JP2005160221A - Control device of electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To overcome the problem that, by vector control that converts a conventional three-phase motor to a d-q axis, a variation in the motor parameter of a part of a phase caused by heat generation exerts influences upon all phases for d-q axis conversion, whereby the variation cannot be controlled so as to be completely corrected, a motor torque ripple is generated, and steering operation with a good feeling has not been achieved in an electric power steering device. <P>SOLUTION: A current command value calculated from a torque command value obtained by steering operation is set to be a current command value at each phase, the current detection of a motor is also performed at each phase, and current control that makes the current command value of each phase and the detected current value as inputs is also performed at each phase independently, whereby the variation in the motor parameter generated at a part of the phase does not exert an influence upon the other phase. Since the control for correcting the variation by executing closing with a control system for only the phase is made possible, the generation of the torque ripple is suppressed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a control device for an electric power steering device, and in particular, in an electric power steering device using a multiphase motor, even when parameter changes such as motor parameters to be controlled occur in some phases, the control is robust. The present invention relates to a control device for an electric power steering device.

  An electric power steering device that applies a steering assist force to a steering device of an automobile by the rotational force of a motor is a steering assist force applied to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer. Is supposed to be granted. A simple configuration of such an electric power steering apparatus will be described with reference to FIG. A shaft 102 of the steering handle 101 is connected to a tie rod 106 of a steering wheel via a reduction gear 103, universal joints 104a and 104b, and a pinion rack mechanism 105. The shaft 102 is provided with a torque sensor 107 that detects the steering torque of the steering handle 101, and a motor 108 that assists the steering force of the steering handle 101 is connected to the shaft 102 via the reduction gear 103. Yes.

  It is necessary to execute the control correctly so that the motor 108 of the electric power steering apparatus having such a configuration outputs a desired torque corresponding to the driver's steering operation. Vector control, which is one of typical control methods for controlling the motor 108 of the electric power steering apparatus, is described in Patent Document 1, and FIG. 5 shows a basic part of the control disclosed in Patent Document 1. FIG.

  The control block diagram will be described. The torque command value Tref calculated by a torque command value calculation unit (not shown) based on the steering torque Tr detected from the torque sensor 107 and the rotation angle θ, which is the electrical angle of the motor 108, are expressed as current commands. Input to the value calculation unit 204. The current command value calculation unit 204 calculates the q-axis component current command value Iqref and the d-axis component current command value Idref. Normally, the current command value Iqref is proportional to the torque command value Tref, and the current command value Idref is 0 (usually Idref = 0). On the other hand, an angle detector is installed to detect the rotation angle θ of the motor 108, and there are an encoder and a hall sensor as the angle detector. Since the signal output from the resolver 201 does not immediately indicate the rotation angle θ, the rotation angle θ is calculated in the position detection circuit 202 configured by an RDC circuit or the like.

  This control block diagram uses feedback control as an example, and it is necessary to detect and feed back the actual motor currents Ia, Ib, and Ic of the motor 108 with respect to the current command values Iqref and Idref described above. Specifically, motor currents Ia and Ic are detected by current detectors 205-1 and 205-2, and motor current Ib is subtracted by Ib = − (Ia + Ic) in subtraction unit 207-3 from the relationship of Ia + Ib + Ic = 0. ). Next, the motor currents Iq and Id are converted by the three-phase / two-phase converter 206 for vector control. For this conversion, the rotation angle θ of the motor described above is used. Next, the motor currents Iq and Id are fed back to the subtraction units 207-1 and 207-2, respectively, and the subtraction unit 207-1 calculates the deviation ΔIq between the current command value Iqref and the motor current Iq, and the subtraction unit 207-2. The deviation ΔId between the current command value Idref (usually Idref = 0) and the motor current Id is calculated.

The proportional integration (PI) control unit 208 is inputted so as to eliminate these deviations, and the voltage command values Vdref and Vqref are outputted. Since the actual motor 108 needs to supply a three-phase current, the voltage command values Vdref and Vqref are converted into three-phase voltage command values Varef, Vbref and Vcref by the two-phase / three-phase conversion unit 209. The PWM control unit 210 generates a PWM control signal based on the voltage command values Varef, Vbref, Vcref, and the inverter circuit 211 supplies a current to the motor 108 based on the PWM control signal, and the deviation from the current command values Iqref and Idref. Motor currents Ia, Ib, and Ic are supplied so that there is no more.
JP 2001-18822 A

  As a feature of such vector control, the motor current of the three-phase motor to be controlled is detected by the three-phase Ia, Ib, Ic, and the motor currents Ia, Ib, Ic are supplied by the inverter circuit. In the middle of vector control, control calculation is performed by two phases converted into d-axis and q-axis. As described above, conversion to the d-axis and the q-axis is convenient when the torque is controlled independently, but also has the following problems.

  For example, when the resistance of the motor winding, which is a motor parameter of the motor 108, changes due to the heat generated by the motor winding, if the heat dissipation condition differs for each phase, for example, the winding resistance Ra of the a-phase motor is different from the other phase. When (Ra + ΔR), the motor current Ia changes to (Ia + ΔI). Assuming that the currents Ib and Ic are energized as usual without changing the winding resistance of the b-phase and c-phase motors, the three-phase / two-phase conversion unit 206 performs the conversion as shown in Equation (1). .

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It becomes.

  That is, the parameter change generated in the a-phase is diffused to the elements of the d-axis and the q-axis, and in particular, after passing through the PI control unit 208, the 2-phase / 3-phase conversion unit 209 returns the voltage command values Varef, Vbref, Vcref. In this case, an error correction value due to a parameter change of the a phase is incorporated into the voltage command values of the b phase and the c phase. Since the parameter change is originally generated only in the a phase, the error correction value is included in the b phase and the c phase even though the error should be corrected only in the a phase. Furthermore, if the motor rotation speed (angular velocity ω) is high-speed rotation, the error (ΔIa · cos θ, ΔIa · sin θ) changes at high speed on the d-axis and q-axis and the current control unit cannot follow the torque ripple. turn into.

  The present invention has been made for the above-described circumstances, and an object of the present invention is to provide a motor control that is robust against parameter changes in each phase when a multiphase motor is used in an electric power steering apparatus. It is an object of the present invention to provide a control device for an electric power steering device with a small torque ripple.

  The present invention relates to a control device for an electric power steering apparatus in which a steering assist force by an n-phase (where n is 3 or more) motor is applied to a vehicle steering system. In order to detect each phase current Im (where m is 1, 2,..., N) of the motor, at least (n−1) current detection means and a current command value Imref (where m is The current command value calculating means for outputting 1, 2,..., N) and n current control means, and the current command value Imref for each phase and the current Im for each phase as inputs. This is achieved by controlling each phase current by the control means. The above-mentioned object of the present invention is achieved by the current control means comprising a feedforward control means and a disturbance observer. Further, the above object of the present invention can be achieved when the n-phase motor is a three-phase motor and the winding of the motor winding is a Y connection or a Δ connection.

  According to the present invention, the current detection of the multiphase motor of the electric power steering apparatus and the calculation of the current command value are performed for each phase, and the current command value for each phase and the detected current value for each phase are input. Since the current control to be performed is also executed for each phase, there is an effect that it is possible to provide a control device for an electric power steering apparatus that can perform motor control robust to changes in control parameters such as motor parameters generated in some phases.

  A preferred embodiment of the present invention will be described with reference to FIG. Those having the same numbers as those used in the description of the prior art have the same functions.

  In this embodiment, the present invention is applied to a three-phase motor in which the motor is n = 3. In the case of n = 3, m = 1, 2, 3 and the current command value Imref of each phase is I1ref, I2ref, I3ref, which are generally expressed as Iaref, Ibref, Icref. Further, although the motor phase currents Im are I1, I2, and I3, they are denoted as Ia, Ib, and Ic for the same reason.

  First, when the torque command value Tref and the rotation angle θ of the motor 108 are input to the current command value calculation unit 10 which is a current command value calculation means, and the current command value Imref of each phase is three phases, Iaref, Ibref, Icref Is output. On the other hand, each phase current Im of the detected motor becomes Ia, Ib, and Ic in the case of a three-phase motor. Therefore, current detectors 205-1 and 205-2, which are current detection means, detect the currents Ia and Ic of the a-phase and c-phase motors, respectively. The b-phase motor current Ib is calculated by the subtraction unit 207-3 as Ib = − (Ia + Ic) from the relationship of Ia + Ib + Ic = 0. In a three-phase motor with n = 3, at least two current detection means of n−1 are required. Of course, three current detection means may be used to directly detect the current Ib.

  Next, each phase current command value Iaref, Ibref, Icref and each detected phase current Ia, Ib, Ic are input to the current control means. A portion surrounded by a broken line A in FIG. The current control means of this embodiment is composed of a feedforward control means and a disturbance observer. Current command values Iaref, Ibref, Icref are fed to the a-phase FF control unit 11-1, b-phase FF control unit 11-2, and c-phase FF control unit 11-3, which are feedforward (hereinafter referred to as FF) control means. Are inputted, and voltage command values Varef, Vbref, Vcref are outputted. The relationship between the current command value and the voltage command value is as shown in Equation 2.

(Equation 2)
Varef = (Rna + s · Lna) · Iaref
Vbref = (Rnb + s · Lnb) · Ibref
Vcref = (Rnc + s · Lnc) · Icref
Here, Rn and Ln are the rated winding resistance value and winding inductance value of the motor, and Rna and Lna are the rated winding resistance value and winding inductance value of the a-phase motor. In design, Rna = Rnb = Rnc = Rn, Lna = Lnb = Lnc = Ln.

  On the other hand, the disturbance observer includes an a-phase disturbance observer 19-1, a b-phase disturbance observer 19-2, and a c-phase disturbance observer 19-3. Each disturbance observer includes a detected motor current I and The sum (Vref + Vdis) of the disturbance value Vdis and the voltage command value Vref, which is the output of each phase disturbance observer, is input, and the disturbance value Vdis is output. For example, for the a phase, the disturbance observer 19-1 receives the a-phase motor current Ia and the a-phase sum (Varef + Vdis) and outputs the a-phase disturbance value Vadis. Similarly, in the b-phase disturbance observer 19-2 and the c-phase disturbance observer 19-3, the b-phase and c-phase motor currents Ib and Ic and the sum (Vbref + Vbdis) and (Vcref + Vcdis) are input, and the disturbance value is obtained. Vbdis and Vcdis are output.

  Specifically, the disturbance observer 19 includes a transfer function 20, a transfer function 21, and a subtracting unit 22. The transfer function 21 simulates (Rn + s · Ln) which is an inverse system of the motor model. The first-order lag function (1 + s · T) in the denominator represents a filter that removes noise generated by the current detection means or the like. On the other hand, the same first-order lag function (1 + s · T) is inserted into the transfer function 20 to balance the time delay with (1 + s · T) representing the noise filter of the transfer function 21. In other words, the output of the transfer function 21 has the relationship of Equation 3 when the first-order lag function as a noise filter is ignored.

(Equation 3)
Va = (Rn + s · Ln) · Ia
Vb = (Rn + s · Ln) · Ib
Vc = (Rn + s · Ln) · Ic
That is, the actual motor voltages Va, Vb, Vc are estimated from the detected actual motor currents Ia, Ib, Ic. Then, the disturbance observers 19-1, 19-2, 19-3 are estimated from the sum of the final voltage command values (Vref + Vdis), (Vref + Vdis), (Vref + Vdis) and the actual motor currents Ia, Ib, Ic. Differences from the motor voltages Va, Vb, and Vc calculated by the subtracting units 22-1, 22-2, and 22-3 are calculated as disturbance values Vadis, Vbdis, and Vcdis, respectively. These disturbance values Vadis, Vbdis, and Vcdis are fed back to the adders 12-1, 12-3, and 12-4, and are voltage command values that are outputs of the FF controllers 11-1, 11-2, and 11-3. The control is corrected by adding to each of Varef, Vbref, and Vcref.

  The sum values (Vref + Vdis), (Vref + Vdis), and (Vref + Vdis), which are the outputs of the adders 12-1, 12-2, and 12-3, are final voltage command values that are input to the PWM controller 210, 210 generates PWM signals Ta, Tb, and Tc based on the voltage command values of each phase, and the inverter circuit 211 is PWM-controlled. The inverter circuit 211 supplies the motor 108 with motor currents Ia, Ib based on the PWM signals Ta, Tb, Tc, that is, based on the summed values (Vref + Vdis), (Vref + Vdis), (Vref + Vdis) which are voltage command values. , Ic.

  The above is an explanation of the operation of the embodiment of the present invention shown in FIG. 1. If the motor control operation is as described above, for example, the motor parameter a-phase motor winding resistance is changed from Ra to (Ra + ΔRa). As a result, even if the a-phase motor current becomes (Ia + ΔIa), the current command values Iaref, Ibref, Icref and the detected motor currents Ia, Ib, Ic are independent in each phase, and current control is performed. Since each phase is controlled independently, the change in the motor parameter of the a phase is closed in the control loop of the a phase (disturbance value Vadis), and is independent of the control of the b phase or the c phase. That is, since the change in the a-phase motor parameter is corrected independently in the a-phase control loop, it is easier to correct the a-phase than in the conventional control, and the other phases are the b-phase and c-phase. Since the phase is not affected, there is an effect that it is not affected by the parameter change of the irrelevant phase as in the conventional control.

  Therefore, even if a control parameter such as a motor parameter occurs only in a part of the phase in the motor of the electric power steering apparatus, the change control can be incorporated and the correction control can be performed. It is possible to provide a control device for an electric power steering device that can be expected to have good steering operation.

  In particular, when the current control unit A is configured with FF control and a disturbance observer as in this embodiment, the motor model (Rn + s · Ln) is used for the FF control and the disturbance observer. Especially good effects can be expected. More specifically, if design parameters of each phase, for example, errors ΔRna and ΔLna from ana Rna and Lna are estimated and used as (Rna + ΔRna) and (Lna + ΔLna) in current control of each phase, The motor parameter change can be compensated.

  FIG. 3 shows an embodiment in which the current control means is performed by feedback control (hereinafter referred to as FB control). In this embodiment, a current command value calculation unit 10 as current command value calculation means for outputting each phase current command value Iaref, Ibref, Icref, and current detection for measuring each phase current Ia, Ib, Ic of the motor. Current detectors 205-1 and 205-2 and a subtracting unit 207-3 as means, and a broken line part B that controls each phase independently and outputs voltage command values Varef, Vbref, and Vcref of each phase. It has a configuration including a current control unit B which is an enclosed current control means.

  As the operation of this embodiment, the current command value calculation unit 10 outputs the current command values Iaref, Ibref, and Icref for each phase. On the other hand, the currents Ia and Ic of each phase of the motor are detected by the current detector 205-1 and the current detector 205-2, and the current Ib is calculated by the subtractor 207-3 from the relationship of Ib = − (Ia + Ic). The The current command values Iaref, Ibref, Icref and the detected motor currents Ia, Ib, Ic are subtracted in the subtraction units 207-4, 207-5, 207-6 by deviations ΔIa = (Iaref−Ia), ΔIb = (Ibref, respectively). −Ib), ΔIc = (Icref−Ic). The deviations ΔIa, ΔIb, ΔIc of each phase are input to the PI control units 13-1, 13-2, 13-3, respectively, and output voltage command values Varef, Vbref, Vcref.

  Therefore, the current command values Iaref, Ibref, Icref of each phase and the detected motor phase currents Ia, Ib, Ic are independently input to the current control unit B, and the calculation in the current control unit B is performed for each phase. The configuration and operation are controlled independently.

  The PWM control unit 210 receives the voltage command values Varef, Vbref, and Vcref, generates and outputs PWM signals Ta, Tb, and Tc for each phase, and the inverter circuit 211 outputs to the motor 108 based on the PWM signal. Currents Ia, Ib, and Ic are supplied so that the deviations ΔIa, ΔIb, and ΔIc become zero.

  Also in this embodiment, the motor 108 is controlled by calculating the current command values Iaref, Ibref, Icref for each phase, and detecting the motor currents Ia, Ib, Ic for each phase. Each current command value and detection current are input, and the current control unit B performs current control independently for each phase. Therefore, even if a control parameter such as a motor parameter of a part of the motor changes, control is performed to independently correct the changed phase. Therefore, the change of the parameter of the phase affects other phases. In addition, since the control for closing and correcting in this phase is executed, effective control is possible.

  As described above, if this embodiment is used, even if a change in the control parameters of some phases occurs, control is performed independently for each phase, so that other phases are not affected and only the relevant phase is affected. Since the control can be performed in a closed form, it is possible to effectively correct and control the change. Therefore, it is possible to control the motor with less torque ripple, and to provide a control device for the electric power steering device that enables a steering operation with a good feeling. it can.

  When the motor is a three-phase motor, as shown in FIG. 3, there are a Y connection and a Δ connection as motor connections. As the motor connection, the Y connection is generally used, but the present invention can also be applied to a Δ connection. In other words, the Y connection and the Δ connection can be impedance-converted as shown in Equation 4, and the present invention can also be applied to a Δ-connection motor if the value is converted according to the conversion equation.

(Equation 4)
Z1 = Z31 · Z12 / (Z12 + Z23 + Z31)
Z2 = Z12 · Z23 / (Z12 + Z23 + Z31)
Z3 = Z23 · Z31 / (Z12 + Z23 + Z31)
If conversion is performed based on this conversion formula, the present invention can be applied regardless of whether the three-phase motor is Y-connected or Δ-connected. Specifically, when Z12 changes to (Z12 + ΔZ12), the errors become Y-connection models (Z1 + ΔZ1), (Z2 + ΔZ2), and (Z3 + ΔZ3), which can be compensated by the current control units of the three phases. Unlike the case where current control is performed on the d-axis and the q-axis, the error ΔZ12 does not change in each phase depending on the rotation angle θ, so that generation of torque ripple can be suppressed even at high-speed rotation.

  In addition, although Example 1 and Example 2 demonstrated the example of the three-phase motor, it is not limited to the three-phase motor of n = 3, This invention is multiphase, such as a five-phase motor of n = 5. It can also be applied to motors.

It is a control block diagram of Example 1 of the present invention. It is a control block diagram of Example 2 of the present invention. It is a figure explaining the impedance conversion of Y connection and (DELTA) connection of a three-phase motor. It is a block diagram of an electric power steering device. It is a conventional control block diagram.

Explanation of symbols

10 current command value calculation unit 11-1, 11-2, 11-3 FF control unit 12-1, 12-2, 12-3 subtraction unit 13-1, 13-2, 13-3 PI control unit 19-1 , 19-2, 19-3 Disturbance observer 20-1, 20-2, 20-3 Transfer function 21-1, 21-2, 21-3 Transfer function 22-1, 22-2, 22-3 Subtractor A , B Current controller

Claims (3)

In a control device for an electric power steering apparatus in which a steering assist force by an n-phase motor (where n is 3 or more) is applied to a steering system of a vehicle, each phase current Im of the motor (where m is 1 or 2) ,..., N) to detect at least (n-1) current detection means and current command values Imref (where m is 1, 2,..., N) for each phase. Each phase current control is performed by the current control means that includes a value calculation means and n current control means and receives the current command value Imref and the phase current Im of each phase. Control device for power steering device. The control device for an electric power steering apparatus according to claim 1, wherein the current control means includes a feedforward control means and a disturbance observer. 3. The control device for an electric power steering apparatus according to claim 1, wherein when the n-phase motor is a three-phase motor, the connection of the windings of the motor is a Y connection or a Δ connection. 4.

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