qa ^* is set in order to generate torque in one direction (for example, clockwise direction), and characteristic L1 ⁻ indicates the other direction (for example, left direction). The lower limit value when the negative q-axis current command value i _qa ^* is set to generate torque in the rotation direction) is shown. In this case, the upper limit value and lower limit value of the q-axis current command value i _qa ^* are respectively in the low and medium speed rotation range where the absolute value of the motor rotation angular velocity ω is equal to or less than a predetermined first threshold value ω1 (for example, ω1 = 800 rpm). In the high speed range where the absolute value of the motor rotational angular velocity ω exceeds the first threshold value ω1, the upper limit value of the q-axis current command value i _qa ^{* is} a constant value α, −α (where α is a positive constant). The lower limit value of the q-axis current command value i _qa ^* increases linearly as the absolute value of the motor rotational angular velocity ω increases (the absolute value decreases). ) Characteristic. That is, the absolute value of the upper limit value and the lower limit value of the q-axis current command value i _qa ^* is held at a constant value in the medium / low speed rotation range below the first threshold value ω1, while it exceeds the first threshold value ω1. In FIG. 4, the characteristic decreases linearly as the motor rotational angular velocity ω increases.

On the other hand, when the flux-weakening control is performed, the q-axis current command value i _qa ^* is limited according to the characteristics L2 ⁺ and L2 ⁻ indicated by the solid _lines . Characteristic L2 ⁺ indicates the upper limit value when setting a positive q-axis current command value i _qa ^* in order to generate torque in one direction (e.g., clockwise), characteristic L2 ^- the other direction (e.g., left The lower limit value when the negative q-axis current command value i _qa ^* is set to generate torque in the rotation direction) is shown. In this case, the q-axis current command value i _qa ^* is in the rotational speed region where the absolute value of the motor rotational angular speed ω is equal to or smaller than the second threshold ω2 (> ω1, eg, ω2 = 900 rpm) larger than the first threshold ω1. The upper limit value and the lower limit value are constant values α and −α, respectively. In the rotational speed range where the absolute value of the motor rotational angular speed ω exceeds the second threshold ω2, the upper limit value of the q-axis current command value i _qa ^* decreases nonlinearly as the motor rotational angular speed ω increases, The lower limit value of the q-axis current command value i _qa ^* is a characteristic that increases nonlinearly (absolute value decreases) as the absolute value of the motor rotational angular velocity ω increases. In other words, the absolute values of the upper limit value and the lower limit value of the q-axis current command value i _qa ^* are kept constant in the rotation speed range below the second threshold value ω2, while in the rotation speed range exceeding the second threshold value ω2. The characteristic is non-linearly decreasing as the motor rotational angular velocity ω increases.

The q-axis current corresponds to the output torque of the electric motor 3. Therefore, when the flux-weakening control is not performed, as understood from the characteristics L1 ⁺ and L1 ⁻ , the absolute value of the motor rotational angular velocity ω increases in a high-speed rotational range where the absolute value of the motor rotational angular velocity ω exceeds the first threshold value ω1. Accordingly, the output torque decreases, and it becomes impossible to generate torque at a certain rotational speed ω10 (for example, ω10 = 1500 rpm). Therefore, in the high-speed rotation region exceeding the first threshold value ω1, the d-axis current command value i _da ^* is set to a significant value other than zero and the magnetic flux weakening control is performed. The output of the electric motor 3 can be increased.

The upper limit value i _{qa_uplim} of the q-axis current command value i _qa ^* when the flux-weakening control is performed is given by the following formula (3), and the lower limit value i _{qa_downlim} is given by the following formula (4). However, the upper limit value i _{qa_uplim} is applied to the positive q-axis current command value i _qa ^* , and the lower limit value i _{qa_downlim} is applied to the negative q-axis current command value i _qa ^* .

Further, the d-axis current command value i _da ^* for the flux weakening control is given by the following equation (5).

FIG. 3 is a flowchart for explaining the operation of the dq-axis current command value calculation unit 26 when the flux-weakening control is performed. dq-axis current command value calculating section 26, the characteristic L2 ⁺ Figure 2, L2 ^- accordingly sets the upper limit value i _{Qa_uplim} and the lower limit value i _{Qa_downlim} corresponding to the motor rotational angular velocity omega (step S1). Further, the dq-axis current command value calculation unit 26 sets the q-axis current command value i _qa ^* based on the vehicle speed, the steering speed, and the like (step S2).

Next, the dq-axis current command value computing unit 26 compares the q-axis current command value i _qa ^* with the upper limit value i _{qa_uplim} (step S3). If the q-axis current command value i _qa ^* is larger than the upper limit value i _{qa_uplim} (step S3: YES), the q-axis current command value i _qa ^* is restricted. That is, the upper limit value i _{qa_uplim} is substituted as the q-axis current command value i _qa ^* for use in the subsequent control (step S4).

On the other hand, if the q-axis current command value i _qa ^* is equal to or less than the upper limit value i _{qa_uplim} (step S3: NO), then the dq-axis current command value calculation unit 26 determines the q-axis current command value i _qa ^* and the lower limit value. i _{qa_downlim} is compared (step S5). If the q-axis current command value i _qa ^* is less than the lower limit value i _{qa_downlim} (step S5: YES), the q-axis current command value i _qa ^* is limited. That is, the lower limit value i _{qa_downlim} is substituted as the q-axis current command value i _qa ^* for use in the subsequent control (step S6).

If the q-axis current command value i _qa ^* set in step S2 is not _more than the upper limit value i _{qa_uplim} (step S3: NO) and not _less than the lower limit value i _{qa_downlim} (step S5: NO), the q The shaft current command value i _qa ^* is used as it is.
Thus, after limiting the q-axis current command value i _qa ^* as necessary, the dq-axis current command value calculation unit 26 sets the d-axis current command value i _da ^* according to the equation (5).

Based on the q-axis current command value i _qa ^* and the d-axis current command value i _da ^* thus obtained, the current deviation is obtained in the subtracting units 27d and 27q, and further based on the current deviation, the current PI control unit is obtained. PI control by 29d and 29q is performed. As a result, the d-axis voltage command value V _da ^* and the q-axis voltage command value V _qa ^* are obtained and provided to the dq / three-phase AC coordinate conversion unit 31.

FIG. 4 is a diagram showing conditions imposed on the d-axis voltage command value V _da ^* and the q-axis voltage command value V _qa ^* for the sine wave drive. In order for the voltage of each phase of the electric motor 3 to be a sine wave, the amplitude of each phase voltage must be ½ or less of the power supply voltage E _d (battery voltage), and the d-axis voltage V _d Regarding the q-axis voltage V _q , the following equation (6) needs to be satisfied (Patent Document 1).
√ (V _d ² + V _q ² ) ≦ E _d √3 / 2√2 = V _lim (6)
On the other hand, the q-axis voltage V _q and the d-axis voltage V _d in the steady state are expressed as follows.

これらを前記（６）式に代入すると、次の（９）式が得られる。

Substituting these into the equation (6) yields the following equation (9).

弱め磁束制御をしないとき、すなわち、ｄ軸電流指令値ｉ_da ^*＝０で前記（９）式が満たされる条件は、次の（１０）式である。

When the flux-weakening control is not performed, that is, the condition for satisfying the expression (9) with the d-axis current command value i _da ^* = 0 is the following expression (10).

これを変形すると、弱め磁束制御をしないときに正弦波駆動を行うための条件は、次の（１１）式で与えられることがわかる。

When this is modified, it can be seen that the condition for performing sine wave drive when the flux-weakening control is not performed is given by the following equation (11).

一方、ｉ_da ^*＝０では前記（１０）式を満たさないとき、すなわち、下記（１２）式の条件のときには、ｄ軸電流指令値ｉ_da ^*≠０とすることにより前記（９）式を満たす必要がある。

On the other hand, when i _da ^* = 0 does not satisfy the above expression (10), that is, under the condition of the following expression (12), the d-axis current command value i _da ^{* is not} equal to 0, thereby It is necessary to satisfy.

そこで、前記（９）式をｉ_da ^*について解くと、下記（１３）式を得る。

Therefore, when the equation (9) is solved for i _da ^* , the following equation (13) is obtained.

Since the motor efficiency decreases as the absolute value of the d-axis current increases, the d-axis command current value i _da ^* may be set to a value having the minimum absolute value that satisfies the condition of the equation (13).
Since A> 0 is self-evident and C> 0 from the above equation (12), the following equations (14) and (15) are obtained.

前記（１５）式のときは、ｄ軸指令電流値ｉ_da ^*が正値となり、ｄ軸の界磁を強める方向に電流を流すことになるので、Ｂ＜０のときは、ｉ_da ^*＝０とする。

In the above equation (15), the d-axis command current value i _da ^* is a positive value, and the current flows in the direction of strengthening the d-axis field. Therefore, when B <0, i _da ^* = 0.

Here, if B ² -AC ≧ 0 is not satisfied, the value of the equation (14) becomes an imaginary number, and there is no i _da ^* that satisfies the equation (14). That is, no matter what q-axis current command value i _da ^* is set, it does not fall within the limit voltage range indicated by the circle in FIG. Therefore, when B ² -AC ≧ 0 is solved for i _qa ^* , the following equation (16) is obtained, and in order to make it within the limit voltage range, that is, to perform sinusoidal drive, the q-axis current command This is a condition imposed on the value i _qa ^* .

Therefore, the q-axis current command value i _qa ^* is limited in advance to the range of the equation (16) (steps S3 to S6 in FIG. 3), and then the d-axis current command value i _da ^* is calculated by the equation (15). What is necessary is just to obtain | require (step S7 of FIG. 3). Thereby, the maximum output can be obtained within the limit voltage range. In other words, the output can be increased without causing vibration even in the high-speed rotation region. Thereby, the steering feeling of the electric power steering apparatus can be improved.

In addition, unlike the prior art disclosed in Patent Document 1 that restricts the q-axis voltage command value afterwards, the q-axis current command value i _qa ^* is limited in advance, and d corresponding to the q-axis current command value i _qa ^* is set. Since the shaft current command value i _da ^* is set, the q-axis current does not fluctuate.
FIG. 5 is a diagram for explaining a second embodiment of the present invention. The upper limit value of the q-axis current command value i _qa ^* set by the dq-axis current command value calculation unit 26 in the configuration of FIG. 1 described above. i _{qa_uplim} and lower limit value i _{qa_downlim} are shown.

In this embodiment, in the rotational speed range where the absolute value of the motor rotational angular speed ω exceeds a predetermined third threshold ω3 (> ω2, for example, ω3 = 3500 rpm), the q-axis current command value i _qa ^* The characteristics L3 ⁺ and L3 ⁻ which apply a restriction larger than the restriction by the equation (16) are applied. That is, in the range where the motor rotational angular velocity absolute value | ω | exceeds the third threshold value ω3, the absolute value of the upper limit value i _{qa_uplim} and the lower limit value i _{qa_downlim} is set smaller than in the case of the equation (16). As the rotational angular velocity absolute value | ω | increases, the absolute values of the upper limit value i _{qa_uplim} and the lower limit value i _{qa_downlim} linearly decrease at a larger change rate than in the case of the above equation (16). The upper limit value i _{qa_uplim} and the lower limit value i _{qa_downlim} are zero at the fourth threshold value ω4, −ω4 (> ω3, for example, ω4 = 4000 rpm).

By adopting such a configuration, it is possible to prevent the motor rotational angular velocity ω from becoming an abnormally large value, so that a variable of software executed by the microcomputer 6 does not overflow and stable control is possible. Become.
FIG. 6 is a diagram for explaining a third embodiment of the present invention. The upper limit value of the q-axis current command value i _qa ^* set by the dq-axis current command value calculation unit 26 in the configuration of FIG. 1 described above. i _{qa_uplim} and lower limit value i _{qa_downlim} are shown.

In this embodiment, the upper limit value i _{qa_uplim of the} q-axis current command value i _qa ^* is determined according to the polygonal line characteristic L2A ⁺ formed by a line segment inscribed in the curve of the characteristic L 2 ^{+ in} FIG. It has been established. Although illustration is omitted, similarly, the lower limit value i _{qa_downlim of the} q-axis current command value i _qa ^* is determined according to the polygonal line characteristic L2A ⁻ composed of a line segment inscribed in the curve of the characteristic L2 ⁻ (line segment in contact from the origin O side). Is to be determined. More specifically, the values of a plurality of vertices 40 forming the polygonal line characteristics L2A ⁺ , L2A ⁻ are stored in a memory (not shown) provided in the microcomputer 6, and a line segment 41 between the vertices 40 is stored. The above value is obtained by linear interpolation. By adopting such a configuration, it is possible to reduce a calculation load for limiting the q-axis current command value i _qa ^* within the limit range of the equation (16).

Although three embodiments of the present invention have been described above, the present invention can be implemented in other forms. For example, the upper limit value i _{qa_uplim} of the q-axis current command value i _qa ^* when performing the flux weakening control may be set to a value between the characteristic L1 ⁺ and the characteristic L2 ⁺ in FIG. The lower limit value i _{qa_downlim} of the q-axis current command value i _qa ^* when performing may be set to a value between the characteristic L 1 ⁻ and the characteristic L 2 ^{− in} FIG. Thus, for example, characteristics L4 ⁺ shown in FIG. 2 by the two-dot chain line, L4 ^- characteristic L2 ⁺ As, L2 ^- than to the characteristics absolute value is set lower limit i _{Qa_uplim} and the lower limit value i _{Qa_downlim} May be. Such characteristics L4 ⁺ and L4 ⁻ are, for example, in consideration of variations in characteristics of circuit elements such as the motor driver 9 (manufacturing variation, temperature change, aging, etc.) and fluctuations in input voltage (battery voltage). Regardless of these variations and fluctuations, the upper limit value i _{qa_uplim} may _fall between the characteristics L1 ⁺ and L2 ⁺ and the lower limit value i _{qa_downlim} may fall within the characteristics L1 ⁻ and L2 ⁻ . In this case, the characteristics L4 ⁺ and L4 ⁻ are obtained by multiplying the right side of the equations (3) and (4) by a constant K (0 <K <1) as shown in the following equations (17) and (18). May be set.

In addition, as shown by a two-dot chain line in FIG. 1, a restriction processing unit 30 is provided between the current PI control units 29 d and 29 q and the dq / three-phase AC coordinate conversion unit 31, similarly to the case of Patent Document 1. The q-axis voltage command value V _qa ^* may be limited. As described above, since the q-axis current command value i _qa ^* is previously limited, the q-axis voltage command value V _qa ^* and the d-axis voltage command value V _da ^* are set to the limit voltage V _lim in the dq coordinate. Although it is rarely set to a value exceeding the above, by providing the restriction processing unit 30, the sine wave drive can be performed more reliably.

Further, in the above-described embodiment, the example in which the present invention is applied to the electric power steering apparatus has been described. However, the present invention is not limited to the control of the motor as the drive source of the electric power steering apparatus, and any other arbitrary use It can be easily extended and applied to the control of motors.
In addition, various design changes can be made within the scope of matters described in the claims.

It is a block diagram for demonstrating the electrical constitution of the electric power steering device which concerns on one Embodiment of this invention. is a diagram for explaining the operation of the dq-axis current command value calculating section, q-axis current command value corresponding to the motor rotational angular velocity i _qa ^* upper limit value i _{Qa_uplim} and lower limit i _{Qa_downlim} is shown. It is a flowchart for demonstrating operation | movement of the dq-axis current command value calculating part when performing a flux-weakening control. It is a figure which shows the conditions imposed on d-axis voltage command value _Vda ^* and q-axis voltage command value _Vqa ^* for a sine wave drive. It is a diagram for explaining the second embodiment of the present invention, showing the q-axis current command value i _qa ^* upper limit value i _{Qa_uplim} and lower limit i _{Qa_downlim} to set dq-axis current command value calculating section. It is a diagram for explaining a third embodiment of the present invention, showing the q-axis current command value i _qa ^* upper limit value i _{Qa_uplim} and lower limit i _{Qa_downlim} to set dq-axis current command value calculating section.

Explanation of symbols

  3 ... Electric motor, 4 ... Resolver, 5 ... Motor controller, 6 ... Microcomputer

Claims (7)

A motor control device for controlling a motor by controlling a d-axis current and a q-axis current on a dq coordinate,
q-axis current command value setting means for setting a q-axis current command value;
upper and lower limit setting means for setting an upper limit value and a lower limit value of the q-axis current;
Comparison means for comparing the q-axis current command value set by the q-axis current command value setting means with the upper limit value and the lower limit value set by the upper limit / lower limit value setting means;
Q-axis current command value limiting means for limiting the q-axis current command value according to the comparison result by the comparison means;
A motor control device including d-axis current command value setting means for setting a d-axis current command value based on the q-axis current command value restricted by the q-axis current command value restriction means.   The motor control device according to claim 1, wherein the upper limit / lower limit value setting means sets an upper limit value and a lower limit value according to a rotational angular velocity of the motor. The motor control device according to claim 2, wherein the upper limit / lower limit setting means determines the upper limit to satisfy the following expression (A), and determines the lower limit to satisfy the following expression (B).

i _{qa_uplim} is the q-axis current upper limit value i _{qa_downlim} is the q-axis current lower limit value R is the stator winding resistance of the motor φ is the magnetic flux on the dq coordinate calculated from the stator linkage flux by the field ω is the motor electrical angle Rotational angular velocity L _d is d-axis inductance L _q is q-axis inductance V _lim is a limit voltage in dq coordinates that can be driven by a sine wave 4. The motor control device according to claim 3, wherein the upper limit / lower limit value setting means determines the upper limit value according to the following equation (A1) and determines the lower limit value according to the following equation (B1).

  In the rotational angular velocity range where the absolute value of the rotational angular velocity exceeds a predetermined value, the upper limit / lower limit setting means determines the upper limit value to be smaller than a value obtained according to the equation (A1), and sets the lower limit value to (B1 The motor control device according to claim 4, wherein the motor control device is determined to be larger than a value obtained according to the formula. 6. The motor control device according to claim 4, wherein the d-axis current command value setting means sets a d-axis current command value according to the following equation (C).

i _da ^* is the d-axis current command value i _qa ^* is the q-axis current command value The motor control device according to claim 6, wherein the d-axis current command value setting means sets a d-axis current command value according to the following equation (C1).

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