Torque ripple suppression control device for permanent magnet motor and electric power steering system

A torque ripple suppression control device for a permanent magnet motor includes a current command conversion unit that outputs a current command value, a position detector that detects a rotational position of the permanent magnet motor, a current detection unit that detects a current at the permanent magnet motor, an induced voltage coefficient setting unit that outputs an information signal related to an induced voltage coefficient for an induced voltage at the permanent magnet motor, a torque ripple suppression operation unit that outputs a current correction command value for the permanent magnet motor, a current control operation unit that outputs a voltage command value based upon addition results obtained by adding together the current command value and the current correction command value and the current detection value, and a power converter that outputs a voltage with which the permanent magnet motor is to be driven.

INCORPORATION BY REFERENCE

The disclosure of the following priority application is herein incorporated by reference: Japanese Patent Application No. 2010-9044 filed Jan. 19, 2010

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technology for suppressing torque ripple caused by an induced voltage distortion in a permanent magnet motor.

2. Description of Related Art

The following is a method known in the related art that may be adopted to suppress torque ripple when the waveform of a voltage induced in a motor is rectangular when there is a distortion in the induced voltage. In the method, three-phase induced voltage waveforms are converted to a d-axis voltage edand a q-axis voltage eqand the torque ripple is canceled out based upon a q-axis current command value Iqrefcalculated as expressed in (1) below.

Trefand ωmin expression (1) respectively represent a torque command value and a mechanical angular speed at the motor. Namely, the q-axis current command value Iqrefcontaining a pulsation waveform can be calculated as expressed in (1) so as to achieve uniformity in the motor torque even when the waveforms of the induced voltages at the motor are rectangular. The torque ripple can be suppressed by executing vector control in conformance to this current command value.

However, since the current command value Iqrefcontains the pulsation waveform, the q-axis current Iqcorresponding to the current command value Iqrefmust be controlled by utilizing a high-response current control system. In other words, the current control response frequency must be set so as to achieve the relationship expressed in (2) below.
n×p/2×ω≦upper limit to current control response frequency  (2)

n in expression (2) represents a wave component, the order of which is equal to or above 5% of the amplification component resulting from frequency analysis of an artificial rectangular wave simulated for the motor. In addition, P represents the number of poles of the motor and ω represents the actual rotation rate of the motor.

The torque ripple suppression method described above is disclosed in patent reference 1.(Patent reference 1) Japanese Laid Open Patent Publication No. 2004-201487

Through the torque ripple suppression method in the related art described above, control under which the torque ripple component that occur when the waveforms of the induced voltages at the motor are rectangular is canceled out, is enabled. The motor torque in this situation is in proportion to the product of a q-axis induced voltage coefficient (notated as Ked), which is in proportion to the q-axis voltage eq, and the q-axis current Iq. For this reason, a torque ripple DC component is generated in correspondence to the product (ΔKed×ΔIq) of a pulsation component ΔKedin the q-axis induced voltage coefficient Kedand a pulsation component ΔIqin the current Iq. This torque ripple DC component, however, cannot be effectively utilized in the torque ripple suppression method in the related art.

An object of the present invention is to provide a torque ripple suppression control device and an electric power steering system that enable effective utilization of the torque ripple DC component.

SUMMARY OF THE INVENTION

A torque ripple suppression control device for a permanent magnet motor according to a 1st aspect of the present invention includes: a current command conversion unit that outputs a current command value based upon a torque command value input thereto from an external source; a position detector that outputs a position detection value by detecting a rotational position of the permanent magnet motor; a current detection unit that outputs a current detection value by detecting a current at the permanent magnet motor; an induced voltage coefficient setting unit that outputs, based upon the position detection value, an information signal related to an induced voltage coefficient for an induced voltage at the permanent magnet motor; a torque ripple suppression operation unit that outputs, based upon the information signal and a preset proportional gain, a current correction command value for the permanent magnet motor; a current control operation unit that outputs, based upon addition results obtained by adding together the current command value and the current correction command value and the current detection value, a voltage command value based upon which the permanent magnet motor is to be driven; and a power converter that outputs, based upon the voltage command value, a voltage with which the permanent magnet motor is to be driven.

According to a 2nd aspect of the present invention, in the torque ripple suppression control device of the 1st aspect for a permanent magnet motor, it is preferable that: the current command conversion unit outputs a d-axis current command value and a q-axis current command value corresponding to a d-axis and a q-axis of a rotation coordinate system of the permanent magnet motor; the induced voltage coefficient setting unit outputs information signals related to a d-axis induced voltage coefficient and a q-axis induced voltage coefficient corresponding to the d-axis and the q-axis; the torque ripple suppression operation unit outputs a d-axis current correction command value and a q-axis current correction command value corresponding to the d-axis and the q-axis; and the current control operation unit outputs a d-axis voltage command value and a q-axis voltage command value corresponding to the d-axis and the q-axis based upon addition results obtained by adding together the d-axis current command value and the d-axis current correction command value, addition results obtained by adding together the q-axis current command value and the q-axis current correction command value, and the current detection value.

According to a 3rd aspect of the present invention, the torque ripple suppression control device of the 2nd aspect of the present invention for a permanent magnet motor may further include a coordinate conversion unit that converts the d-axis voltage command value and the q-axis voltage command value to three-phase voltage command values in a stator coordinate system of the permanent magnet motor. In this torque ripple suppression control device for a permanent magnet motor, it is preferred that the power converter outputs the voltage based upon the three-phase voltage command values.

According to a 4th aspect of the present invention, in the torque ripple suppression control device of the 2nd or 3rd aspect of the present invention for a permanent magnet motor, it is preferable that the induced voltage coefficient setting unit outputs, as the information signals, an induced voltage coefficient average value and a pulsation component amplitude value corresponding to at least either the d-axis or the q-axis in addition to the d-axis induced voltage coefficient and the q-axis induced voltage coefficient.

According to a 5th aspect of the present invention, in the torque ripple suppression control device of the 4th aspect of the present invention for a permanent magnet motor, it is desirable that the d-axis induced voltage coefficient and the q-axis induced voltage coefficient each change in correspondence to the position detection value whereas the average value and the pulsation component amplitude value both remain constant, unaffected by the position detection value.

According to a 6th aspect of the present invention, in the torque ripple suppression control device of the 4th or 5th aspect of the present invention for a permanent magnet motor, it is possible that the torque ripple suppression operation unit outputs the q-axis current correction command value based upon a pulsation component in the d-axis induced voltage coefficient and the induced voltage coefficient average value corresponding to the d-axis.

According to a 7th aspect of the present invention, in the torque ripple suppression control device of the 6th aspect of the present invention for a permanent magnet motor, the torque ripple suppression operation unit may output the q-axis current correction command value ΔIq* based upon an expression below:

Δ⁢⁢Iq*=∑n=1∞⁢(-Δ⁢⁢KedKed_)n·Iq_,
with n, ΔKed,−Kedand−Iqin the expression respectively representing an integer, the pulsation component in the d-axis induced voltage coefficient, the induced voltage coefficient average value corresponding to the d-axis and a current average value corresponding to the q-axis.

According to an 8th aspect of the present invention, in the torque ripple suppression control device of any one of the 4th through 7th aspects of the present invention for a permanent magnet motor, the torque ripple suppression operation unit may output the q-axis current correction command value based upon the proportional gain, pulsation component amplitude values in the d-axis induced voltage coefficient and the q-axis induced voltage coefficient, a pulsation component in the q-axis induced voltage coefficient and the induced voltage coefficient average value corresponding to the d-axis.

According to a 9th aspect of the present invention, in the torque ripple suppression control device of the 8th aspect of the present invention for a permanent magnet motor, the torque ripple suppression operation unit may output the d-axis current correction command value ΔId* based upon an expression below:

According to a 10th aspect of the present invention, in the torque ripple suppression control device of any one of the 1st through 9th aspects of the present invention for a permanent magnet motor, the current control operation unit may include a pulsation disturbance current control operation unit that outputs a pulsation compensation value obtained based upon the position detection value and a value representing an order of a pulsation frequency in the torque at the permanent magnet motor. In this torque ripple suppression control device for a permanent magnet motor, it is preferable that the current control operation unit adds the pulsation compensation value to a first voltage command value, which is calculated based upon the current detection value and a sum of the current command value and the current correction command value, and outputs addition results as the voltage command value.

According to an 11th aspect of the present invention, in the torque ripple suppression control device of the 10th aspect of the present invention for a permanent magnet motor, the pulsation disturbance current control operation unit may include: a sine signal generation unit that generates a sine signal based upon the position detection value and the value representing the order of the pulsation frequency; a cosine signal generation unit that generates a cosine signal based upon the position detection value and the value representing the order of the pulsation frequency; a sine operation unit that determines a first operation value by multiplying the sine signal by a current deviation representing a difference between the current command value and the current detection value, by multiplying initial multiplication results by a constant and by further multiplying second multiplication results by the sine signal; and a cosine operation unit that determines a second operation value by multiplying the cosine signal by the current deviation, by multiplying initial multiplication results by the constant and by further multiplying second multiplication results by the cosine signal. In this torque ripple suppression control device for a permanent magnet motor, it is possible that the pulsation disturbance current control operation unit outputs, as the pulsation compensation value, a value obtained by doubling a value representing a sum of the first operation value and the second operation value.

According to a 12th aspect of the present invention, in the torque ripple suppression control device of the 11th aspect of the present invention for a permanent magnet motor, the sine signal generation unit and the cosine signal generation unit can respectively output a sine value and a cosine value corresponding to a value obtained by multiplying the position detection value by the value representing the order of the pulsation frequency as the sine signal and the cosine signal.

According to a 13th aspect of the present invention, in the torque ripple suppression control device of any one of the 10th through 12th aspects of the present invention for a permanent magnet motor, it is preferable that: the pulsation disturbance current control operation unit outputs the pulsation compensation value in correspondence to at least either the d-axis or the q-axis in the rotation coordinate system of the permanent magnet motor; and the current control operation unit outputs, as the voltage command value, a sum of the first voltage command value and the pulsation compensation value in correspondence to an axis for which the pulsation compensation value has been output by the pulsation disturbance current control operation unit and outputs, as the voltage command value, the first voltage command value in correspondence to an axis for which the pulsation compensation value has not been output by the pulsation disturbance current control operation unit.

According to a 14th aspect of the present invention, in the torque ripple suppression control device of any one of the 2nd through 9th aspects of the present invention for a permanent magnet motor, it is possible that the induced voltage coefficient setting unit outputs information signals related to the d-axis induced voltage coefficient and the q-axis induced voltage coefficient based upon the position detection value, the d-axis voltage command value and the q-axis voltage command value.

According to a 15th aspect of the present invention, in the torque ripple suppression control device of any one of the 10th through 13th aspects of the present invention for a permanent magnet motor, it is possible that: the pulsation disturbance current control operation unit outputs a d-axis pulsation compensation value and a q-axis pulsation compensation value in correspondence to a d-axis and a q-axis of a rotation coordinate system of the permanent magnet motor; and the induced voltage coefficient setting unit outputs information signals related to a d-axis induced voltage coefficient and a q-axis induced voltage coefficient corresponding to the d-axis and the q-axis based upon the position detection value, the d-axis pulsation compensation value and the q-axis pulsation compensation value.

According to a 16th aspect of the present invention, in the torque ripple suppression control device of any one of the 1st through 15th aspects of the present invention for a permanent magnet motor, it is desirable that the power converter increases a DC torque in the permanent magnet motor by an extent equivalent to substantially half of an amplitude of a pulsating torque component in a twelfth-order harmonic in the permanent magnet motor, relative to a DC torque generated by driving the permanent magnet motor based upon a voltage command value output from the current control operation unit without adding the current correction command value to the current command value.

An electric power steering system according to a 17th aspect of the present invention includes: a torque ripple suppression control device for a permanent magnet motor according to any one of the 1st through 16th aspects; the permanent magnet motor; a steering shaft mechanically connected to the permanent magnet motor via a reduction gear unit; a steering wheel mechanically connected to the steering shaft; a torque sensor that detects an operation input via the steering wheel; and a torque command unit that outputs the torque command value based upon operation detection results provided by the torque sensor.

The present invention provides a torque ripple suppression control device and an electric power steering system that enable effective utilization of the torque ripple DC component.

DESCRIPTION OF PREFERRED EMBODIMENTS

The following is a detailed description of embodiments of the present invention, given in reference to the drawings.

First Embodiment

FIG. 1presents an example of a structure that may be adopted in a permanent magnet motor torque ripple suppression control device achieved in an embodiment of the present invention. A magnet motor1outputs a motor torque generated by combining a torque component attributable to magnetic fluxes from permanent magnets and a torque component attributable to the inductance at an armature winding. A power converter2outputs voltages in proportion to three-phase AC voltage command values vu*, vv* and vw* so as to adjust the output voltage and the rotation rate of the magnet motor1.

A DC power source3provides a DC voltage to the power converter2. A current detection unit4detects three-phase AC currents iu, ivand iwflowing at the magnet motor1and outputs current detection values iuc, ivcand iwc. A position detector5detects a rotational position θ of the motor and outputs a position detection value θdc. The position detector5may be constituted with, for instance, a resolver or an encoder.

A coordinate conversion unit6calculates, through operation executed by using the three-phase AC current detection values iuc, ivcand iwcand the position detection value θdcmentioned above, a d-axis current detection value Idcand a q-axis current detection value Iqc, and outputs the calculated current detection values. A current command conversion unit7calculates, through operation executed based upon a torque command value τ* a d-axis current command value Id0* and a q-axis current detection value Iq0*, and outputs the calculated current command values.

An induced voltage coefficient setting unit8, to which the position detection value θdcfrom the position detector5is input, outputs induced voltage coefficient information signals Ked,−Ked,−ΔKed, Keqand−ΔKeq. It is to be noted that the specific information provided in these induced voltage coefficient information signals is to be described in detail later. A torque ripple suppression operation unit9outputs a d-axis current correction command value ΔId* and a q-axis current correction command value ΔIq* calculated based upon the various information signals output from the induced voltage coefficient setting unit8as described above. These current correction command values ΔId* and ΔIq* are respectively added to the d-axis current command value Id0* and the q-axis current command value Iq0* output from the current command conversion unit7. Current command values Id0* and Iq0* indicating the sums are input as new current command values Id* and Iq* to a current control operation unit10.

The current control operation unit10executes proportional·integration operation based upon the current command values Id* and Iq* so that the d-axis current detection value Idcand the q-axis current detection value Iqcrespectively conform to the current command values Id* and Iq* and outputs a d-axis voltage command value Vdc* and a q-axis voltage command value Vqc* to a coordinate conversion unit11in correspondence to the proportional·integration operation results. The coordinate conversion unit11outputs three-phase AC voltage command values vu*, vv* and vw*, determined by using the d-axis voltage command value Vdc* and the q-axis voltage command value Vqc* provided by the current control operation unit10and the position detection value θdcprovided by the position detector5, to the power converter2. Drive control for the magnet motor1is executed as the power converter2adjusts the output voltage and the rotation rate of the magnet motor1as described earlier based upon the voltage command values vu*, vv* and vw*.

Next, the basic voltage control operation and the basic phase control operation executed by adopting a vector control method are described. The basic voltage control operation is first explained.FIG. 2shows the structure of the current control operation unit10.FIG. 2shows that the d-axis current command value Id* and the d-axis current detection value Idcare input to a d-axis current control operation unit10aand that the q-axis current command value Iq* and the q-axis current detection value Iqcare input to a q-axis current control operation unit10b. The current control operation units10aand10brespectively output the d-axis voltage command value Vdc* and the q-axis voltage command value Vqc* by individually executing proportional·integration operation as expressed in (3) below so as to ensure that the current detection values Idcand Iqccorresponding to the respective components conform to the current command values Id0* and Iq0*.

In expression (3), Kpdrepresents a proportional gain for d-axis current control, Kidrepresents an integral gain for the d-axis current control, Kpqrepresents a proportional gain for q-axis current control and Kiqrepresents an integral gain for the q-axis current control.

In the phase control operation, the position detection value θdcis obtained by detecting the rotational position θ of the magnet motor1via the position detector5, which may be constituted with a resolver, an encoder, a magnetic pole position detector or the like. Based upon the position detection value θdc, the coordinate conversion units6and11execute coordinate conversion respectively as expressed in (4) and (5) below.

The basic voltage control operation and the basic phase control operations are executed as described above.

Next, the control characteristics that will manifest in a structure that does not include the induced voltage coefficient setting unit8and the torque ripple suppression operation unit9, i.e., the features characterizing the present invention, are described.FIGS. 3 and 4show the effect of the waveform euvof an induced voltage (u-phase v-phase line voltage) at the permanent magnet motor1on the torque characteristics of the magnet motor1under control executed by the control device inFIG. 1.

FIG. 3indicates the relationship that will be manifested by the induced voltage waveform euvand the motor torque τ when the induced voltage waveform euvis sinusoidal. AsFIG. 3indicates, the motor torque τ equals 100% of the command value τ*, which means that stable control is achieved with no torque ripple.

FIG. 4indicates the relationship that may be manifested by the induced voltage waveform euvand the motor torque τ when the induced voltage waveform euvis rectangular. In the example presented inFIG. 4, the waveforms of the induced voltages in the individual phases (the u-phase, the v-phase and the w-phase) each include a fifth-order harmonic component at a ration of 10%. The figure indicates that torque ripple Δτ occurs at a rate as high as 20% in a sixth-order harmonic component relative to the torque command value τ* representing 100%.

Next, the structures adopted for the induced voltage coefficient setting unit8and the torque ripple suppression operation unit9, which are features characterizing the present invention, are described.FIG. 5shows the structure of the induced voltage setting unit8. The position detection value θdcis input to a reference table8aat the induced voltage setting unit8. The reference table8ais created by storing in advance induced voltage coefficient values corresponding to various motor rotational positions, in a table format. By referencing the induced voltage coefficient values in this table, the induced voltage setting unit8is able to output the induced voltage coefficient information signals Ked,−Ked,−ΔKed, Keqand−ΔKeqcorresponding to the position detection value θdchaving been input to the table.

FIG. 6shows the relationship between the position detection signal θdcand the induced voltage coefficient information signals output from the induced voltage setting unit8. As the position detection signal θdcchanges, induced voltage coefficient information signals Ked,−Ked,−ΔKed, Keqand−ΔKeqsuch as those indicated in the third diagram inFIG. 6are output from the reference table. These induced voltage coefficient information signals are obtained by breaking down three-phase AC induced voltage coefficients Ke(each obtained by dividing an induced voltage value by an electrical angular speed ω of the motor) in a stator coordinate system into a d-axis component value Kedand a q-axis component value Keqin a rotor coordinate system. It is to be noted that the second diagram inFIG. 6indicates the induced voltage waveform euvinFIG. 4for reference.

Kedand KeqinFIG. 6respectively indicate a d-axis induced voltage coefficient and a q-axis induced voltage coefficient. In addition,−Kedindicates an average of d-axis induced voltage coefficients Ked,−ΔKedindicates an amplitude value of a pulsation component in the d-axis induced voltage coefficient Kedand−ΔKeqindicates an amplitude value of a pulsation component in the q-axis induced voltage coefficient Keq. AsFIG. 6indicates, the d-axis induced voltage coefficient Kedand the q-axis induced voltage coefficient Keqboth change in correspondence to the position detection value θdc. In contrast, the average−Kedof the d-axis induced voltage coefficients and the amplitude values−ΔKedand−ΔKeqof the pulsation components in the d-axis induced voltage coefficient and the q-axis induced voltage coefficient all remain constant even if the position detection value θdcchanges.

The structure of the torque ripple suppression operation unit9is shown inFIG. 7. The signals Kedand−Ked, among the induced voltage coefficient information signals output from the induced voltage setting unit8as described above, are input to a subtraction unit9aof the torque ripple suppression operation unit9. Based upon the signals Kedand−Kedinput thereto, the subtraction unit9acalculates the pulsation component ΔKedin the d-axis induced voltage coefficient Kedas expressed in (6) below.
ΔKed=Ked−Ked(6)

It is to be noted that since the signal Keqprovided from the induced voltage setting unit8contains no DC component, the signal Keqitself is designated as the pulsation component ΔKeqin the q-axis induced voltage coefficient KeqinFIG. 7.

The pulsation component ΔKedin the d-axis induced voltage Kedand the pulsation component ΔKeqin the q-axis induced voltage coefficient Keqdescribed above are all input to a current correction command operation unit9btogether with the amplitude value−ΔKedof the pulsation component in the d-axis induced voltage Kedand the amplitude value−ΔKeqof the pulsation component ΔKeqin the q-axis induced voltage coefficient Keqoutput from the induced voltage setting unit8. The current correction command operation unit9bcalculates a d-axis current correction command value ΔId* and a q-axis current correction command value ΔIq* as expressed in (7) below based upon these values input thereto.

While the order n in expression (7) should ideally be infinite, a fully satisfactory effect can be achieved with n set to approximately 3 in reality. In addition, G in expression (7) represents a proportional gain. As explained later, the ripple component and the DC component in the torque ripple can be controlled so as to sustain a desired specific relationship by adjusting the value of the proportional gain G.

Next, the principle upon which the torque ripple suppression operation unit9characterizing the present invention operates is described. The motor torque τmmanifesting on the d-q axes may be calculated as expressed in (8) below.

Pm, Ldand Lqin expression (8) respectively represent the number of pairs of poles at the motor, the inductance value assumed on the d-axis and the inductance value assumed on the q-axis.

In addition, the d-axis induced voltage coefficient Kedand the q-axis induced voltage coefficient Keqcan be expressed as in (9) below by using the pulsation components ΔKedand ΔKeqand the average−Kedof d-axis induced voltage coefficients Ked.

In addition, the d-axis current Idand the q-axis current Iqcan be expressed as in (10), in which ΔIdand ΔIqrespectively represent the pulsation components of the currents Idand Iqand−Idand−Iqrespectively represent the average values of the currents Idand Iq.

The motor torque expression in (8) can be rewritten as (11) below by using expressions (9) and (10) above for substitution in expression (8).

A relationship expressed as Ld=Lqexists in a motor with non-salient poles and thus, expression (11) can be modified to expression (12) in conjunction with a motor with non-salient poles.

Sinusoidal control whereby the AC current iu, ivand iw, at the magnet motor1are controlled to achieve a sine wave is now contemplated. Under such circumstances, assuming that ideal current control is possible with Id=0 (ΔId=−Id=0) and Iq=Iq* (ΔIq=0), expression (12) can be rewritten as expression (13) below.

In addition, since the sixth-order harmonic component of the electrical angle is superimposed on the motor torque, the pulsation component ΔKedin the d-axis induced voltage coefficient Kedcan be defined as in (14) below.
ΔKed=ΔKed·sin(6θ)  (14)

The following expression (15) is obtained by using expression (14) for substitution in expression (13).

FIG. 8indicates the torque control characteristics achieved as expressed in (15). These control characteristics are torque characteristics manifesting when the drive of the magnet motor1is controlled without implementing the suppression compensation according to the present invention, i.e., the torque characteristics manifesting when the drive of the magnet motor1is controlled by using the voltage command values output from the current control operation unit10without adding the current correction command values ΔId* and ΔIq* provided from the torque ripple suppression operation unit9to the current command values Id0* and Iq0*.FIG. 8indicates that while the u-phase current iu, assumes a sine wave, torque pulsation (torque ripple) occurs to an extent of 20% (±10%) due to ΔKed.

Next, a method that may be adopted for torque ripple suppression is described. The q-axis pulsation current command value ΔIq* is calculated as expressed in (16) below through operation executed in the torque ripple suppression operation unit9.

The order n in expression (16) is an integer equal to or greater than 1. For instance, expression (16) can be modified as expression (17) below by assuming that the expression includes up to a third-order term.

The motor torque τm, can be calculated as expressed in (18) by using expression (17) for substitution in expression (12) described earlier.

The intensity of the pulsating torque component in expression (18) can be expressed as in (19) below.

Namely, the pulsating torque component can be reduced to almost 0.

However, no DC torque increase/decrease can be induced simply by eliminating the pulsating torque component almost completely, as described above. Accordingly, a DC torque component must be secured by using the d-axis pulsation current command value ΔId*. More specifically, ΔId* is calculated as expressed in (20) below.

In a manner similar to that through which expression (18) is obtained as described earlier, expression (21), through which the motor torque τmis calculated, can be obtained by using expressions (17) and (20) for substitution in expression (12).

The relationship expressed in (19) allows expression (21) to be rewritten as expression (22) below.

By selecting an optimal value for the proportional gain G in expression (22), the DC torque component can be increased by an extent equivalent to ½ of the peak-to-peak wave height value (i.e., the amplitude) of the pulsating torque component in a twelfth-order harmonic.FIG. 9shows torque characteristics that may be achieved by executing such torque ripple suppression compensation. Through this suppression compensation, the sixth-order harmonic component can be greatly reduced, as indicated inFIG. 9, compared to the sixth-order harmonic component in the characteristics inFIG. 8observed when no suppression compensation is implemented. Furthermore, the DC torque component can be increased by an extent equivalent to ½ of the amplitude Δτm12in the twelfth-order harmonic pulsating torque component at the magnet motor1. In other words, by adjusting the proportional gain G, the ripple component and the DC component in the torque ripple can be controlled as desired. This, in turn, enables effective utilization of the DC component in the torque ripple.

Second Embodiment

FIG. 10presents an example of a structure that may be adopted in the permanent magnet motor torque ripple suppression control device in the second embodiment of the present invention. While the current control operation unit10adopts a proportional·integration operation method in the first embodiment described earlier, the current control operation unit in this embodiment has an added capability for pulsation disturbance current control operation with sensitivity to the frequency component of the torque ripple, as described below.

There is an issue yet to be addressed in the first embodiment shown inFIG. 1in that when the individual control gains Kpd, Kid, Kpqand Kiqset as expressed in (3) by the current control operation unit10assume small values, the conformity of the current values to the current command values will be compromised in a high speed range. For instance, if an inexpensive microcomputer is used to constitute the current control operation unit10, the control operation cycle will be set to an order of several milliseconds, which, in turn, will restrict the current control response frequency to approximately several tens of hertz.

FIG. 11shows the operational waveforms of the d-axis and q-axis current information signals Id*, Idc, Iq* and Iqcand the u-phase alternating current iucthat may register when the rotation rate of the permanent magnet motor1is in a high range.FIG. 11indicates that the current detection values Idcand Iqcdo not conform to the respective current command values Id* and Iq* when the motor rotation rate is in the high range. Under these circumstances, the extent of torque ripple is bound to increase even if suppression compensation such as that described in reference to the first embodiment is implemented.

Accordingly, control that incorporates pulsation disturbance current control operation with sensitivity to the frequency component of the torque ripple is executed by the torque ripple suppression control device shown inFIG. 10in the embodiment. This torque ripple suppression control device includes a current control operation unit10′ in place of the current control operation unit10shown inFIG. 1. It is to be noted that the other components of the torque ripple suppression control device are identical to those inFIG. 1.

The current control operation unit10′ executes another current control operation assuming sensitivity to the frequency component of the torque ripple, as well as the current control operation shown inFIG. 2. It then adds the output values resulting from the other current control operation to output values resulting from the current control operation shown inFIG. 2and outputs the sums as a d-axis voltage command value Vdc** and a q-axis voltage command value Vqc**.

In reference toFIG. 12, the current control operation unit10′ is described in more specific detail. A d-axis pulsation disturbance current control operation unit10′ain the current control operation unit10′ outputs a signal ΔVdc*, generated based upon the d-axis current deviation ΔId(=Id*−Idc) input thereto, with which a component value matching the torque ripple frequency component is to be suppressed. In addition, a q-axis pulsation disturbance current control operation unit10′boutputs a signal ΔVqc*, generated based upon the q-axis current deviation ΔIqc=(Iq*−Iqc) input thereto, with which a component value matching the torque ripple pulsation frequency component is to be suppressed. The current control operation unit10′ adds these signals ΔVdc* and ΔVqc* respectively to the d-axis voltage command value Vdc* and the q-axis voltage command value Vqc* and outputs the sums as a new d-axis voltage command value Vdc** and a new q-axis voltage command value Vqc**.

Next, in reference toFIG. 13, the structure of the d-axis pulsation disturbance current control operation unit10′ais described. The position detection value θdcprovided by the position detector5and a constant N provided by a constant generation unit10′a1are input to both a cosine signal generation unit10′a2and a sine signal generation unit10′a3at the d-axis pulsation disturbance current control operation unit10′a. The cosine signal generation unit10′a2and the sine signal generation unit10′a3respectively output a cosine signal cos(N·θdc) and a sine signal sin(N·θdc) based upon the position detection value θdcand the constant N input thereto. These signals are then both multiplied by the d-axis current deviation ΔId. Subsequently, the signals are further multiplied by a constant Kdrespectively at a constant multiplying unit10′a4and a constant multiplying unit10′a5. The values obtained by multiplying the cosine signal cos(N·θdc) by the d-axis current deviation ΔIdand the constant Kdand by multiplying the sine signal sin(N·θdc) by the d-axis current deviation ΔIdand the constant Kdare respectively multiplied by the cosine signal cos(N·θdc) and the sine signal sin(N·θdc) again and then are added together. A value obtained by doubling the sum is output as the d-axis pulsation compensation value ΔVdc* from the d-axis pulsation disturbance current control operation unit10′a.

Next, in reference toFIG. 14, the structure of the q-axis pulsation disturbance current control operation unit10′bis described. The position detection value θdcprovided by the position detector5and a constant N provided by a constant generation unit10′b1are input to both a cosine signal generation unit10′b2and a sine signal generation unit10′b3at the q-axis pulsation disturbance current control operation unit10′b. The cosine signal generation unit10′b2and the sine signal generation unit10′b3respectively output a cosine signal cos(N·θdc) and a sine signal sin(N·θdc) based upon the position detection value θdcand the constant N input thereto, in much the same way as that described in reference toFIG. 13. These signals are then both multiplied by the q-axis current deviation ΔIq. Subsequently, the signals are further multiplied by a constant Kqrespectively at a constant multiplying unit10′b4and a constant multiplying unit10′b5. The values obtained by multiplying the cosine signal cos(N·θdc) by the d-axis current deviation ΔIqand the constant Kdand by multiplying the sine signal sin(N·θdc) by the q-axis current deviation ΔIqand the constant Kqare respectively multiplied by the cosine signal cos(N·θdc) and the sine signal sin(N·θdc) again and then are added together in much the same way as that described in reference toFIG. 13. A value obtained by doubling the sum is output as the q-axis pulsation compensation value ΔVqc* from the q-axis pulsation disturbance current control operation unit10′b.

The principle of the operations executed by the pulsation disturbance current control operation units10′aand10′b, which characterizes the present invention, is now described. The following explanation focuses on the pulsation disturbance current control operation unit10′bas a representative of the two operation units. As described earlier, the position detection value θdcand the constant N indicating the order of the torque pulsation frequency (the order of the largest harmonic component contained in a single cycle of the electric frequency) are both input to the cosine signal generation unit10′b2and the sine signal generation unit10′b3at the pulsation disturbance current control operation unit10′b, as has been described earlier. Then, a cosine signal and a sine signal are respectively calculated by the cosine signal generation unit10′b2and the sine signal generation unit10′b3, each based upon a product of the input values (N·θdc).

A harmonic component ΔIqripcontained in the q-axis current detection value Iqcis defined as expressed in (23) below.
ΔIqrip=|ΔIqrip|·sin(N·θdc)  (23)

|ΔIqrip| in expression (23) represents the amplitude value of the Nth-order harmonic component.

Ia1and Ib1respectively representing the results obtained by multiplying the output signals from the cosine signal generation unit10′b2and the sine signal generation unit10′b3by the amplitude value |ΔIqrip| of the harmonic component defined in expression (23) above, are expressed as in (24) below.

Ia2and Ib2respectively representing the results obtained by multiplying the signals Ia1and Ib1in expression (24) by a predetermined proportional gain Kqat the constant multiplying units10′b4and10′b5are expressed as in (25) below.

Next, the q-axis pulsation compensation value ΔVqc* is calculated through operation executed as expressed in (26) below by using the signals Ia2and Ib2having been calculated as expressed in (25).

Expression (26) indicates that the voltage value can be corrected with the value obtained by multiplying the harmonic component ΔIqripby the gain Kq.

The d-axis pulsation compensation value ΔVdc* is calculated through similar operation executed in correspondence to the d-axis. These calculated values ΔVdc* and ΔVqc* are respectively added to the d-axis voltage command value Vdc* and the q-axis voltage command value Vqc* and the inverter output voltages are thus controlled. Through these measures, pulsation disturbance current control achieving sensitivity to the torque ripple frequency component N is enabled.

FIG. 15shows the control characteristics achieved by adopting the present invention. The control characteristics indicate that by incorporating the torque ripple suppression compensation described above, current detection values Idcand Iqccan be made to conform to the respective current command values Id* and Iq* with a higher degree of precision, even in a high motor rotation rate range, in comparison to the control characteristics inFIG. 11, which are observed when no suppression compensation is implemented. In other words, the torque pulsation can be suppressed effectively in the high speed range.

It is to be noted that the current control operation unit10′ in the second embodiment of the present invention described above may calculate only either the d-axis pulsation compensation value ΔVdc* or the q-axis pulsation compensation value ΔVqc*. Namely, the current control operation unit does not need to include both the d-axis pulsation disturbance current control operation unit10′aand the q-axis pulsation disturbance current control operation unit10′b. In such a case, in correspondence to the d-axis or the q-axis, for which the pulsation compensation value is not calculated, the voltage command value Vdc* or Vqc* should be directly output from the current control operation unit10′ to the coordinate conversion unit11, as in the first embodiment.

Third Embodiment

FIG. 16presents an example of a structure that may be adopted in the permanent magnet motor torque ripple suppression control device in a third embodiment of the present invention. While the induced voltage coefficient information signals are output from the reference table8ain the first and second embodiments described above, induced voltage coefficient information signals generated through estimating operation executed by using the output values resulting from the pulsation disturbance current control are utilized in the torque ripple suppression compensation operation in the embodiment described below.

The torque ripple suppression control device shown inFIG. 16includes an induced voltage coefficient identification unit8′ in place of the induced voltage setting unit8shown inFIGS. 1 and 10. It is to be noted that the other components of the torque ripple suppression control device are identical to those inFIG. 10.

The position detection value θdcprovided by the position detector5and the output values ΔVdc* and ΔVqc* from the d-axis pulsation disturbance current control operation unit10′aand the q-axis pulsation disturbance current control operation unit10′bin the current control operation unit10′ having been described earlier in reference to the second embodiment are input to the induced voltage coefficient identification unit8′. Based upon these input values, the induced voltage coefficient identification unit8′ outputs estimated values Ked′,−Ked′,−Keq′ and−ΔKeq′, estimated respectively in correspondence to the induced voltage coefficient information signals Ked,−Ked,−ΔKed, Keqand−ΔKeqexplained earlier in reference to the first embodiment.

An example of a structure that may be adopted in the induced voltage coefficient identification unit8′ is presented inFIG. 17. As indicated inFIG. 17, the position detection signal θdcprovided by the position detector5is input to a differentiation operation unit8′a1. The differentiation operation unit8′a1executes operation expressed in (27) below and outputs a motor angular speed calculation value ωdc.

The signal ωdcoutput from the differentiation operation unit8′a1as described above, is input to a dividing unit8′a2together with the output value ΔVdc* from the pulsation disturbance current control operation unit10′aand input to a dividing unit8′a3together with the output value ΔVqc* from pulsation disturbance current control operation unit10′b. The dividing units8′a2and8′a3calculate an estimated d-axis induced voltage coefficient value Ked^ and an estimated q-axis induced voltage coefficient value Keq^ through operation executed as expressed in (28) below based upon the signal ωdcand the value ΔVdc* and based upon the signal ωdcand the value ΔVqc* having been input.

The estimated values Ked^ and Keq^ having been calculated at the dividing units8′a2and8′a3are input to a memory unit8′a4together with the position detection signal θdc. Based upon data related to the induced voltage coefficient information Ked,−Ked,−ΔKed, Keqand−ΔKeq, which are stored therein in advance, the memory unit8′a4outputs estimated values Ked′,−Kea′,−ΔKed′, Keq′ and−ΔKeq′ corresponding to the signal θdchaving been input.

It is to be noted that the data may be stored into the memory unit8′a4during a test operation of the device or while the device is adjusted. Furthermore, the data may be stored while the device is engaged in actual operation, instead. In any case, the data related to the induced voltage coefficient information should first be stored into the memory unit8′a4and the individual estimated values Ked′,−Ked′,−ΔKed′, Keq′ and−ΔKeq′ should then be output in correspondence to the position detection value θdc.

As an alternative, the induced voltage coefficient information signals may be extracted during actual operation and these signals may be output as estimated values Ked′,−Ked′,−ΔKed′, Keq′ and−ΔKeq′ instead of storing in advance the data related to the induced voltage coefficient information Ked,−Ked, ΔKed, Keqand−ΔKeqas described above.

Such an alternative may be adopted in conjunction with an induced voltage coefficient identification unit8′ assuming a structure such as that shown inFIG. 18.FIG. 18indicates that the position detection signal θdcprovided by the position detector5is input to a differentiation operation unit8′b1. As does the differentiation operation unit8′a1inFIG. 17, the differentiation operation unit8′b1outputs a motor angular speed calculation value ωdcobtained through operation executed as expressed in (27). The signal ωdcis input to a dividing unit8′b2together with the output value ΔVdc* from the pulsation disturbance current control operation unit10′aand input to a dividing unit8′b3together with the output value ΔVqc* from pulsation disturbance current control operation unit10′ b. As do the dividing units8′a2and8′a3inFIG. 17, the dividing units8′b2and8′b3calculate an estimated d-axis induced voltage coefficient value Kea^ and an estimated q-axis induced voltage coefficient value Keq^ through operation executed as expressed in (28) based upon the signal ωdcand the value ΔVdc* and based upon the signal ωdcand the value ΔVqc* having been input.

The estimated values Ked^ and Keq^ having been calculated are input to an induced voltage coefficient information extraction unit8′b4. Based upon these estimated values having been input thereto, the induced voltage coefficient information extraction unit8′b4calculates estimated values Ked′,−Ked′,−Ked′, Keq′ and−ΔKeq′ corresponding to the various induced voltage coefficient information signals and outputs the estimated values having been calculated.

FIG. 19presents an example of an application in which the permanent magnet motor torque ripple suppression control device achieved in any of the first through third embodiments described above is adopted in an electric power steering system. InFIG. 19, reference numeral101indicates a steering wheel, reference numeral102indicates a steering shaft mechanically connected to the steering wheel101, reference numeral103indicates a torque sensor, reference numeral104indicates a reduction gear unit that mechanically connects the magnet motor1with the steering shaft102, reference numeral105indicates an ECU (engine control unit), reference numeral106indicates a rack and pinion mechanism, reference numeral107indicates a linking mechanism such as a tie rod and reference numeral108indicates a steerable drive wheel. The permanent magnet motor torque ripple suppression control device in any of the first through third embodiments is mounted at the ECU105. It is to be noted that the DC power source3, the current detection unit4and the position detector5are identical to those inFIGS. 1,10and16.

The torque sensor103detects a steering operation performed by the driver via the steering wheel101. The ECU105includes a torque command unit that outputs a torque command value τ* to the current command conversion unit7of the torque ripple suppression control device based upon steering operation detection results provided by the torque sensor103. The torque ripple suppression control device controls the three-phase voltage command values so as to match the output torque with the torque command value provided by the torque command unit. The magnet motor1assists the steering operation performed by the driver via the steering wheel101as it applies an assisting force to the steering shaft102via the reduction gear unit104.

The permanent magnet motor torque ripple suppression control device in the ECU105executes the torque ripple suppression control described earlier. As a result, high precision torque control is realized even if an inexpensive magnet motor1manifesting distortion in the induced voltages is used in the electric power steering system inFIG. 19. For instance, while the torque control may be executed by primarily focusing on torque ripple component suppression in a speed range over which the magnet motor1rotates at low speed, settings for assuring generation of a satisfactory level of DC component can be selected in a high speed range. Consequently, a sense of smooth-response steering can be created when, for instance, the driver turns the steering wheel101slowly. In addition, when the magnet motor1rotates at high speed, a higher output from the magnet motor1can be assured by ensuring that a substantial DC torque component is generated. The magnet motor1can thus be provided as a compact unit, as well.

In the embodiments described above, the vector control is executed by creating voltage command values Vdc* and Vqc* based upon the current command values Id* and Iq* and the current detection values Idcand Iqc. However, the present invention is not limited to this example and may be adopted in the vector control executed by creating voltage correction values ΔVdand ΔVqbased upon the current command values Id* and Iq* and the current detection values Idcand Iqcand calculating voltage command values Vdc* and Vqc* through operation executed as expressed in (29) below based upon the voltage correction values, the current command values Id* and Iq*, a calculated speed value ωcdand a constant related to the magnet motor1.

As an alternative, the present invention may be adopted in vector control executed as expressed in (30) below by using second current command values Id** and Iq** created based upon the current command values Id* and Iq* and the current detection values Idcand Iqc.

As a further alternative, the present invention may be adopted in vector control executed as expressed in (31) or (32) below instead of (29) or (30) above, in which the vector control is executed by using an induced voltage coefficient Ke*. This alternative makes it possible to reduce the onus placed on the current control operation unit10inFIG. 1or the current control operation unit10′ inFIGS. 10 and 16, which will obviously improve the conformity to the current command values.

It is to be noted that in expressions (31) and (32), the induced voltage coefficient information signals Kedand Keqthat are set in advance as has been described in reference to the first embodiment are used. However, instead of these induced voltage coefficient information signals, the estimated values Ked′ and Keq′ for the induced voltage coefficient information described in reference to the third embodiment may be used.

In addition, while the AC currents iu, ivand iwthat are directly detected by the current detector4are used in the first through third embodiments, AC currents iu, ivand iwmay be replicated in correspondence to a DC current flowing through a one-shunt resistor installed for purposes of over-current detection at the power converter2.

Furthermore, while the rotational position of the magnet motor1is detected by the position detector5constituted with an encoder, a resolver, a magnetic pole position sensor or the like in the first through third embodiments, the present invention may also be adopted in a device that executes motor control through a method employing no position sensor.

For instance, a phase error Δθcrepresenting the deviation of the motor phase value relative a phase command value may be calculated through operation executed as expressed in (33) below based upon the voltage command values Vdc* and Vqc*, the current detection values Idcand Iqcand the motor constant.

Motor control can then be executed by controlling an estimated frequency value ωdc′ so as to reduce the signal Δθccalculated as expressed in (33) to 0. In this manner, the present invention can also be adopted effectively in conjunction with a control method employing no position sensor.

It is to be noted that any of the embodiments described above may be adopted in combination with one of, or a plurality of the variations. In addition, the variations may be adopted in any conceivable combination.

The embodiments described above and the variations thereof are simply provided as examples and components other than those in the embodiments may be used as long as the features characterizing the present invention are not compromised.