JP2009189089A - Motor controller and electric power steering machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To drive a brushless motor so that the occurrence of torque ripple caused by a resistance difference between phases may be suppressed. <P>SOLUTION: In a motor controller, an open loop control unit 22 gets a voltage commands v<SB>d</SB>and v<SB>q</SB>on an axis dq, based on current commands i<SB>d</SB><SP>*</SP>and i<SB>q</SB><SP>*</SP>on the axis dq, and the number Φ of interlinkage fluxes of an armature coil and the angular velocity ω<SB>e</SB>of the rotor in the motor, and an axis dq/three-phase converter 23 converts the voltage commands v<SB>d</SB>and v<SB>q</SB>into phase voltage commands Vu, Vv and Vw. On the other hand, a phase current computer 41 computes each phase current detected value Ix in order from a detected value Ia by a current sensor 15, and a memory 42 stores each phase voltage command Vux, Vvx and Vwx at the point of detection of each phase current detected value Ix (regarding as x=u, v and w). A phase resistance computer 43 computes phase resistance Ru, Rv and Rw, using each phase current detected value Ix and each phase voltage commands Vux, Vvx and Vwx described above, and a corrector 44 corrects phase voltage commands Vu, Vv and Vw obtained by the axis dq/three-phase converter 23, based on these computed values. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a motor control device for driving a brushless motor, and an electric power steering device including such a motor control device.

  2. Description of the Related Art Conventionally, an electric power steering device that applies a steering assist force to a steering mechanism of a vehicle by driving an electric motor according to a steering torque applied to a steering wheel (steering wheel) by a driver has been used. Conventionally, a brush motor has been widely used as an electric motor of an electric power steering apparatus. However, a brushless motor has also been used in recent years from the viewpoint of improving reliability and durability and reducing inertia.

  In general, a motor control device detects a current flowing through a motor in order to control torque generated by the motor, and performs PI control (proportional integral control) based on a difference between the current to be supplied to the motor and the detected current. A motor control device that drives a three-phase brushless motor is provided with two or three current sensors in order to detect a current of two or more phases.

In relation to the present invention, Patent Document 1 discloses that an offset correction of the output signal of the motor current detecting means is performed when the estimated current or the detected current for the motor is equal to or less than a predetermined value in order to suppress torque ripple. An electric power steering device is disclosed. In Patent Document 2, in order to perform zero point correction (offset correction) of the electric power steering device with high accuracy, the motor drive unit is stopped when the target current is equal to or less than a predetermined value during operation of the electric power steering device. A zero point correction method for correcting the zero point of the current sensor is disclosed.
JP 2007-069836 A JP 2004-130901 A

  In the motor control device included in the electric power steering device, the current sensor needs to detect a large current of 100 A or more. This current sensor is large in size and hinders downsizing of the control device of the electric power steering device. For this reason, in a motor control device included in an electric power steering device or the like, reduction of current sensors is an issue. If the number of current sensors can be reduced, the cost and power consumption of the motor control device can be reduced.

  Possible ways to reduce the number of current sensors are to reduce the number of current sensors to one and perform the same feedback control as before, or remove all current sensors and perform open loop control according to the motor circuit equation. It is done.

Among these methods, the former method has a problem that, depending on the rotational position of the rotor of the motor, a single current sensor may not be able to detect multiple phases of current necessary for feedback control, and the motor control becomes discontinuous. There is. In contrast, the latter method does not cause such a problem. However, the latter method has a problem that a ripple (referred to as “torque ripple”) occurs in the output torque of the motor when a difference in resistance value occurs between the phases due to the following factors.
i) By arranging relays in two phases for fail-safe, a resistance difference corresponding to the contact resistance of the relay is generated between the phases.
ii) The contact resistance of the connector for connecting the motor control device and the motor differs between phases.

  In particular, in an electric power steering apparatus, since smoothness of the output torque of a motor is regarded as important from the viewpoint of improving steering feeling, it is required to suppress the occurrence of such torque ripple.

  Therefore, an object of the present invention is to provide a motor control device capable of driving a brushless motor so that generation of torque ripple due to resistance difference between phases is suppressed. Another object of the present invention is to provide an electric power steering apparatus provided with such a motor control device.

A first invention is a motor control device for driving a brushless motor,
Current detection means for detecting each phase current flowing through the brushless motor;
Control calculation means for obtaining a command value indicating each phase voltage to be applied to the brushless motor, and outputting the command value as a phase voltage command value;
Phase resistance calculating means for calculating the resistance value of each phase based on the detected value of each phase current detected by the current detecting means and the command value of each phase voltage applied to the brushless motor at the time of detection of the detected value When,
Correction means for correcting the phase voltage command value according to the resistance value of each phase calculated by the phase resistance calculation means;
Drive means for driving the brushless motor based on the phase voltage command value corrected by the correction means.

According to a second invention, in the first invention,
The phase resistance calculating means calculates a resistance value of each phase when the magnitude of the current flowing through the brushless motor is smaller than a predetermined value.

According to a third invention, in the first invention,
A storage means for storing the corrected phase voltage command value at the time when each phase current is detected by the current detection means;
The phase resistance calculation unit calculates a resistance value of each phase based on a detected value of each phase current detected by the current detection unit and a phase voltage command value stored in the storage unit.

According to a fourth invention, in the third invention,
The current detection means includes
A single current sensor for detecting a current flowing in the brushless motor;
Phase current calculation means for sequentially obtaining the detected value of each phase current based on the detected value of the current detected by the current sensor,
The control calculation means is
An open loop control means for obtaining the phase voltage command value according to a circuit equation of a brushless motor based on a command value indicating a current to be supplied to the brushless motor and an angular velocity of a rotor of the brushless motor;
Parameter calculation means for obtaining a value of a parameter to be used when obtaining the phase voltage command value according to the circuit equation based on a detected value of the current detected by the current sensor;
The storage means stores the phase voltage command value every time a detected value of any phase current is obtained by the phase current calculation means.

A fifth invention is an electric power steering device that applies a steering assist force to a steering mechanism of a vehicle by a brushless motor,
A motor control device according to any one of the first to fourth inventions;
The motor control device drives a brushless motor that applies a steering assist force to the steering mechanism.

  According to the first aspect of the invention, the resistance value of each phase is calculated based on the detected value of each phase current obtained by the current detecting means and the command value of each phase voltage obtained by the control calculating means. By correcting the command value of each phase voltage to be applied to the brushless motor according to the phase resistance value, the phase resistance difference is compensated, and the torque ripple caused by the phase resistance difference is reduced.

  According to the second aspect of the invention, the resistance value of each phase is calculated when the magnitude of the current flowing through the brushless motor is smaller than a predetermined value. At the time of the calculation, the increase in the resistance value due to heat generation by the current is calculated. Since the resistance difference between the phases is small and relatively large, a highly accurate calculated value can be obtained for the resistance of each phase. Thereby, the compensation of the interphase resistance difference by the correction of the command value of each phase voltage is performed more accurately, so that the torque ripple can be sufficiently reduced.

  According to the third aspect of the invention, the command value of each phase voltage applied to the brushless motor at the time of detection of each phase current is stored in the storage means, and the detected value of each phase current and each phase stored in the storage means The resistance value of each phase is calculated based on the voltage command value. Therefore, since there is only one current sensor, currents of all phases cannot be detected simultaneously, and current detection values of each phase can be obtained sequentially based on the current detection values obtained by the current sensors. However, it is possible to reduce the torque ripple by calculating the resistance value of each phase and correcting the command value of each phase voltage according to the resistance value of each phase.

  According to the fourth aspect of the invention, the parameter value used when obtaining the command value of each phase voltage is obtained based on the detected value of the current detected by the single current sensor, and the single current is obtained. According to the resistance value of each phase calculated based on the detected value of each phase current sequentially obtained by the current detection means including the sensor and the command value of each phase voltage stored in the storage means, The command value is corrected. This reduces the cost and current consumption compared to using multiple current sensors, and drives the brushless motor with high accuracy even when the values of the above parameters fluctuate due to manufacturing variations or temperature changes. Can be obtained.

  According to the fifth aspect of the invention, by correcting the command value of each phase voltage indicating the voltage to be applied to the brushless motor that gives the steering assist force, the generation of torque ripple due to the interphase resistance difference is suppressed. Therefore, it is possible to provide an electric power steering device with good steering feeling.

<1. Electric power steering device>
FIG. 1 is a schematic diagram showing the configuration of an electric power steering apparatus according to an embodiment of the present invention, together with the configuration of a vehicle related thereto. The electric power steering apparatus shown in FIG. 1 includes a brushless motor 1, a speed reducer 2, a torque sensor 3, a vehicle speed sensor 4, a position detection sensor 5, and an electronic control unit (hereinafter referred to as "ECU") 10. This is a column assist type electric power steering apparatus.

  As shown in FIG. 1, a steering wheel (steering wheel) 101 is fixed to one end of the steering shaft 102, and the other end of the steering shaft 102 is connected to a rack shaft 104 via a rack and pinion mechanism 103. Both ends of the rack shaft 104 are connected to a wheel 106 via a connecting member 105 composed of a tie rod and a knuckle arm. When the driver rotates the handle 101, the steering shaft 102 rotates, and the rack shaft 104 reciprocates accordingly. As the rack shaft 104 reciprocates, the direction of the wheels 106 changes.

  The electric power steering device performs the following steering assistance in order to reduce the driver's load. The torque sensor 3 detects a steering torque T applied to the steering shaft 102 by operating the handle 101. The vehicle speed sensor 4 detects the vehicle speed S. The position detection sensor 5 detects the rotational position P of the rotor of the brushless motor 1. The position detection sensor 5 is composed of, for example, a resolver.

  The ECU 10 is supplied with electric power from the in-vehicle battery 100 and drives the brushless motor 1 based on the steering torque T, the vehicle speed S, and the rotational position P. The brushless motor 1 generates a steering assist force when driven by the ECU 10. The speed reducer 2 is provided between the brushless motor 1 and the steering shaft 102. The steering assist force generated by the brushless motor 1 acts to rotate the steering shaft 102 via the speed reducer 2.

  As a result, the steering shaft 102 is rotated by both the steering torque applied to the handle 101 and the steering assist force generated by the brushless motor 1. As described above, the electric power steering apparatus performs steering assist by applying the steering assist force generated by the brushless motor 1 to the steering mechanism of the vehicle.

  The electric power steering device according to the embodiment of the present invention is characterized by a control device (motor control device) that drives the brushless motor 1. Therefore, hereinafter, a motor control device included in the electric power steering device according to each embodiment will be described.

<2. First Embodiment>
FIG. 2 is a block diagram showing the configuration of the motor control device according to the first embodiment of the present invention. The motor control device shown in FIG. 2 is configured using an ECU 10 and drives a brushless motor 1 having u-phase, v-phase, and w-phase three-phase windings (not shown). The ECU 10 includes a phase compensator 11, a microcomputer (hereinafter abbreviated as “microcomputer”) 20, a three-phase / PWM (Pulse Width Modulation) modulator 12, a motor drive circuit 13, and a current sensor 14.

  The ECU 10 receives the steering torque T output from the torque sensor 3, the vehicle speed S output from the vehicle speed sensor 4, and the rotational position P output from the position detection sensor 5. The phase compensator 11 performs phase compensation on the steering torque T. The microcomputer 20 functions as control means for obtaining a voltage command value used for driving the brushless motor 1. Details of the function of the microcomputer 20 will be described later.

  The three-phase / PWM modulator 12 and the motor drive circuit 13 are configured by hardware (circuit) and function as motor drive means for driving the brushless motor 1 using the voltage of the voltage command value obtained by the microcomputer 20. . The three-phase / PWM modulator 12 generates three types of PWM signals (U, V, and W shown in FIG. 2) having a duty ratio corresponding to the three-phase voltage command value obtained by the microcomputer 20. The motor drive circuit 13 is a PWM voltage source inverter circuit including six MOS-FETs (Metal Oxide Semiconductor Field Effect Transistors) as switching elements. The six MOS-FETs are controlled by three types of PWM signals and their negative signals. By controlling the conduction state of the MOS-FET using the PWM signal, three-phase driving currents (u-phase current, v-phase current and w-phase current) are supplied to the brushless motor 1.

  The current sensor 14 detects a current flowing through the brushless motor 1. In the present embodiment, the current sensor 14 and a phase current calculation unit 41 described later constitute current detection means for detecting u-phase, v-phase, and w-phase currents Iu, Iv, and Iw of the brushless motor 1. The current sensor 14 is constituted by, for example, a resistor or a Hall element, and only one current sensor 14 is provided between the motor drive circuit 13 and the power source. In the example shown in FIG. 2, the current sensor 14 is provided between the motor drive circuit 13 and the negative side (ground) of the power supply. However, the current sensor 14 is provided between the motor drive circuit 13 and the positive side of the power supply. It may be provided.

  While the brushless motor 1 is rotating, the current value detected by the current sensor 14 changes according to the PWM signal. Within one cycle of the PWM signal, there are a case where the current sensor 14 detects a one-phase driving current and a case where the sum of the two-phase driving currents is detected. Since the sum of the three-phase drive currents becomes zero, the remaining one-phase drive current can be obtained based on the sum of the two-phase drive currents. Therefore, the three-phase drive current can be detected by using one current sensor 14 while the brushless motor 1 is rotating. The current value Ia detected by the current sensor 14 is input to the microcomputer 20.

  The microcomputer 20 executes a program stored in a memory (not shown) built in the ECU 10 to thereby execute a command current calculation unit 21, an open loop control unit 22, a dq axis / three-phase conversion unit 23, and an angle calculation unit. 24, angular velocity calculation unit 25, Φ calculation unit 26, phase current calculation unit 41, storage unit 42, phase resistance calculation unit 43, and correction unit 44. The command current calculation unit 21, the open loop control unit 22, the dq axis / three-phase conversion unit 23, the angular velocity calculation unit 25, and the Φ calculation unit 26 determine the phase voltage command value used for driving the brushless motor 1. The required control calculation means is configured.

  As shown below, the microcomputer 20 determines the voltage to be applied to the motor drive circuit 13 according to the circuit equation of the motor based on the current command value indicating the current to be supplied to the brushless motor 1 and the angular velocity of the rotor of the brushless motor 1. The voltage command value shown is obtained.

The angle calculation unit 24 obtains the rotation angle (hereinafter referred to as “angle θ”) of the rotor of the brushless motor 1 based on the rotation position P detected by the position detection sensor 5. The angular velocity calculation unit 25 obtains the angular velocity ω _e of the rotor of the brushless motor 1 based on the angle θ. As shown in FIG. 3, when the u axis, the v axis, and the w axis are set for the brushless motor 1, and the d axis and the q axis are set for the rotor 6 of the brushless motor 1, the u axis and the d axis are set. Is an angle θ. That is, the angle calculation unit 24 calculates the electrical angle θ in the brushless motor 1.

The command current calculation unit 21 obtains the d-axis component and the q-axis component of the target value of the current to be supplied to the brushless motor 1 based on the steering torque T after phase compensation (the output signal of the phase compensator 11) and the vehicle speed S. (Hereinafter, the former value is referred to as “d-axis current command value i _d ^* ”, and the latter value is referred to as “q-axis current command value i _q ^* ”). More specifically, the command current calculation unit 21 has a built-in table (hereinafter referred to as “assist map”) that stores the correspondence between the steering torque T and the command current using the vehicle speed S as a parameter. Refer to the current command value. By using the assist map, when a certain amount of steering torque is applied, the current to be supplied to the brushless motor 1 in order to generate a steering assist force having an appropriate magnitude according to the magnitude is shown. The d-axis current command value i _d ^* and the q-axis current command value i _q ^* can be obtained.

The q-axis current command value i _q ^{* obtained} by the command current calculation unit 21 is a signed current value, and the sign indicates the steering assist direction. For example, when the sign is positive, steering assistance for turning to the right is performed, and when the sign is minus, steering assistance for turning to the left is performed. Further, the d-axis current command value i _d ^* is typically set to zero.

The open loop control unit 22 determines the d-axis component and the q-axis component of the target value of the voltage to be applied to the brushless motor 1 based on the d-axis current command value i _d ^* , the q-axis current command value i _q ^* and the angular velocity ω _e. (Hereinafter, the former value is referred to as “d-axis voltage command value v _d ” and the latter value is referred to as “q-axis voltage command value v _q ”). The d-axis voltage command value v _d and the q-axis voltage command value v _q are calculated using the motor circuit equations shown in the following equations (1) and (2).
v _d = (R + PL _d ) i _d ^* −ω _e L _q i _q ^* (1)
v _q = (R + PL _q ) i _q ^* + ω _e L _d i _d ^* + ω _e Φ (2)
In equations (1) and (2), v _d is a d-axis voltage command value, v _q is a q-axis voltage command value, i _d ^* is a d-axis current command value, i _q ^* is a q-axis current command value, ω _e is the rotor angular velocity, R is the circuit resistance including the armature winding resistance, L _d is the d-axis self-inductance, L _q is the q-axis self-inductance, and Φ is the U, V, W-phase armature winding chain √ (3/2) times the maximum value of the number of magnetic flux exchanges, P is a differential operator. Of these, R, L _d , L _q and Φ are treated as known parameters. The circuit resistance indicated by R includes the wiring resistance between the brushless motor 1 and the ECU 10, the resistance of the motor driving circuit 13 in the ECU 10, the wiring resistance, and the like. This is the same in other embodiments.

The dq-axis / 3-phase converter 23 converts the d-axis voltage command value v _d and the q-axis voltage command value v _q obtained by the open loop control unit 22 into a voltage command value on the three-phase AC coordinate axis. More specifically, the dq-axis / three-phase conversion unit 23 uses the following equations (3) to (5) based on the d-axis voltage command value v _d and the q-axis voltage command value v _q to determine the u-phase voltage command value. Vu, v-phase voltage command value Vv, and w-phase voltage command value Vw are obtained.
Vu = √ (2/3) × {v _d × cos θ−v _q × sin θ} (3)
Vv = √ (2/3) × {v _d × cos (θ-2π / 3)
−v _q × sin (θ−2π / 3)} (4)
Vw = −Vu−Vv (5)
The angle θ included in the above formulas (3) and (4) is an electrical angle obtained by the angle calculation unit 24. The u-phase voltage command value Vu, the v-phase voltage command value Vv, and the w-phase voltage command value Vw are collectively referred to as “phase voltage command values Vu, Vv, Vw”. Further, the u-phase voltage command value, the v-phase voltage command value, and the w-phase voltage command value after correction by the correction unit 44 described later are collectively referred to as “corrected phase voltage command values Vuc, Vvc, Vwc”.

  As described above, the three-phase drive current can be detected by using one current sensor 14 while the brushless motor 1 is rotating. Therefore, in the present embodiment, the phase current calculation unit 41 determines the values of the u-phase, v-phase, and w-phase currents flowing to the brushless motor 1 from the current value Ia detected by the current sensor 14 (hereinafter referred to as “u-phase current detection values” Iu ”,“ v-phase current detection value Iv ”,“ w-phase current detection value Iw ”, which are also collectively referred to as phase current detection values Iu, Iv, and Iw). The storage unit 42 also corrects the phase voltage after correction at the detection time of each phase current detection value Ix (x = u, v, w), that is, the detection time of the current value Ia used for calculation of each phase current detection value Ix. Command values Vuc, Vvc, Vwc are stored. In the following, corrected phase voltage command values Vuc, Vvc, Vwc at the time of detection of the x-phase current detection value Ix are indicated by symbols “Vux”, “Vvx”, “Vwx”, respectively (x = u , V, w).

  The phase resistance calculation unit 43 includes each phase current detection value Ix detected by the current detection means including the phase current calculation unit 41 and the current sensor 14 as described above, and a corrected phase voltage command value Vux, Based on Vvx, Vwx (x = u, v, w), values of u-phase resistance Ru, v-phase resistance Rv, and w-phase resistance Rw (see FIG. 4) are obtained. Here, the u-phase resistance, the v-phase resistance, and the w-phase resistance mean circuit resistances including armature winding resistances for the u-phase, v-phase, and w-phase, respectively, and symbols “Ru” and “Rv”, respectively. "," Rw ". The symbols “Ru”, “Rv”, and “Rw” also indicate the values of the u-phase resistance, the v-phase resistance, and the w-phase resistance, respectively. Hereinafter, the u-phase resistance, the v-phase resistance, and the w-phase resistance are collectively referred to as “phase resistance”. The circuit resistance corresponding to these phase resistances includes wiring resistance between the brushless motor 1 and the ECU 10, resistance of the motor drive circuit 13 in the ECU 10, wiring resistance, and the like. This is the same in other embodiments. Details of the calculation method of the phase resistances Ru, Rv, Rw in the phase resistance calculation unit 43 will be described later.

The correction unit 44 includes values of the phase resistances Ru, Rv, and Rw calculated by the phase resistance calculation unit 43, an armature winding linkage magnetic flux number Φ calculated by the Φ calculation unit 26, and an angular velocity calculation unit 25. The calculated angular velocity ω _e is input, and the correction unit 44 corrects the phase voltage command values Vu, Vv, and Vw according to the following equations (7) to (9).
_{Vuc = (Vu-e u)} · Ru / Rr + e u ... (7)
_{Vvc = (Vv-e v)} · Rv / Rr + e v ... (8)
Vwc = (Vw−e _w ) · Rw / Rr + e _w (9)
In the above formulas (7) to (9), Rr is a resistance value (hereinafter referred to as “reference resistance value”) to be set in common for each phase, and as this reference resistance value Rr, for example, each phase An average value of resistance values can be used, and a resistance value of a specific phase at a predetermined time point may be used. Furthermore, the reference resistance value Rr is not necessarily a fixed value. When the values of the phase resistances Ru, Rv, Rw have not been calculated, the value of the reference resistance Rr is determined in advance, and the corrected phase voltage command values Vuc, Vvc, Vwc are calculated with Ru = Rv = Rw = Rr. May be.

In the above formula (7) ~ (9), e u, e v, e w are each, u phases in the brushless motor 1, v-phase, a counter electromotive force of the w-phase (induced voltage). Incidentally, the q-axis component of the back electromotive force of the brushless motor 1 is ω _e Φ, and the d-axis component is zero. Therefore, the correction unit 44 converts the d-axis component and the q-axis component of these back electromotive forces into back electromotive forces on the three-phase AC coordinate axes according to the following equations (10) to (12), and for each phase obtained by the conversion: counter electromotive force e _u, e _v, the equation using e _w (7) the phase voltage command value after correction in accordance with ~ (9) Vuc, Vvc, and calculates the Vwc.
e _u = √ (2/3) × {0 × cos θ−ω _e Φ × sin θ} (10)
e _v = √ (2/3) × {0 × cos (θ−2π / 3)
−ω _e Φ × sin (θ−2π / 3)} (11)
e _w = −e _u −e _v (12)
The angle θ included in the equations (10) and (11) is an electrical angle obtained by the angle calculation unit 24.

As described above, the microcomputer 20 obtains the current command values i _d ^* and i _q ^* on the dq coordinate axis, obtains the voltage command values v _d and v _q on the dq coordinate axis according to the motor circuit equation, and the d axis. And a process for converting the q-axis voltage command values v _d and v _q into the phase voltage command values Vu, Vv, and Vw and a process for correcting the phase voltage command values Vu, Vv, and Vw. The three-phase / PWM modulator 12 outputs three types of PWM signals based on the corrected phase voltage command values Vuc, Vvc, Vwc obtained by the microcomputer 20. As a result, a sinusoidal current corresponding to the corrected voltage command values Vuc, Vvc, and Vwc of each phase flows through the three-phase windings of the brushless motor 1, and the rotor of the brushless motor 1 rotates. Accordingly, a torque corresponding to the current flowing through the brushless motor 1 is generated on the rotating shaft of the brushless motor 1. The generated torque is used for steering assistance.

The current value Ia detected by the current sensor 14, the electrical angle θ calculated by the angle calculator 24, and the angular velocity ω _e calculated by the angular velocity calculator 25 are input to the Φ calculator 26. The Φ calculating unit 26 first obtains the values of the u-phase and v-phase currents flowing through the brushless motor 1 based on the current value Ia, that is, the u-phase current detection value Iu and the v-phase current detection value Iv, and these are expressed by the following formula (13 ) And (14) are used to convert the current value on the dq coordinate axis to obtain the d-axis current detection value _id and the q-axis current detection value _iq .
i _d = √2 × {Iv × sin θ−Iu × sin (θ−2π / 3)} (13)
i _q = √2 × {Iv × cos θ−Iu × cos (θ−2π / 3)} (14)

Next, when ω _e ≠ 0, the Φ calculating unit 26 uses the following formula ( _q) based on the q-axis voltage command value v _q , the d-axis current detection value i _d , the q-axis current detection value i _q and the angular velocity ω _e. 15) is used to determine the number of armature winding linkage magnetic fluxes Φ included in the equation (2).
Φ = {v _q − (R + PL _q ) i _q −ω _e L _d i _d } / ω _e (15)
Equation (15) substitutes d-axis current detection value i _d and q-axis current detection value i _q for d-axis current command value i _d ^* and q-axis current command value i _q ^* of equation (2), and The equation is solved for Φ.

The Φ calculating unit 26 outputs the obtained Φ value to the open loop control unit 22. The open loop control unit 22 uses the Φ value calculated by the Φ calculation unit 26 when _{obtaining the} q-axis voltage command value v _q using the equation (2). As described above, the microcomputer 20 obtains the armature winding linkage magnetic flux number Φ included in the motor circuit equation, and uses the Φ value when obtaining the q-axis voltage command value v _q .

The Φ calculating unit 26 may obtain the Φ value at an arbitrary timing as long as ω _e ≠ 0. For example, the Φ calculating unit 26 may obtain the Φ value at a predetermined time interval, obtain the Φ value only once after the start of the driving of the brushless motor 1, or the Φ value when the state such as temperature changes. You may ask for. In addition, since an error is likely to occur in the Φ value obtained when ω _e is close to zero, the Φ calculation unit 26 may obtain the Φ value only when ω _e is equal to or greater than a predetermined threshold.

  As described above, the motor control device according to the present embodiment obtains the voltage command value by open loop control according to the motor circuit equation based on the current command value and the angular velocity of the rotor, and the current value detected by the current sensor. Φ included in the circuit equation of the motor is obtained based on the above, and the Φ value is used when obtaining the voltage command value. Therefore, according to the motor control device according to the present embodiment, even when the Φ value included in the circuit equation of the motor fluctuates due to manufacturing variation or temperature change, the Φ value is obtained based on the current value detected by the current sensor. The brushless motor can be driven with high accuracy, and a desired motor output can be obtained.

  Further, the motor control device according to the present embodiment is provided with only one current sensor. Therefore, according to the motor control device according to the present embodiment, it is possible to reduce the size, cost and power consumption of the motor control device by reducing the number of current sensors. Furthermore, since the motor control device according to the present embodiment performs open loop control, the motor control does not become discontinuous, unlike the motor control device that performs feedback control using one current sensor. Therefore, according to the motor control device according to the present embodiment, it is possible to suppress sound and vibration.

In the present embodiment, R, Φ, and the like used for _{obtaining the} d-axis voltage command value v _d and the q-axis voltage command value v _q in the open loop control unit 22 are treated as known parameters. The value calculated by the Φ calculating unit 26 is used. That is, Φ is appropriately corrected by the Φ calculating unit 26 as parameter calculating means while being treated as a known parameter. However, the present invention is not limited to such a configuration, and instead of the Φ calculating unit 26 or with the Φ calculating unit 26, an R calculating unit as a parameter calculating unit is provided, and the d-axis voltage command values v _d and q When calculating the shaft voltage command value v _q , R calculated by the R calculating unit may be used (this is the same in other embodiments described below). When the R calculation unit is provided, the R calculation unit, for example, when i _q ≠ 0, the q-axis voltage command value v _q , the d-axis current detection value i _d , and the q-axis current detection value i _{Based on q} and the angular velocity ω _e , the electric winding resistance R included in the above formulas (1) and (2) is obtained using the following formula.
R = (v _q −PL _q i _q −ω _e L _d i _d −ω _e Φ) / i _q

Next, a method for calculating the phase resistances Ru, Rv, Rw in the phase resistance calculation unit 43 will be described. In this embodiment, it is assumed that the current of the x phase is detected when the temporal change of the current of the x phase is gentle, and the voltage drop caused by the inductance of the x phase can be ignored (x = u, v , W). In this case, the u-phase, v-phase, and w-phase back electromotive forces (induced voltages) in the brushless motor 1 at the time of detection of the x-phase current detection value Ix are respectively represented by “Eux”, “Evx”, and “Ewx” And the current values of the u-phase, v-phase, and w-phase at the time of detection of the x-phase current detection value Ix are denoted by “Iux”, “Ivx”, and “Iwx”, respectively (x = u, v, w ), The following formula is established.
Vuu = Iuu · Ru + Euu (16a)
Vvu = Ivu · Rv + Evu (16b)
Vwu = Iwu · Rw + Ewu (16c)
Vuv = Iuv · Ru + Euv (17a)
Vvv = Ivv · Rv + Evv (17b)
Vwv = Iwv · Rw + Ewv (17c)
Vuw = Iu · Ru + Eu (18a)
Vvw = Ivw · Rv + Evw (18b)
Vww = Iw · Rw + Ew (18c)
Iuu + Ivu + Iwu = 0 (19a)
Iuv + Ivv + Iwv = 0 (19b)
Iuw + Ivw + Iw = 0 (19c)
Eu + Evu + Ewu = 0 (20a)
Euv + Evv + Ewv = 0 (20b)
Euw + Evw + Ew = 0 (20c)
Vuu + Vvu + Vwu = 0 (21a)
Vuv + Vvv + Vwv = 0 (21b)
Vuw + Vvw + Vw = 0 (21c)

  In the 18 equations (16a) to (21c), the phase voltage command values Vux, Vvx, Vwx (x = u, v, w) and the phase current detection values Iuu, Ivv, Iww are known, and the unknowns are the phases. Since there are 18 resistors Ru, Rv, Rw, phase current values Ivu, Iwu, Iuv, Iwv, Iuw, Ivw and induced voltages Eux, Evx, Ewx (x = u, v, w), the above equation (6a) The phase resistances Ru, Rv, Rw can be obtained from (21c). Specifically, the phase resistances Ru, Rv, Rw are obtained as follows.

When the u-phase current is detected, the phase current calculation unit 41 outputs the u-phase current detection value Iu, and the storage unit 42 corrects the voltage command values for the u-phase, v-phase, and w-phase at the time of detection. Vuc, Vvc, and Vwc are stored as Vuu, Vvu, and Vwu, respectively. When Iu ≠ 0, the phase resistance calculation unit 43 uses the u-phase current detection value Iu and the phase voltage command values Vuu, Vvu, and Vwu at the time of detection to calculate Ua and Ub given by the following equations. .
Ua = (Vuu−Vvu) / Iu (22a)
Ub = (Vuu−Vwu) / Iu (22b)

When the v-phase current is detected, the phase current calculation unit 41 outputs the v-phase current detection value Iv, and the storage unit 42 corrects u-phase, v-phase, and w-phase voltage command values at the time of detection. Vuc, Vvc, and Vwc are stored as Vuv, Vvv, and Vwv, respectively. When Iv ≠ 0, the phase resistance calculation unit 43 uses the v-phase current detection value Iv and the phase voltage command values Vuv, Vvv, and Vwv at the time of detection to calculate Va and Vb given by the following equations: To do.
Va = (Vvv−Vwv) / Iv (23a)
Vb = (Vvv−Vuv) / Iv (23b)

When the w-phase current is detected, the phase current calculation unit 41 outputs the w-phase current detection value Iw, and the storage unit 42 corrects the voltage command values for the u-phase, v-phase, and w-phase at the time of detection. Vuc, Vvc, and Vwc are stored as Vuw, Vvw, and Vww, respectively. When Iw ≠ 0, the phase resistance calculation unit 43 uses the w-phase current detection value Iw and the phase voltage command values Vuw, Vvw, and Vww at the time of detection to calculate Wa and Wb given by the following equations: To do.
Wa = (Vww−Vuw) / Iw (24a)
Wb = (Vww−Vvw) / Iw (24b)

Then, the calculated Ua, Ub, using Va, Vb, Wa, the Wb, r _a given by the following equation, r _b, r _c, calculates a r _{d.
r a = Ua · Va · Wa} -Ub · Vb · Wb ... (25a)
r _b = Wa · Ua−Wa · Vb + Ub · Vb (25b)
r _c = Ua · Va−Ua · Wb + Vb · Wb (25c)
r _d = Va · Wa−Va · Ub + Wb · Ub (25d)

Then, the calculated _{r a, r b, r c} , with r _d, and calculates phase resistance Ru by the following formula, Rv, and Rw.
Ru = r _a · r _b / (r _b · r _c + r _c · r _d + r _d · r _b ) (26a)
Rv = r _a · r _c / (r _b · r _c + r _c · r _d + r _d · r _b ) (26b)
Rw = r _a · r _d / (r _b · r _c + r _c · r _d + r _d · r _b ) (26c)

  The values of the phase resistances Ru, Rv, Rw necessary for the correction of the phase voltage command values Vu, Vv, Vw by the above-described equations (7) to (9) are the detected current values Iu of the u phase, the v phase, and the w phase. , Iv, Iw can be calculated as described above, but when the current flowing through the brushless motor 1 increases, the calculation accuracy of the phase resistances Ru, Rv, Rw decreases due to heat generation. This point will be described below.

Now, the difference of the v-phase resistance Rv with respect to the u-phase resistance Ru is 1 mΩ, and the difference of the w-phase resistance Rw with respect to the u-phase resistance Ru is 2 mΩ. In this case, if Ru = 10 mΩ, Rv = 11 mΩ and Rw = 12 mΩ. Therefore, the resistance ratios Rv / Ru, Rw / Ru are
Rv / Ru = 11/10 = 1.1
Rw / Ru = 12/10 = 1.2
Therefore, when the resistance difference is expressed as a relative value, the difference of the v-phase resistance Rv with respect to the u-phase resistance Ru is 10%, and the difference of the w-phase resistance Rw with respect to the u-phase resistance Ru is 20%.

In general, the resistance difference between the phases is not affected by the heat generated by the current flowing through the motor. For this reason, if the u-phase resistance Ru becomes, for example, Ru = 20 mΩ due to heat generated by the current, Rv = 21 mΩ and Rw = 22 mΩ. The resistance ratios Rv / Ru and Rw / Ru at this time are
Rv / Ru = 21/20 = 1.05
Rw / Ru = 22/20 = 1.1
Therefore, when the resistance difference is expressed as a relative value, the difference in the v-phase resistance Rv with respect to the u-phase resistance Ru is 5%, and the difference in the w-phase resistance Rw with respect to the u-phase resistance Ru is 10%.

  Thus, when the resistance value increases due to heat generated by the current, the resistance difference between the phases becomes relatively small. Therefore, from the viewpoint of the resistance difference between the phases, the heat generation due to the current reduces the calculation accuracy of the phase resistance. Therefore, it is preferable to calculate the phase resistance when the heat generated by the current is small. Therefore, in the present embodiment, the phase resistances Ru, Rv, and Rw are calculated as described above when the command value or detection value of the u-phase, v-phase, and w-phase currents is smaller than a predetermined threshold value. Hereinafter, the operation of the phase resistance calculation unit 43 in the present embodiment will be described.

  FIG. 5 is a flowchart for explaining an operation example of the phase resistance calculation unit 43 in the present embodiment. In this operation example, the phase resistance calculation unit 43 calculates the phase resistances Ru, Rv, Rw by the following procedure. As described above, the phase current calculation unit 41 calculates the current detection value Ix from the current detection value Ia obtained by the current sensor 14 every time one of the u-phase, v-phase, and w-phase current detection values is calculated. The resistance calculation unit 43 is given (x is any one of u, v, and w), and the phase resistance calculation unit 43 sequentially receives the phase current detection value Ix (step S10). When the received phase current detection value Ix is zero, the phase resistance calculation unit 43 returns to step S10 and receives the next calculated phase current detection value Iy (y is any one of u, v, and w). When the non-zero u-phase, v-phase, and w-phase current detection values Iu, Iv, and Iw are received by repeating steps S10 and S12 in this manner, the phase resistance calculation unit 43 calculates the absolute value of these phase current detection values. It is determined whether the values | Iu |, | Iv |, | Iw | are all smaller than a predetermined threshold value Ith, and as a result, any of | Iu |, | Iv |, | Iw | If it is equal to or greater than Ith, the process returns to step S10. If all of | Iu |, | Iv |, | Iw | are smaller than the threshold value Ith, the process proceeds to step S16. Here, the threshold value Ith is introduced in order to prevent a decrease in calculation accuracy of the phase resistance due to heat generation due to current as described above, and the phase resistance is within a relatively small range of increase in phase resistance due to heat generation. Set to be calculated. The specific value differs depending on the brushless motor and the motor control device that drives the brushless motor, and is actually determined using experiments, computer simulations, and the like for the individual brushless motors and motor control devices.

  When the process proceeds to step S16, each phase current detection value Ix (x = u, v, w) that is not zero and whose absolute value is smaller than the threshold value Ith is obtained. The phase resistance calculation unit 43 extracts the phase voltage command values Vux, Vvx, Vwx (after correction) at the time of detection of the phase current detection values Ix from the storage unit 42, and the phase voltage command values Vux, Vvx. , Vwx (x = u, v, w) and the respective phase current detection values Ix are used to calculate the phase resistances Ru, Rv, Rw based on the aforementioned equations (22a) to (26c).

  The calculated values of the phase resistances Ru, Rv, Rw obtained as described above are given from the phase resistance calculation unit 43 to the correction unit 44 (step S20). The correction unit 44 corrects the phase voltage command values Vu, Vv, Vw based on the above-described equations (7) to (9) using the calculated values of the phase resistances Ru, Rv, Rw.

  After calculating the phase resistances Ru, Rv, Rw in this way, the process returns to step S10 to calculate the phase resistances Ru, Rv, Rw based on the new detected phase current values Ix.

  The operation of the phase resistance calculation unit 43 according to the processing procedure illustrated in FIG. 5 is an example, and the operation of the phase resistance calculation unit 43 is not limited to such a processing procedure. For example, the processes in steps S10 to S20 shown in FIG. 5 may be executed at predetermined time intervals. Further, the processing of steps S10 to S20 shown in FIG. 5 may be executed only once after the start of driving the brushless motor 1, or may be executed when a state such as temperature changes.

  In the operation example shown in FIG. 5, when the determination result of step S12 is “No” and the determination result of step S14 is “Yes”, the command values Vux, Vvx, Vwx of each phase voltage at the time of detection of each phase current are Although it is taken out from the storage unit 42, each time the current detection value Ix of any phase is obtained, whether the phase current detection value Ix is not zero or whether the absolute value is smaller than the threshold value Ith. If the phase current detection value Ix is not zero and the absolute value is smaller than the threshold value Ith, based on the formula (22a) (22b) or (23a) (23b) or (24a) (24b) Intermediate parameter values Xa and Xb corresponding to the current detection value Ix may be calculated (x = u, v, w; X = U, V, W).

In the operation example shown in FIG. 5, it is determined in step S14 whether or not the absolute value of the detected value of each phase current is smaller than the threshold value Ith. You may make it determine whether an absolute value is smaller than the threshold value Ith. In this case, the command value of each phase current can be obtained by converting the d-axis and q-axis current command values i _d ^* and i _q ^* obtained by the command current calculation unit 21 into values on the three-phase AC coordinate axes. it can. Alternatively, the determination may be made based on whether the absolute value or sum of squares of the d-axis and q-axis current command values i _d ^* and i _q ^* is smaller than a predetermined threshold value. More generally, by calculating the phase resistances Ru, Rv, Rw when the magnitude of the current flowing through the brushless motor 1 is smaller than a predetermined value, it is possible to prevent a decrease in the accuracy of calculation of the phase resistance due to heat generated by the current. I can do it.

  Further, even when the absolute value of the current value of each phase is smaller than a predetermined threshold value and the heat generation is small, the current values Iu, Iv, Iw in the formulas (22a) to (24b) are close to zero. Since an error is likely to occur, it is determined whether or not the absolute values | Iu |, | Iv |, | Iw | of each phase current detection value are larger than another threshold value Ith2 in addition to the determination in step S14. (However, Ith> Ith2), the phase resistance may be calculated only when it is larger than the threshold value Ith2.

  As described above, according to the present embodiment, the phase resistance Ru using the detected value Ix of each phase current and the command values Vux, Vvx, Vwx (x = u, v, w) of each phase voltage at the time of detection. , Rv, Rw are calculated, and the current command value Vy of each phase voltage is corrected according to the value of the resistance Ry of the phase (y = u, v, w). That is, the phase voltage command values Vu, Vv, Vw are corrected by the equations (7) to (9) using the calculated values of the phase resistances Ru, Rv, Rw. Here, the equations (7) to (9) are obtained by changing each phase voltage command value so that a portion of each phase voltage command value Vy corresponding to the voltage applied to the resistance Ry of the phase is proportional to the value of the resistance Ry. This indicates that Vy is corrected (y = u, v, w). By such correction, the interphase resistance difference is compensated, and the torque ripple caused by the interphase resistance difference is reduced. Therefore, according to the electric power steering apparatus using the motor control apparatus according to the present embodiment, the output torque of the motor becomes smooth and the steering feeling is improved.

  Moreover, according to the present embodiment, the values of the phase resistances Ru, Rv, Rw used for correcting the phase voltage command value are calculated when each phase current is small and the resistance value increase due to heat generation is small. The phase resistances Ru, Rv, Rw are calculated well. Thereby, the compensation of the interphase resistance difference by the correction of the phase voltage command value is performed more accurately, and as a result, the torque ripple can be sufficiently reduced.

<3. Second Embodiment>
FIG. 6 is a block diagram showing a configuration of a motor control device according to the second embodiment of the present invention. The motor control device according to the present embodiment is obtained by replacing the microcomputer 20 and the current sensor 14 with the microcomputer 30 and the current sensor 15 in the motor control device according to the first embodiment. This motor control device performs feedback control when the current sensor 15 is operating normally, and performs open loop control when the current sensor 15 fails.

  One current sensor 15 is provided on the path through which the three-phase drive current supplied to the brushless motor 1 flows, and individually detects the three-phase drive current. Three-phase current values detected by the current sensor 15 (hereinafter referred to as “u-phase current detection value Iu”, “v-phase current detection value Iv”, and “w-phase current detection value Iw”) are input to the microcomputer 30. The

  The microcomputer 30 is obtained by adding a three-phase / dq axis conversion unit 31, a subtraction unit 32, a feedback control unit 33, a failure monitoring unit 34, and a command voltage selection unit 35 to the microcomputer 20. The microcomputer 30 also includes a phase resistance calculation unit 53 and a correction unit 54 as in the first embodiment, but in this embodiment, three-phase drive currents supplied to the brushless motor 1 are individually provided. Therefore, the phase current calculation unit 41 and the storage unit 42 are not provided.

The three-phase / dq-axis conversion unit 31 uses the following equations (27) and (28) based on the u-phase current detection value Iu and the v-phase current detection value Iv detected by the current sensor 15 to detect the d-axis current detection value. i _d and q-axis current detection value i _q are obtained.
i _d = √2 × {Iv × sin θ−Iu × sin (θ−2π / 3)} (27)
i _q = √2 × {Iv × cos θ−Iu × cos (θ−2π / 3)} (28)

Subtraction unit 32, d-axis current command value i _d ^* and the d-axis current detection value i _d deviation E _d, and a deviation E _q of the q-axis current command value i _q ^* and the q-axis current detection value i _q . The feedback control unit 33 performs a proportional-integral calculation shown in the following equations (29) and (30) on the deviations E _d and E _q to obtain the d-axis voltage command value v _d ^# and the q-axis voltage command value v _q ^#. Ask for.
v _d ^# = K × {E _d + (1 / T) ∫E _d · dt} (29)
v _q ^# = K × {E _q + (1 / T) ∫E _q · dt} (30)
In equations (29) and (30), K is a proportional gain constant, and T is an integration time.

  The failure monitoring unit 34 checks whether or not the three-phase current values detected by the current sensor 15 are within the normal range, and determines whether the current sensor 15 is operating normally or has failed. The failure monitoring unit 34 determines “normal” when all three-phase current values are within the normal range, and determines “failure” when one-phase or more current values are outside the normal range. The failure monitoring unit 34 outputs a control signal indicating the determination result.

When the failure monitoring unit 34 determines that the command voltage selection unit 35 is normal, the command voltage selection unit 35 outputs the d-axis voltage command value v _d ^# and the q-axis voltage command value v _q ^# obtained by the feedback control unit 33, and the failure monitoring unit If it is determined in 34 that a failure has occurred, the d-axis voltage command value v _d and the q-axis voltage command value v _q obtained by the open loop control unit 22 are output.

  When the current sensor 15 is operating normally, the failure monitoring unit 34 determines that it is normal, and the command voltage selection unit 35 selects the output of the feedback control unit 33. At this time, the command current calculation unit 21, the dq axis / three-phase conversion unit 23, the angle calculation unit 24, the three-phase / dq axis conversion unit 31, the subtraction unit 32, and the feedback control unit 33 operate to perform feedback control. In addition to this, while the current sensor 15 is operating normally, the angular velocity calculation unit 25 and the Φ calculation unit 26 also operate. The Φ calculating unit 26 obtains the armature winding linkage magnetic flux number Φ included in the equation (2) using the equation (15) while the current sensor 15 is operating normally.

  The phase resistance calculation unit 53 also calculates the phase resistances Ru, Rv, Rw in the same manner as in the first embodiment while the current sensor 15 is operating normally. That is, the phase resistance calculation unit 43 is based on the phase current detection values Iu, Iv, Iw detected by the current sensor 15 and the corrected phase voltage command values Vuc, Vvc, Vwc at the time of detection. The values of u-phase resistance Ru, v-phase resistance Rv, and w-phase resistance Rw in 1 are obtained. Here, the u-phase, v-phase and w-phase current detection values Iu, Iv and Iw are detected simultaneously. For this reason, the phase voltage command values Vuc, Vvc, Vwc at the detection time are the phase voltage command values Vux, Vvx, Vwx (x = u, v, w) at the detection time of each phase current in the first embodiment. Corresponding to Therefore, if “Vux, Vvx, Vwx (x = u, v, w)” in the flowchart shown in FIG. 5 is replaced with “Vuc, Vvc, Vwc”, this flowchart shows an operation example in this embodiment. Therefore, detailed description of the phase resistance calculation unit 53 is omitted.

The calculated values of the phase resistances Ru, Rv, Rw obtained by the phase resistance calculation unit 53 are given to the correction unit 54. As in the case of the first embodiment, the correction unit 54 includes the calculated values of the phase resistances Ru, Rv, and Rw, the armature winding interlinkage magnetic flux number Φ from the Φ calculation unit 26, and the angular velocity calculation. An angular velocity ω _e is given from the unit 25. Further, the correction unit 54 is also given a control signal indicating the determination result in the failure monitoring unit 34.

Incidentally, while the current sensor 15 is operating normally, d-axis current command value i _d ^* and the d-axis current detection value i _d deviation E _d, and, q-axis current command value i _q ^* and the q-axis current since the feedback control so that the deviation E _q of the detection value i _q is canceled performed normally, the occurrence of torque ripple caused by the interphase resistance difference is not a problem. Therefore, in the present embodiment, the correction unit 54 is based on the control signal from the failure monitoring unit 34 while the current sensor 15 is operating normally, that is, while feedback control is being performed. The phase voltage command values Vu, Vv, Vw output from the conversion unit 23 are supplied to the three-phase / PWM modulator 12 as they are without correction. That is, Vu = Vuc, Vv = Vvc, Vw = Vwc. However, even during feedback control, the phase voltage command values Vu, Vv, Vw may be corrected using the calculated values of the phase resistances Ru, Rv, Rw.

Thereafter, when the current sensor 15 fails, the failure monitoring unit 34 determines that there is a failure, and the command voltage selection unit 35 selects the output of the open loop control unit 22. At this time, the command current calculation unit 21, the open loop control unit 22, the dq axis / 3-phase conversion unit 23, and the angle calculation unit 24 operate to perform open loop control. The open loop control unit 22 obtains the d-axis voltage command value v _d and the q-axis voltage command value v _q using the Φ value obtained while the current sensor 15 is operating normally. The d-axis voltage command value v _d and the q-axis voltage command value v _q are given to the dq-axis / 3-phase conversion unit 23 via the command voltage selection unit 35, where the phase voltage command values Vu, Vv, Vw Converted. These phase voltage command values Vu, Vv, Vw are given to the correction unit 54.

Based on the control signal from the failure monitoring unit 34, the correction unit 54 uses the phase resistances Ru, Rv, and the like from the phase resistance calculation unit 53 as in the case of the first embodiment when the current sensor 15 has failed. Using the calculated value of Rw, the number of armature winding linkage magnetic fluxes Φ from the Φ calculating unit 26 and the angular velocity ω _e from the angular velocity calculating unit 25, the phase voltage command value according to the above-described formulas (7) to (12) Vu, Vv, and Vw are corrected. The corrected phase voltage command values Vuc, Vvc, Vwc are given to the three-phase / PWM modulator 12. The motor driving means comprising the three-phase / PWM modulator 12 and the motor driving circuit 13 drives the brushless motor 1 with the voltages of these phase voltage command values Vuc, Vvc, Vwc.

  As described above, when the current sensor is operating normally, the motor control device according to the present embodiment performs a proportional integral operation on the difference between the current command value and the current value detected by the current sensor to The command value is obtained, and when the current sensor fails, the voltage command value is obtained by performing open loop control according to the circuit equation of the motor based on the current command value and the angular velocity of the rotor. When performing open loop control, the Φ value (the number of armature winding linkage magnetic fluxes Φ) obtained while the current sensor is operating normally is used. Therefore, according to the motor control device according to the present embodiment, while the current sensor is operating normally, feedback control can be performed and the brushless motor can be driven with high accuracy. In addition, when the current sensor fails and feedback control cannot be performed, the open-loop control is performed using the armature winding interlinkage magnetic flux number Φ obtained during the feedback control, so that the brushless motor is highly accurate. To obtain a desired motor output.

  Further, according to the present embodiment, when performing open loop control, the resistance difference between phases is compensated using the values of the phase resistances Ru, Rv, Rw obtained while the current sensor is operating normally. As described above, the phase voltage command values Vu, Vv, and Vw are corrected by the correction unit 54 (see equations (7) to (9)). For this reason, according to the motor control apparatus which concerns on this embodiment, generation | occurrence | production of the torque ripple resulting from an interphase resistance difference is suppressed. Therefore, even when the current sensor fails and feedback control cannot be performed, a good steering feeling can be obtained.

<4. Modification>
In the first embodiment, only one current sensor 14 is provided, but a plurality (two or three) may be provided. For example, when u-phase and v-phase current sensors are provided, the u-phase and v-phase current detection values used for the calculation of the phase resistances Ru, Rv, Rw in the phase resistance calculation unit 43 are the u The u-phase current detection value Iu and the v-phase current detection value Iv output from the phase and v-phase current sensors may be used, and the w-phase current detection value Iw may be obtained by the following equation in the phase current calculation unit 41. .
Iw = −Iu−Iv
When a plurality of current sensors 14 are provided, the u-phase, v-phase, and w-phase current detection values can be obtained at the same time, and therefore the storage unit 42 is not always necessary. When three are provided (when the number equal to the number of phases is provided), the phase current calculation unit 41 is not necessary. In this case, a current detection means is constituted by the plurality of current sensors.

  In the first and second embodiments, the phase voltage command values Vu, Vv, Vw are corrected by the equations (7) to (9) based on the phase resistances Ru, Rv, Rw. The correction is not limited to such equations (7) to (9). More generally, in order to compensate for the resistance difference between the phases, each of the phase voltage command values Vx so that the portion corresponding to the voltage applied to the resistance Rx of the phase has a positive correlation with the value of the resistance Rx. The phase voltage command value Vx may be corrected (x = u, v, w).

By the way, when the angular velocity ω _e of the rotor of the brushless motor 1 is large, the counter electromotive force is large and the ratio of the voltage applied to the phase resistances Ru, Rv, Rw is small. It becomes easy and the calculation precision of phase resistance Ru, Rv, Rw falls. Therefore, it provided the threshold per angular velocity omega _e, phase resistance Ru only when the angular speed omega _e is smaller than the threshold value, Rv, may be calculated Rw.

  Moreover, although the motor control apparatus according to the first and second embodiments is configured to drive the three-phase brushless motor 1, the present invention is not limited to this, and four or more phases are used. The present invention can also be applied to a motor control device that drives a brushless motor.

  In the motor control device according to the second embodiment, the feedback control and the open loop control are switched based on the determination result in the failure monitoring unit 34. However, the determination is not based on the determination in the failure monitoring unit 34 (for example, the driver Feedback control and open loop control may be switched).

  The present invention can be applied not only to the above-described column assist type electric power steering apparatus but also to a pinion assist type or rack assist type electric power steering apparatus. The present invention can also be applied to motor control devices other than the electric power steering device.

It is a block diagram which shows the structure of the electric power steering apparatus which concerns on embodiment of this invention. It is a block diagram which shows the structure of the motor control apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the three-phase alternating current coordinate and dq coordinate in a three-phase brushless motor. It is a figure for demonstrating the calculation method of the phase resistance in the said 1st Embodiment. It is a flowchart for demonstrating the operation example of the phase resistance calculation part in the said 1st Embodiment. It is a block diagram which shows the structure of the motor control apparatus which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 6 ... Rotor, 10 ... ECU, 13 ... Motor drive circuit, 14, 15 ... Current sensor (current detection means), 20, 30 ... Microcomputer, 26 ... Φ calculation part (parameter calculation means), 32 ... Subtraction part, 35 ... Command voltage selector.

Claims (5)

A motor control device for driving a brushless motor,
Current detection means for detecting each phase current flowing through the brushless motor;
Control calculation means for obtaining a command value indicating each phase voltage to be applied to the brushless motor, and outputting the command value as a phase voltage command value;
Phase resistance calculating means for calculating the resistance value of each phase based on the detected value of each phase current detected by the current detecting means and the command value of each phase voltage applied to the brushless motor at the time of detection of the detected value When,
Correction means for correcting the phase voltage command value according to the resistance value of each phase calculated by the phase resistance calculation means;
A motor control device comprising: drive means for driving the brushless motor based on the phase voltage command value corrected by the correction means.   2. The motor control device according to claim 1, wherein the phase resistance calculation unit calculates a resistance value of each phase when a magnitude of a current flowing through the brushless motor is smaller than a predetermined value. A storage means for storing the corrected phase voltage command value at the time when each phase current is detected by the current detection means;
The phase resistance calculating means calculates a resistance value of each phase based on a detected value of each phase current detected by the current detecting means and a phase voltage command value stored in the storage means, The motor control device according to claim 1. The current detection means includes
A single current sensor for detecting a current flowing in the brushless motor;
Phase current calculation means for sequentially obtaining the detected value of each phase current based on the detected value of the current detected by the current sensor,
The control calculation means is
An open loop control means for obtaining the phase voltage command value according to a circuit equation of a brushless motor based on a command value indicating a current to be supplied to the brushless motor and an angular velocity of a rotor of the brushless motor;
Parameter calculation means for obtaining a value of a parameter to be used when obtaining the phase voltage command value according to the circuit equation based on a detected value of the current detected by the current sensor;
4. The motor control device according to claim 3, wherein the storage unit stores the corrected phase voltage command value every time a detected value of any phase current is obtained by the phase current calculation unit. 5. . An electric power steering device that applies a steering assist force to a steering mechanism of a vehicle by a brushless motor,
A motor control device according to any one of claims 1 to 4, comprising:
The electric power steering device according to claim 1, wherein the motor control device drives a brushless motor that applies a steering assist force to the steering mechanism.

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