JPH06105581A - Vector controller for induction motor - Google Patents

Abstract

PURPOSE:To enhance the response of a torque control while securing the stability of a current control system. CONSTITUTION:A vector control for an induction motor obtains a torque shaft voltage VQ and an exciting shaft voltage VD by a current control system of a digital calculation from a torque current command IT and an exciting current command IO, PWM-controls it from the voltage, and obtains a primary voltage V1 from the voltages VQ, VD. The control comprises a limiter 11e for correcting a previous value stored in 1/Z with deviations VDerr, VQerr when the voltage V1 exceeds a maximum voltage (control ratio 1) Vmax of the PWM-control, limits the integrated value of an integrating item to the voltages VD, VQ corresponding to the Vmax, and fastens the return of the integrated value when the primary voltage becomes low.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction motor vector controller, and more particularly to a vector controller having a current control system.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional vector control device. The output of the speed control unit 2 of the induction motor 1 is used as the torque current command I _T, and the polar coordinate conversion unit 3 calculates the current I ₁ and the phase angle φ from the exciting current command I _O that is orthogonal to this. Further, the slip frequency ω _S is obtained by the slip frequency calculation unit 4 from the torque current command I _T , the exciting current command I _O, and the secondary time constant τ _{2 of the} induction motor 1.

The slip frequency ω _S is added to the detection speed ω _n of the speed detection unit 5 of the induction motor 1 to be converted into a primary angular velocity ω ₀ , and the angular velocity ω ₀ and the phase angle φ are fed to the sine wave generator 6. Get the sine wave of the phase.

The D / A converter 7 obtains two-phase current commands i _a and i _c from the current command I ₁ and the two-phase sine wave, and a current controller 8 which performs a proportional-integral calculation from the current command and the detected current. To obtain the two-phase voltage commands V _a and V _c , the two-phase voltage command V _b from the two phases, and obtain the three-phase PWM voltage output to the PWM conversion unit 9.

[0005]

In the conventional vector control device, the induced voltage of the induction motor also increases as the speed ω _n of the induction motor increases, and the primary voltage is increased when an excessive torque load is applied in the high speed range. Maximum voltage V of PWM control
_It exceeds _max (= DC power supply voltage V _DC / 2).

Therefore, conventionally, a limiter circuit is provided in the PWM converter 9. For example, the PWM converter 9
Control voltage V _a is the inner, V _b, and generates a PWM waveform by the level comparison of V _c and the triangular wave (carrier wave), the primary voltage V _a, V _b, V _c is controlled rate 1 or more exceeding the maximum voltage V _max In order to obtain an accurate sine wave PWM waveform, the voltages V _a , V _b and V _c are prevented from exceeding the triangular wave level through the limiter circuit.

In the voltage limitation at the stage of generating the PWM waveform as described above, the integral amount by the current controller 8 increases to an excessive amount during the voltage limitation. Therefore, even after the reduction of the load torque, the return of the integration amount of the current control unit 8 is delayed, the limiter operation time of the PWM conversion unit 9 becomes long, and the improvement of the torque control responsiveness is impeded.

To solve this problem, it is conceivable to reduce the integral time constant of the current control unit 8, but it makes the current control system unstable.

An object of the present invention is to provide a vector control device which enhances the responsiveness of torque control while ensuring the stability of the current control system.

[0010]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides an induction motor with a current control system including a digital operation integral term from a torque current command I _T and an exciting current command I _O of the induction motor. In the vector control device that obtains the torque axis voltage V _Q and the excitation axis voltage V _D , and vector-controls the induction motor from the voltages V _Q and V _D by PWM control, the current control system includes the torque axis voltage V _Q and the excitation. The primary voltage V ₁ is obtained from the axial voltage V _D , and this voltage V ₁ is PWM
A deviation when the maximum voltage V _max for control is _exceeded is obtained as error components V _Qerr and V _Derr of the torque axis component and the excitation axis component, and a limiter unit is provided to correct the previous value of the integral term by this error amount. It is characterized by that.

[0011]

When the primary voltage of the induction motor becomes excessive, the value of the integral term of the current control system is limited to the torque axis voltage and the excitation axis voltage corresponding to the maximum voltage V _max so that the primary voltage V ₁ becomes maximum. When the voltage becomes lower than the voltage V _max, the return operation from the limiter value of the integral term is accelerated.

In the current control system of digital operation, when adding the deviation of this time to the previous value in the integration operation, the previous voltage is corrected by the error so that the primary voltage V ₁ becomes the maximum voltage V _1.
Limit not to exceed _max .

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of an apparatus showing an embodiment of the present invention. This embodiment shows a case of digital calculation in which control calculation is performed by a computer.

The current control section 11 responds to the torque current command I _T and the exciting current command I _O by detecting the respective torque current values I.
The deviation between the _TFB and the exciting current detection value I _OFB is calculated by proportional integral calculation to obtain the torque axis voltage V _Q and the exciting axis voltage V _D at the rotational coordinates.

The detection of the torque current detection value I _TFB and the excitation current detection value I _OFB is performed by converting the two-phase currents I _a and I _b of the induction motor 1 into digital values by the A / D converter 12, and adding them. The C-phase current I _c is also calculated by the following, and each current value I _a ,
I _b, is converted into two-phase currents of the fixed coordinates in the three-phase / two-phase conversion unit 13 from the I _c, which is converted to the torque current I _TFB rotational coordinate by the coordinate transformation unit 14 to the exciting current I _OFB.

The voltage control signal V _D from the current controller 11
V _Q is converted from two-dimensional voltages V _1D and V _1Q of fixed coordinates by the coordinate conversion unit 15, and three-phase voltage signals V _a , V _b and V _c are converted by the two-phase / three-phase conversion unit 16. To do.

The phase angle θ ₀ for conversion by the coordinate conversion units 14 and 15 is obtained by integrating the angular velocity ω ₀ by the integrating unit 17.

Here, the current control unit 11 has the configuration shown in FIG. In the figure, 11a is a torque current proportional-integral calculation means, 11b is a first interference term compensation means, and
1c serves as a proportional-integral calculation means for the exciting current, and 11d serves as a second interference term compensating means.

The interference term compensating means 11b and 11d generate an interference term in which the exciting current and the torque current include information of the speed ω ₀ in the electric motor in the vector control state of the induction motor 1, and the interference term causes a low speed range. And compensate for the change in the response of the current control system in the high speed range.

Next, the limiter section 11e performs limiter control of the current control system. This limiter control is based on the voltage V _D ,
From V _Q to primary voltage V ₁

[0021]

[Equation 1]

Then, the primary voltage V ₁ is compared with the maximum voltage V _max (= V _DC / 2) of the control rate 1 to obtain the primary voltage V ₁
When V exceeds the maximum voltage V _max , the error components V _Derr and V _Qerr of the D axis and the Q axis are _calculated from the following equations.

[0023]

[ _Formula 2] V _Derr = (V ₁ −V _max ) cos θ ₀ (2)

[0024]

## _EQU3 ## V _Qerr = (V ₁ −V _max ) sin θ ₀ (3) FIG. 3 shows the relationship between the error components V _Derr and V _Qerr and the primary voltages V ₁ and V _max . This error is proportional to the integral calculation means 11
The primary voltage V ₁ is prevented from _{exceeding the} maximum voltage V _max by using the previous value correction value of the integral terms of a and 11c.

Since the integral term is digitally calculated in the same manner as the proportional term, 1 / Z thereof is the proportional integral calculation cycle and the previous calculated value is stored to perform the integral calculation. For example, for torque current control, the current value V _QQ (n) is compared with 1 / Z by the previous value V _QQ (n).
_QQ (n-1) is stored, and the current value V _QQ (n) is added to integrate the torque current deviation. Similarly, in the excitation current control, the previous value V _DD (n-1) is stored as 1 / Z for the current value V _DD (n).

Therefore, the limiter operation by the limiter section 11e is such that when the primary voltage V ₁ exceeds V _max , its D axis and Q
Calculate the axis error and use this error to calculate the previous integrated value V _QQ
(N-1), V _DD (n-1) is corrected so that the primary voltage V ₁ does not exceed V _max . The previous values V _DD (n-1) and V _QQ (n-1) at this time are

[0027]

## EQU4 ## V _DD (n-1) = V _DD (n) -V _Derr

[0028]

[ _Formula 5] V _QQ (n-1) = V _QQ (n) -V _Qerr is stored as the previous value by calculation.

By the limiter processing of the current control section described above,
Even when the primary voltage V ₁ exceeds the maximum voltage V _max for PWM control, the integral amount of the integral term is held at the maximum voltage V _max, and the integral amount is maintained even when the duration of V ₁ > V _max becomes long. Is prevented from becoming excessively large, and when the load torque is reduced, the limiter operation is immediately returned to the normal operation, and the responsiveness of torque control is improved. Further, the integration time constant can be set to a value that makes the current control system sufficiently stable.

[0030]

As described above, according to the present invention, the current control system for obtaining the torque axis voltage and the excitation axis voltage of the induction motor,
An error component when the primary voltage V ₁ exceeds the maximum voltage V _max for PWM control is obtained as a torque axis component and an excitation axis component, and the previous value of the integral term is corrected by this error component. Even when the primary voltage becomes excessive, the integrated amount of the current control system can be limited to a value corresponding to the maximum voltage, and the deviation from the limit value can be accelerated to improve the responsiveness of torque control.

Further, the integration time constant of the current control system can be set to a value sufficient for stabilizing the system.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram of a current control unit in the embodiment.

FIG. 3 is a relational diagram of an error amount due to the primary voltage V ₁ and the maximum voltage V _max .

FIG. 4 is a block diagram of a conventional vector control device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Induction motor 11 ... Current control part 11a ... Torque current proportional-integral calculation means 11b ... 1st interference term compensation means 11c ... Excitation current proportional-integration calculation means 11d ... 2nd interference term compensation means 11e ... Limiter part

Claims (1)

[Claims] 1. A torque axis voltage V _Q and an excitation axis voltage V _D of the induction motor are obtained from a torque current instruction I _T of the induction motor and an excitation current instruction I _O by a current control system including an integral term of a digital operation. In a vector controller for vector-controlling an induction motor from V _Q and V _D by PWM control, the current control system obtains a primary voltage V ₁ from the torque axis voltage V _Q and the excitation axis voltage V _D , and this voltage V ₁ Is PWM
A deviation when the maximum voltage V _max for control is _exceeded is obtained as error components V _Qerr and V _Derr of the torque axis component and the excitation axis component, and a limiter unit is provided to correct the previous value of the integral term by this error amount. A vector control device for an induction motor.