JP2001186784A - Torque ripple-reducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem where an offset current is allowed to flow in a motor, and a torque ripple is generated in the generation torque of the motor since the offset of a current control system cannot be corrected by a fixed amount of correction when the offset of the current control system is changed by temperature or the like. SOLUTION: This torque ripple-reducing device is equipped with a first operation part 51 that calculates the total sum of the product of a torque command for each period of the electric angle of a motor and sin (θ deg.-0 deg.), a second operation part 512 that calculates the total sum of the product of the torque command for each period of the electric angle of the motor and sin (θdeg.-120 deg.), and an update judgment part 54 that judges whether the amount of correction is to be updated or not according to the speed signal of one period of the electric angle of the motor and the torque command, first and second update value decision parts 521 and 522 that decide a value for updating the amount of correction based on the result of the first and second operation parts, and first and second amount-of-correction update parts 531 and 532 that add the value of the update value decision parts 1 and 2 to the amount of correction based on the judgment of the update judgment part 54.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor control device such as a servo amplifier or an inverter having current feedback control, and more particularly to a device for reducing torque ripple generated due to an offset existing in a current control system.

[0002]

2. Description of the Related Art A block diagram of a conventional servo amplifier for controlling a motor is shown in FIG. In the figure, 1 is a motor, 2 is an encoder, 31 is a position control unit,
32 is a speed controller, 33 is a current controller, 34 is a power converter, 35 is a position detector, 36 is a speed detector, 371 is a U-phase current detector, 372 is a V-phase current detector, and 38 is si.
n (sine wave) table 411 is a first adder, 412
Is the second adder, 421 is the first correction amount, and 422 is the second correction amount.
Is the correction amount. Generally, the current controller 33, the power converter 34, the U-phase current detector 371, and the V-phase current detector 37
The offset exists in the current control system composed of the motor 2, and the offset current flows through the output of the power converter 34, that is, the motor 1. Therefore, the torque generated by the motor varies depending on the rotation angle. Hereinafter, this torque fluctuation is referred to as torque ripple. Therefore, in the prior art, in order to reduce the torque ripple due to the offset current, the first correction amount 42 is used for each of the U-phase current detection value and the V-phase current detection value.
The offset of the current control system is corrected by adding the first and second correction amounts 422. If the first and second correction amounts are set at the time of shipment or the like, they are fixed thereafter.

[0003]

However, in the prior art, when the offset of the current control system changes due to temperature or the like, the offset of the current control system cannot be corrected with a fixed correction amount. Therefore, there has been a problem that an offset current flows through the motor and torque ripple occurs in the generated torque of the motor. Therefore, an object of the present invention is to provide a torque ripple reduction device that can automatically update the correction amount even if the offset of the current control system changes, and reduce the torque ripple generated by the motor.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention detects a phase current flowing through a motor to perform current control, and detects a speed from the rotation of the motor to perform speed control. In a motor control device that corrects an offset of a current control system by adding a correction amount to a value, a torque command and a sin
(Θ ° −0 °), a first calculating unit that calculates the sum of the products, the torque command for each cycle of the electric angle of the motor, and sin (θ ° −1)
20 °), an update determining unit that determines whether or not to update the correction amount based on a speed signal and a torque command for one cycle of the electrical angle of the motor, and the first arithmetic unit. A first update value determining unit that determines a value for updating the first correction amount based on a result of the unit, and determines a value for updating the second correction amount based on a result of the second arithmetic unit A second update value determination unit that performs a first correction amount update unit that uses the value of the first update value determination unit as a correction amount based on the determination of the update determination unit; A second correction value updating unit that uses the value of the second update value determination unit as a correction value.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the relationship between the offset current and the torque ripple will be described. The three-phase currents i _u , i _v , and i _w including the offset current can be expressed by Equation 1. θ ° is the electrical angle,
i is the amplitude of the current, I _0u offset current, I _{0 v} of the U-phase indicates the offset current of the V phase. Servo amplifier is U phase and V
When the phase current feedback control is performed, an offset current is given to the U-phase current and the V-phase current, and these are absorbed in the W-phase. The phase current can be given an offset current by selecting any two phases.

[0006]

(Equation 1)

[0007] When the current of equation (1) flows through the motor, the torque τ generated by the motor can be expressed by equation (2).

[0008]

(Equation 2)

As can be seen from Equation 2, the generated torque includes a term τ ₀ that is proportional to the current and a term τ ₁ that varies with the electrical angle.
k _t and k ₁ are proportional constants. The term that varies with the electrical angle is the torque ripple. Torque ripple, offset current I _0u, determined by I _{0 v.} Next, the relationship between the torque command and the offset current when the servo amplifier performs the speed feedback control will be described. The torque command τ _r can be expressed by Expression 3.

[0010]

(Equation 3)

As can be seen from Equation 3, the torque command includes a variation term τ _r1 due to the offset current. k ₂ is a proportionality constant. Next, a method of obtaining an offset current from a torque command that is a discrete value will be described. Electrical angle of 360 ° to n
In the case of division, the offset currents of the U and V phases can be independently obtained by the calculation of Expression 4 from the theory of the finite Fourier series.

[0012]

(Equation 4)

[0013] Briefly, I _0u is orthogonal to the phase -90 ° sections I _{0 v,} close to the phase -30 ° sections I _0u s
in (θ ° −0 °) and the torque command. I _{0 v} is orthogonal to the phase -30 ° sections I _0u, close to the phase -90 ° sections I _0v sin (θ ° -12
0 °) and the torque command. Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 511 is a first calculation unit, 512 is a second calculation unit,
521 is a first update value determination unit, 522 is a second update value determination unit, 532 is a first correction amount update unit, 532 is a second correction amount update unit, 54 is an update determination unit, and 61 is a speed signal. , 62
Is a torque command, 631 is sin (θ ° -0 °), 632 is sin
(θ ° -120 °). First and second calculation units 511 and 51
2 is the torque command 62 and the output sin of the sin table 38
Using (θ ° −0 °) (631) and sin (θ ° −120 °) (632), calculations 1 and 2 of Expression 5 are performed, and values A and A proportional to the respective offset currents of the U and V phases are obtained. Find B.

[0014]

(Equation 5)

First and second update value determination units 521 and 522
Determines update values a and b as shown in Expression 6 based on the results A and B of the first and second calculation units 511 and 512, respectively. f indicates a function for determining an update value, an example of which is shown in FIG.

[0016]

(Equation 6)

In brief, the first and second arithmetic units 5
When the results A and B of 11, 512, that is, the offset current is small, the update value is 0. When A and B increase, the update values a and b are increased in two stages. Further, when A and B are large, it is determined that there is something abnormal, and the update value is set to 0. The first and second correction amount update units 531 and 532 calculate the correction amounts I _cu and I
Update _cv .

[0018]

(Equation 7)

The updated correction amounts I _cu and I _cv are
First and second adders 411 and 412 respectively add the detected U-phase current value and the detected V-phase current value. Update determination unit 54
Determines whether to update the correction amount from the speed signal 61 and the torque command 62 for one cycle of the electrical angle. The correction amount is updated when one of the electrical angles is satisfied and all of the following conditions (a) to (d) are satisfied. (B) The angle monotonically increases or decreases. (B) The minimum rotation speed is higher than the set value and the maximum rotation speed is lower than the set value. (C) Speed fluctuation is below the set value. (D) The torque command fluctuation is below the set value. As described above, according to the present invention, the offset current for two phases is independently obtained from the torque command for one cycle of the electrical angle, the correction amount to be added to the current detection value is updated based on the result, and the offset is always calculated. Since it acts so as to cancel the current, even if the offset of the current control system changes, the offset current does not flow through the motor, and the motor does not generate torque ripple. FIG. 1 showing an embodiment of the present invention has a configuration in which calculations 1 and 2 of Equation 5 and an update determination are sequentially performed in each control cycle. The angle, speed signal, and torque command for one electrical angle cycle are stored in a storage device. The information may be stored, and then the calculation or the update determination may be performed. In that case, it is not necessary to store all data for each data in order to save the capacity of the storage device. For example, the electrical angle may be divided into 256, and 256 data may be stored and calculated. FIG. 1 showing the embodiment of the present invention is a case where the current feedback control of the U-phase and the V-phase is performed. In the case of the current feedback control of the U-phase and the W-phase, the calculation 2 of the second calculation unit is performed. Into Equation 8 and the second
May be added to the W-phase current detection value.

[0020]

(Equation 8)

[0021]

As described above, according to the present invention, when the offset of the current control system of the servo amplifier changes due to the influence of temperature or the like and an offset current flows to the motor, two phases from the torque command are obtained from the torque command. Since the offset current is obtained independently, the offset correction amount is updated, and the offset of the current control system is cancelled, the offset current does not flow through the motor, so that there is an effect that the torque ripple can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a function of an update determination unit;

FIG. 3 is a block diagram showing a conventional technique.

[Explanation of symbols]

 Reference Signs List 1 motor 2 encoder 31 position control unit 32 speed control unit 33 current control unit 34 power conversion unit 35 position detection unit 36 speed detection unit 371 U-phase current detection unit 372 V-phase current detection unit 38 sin table 411 first addition unit 412 Second adder 421 First correction amount 422 Second correction amount 511 First calculation unit 512 Second calculation unit 521 First update value determination unit 522 Second update value determination unit 531 First correction Amount update unit 532 Second correction amount update unit 54 Update determination unit 61 Speed signal 62 Torque command 631 sin (θ ° -0 °) 632 sin (θ ° -120 °)

Claims (1)

[Claims] An electric current control is performed by detecting a phase current flowing in a motor, a speed is detected by detecting a speed from a rotation of the motor, a correction amount is added to a current detection value, and an offset of a current control system is adjusted. In the motor control device, the torque command for each electric angle cycle of the motor and sin (θ
(° −0 °), a first arithmetic unit that calculates the sum of the products of the motor and the torque command for each electrical angle cycle of the motor and sin (θ ° −120).
°), an update judging unit for judging whether or not to update the correction amount from a speed signal and a torque command for one cycle of the electric angle of the motor, and the first arithmetic unit. A first update value determining unit that determines a value for updating the first correction amount based on the result of the above, and determines a value for updating the second correction amount based on the result of the second arithmetic unit. A second update value determination unit, a first correction amount update unit that uses the value of the first update value determination unit as a correction amount based on the determination of the update determination unit, A second correction value updating unit that uses the value of the second update value determination unit as a correction value.