JPH0487591A - Controller of induction motor - Google Patents

Abstract

PURPOSE:To approximately coincide with the secondary magnetic flux actual value to the command value by providing a presuming means, which presumes the magnitude of the secondary magnetic flux of an induction motor when the output of said controller is off by instantaneous power stop, and using the value, which is gotten through this presuming means, as a secondary magnetic flux command value when the output of the controller is on. CONSTITUTION:This is provided with a changeover switch 8 and a primary filter 9. This primary filter 9 is one which presumes the secondary magnetic flux actual value of a motor when a control circuit is off by instantaneous power stoppage, and the time constant is the same as the secondary time constant T2 of the motor. Accordingly, when the control circuit turns off by instantaneous power stoppage, a switch 8 is changed over to go through the primary filter 9 by the changeover signal S', and the secondary magnetic flux actual value is presumed by the filter 9, whereby it approximately conforms to the command value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control device for an induction motor (also simply referred to as a motor) that is controlled via a power conversion device including an inverter.

[Conventional technology]

FIG. 3 is a block diagram showing a conventional example of such a control device.

In the figure, a converting device 1 is a device including a control circuit including a current control circuit and a power converter main circuit such as an inverter main circuit, and a current command value im+'b+ of each phase of a motor 2.
1e is input, and a current according to the command value is supplied to the motor 2.

Here, in order to perform vector control, the torque command value τ
1 and secondary magnetic flux command value Φ! From 9, the following (1), (2)
According to the formula, the current command value iM* of the component of the primary current parallel to the secondary magnetic flux and the current command value i of the component perpendicular to the secondary magnetic flux?
Calculate.

1+pTz 1M11=Φ2...(1
) However, p=d/dt, T is the motor secondary time constant 1M
indicates mutual inductance.

iT″ = τshin/Φ8
... (2) The arithmetic circuit 3 executes the calculation of the above equation (1), and the divider 4 executes the calculation of the equation (2).

The coordinate converter 5 converts the various quantities of the rotating secondary magnetic flux coordinate system into the various quantities of the stator coordinate system.If the angle between the a-phase winding of the stator and the secondary magnetic flux is φ2, then the relationship is The formula is as follows (
3) It becomes like the formula.

(3) The changeover switch 6 is used to select whether to directly transmit the secondary magnetic flux command value Φ2 to the arithmetic circuit 3 or to transmit it via the −th order filter. The switching signal S of the changeover switch 6 is passed through the primary filter when an operation command is input after the control device is powered on, and thereafter, when the difference between the input and output of the secondary filter becomes so small that it can be ignored.
This is a signal for switching to transmit the secondary magnetic flux command value Φ2* directly to the arithmetic circuit 3 again. - When the rate of change of the magnetic flux command value is high (changes stepwise), for example at the time of startup mentioned above, the output of the differential term of the arithmetic circuit 3 becomes impulse-like, which wastes the converter at the subsequent stage. Considering time, a high impulse-like frequency component does not become an actual current regardless of its magnitude, so it is provided to attenuate this. Further, the time constant T2 of the -th order filter tough is determined with respect to the motor secondary time constant T2 so that the following equation holds true.

T y < T z
(4) This is because if T F > T z, there is no point in differentiating it.

[Problem to be solved by the invention]

However, in the above-mentioned control, for example, when the input voltage of the converter 1 drops below the guaranteed operation range,
If a short power outage (such as when the power supply of the control circuit that calculates the current command value 1a+lb+le is established) occurs, there is a problem that the secondary magnetic flux will no longer match the command value.

This will be explained below with reference to FIG.

Now, if an instantaneous power failure occurs at time t1 and the converter output is turned off, and operation is restarted at the next time t2, the secondary magnetic flux command value Φ2''' is 0 between t and t2.
At 11, Φ2' returns to 1, the previous value. What is the primary filter tough output Φ at that time? ° in Figure 4 (b),
t and 11 are shown in FIG. 4 (c), and FIG. 4 (a) shows the secondary magnetic flux command value φ2.

Here, if the time from 11 to t, L is smaller than the motor secondary time constant T2, the actual value of the motor secondary magnetic flux will be as shown by the dotted line in Figure 4 (a), and operation will be restarted. Time 1
．． Then, a portion of the size of Φz(2) remains. Therefore, when iM* is calculated in the example of Figure 3, it actually becomes Φ! (2)
-Φ2(1) where the magnetic flux should be changed, 〇-Φ
In order to change the value to (1), IN* is calculated, and the secondary magnetic flux value (actual value) ends up being larger than the command value.

By the way, the motor generated torque τ is determined by the relationship τ=Φ×17, so i) If the secondary magnetic flux value (actual value) becomes too large, the actual torque will be larger than the torque command value τ1. It ends up.

ii) Also, since there is a limit to the voltage that the converter 1 can supply, an excessive excitation current i. If the supplyable voltage is exceeded when attempting to flow the torque current iT, the torque current iT will no longer flow, and there may be a case where only a smaller torque than the command value can be produced.

Such problems arise.

Therefore, an object of the present invention is to make it possible to make the actual value of the secondary magnetic flux coincide with the command value even in the event of a momentary power failure.

[Means to solve the problem]

In a control device that controls the torque of an induction motor by dividing the primary current of the induction motor into a component parallel to its secondary magnetic flux and a component perpendicular to its secondary magnetic flux, and by passing a current according to the current command value of each component, Estimating means for estimating the magnitude of the induction motor secondary magnetic flux when the output of the control device is off is provided, and a value obtained through this estimating means is used as the secondary magnetic flux command value when the output of the control device is on.

[Effect]

Estimating means for estimating the magnitude of the induction motor secondary magnetic flux when the output of the control device is turned off due to an instantaneous power failure is provided, and the value obtained through this estimating means is used as the secondary magnetic flux command value when the output of the control device is turned on. This allows the actual value of the secondary magnetic flux to substantially match its command value.

〔Example〕

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

As is clear from the figure, this embodiment is different from the conventional example shown in FIG. 3 in that a changeover switch 8 and a primary filter 9 are provided. This -order filter 9 estimates the actual value of the motor secondary magnetic flux when the control circuit is turned off due to an instantaneous power failure, and its time constant is the same as the motor secondary time constant T2. Therefore, when the control circuit (not shown) is turned off due to an instantaneous power failure, the switch 8 is switched to pass through the primary filter 9 using the switching signal S°, and the filter 9
By estimating the actual value of the secondary magnetic flux, it is made to almost match the command value.

FIG. 2 is a time chart for explaining the operation of FIG. 1.

In other words, the secondary magnetic flux value Φ2' estimated by the primary filter 9 at the time of a momentary power failure becomes as shown in FIG. Φ
Since i- for making y(I) is calculated by the primary filter as shown in FIG. 2(c), the inconvenience as in the case of FIG. 4 does not occur. In addition, Φ! (3)=Φ2(2).

〔Effect of the invention〕

According to this invention, an estimation means is provided for estimating the magnitude of the induction motor secondary magnetic flux when the output of the control device is turned off due to an instantaneous power failure, and when the output of the control device is turned on, the value obtained through this estimation means is doubled. Since it is used as the next magnetic flux command value,
The actual value of the secondary magnetic flux can be made to substantially match the command value, allowing good control.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a time chart for explaining the operation of Fig. 1, Fig. 3 is a block diagram showing a conventional example, and Fig. 4 is a block diagram of Fig. 3. It is a time chart for explaining the operation. 1... Conversion device, 2... Induction motor (motor), 3
. . . Arithmetic circuit, 4 . . . Divider, 5 . . . Coordinate converter, 68 .

Claims (1)

[Claims] 1) Torque control of the induction motor is performed by decomposing the primary current of the induction motor into a component parallel to the secondary magnetic flux and a component perpendicular to the secondary magnetic flux, and flowing a current according to the current command value of each component. In the control device that performs the control, an estimation means is provided for estimating the magnitude of the secondary magnetic flux of the induction motor when the output of the control device is turned off due to an instantaneous power failure, and when the output of the control device is turned on, the value obtained through this estimation means is used as the secondary magnetic flux. A control device for an induction motor, characterized in that it is used as a magnetic flux command value.