JP2002044974A - Torque ripple correction method and motor control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable uniform speed motor drive by making torque ripple correction, in a short time, with a low cost, in a simple way and moreover with high accuracy. SOLUTION: In a torque ripple correction method, which is provided with a current control means 12 which drives an AC motor 11, a PMW power converter unit 13; a current detection means 14 for the AC motor 11; an electrical angle (θfb) detection means 15 for the AC motor, a detection speed calculation means 16, which calculates a detection speed ωfb from the detection electrical angel θfb; a speed error calculation means 17, which calculates a difference Δωbetween an instruction speed ω* and the detection speed ωfb; a speed proportion integral control part 18, which calculates an instruction speed by multiplying the speed error by a speed proportion integral gain, prescribed torque ripples are extracted from the instruction torque by a filter, which passes a prescribed frequency band; and a new instruction torque is derived by subtracting the prescribed torque ripples from the instruction torque.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque ripple correction method and a motor control circuit for correcting torque ripple generated from an AC motor, a current detector, and a PWM converter to reduce rotation unevenness.

[0002]

2. Description of the Related Art Torque ripple includes cogging torque, dead time ripple, offset ripple, gain ripple,
Load ripple and the like can be considered. These ripples other than the load ripple have a relationship proportional to the rotation frequency (or the output frequency of the PWM drive). Among the torque ripples described above, the cogging torque is the torque ripple generated by the AC motor structure, that is, per rotation of the AC motor rotor,
Ripple that is repeated at the greatest common multiple of the number of poles and the number of slots has a serious adverse effect such as giving uneven rotation at low speed and low torque, and has been a problem in application fields requiring high precision. As a conventional technique for correcting the cogging torque, for example, there is a technique described in Japanese Patent Application Laid-Open No. 7-46878. According to the technique, a cogging torque component is individually measured by an AC motor test, and the component is combined with a mechanical angle. In such a case, a cogging torque component corresponding to the mechanical angle is called during operation to correct the command torque. However, this method has a drawback that it takes time and cost, and has a problem that it cannot be applied when there is a phase transmission delay. Trp cg = Trp cgmax (θm) (1) where Trp cg: cogging torque Trp cgmax: cogging torque amplitude θm: mechanical rotation position (mechanical angle, θm = θe / P) θe: electric rotation position (electricity) Angle) P: Number of pole pairs.

[0003]

However, in the prior art, an individual test is performed on an AC motor to measure the cogging torque with respect to the mechanical angle position (one rotation), and the cogging torque of the mechanical position with respect to the mechanical position in equation (1) is obtained. In this method, the values are stored in the memory, and the cogging torque corresponding to the mechanical angle is called from the memory during operation to correct the command torque. Therefore, it takes time for the individual test of the AC motor, and the cost of using the memory is reduced. This causes a problem that the correction is erroneous when there is a position transmission delay, which causes an increase in torque ripple, and the like. The present invention solves these problems, and requires less time, cost reduction, correction of torque ripple other than cogging torque, and easy correction of torque ripple. It is an object of the present invention to realize a motor drive without rotation unevenness in an applied field.

[0004]

In order to solve the above problem, the invention of a torque ripple correction method according to claim 1 of the present application provides a current control means for driving an AC motor according to a command torque, a PWM power conversion device, A current detecting means for detecting a current of the AC motor; an electric angle detecting means for detecting an electric angle (position) of the AC motor; a detected speed calculating means for calculating a detected speed from the detected electric angle; A torque error correction method comprising: a speed error calculating means for calculating a speed error by subtracting a detected speed; and a speed proportional integral control unit for calculating a command torque by multiplying the speed error by a speed proportional integral gain. A filter that passes a band extracts predetermined torque ripple from the command torque, and subtracts the predetermined torque ripple from the command torque. Wherein the obtaining a new command torque by. The invention described in claim 2 is the first invention.
In the torque ripple correction method described above, a torque ripple correction process is performed using a value obtained by multiplying a predetermined gain by a ripple gain. According to a third aspect of the present invention, in the torque ripple correction method according to the first or second aspect, a plurality of filters and ripple gains that pass a predetermined frequency band are provided, and these are processed in parallel. The invention according to claim 4 is the invention according to claims 1 to 3.
5. The torque ripple correction method according to claim 1, wherein the filter that passes a predetermined frequency band is a bandpass filter or a hybrid filter formed by a combination of a lowpass filter and a high-pass filter. . According to a fifth aspect of the present invention, in the torque ripple correction method according to any one of the first to fourth aspects, in order to calculate a cutoff frequency of the filter, the reference speed frequency is the detected speed frequency,
Alternatively, it is the command speed frequency, and one of the detected speed and the command speed is selected by a first speed switch. The invention according to claim 6 is
The torque ripple correction method according to any one of claims 1 to 5, wherein a cutoff frequency of the filter is automatically changed in accordance with the reference speed frequency (or an output frequency of the PWM power converter). It is characterized by the following. According to a seventh aspect of the present invention, there is provided the torque ripple correction method according to any one of the first to sixth aspects, wherein a torque area determining means for determining a correction effective area from the command torque;
A speed region determination unit that determines a correction effective region from the speed, and a torque ripple process calculation by the filter is adjusted based on a combination result of the region determination values obtained from the torque region determination unit and the speed region determination unit. A filter adjusting means is provided. According to an eighth aspect of the present invention, in the torque ripple correction method according to any one of the first to sixth aspects, the torque ripple calculated from the filter is set to the command torque based on a combination result of the area determination values of the seventh aspect. The second switch for ripple correction selects whether or not to perform correction. According to a ninth aspect of the present invention, in the torque ripple correction method according to the first aspect, the torque ripple is generated from the AC motor, the ripple due to the offset and the gain of the current detector, and the ripple due to the offset and the gain of the PWM converter. , One or more of ripples due to dead time, wherein the torque ripple is related to the speed frequency at a constant frequency.
According to a tenth aspect of the present invention, there is provided a motor control circuit for driving an AC motor in accordance with a command torque and a PWM.
A power converter, current detection means for detecting the current of the AC motor, electric angle detection means for detecting an electric angle (position) of the AC motor, and detection speed calculation means for calculating a detection speed from the detected electric angle Speed error calculating means for calculating a speed error by subtracting the detected speed from the command speed,
A speed proportional integral control unit that calculates a command torque by multiplying the speed error by a speed proportional integral gain; anda motor control circuit including a filter that passes a predetermined frequency band to extract a predetermined torque ripple from the command torque. A new command torque is obtained by subtracting a predetermined torque ripple from the command torque. According to an eleventh aspect of the present invention, in the motor control circuit according to the tenth aspect, the torque ripple correction processing means performs a torque ripple correction process by multiplying a predetermined torque ripple by a ripple gain.

[0005]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a speed control loop including a torque ripple correction method handled by the present invention. In FIG. 1, reference numeral 11 denotes an AC motor, and the AC motor 11 is driven by a current control means 12 and a PWM power converter 13 according to a command torque. Current Ifb of AC motor 11
Is detected by the current detecting means 14, and the electrical angle (position) θfb of the AC motor is detected by the electrical angle detecting means (encoder) 15. The detection speed calculating means 16 is an electric angle detecting means 15
The detection speed ωfb is calculated from the detected electrical angle θfb detected in the step (1). The speed error calculating means 17 calculates the speed error Δω by subtracting the detected speed ωfb from the command speed ω *, and the speed proportional integral controller 18 calculates the command torque Tp * by multiplying the speed error Δω by the speed proportional integral gain. Conventionally, this value Tp * is directly input to the current control means 12, and the current control means 12 obtains the command voltage V from the information of the command torque Tp *, the current Ifb of the AC motor and the electrical angle (position) θfb of the AC motor. * Is calculated and input to the PWM power converter 13, and the PWM power converter 13 generates an output voltage and
The C motor was being driven. However, in the present invention, a new command torque Ta * is calculated via the torque ripple correction processing means 1 according to the present invention without directly inputting the command torque Tp * from the speed proportional integral control section 18 to the current control means 12. Are input to the current control means 12. In the torque ripple correction processing means 1p, a predetermined torque ripple is extracted from the command torque Tp * by a filter that passes a predetermined frequency band, and the predetermined torque ripple Trp is extracted.
A new command torque Ta * is calculated using the command torque Tp *. FIG. 2 shows a torque ripple correction method according to the first embodiment performed by the torque ripple correction processing means 1p, and is a block diagram of a correction method particularly effective for cogging torque. For torque ripple,
Cogging torque, dead time ripple, offset ripple, gain ripple, load ripple (load disturbance) and the like can be considered. Among the torque ripples described above, the torque ripple other than the load ripple is a ripple having the following frequency components in proportion to the rotation frequency (f = ω / 2π). Cogging torque (Trp cg): nf Offset ripple (Trp offset): 1f Gain ripple (Trp gain): 2f Dead time ripple (Trp dead): 6f where n is the greatest common multiple of the number of poles and the number of slots, and f is the rotation frequency ,. Therefore, the present invention focuses on the torque ripple (k × f, k is an arbitrary constant) generated in a constant relationship with the rotation frequency f of the AC motor (or the output frequency of the PWM power converter), and reduces and corrects the torque ripple. Is what you do. Such torque ripple is a partial torque ripple generated from the AC motor 11, the current detector 14, and the PWM power converter 13.

In FIG. 2, reference numeral 104 denotes a first switch for speed, 105 denotes a second switch for ripple correction, 106 denotes speed frequency calculating means, 107 denotes area determining means from the speed frequency f and the command torque Tp *, and 108 denotes zero ripple. Of the correction value Trp zero. 101 is a bandpass filter unit (BPF), 1011a is a bandpass filter,
Reference numeral 1011b denotes a generator for the cutoff frequency of the band-pass filter. Reference numeral 102 denotes a ripple gain unit,
21 is a ripple gain Krp. In the torque ripple correction method shown in FIG. 2, the reference speed for calculating the cutoff frequency of the filter is the command speed or the detected speed, and either one of them is selected by the first speed switch. ing. First, the frequency component (eg, frp = 8f) of the cogging torque Trp cg to be corrected is checked, and the normal cutoff frequency fc nor is calculated from the torque ripple frequency component frp and the normal bandwidth Δfc norm according to equation (2).
Set m (fcrl norm, fcr norm). Thereafter, the first switch (selecting the terminal 2 of SW1) is switched so as to obtain the reference speed frequency f (= ω / 2π) from the detected speed. fc norm = FNC (Δfc norm, frp) (2) where fc is the cut-off frequency of the band-pass filter, fc norm is the normal cut-off frequency when f is 1 Hz, and Δfc norm is the normal bandwidth (fcr norm). -Fcl nor
m) frp: frequency component of torque ripple FNC: function. Further, the area judging means 107 including a torque area judging means for judging a correction effective area from the command torque and a speed frequency area judging means for judging the correction effective area from the speed frequency, from the information of the command torque Tp * and the detected speed frequency f Ripple correction effective area (low speed frequency area, low torque area AN
D condition), and based on this, it is determined whether the torque ripple is to be corrected or not.
Switch (SW2) 105 (S for ripple correction)
When the ripple correction is not performed, 1 at the W2 terminal is selected with 0) at the SW2 terminal. Through a band-pass filter 101 having a cut-off frequency set for extracting cogging torque ripple, a command torque T
Predetermined torque ripple (cogging torque component) from p *
Trp is extracted and multiplied by a ripple gain (Krp) 102,
A predetermined torque ripple Trp is subtracted from the command torque Tp * by the ripple correction calculating means 103 to obtain a new command torque Ta.
Calculate * to correct the cogging torque. In addition, ripple correction can be performed with respect to torque ripple (dead time ripple, gain ripple, offset ripple, etc.) other than cogging torque by the above-described torque ripple correction method.

FIG. 4 shows a bandpass filter used in the present invention. The gain at the center frequency fo of the bandpass filter is set to 0 db, and the gain is lower than fo by -3 db.
Let the left and right frequencies be the cutoff frequency fc (left cutoff frequency: fcl, right cutoff frequency: fcr)
The frequency components in this range Δfc are passed. Instead of this bandpass filter, a hybrid filter using a combination of a lowpass filter and a high-pass filter can be used. In addition, by automatically changing the cutoff frequency of the filter according to the reference speed frequency, more accurate correction can be performed in proportion to the speed frequency.

FIG. 3 shows a torque ripple correction method performed by the torque ripple correction processing means 1q according to the second embodiment of the present invention. In particular, FIG. 3 is a block diagram of a torque ripple correction method for performing ripple correction for a large number of torque ripples. . In FIG. 3, reference numeral 104 denotes a first speed switch, 10
5 is a second switch for ripple correction, 106 is a speed frequency calculating means, 107 is a region judging means from the speed frequency f and the command torque Tp *, and 108 is a correction value Trpzer of zero ripple.
o generator. 101q is a band pass filter unit (BPF), and 1011a to 101na are the first
The first to n-th bandpass filters, 1011b to 101nb, are generators of the cutoff frequencies of the first to n-th bandpass filters, respectively. Reference numeral 102 denotes a ripple gain unit, and reference numerals 1021 to 102n denote first to n-th ripple gains. As described above, when it is desired to provide a filter that allows a predetermined number of frequency bands to pass, the first bandpass filter to the nth bandpass filter having a parallel configuration as shown by 101q in FIG. 3 can be used. Individual bandpass filter B
PF_1 to BPF_n and a predetermined cutoff frequency fc1 to
The operations of fcn and the ripple gains Krp1 to Krpn are in principle the same as the operations of the bandpass filter BPF, cutoff frequency fc, and ripple gain Krp shown in FIG.

[0009]

As described above, according to the present invention, a predetermined torque ripple is extracted from the command torque by a filter that passes a predetermined frequency band, and the predetermined torque ripple is subtracted from the designated torque to obtain a new command torque. Is calculated and the torque ripple correction processing is performed. 1) It takes less time and effort, 2) Cost can be reduced, 3) Torque ripple correction can be easily realized, and 4) High precision application fields Rotational unevenness can be reduced. This has the effect.

[Brief description of the drawings]

FIG. 1 is a block diagram of a speed control loop including a torque ripple correction method handled by the present invention.

FIG. 2 is a block diagram of a torque ripple correction method according to the first embodiment of the present invention, which is particularly effective for cogging torque.

FIG. 3 is a block diagram of a torque ripple correction method according to a second embodiment of the present invention, which is effective particularly when ripple correction is performed on a large number of torque ripples.

FIG. 4 shows a bandpass filter used in the present invention.

[Explanation of symbols]

* Subscript representing command fb Subscript representing detection T * Command torque Tp * Command torque calculated from speed proportional integral control unit Ta * Command torque after torque ripple correction processing of the present invention is performed Trp Bandpass filter processing and ripple gain calculation Torque ripple after Trp1 to Trpn First to nth torque ripple after band-pass filter processing and ripple gain calculation Krp Ripple gain Krp1 to Krpn First to nth ripple gain ω * Command speed ωfb Detection speed frp Ripple frequency Δω Speed error V * Command Voltage V Output voltage θfb Detector angle (position) θe Electrical angle θm Mechanical angle P Number of pole pairs Ifb Detected current BPF Bandpass filters BPF_1 to BPF_n First to nth bandpass filters fo Center frequency of bandpass filters fo1 to fon 1 to the center frequency of the n-th band-pass filter fc Toe-off frequency fc1 to fcn Cut-off frequency of the first to n-th band-pass filters fcl Cut-off frequency on the left of the center frequency of the band-pass filter fcr Cut-off frequency on the right of the center frequency of the band-pass filter sgnl1 Speed selection of SW1 Signal sgnl2 SW2 ripple correction selection signal Trp cg Cogging torque of AC motor Trp cgmax Cogging torque amplitude value Trp offset Offset ripple (current detector or PW
Trp gain Gain ripple (ripple due to gain imbalance of current detector or PWM converter) Trp dead Dead time ripple (ripple due to dead time of PWM converter) 1 Torque ripple correction means 1p of the present invention Torque ripple correction means 1q of the first embodiment of the invention 1q Torque ripple correction means of the second embodiment of the invention 11 AC motor 12 Current control means 13 PWM power conversion device 14 Current detector (CT) 15 Electric angle detection means (encoder) 16 Detected speed calculating means 17 Subtractor (speed error calculating means) 18 Speed proportional integral control section 101 Bandpass filter section (or hybrid filter section) 102 Ripple gain section of the first embodiment 103 Subtractor (ripple correction calculating means) 104 Speed First switch 105 lip Correction second switch 106 Speed frequency calculation means 107 Speed frequency and command torque area determination means 108 Generator of zero ripple correction value 1011a to 101na 1st to nth bandpass filter 1011b to 101nb 1st to nth bandpass filter Generator of cut-off frequency of 1021 to 102n 1st to nth ripple gain

Claims (11)

[Claims] 1. A current control means and a PWM power conversion device for driving an AC motor according to a command torque, a current detection means for detecting a current of the AC motor, and an electric angle (position) of the AC motor. Electrical angle detection means, detection speed calculation means for calculating a detection speed from the detected electrical angle,
In a torque ripple correction method comprising: a speed error calculating unit that calculates a speed error by subtracting the detected speed from a command speed; and a speed proportional integral control unit that calculates a command torque by multiplying the speed error by a speed proportional integral gain. A torque ripple correction method, wherein a predetermined torque ripple is extracted from the command torque by a filter that passes a predetermined frequency band, and a new command torque is obtained by subtracting the predetermined torque ripple from the command torque. 2. The torque ripple correction method according to claim 1, wherein a torque ripple correction process is performed using a value obtained by multiplying the predetermined torque ripple by a ripple gain. 3. The torque ripple correction method according to claim 1, wherein a plurality of filters and ripple gains that pass a predetermined frequency band are provided, and these are processed in parallel. 4. The filter according to claim 1, wherein the filter that passes a predetermined frequency band is a band-pass filter or a hybrid filter formed by a combination of a low-pass filter and a high-pass filter. The torque ripple correction method according to claim 1. 5. The calculation of a cutoff frequency of the filter, wherein the reference speed frequency is the detected speed frequency or the commanded speed frequency, and one of the detected speed and the commanded speed is a speed. The torque ripple correction method according to any one of claims 1 to 4, wherein the first switch is selected by a first switch. 6. The filter according to claim 1, wherein the cutoff frequency of the filter is automatically changed in accordance with the reference speed frequency (or the output frequency of the PWM power converter). The torque ripple correction method according to claim 1. 7. A torque area judging means for judging a correction effective area from a command torque, a speed area judging means for judging a correction effective area from the speed, a torque area judging means and a speed area judging means. 7. The torque ripple correction method according to claim 1, wherein a filter adjustment unit is provided so as to adjust a torque ripple processing operation by the filter based on a combination result of the area determination values. 8. A ripple correction second switch is used to select whether or not to correct the torque ripple calculated from the filter to the command torque, based on a combination result of the area determination values according to claim 7. The torque ripple correction method according to claim 1, wherein: 9. The torque ripple is one or more of a ripple generated from the AC motor, a ripple caused by an offset and a gain of the current detector, a ripple caused by an offset and a gain of a PWM converter, and a ripple caused by a dead time. The torque ripple correction method according to claim 1, wherein the torque ripple is related to the speed frequency at a constant frequency. 10. A current control unit and a PWM power conversion device for driving an AC motor according to a command torque, a current detection unit for detecting a current of the AC motor, and an electric angle (position) of the AC motor. An electrical angle detecting means; a detected speed calculating means for calculating a detected speed from the detected electrical angle; a speed error calculating means for calculating a speed error by subtracting the detected speed from a commanded speed; and a speed proportional integral gain to the speed error And a speed proportional integral control unit that calculates a command torque by multiplying the command torque by extracting a predetermined torque ripple from the command torque with a filter that passes a predetermined frequency band. A motor control circuit for obtaining a new command torque by subtracting a torque ripple. 11. The motor control circuit according to claim 10, wherein said torque ripple correction processing means performs a torque ripple correction process by multiplying said predetermined torque ripple by a ripple gain.