JPH05268787A - Controller for induction motor - Google Patents

Abstract

PURPOSE:To make it possible to prevent positive feedback from taking place in a control loop by disabling the integration operation of a speed estimating/ operating unit upon occurrence of a difference in the rotational direction polarity between a speed command and an estimated speed while furthermore limiting the upper and lower limits of estimated speed so that the rotational direction polarity is not reverse to an actual rotational direction polarity. CONSTITUTION:If a speed command omegar has + polarity and a comparator 24 produces an ON output while a speed estimation operating unit 8 produces an output in the direction of + polarity during forward rotation of an induction motor, a comparator 25 produces an ON output, a SW30 is turned OFF while SW31, SW32 are turned ON and a sum of signals from a proportional operating circuit 21 and an integrating operation circuit 22 is outputted, as a speed estimation value bar omegar having + polarity, through a limiter circuit 16. Upon inversion of the output from the speed estimation operating unit 8 to - polarity due to variation of load or abrupt deceleration, output of the comparator 25 is turned OFF thus turning the SW32 OFF. Consequently, the speed estimation value bar omegar is limited to the lower limit of a limiter circuit 23 and a '0' is outputted to disable an integrating circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed control of an induction motor which controls a variable speed by using a frequency converter, and more particularly, to an induction motor which can control the speed with sufficient accuracy without using a speed detector. Regarding the control device.

[0002]

2. Description of the Related Art As a conventional technique, there is a vector control method in which a primary current of an induction motor is separated into a torque component and an excitation component current, and they are independently controlled to enable speed control with a fast response. Vector control methods include a magnetic field orientation type and a slip frequency type. The slip frequency type vector control method is described in, for example, Japanese Patent Publication No. 62-26271. However, the slip frequency type requires a speed detector that detects the speed of the induction motor, which makes installation difficult and complicates the structure around the motor, and also requires a long distance for signal transmission from the speed detector. There are inconveniences such as the need for a cable. As a method for solving such an inconvenience, Japanese Patent Publication No. 63-34718 proposes a control method capable of realizing a speed response equivalent to that of a slip frequency vector control method without using a speed detector. .. This control method is called a speed sensorless vector control method because there is no speed detector. In the speed sensorless vector control method, the torque current component is obtained from the primary current detection value of the induction motor, and the speed estimation value of the induction motor is calculated based on the torque current command and the torque current component detection value. Then, the speed command value and the speed estimated value are compared to determine the torque current command value, and the primary frequency of the induction motor is controlled by the deviation between the torque current command and the torque current component.

[0003]

In the above speed sensorless vector control method, a speed estimated value is obtained by performing a proportional + integral operation on the deviation between the torque current command and the torque current component detection value, and this speed estimated value is calculated. The output frequency is controlled based on it. Therefore, if the rotation direction of the estimated speed value and the actual rotation direction of the motor are different, the direction of change of the torque current component is opposite to the direction of change of the frequency, and the deviation between the torque current command and the detected value of the torque current component is As a result, the loop that controls the output frequency becomes a positive feedback loop, and there is a problem that the current cannot be controlled stably. In particular, when an excessive load is applied during low speed operation, or when the high speed region is decelerated to an extremely low speed or zero speed, the above-mentioned problem appears remarkably. An object of the present invention is to solve the above problems in speed sensorless vector control and to provide a control device for an induction motor capable of stable speed control in a wide speed range.

[0004]

In order to achieve the object of the present invention, the output frequency is controlled in accordance with the speed estimated value obtained by the proportional plus integral calculation of the deviation between the torque current command and the torque current component. Speed sensorless vector control,
The direction of rotation of the induction motor is obtained from the polarity of the speed command, and when there is a difference between the polarity of the direction of rotation obtained from the polarity of the speed command and the polarity of the direction of rotation output as the speed estimation value, or when the torque current command is the limiting means When there is a difference between the rotation direction polarity obtained from the polarity of the torque current command and the rotation direction polarity output as the speed estimation value, the integral operation of the speed estimation calculation is stopped. .. Further, the estimated speed value is limited to the upper limit value or the lower limit value by the switching circuit having the limiter circuit so as not to become the reverse polarity to the rotation direction polarity obtained from the polarity of the speed command or the polarity of the torque current command.

[0005]

In the speed sensorless vector control in which the output frequency is controlled according to the speed estimated value calculated based on the deviation between the torque current command and the torque current component, during normal operation, that is, in the rotation direction of the speed estimated value, When the rotation directions of the actual electric motor are the same, if the output frequency command is increased, the torque current component also increases. Therefore, the increasing / decreasing direction of the frequency command and the increasing / decreasing direction of the torque current component are the same. However, when an excessive load is applied during low speed operation or when the speed is reduced from the high speed range to the extremely low speed range, a large error transiently occurs between the estimated speed value and the actual speed. That is, since the load torque is excessively large, the actual speed of the electric motor is reduced and a large torque current component flows. Therefore, the estimated speed value may be further reduced and may be reduced to more than the actual speed.
If the polarity of the estimated speed value is opposite to the direction of rotation of the actual speed, the direction of change of the torque current becomes opposite to the direction of change of the output frequency, and a positive feedback loop that the output frequency command further increases is configured. The current cannot be controlled, and problems such as overcurrent occur. Therefore, the fact that the actual rotation direction and the rotation direction of the speed estimation value are different is detected from the polarity change of the speed estimation value, and the integration operation for calculating the speed estimation value is stopped. Further, the estimated speed value is limited to the upper limit value or the lower limit value so as not to have a polarity opposite to the actual rotation direction polarity. In this way, the loop that controls the output frequency is prevented from becoming a positive feedback loop, and control is continued stably without causing problems such as overcurrent.

[0006]

FIG. 1 shows an embodiment of the present invention. In the figure, a PWM inverter 1 converts a DC voltage from a DC power supply into an AC output having a variable voltage and a variable frequency, and this AC output is supplied to the induction motor 2. The primary current of the induction motor 2 is detected by the current detectors 3U, 3V, 3W provided at the output end of the PWM inverter 1, and the current vector component detector 4 produces a torque current component Iq and an exciting current component Id, respectively. Separately detected. Torque current component I
Using q as a feedback signal, the deviation between this feedback signal and the torque current command signal It * is input to the speed estimation calculator 8 and the estimated speed value ω⌒r is output. On the other hand, the estimated speed value ω⌒r is used as a feedback signal, and this feedback signal and the speed command ωr * from the speed command circuit 5 are used.
The deviation of the above is input to the speed control circuit 6, and a signal obtained by limiting the output signal of the speed control circuit 6 by the limiting circuit 7 is output as the torque current command signal It *. Primary frequency command ω ₁
* Is obtained by adding the torque current command It * as an input and adding the slip frequency command ωs * calculated in the slip frequency calculation circuit 10 and the output of the speed estimation calculator 8 described above. Output signal Im from excitation current command 12
Based on *, the torque current command It *, and the primary frequency command ω ₁ *, the voltage command calculation circuit 13 outputs d, q-axis component voltage command V
d *, Vq * are output, and the Vd *, Vq * and the output signal of the two-phase sine wave generator 11 are input, and a three-phase AC voltage command is output from the AC voltage command calculation circuit 14 to generate the AC voltage command. The AC voltage corresponding to is output from the PWM inverter 1 via the PWM pulse generation circuit 15.

The circuit configuration described above is a circuit configuration known as a conventional speed sensorless vector control system. A feature of the present invention is that the switching circuit 16 limits the estimated speed value ω⌒r which is the output of the speed estimation calculator 8 in the above-described circuit configuration.

FIG. 2 shows a detailed circuit configuration of the speed estimation calculator 8 and the switching circuit 16 which are features of the present invention. In FIG. 2, the speed estimation calculator 8 includes a proportional calculation circuit 21 having a proportional gain KP and an integral calculation circuit 2 having an integral time constant TI.
2 and the switching circuit 16 includes a limiter circuit 2
3, circuit changeover switch elements SW30, 31, 32 for switching circuits by a switching signal, a comparator 24 for discriminating the polarity of the speed command ωr *, and a comparator 25 for discriminating the polarity of the output of the speed estimation calculator 8. , EOR logic circuit 26 and signal inversion circuit 27. Conventionally, the output of the speed estimation calculator 8 is directly output as the speed estimation value ω⌒r, whereas in the present invention, the speed estimation calculator 8 is output.
The limiter circuit 23 is added to the output of the
While switching the upper and lower limit values of SW30, 31,
The output of the integration calculation circuit 22 is switched by the SW 32 to stop the integration operation.

The circuit operation of FIG. 2 will be described with reference to the table of FIG. For example, when the induction motor 2 is rotating in the forward rotation direction, the speed command ωr * has a positive polarity and the comparator 24
Is ON, and when the polarity of the output of the speed estimation calculator 8 is + polarity in the same direction, the output of the comparator 25 is ON.
However, SW30 is OFF, and SW31 and SW32 are ON. In this state, the addition signal of the proportional calculation circuit 21 and the integral calculation circuit 22 is output as the speed estimated value ω⌒r with the + polarity via the limiter circuit 23. In the above operating state, when the proportional + integral calculation output of the speed estimation calculation has a negative polarity due to load fluctuation, rapid deceleration operation, etc., the output of the comparator 25 turns off and the SW 32 turns off. As a result, the estimated speed value ω⌒r is limited to the lower limit limiter value of the limiter circuit 23, "0" is output, and the integration circuit operation is stopped.
Further, when the induction motor 2 is rotated in the reverse direction, the speed command ωr * has a negative polarity. At this time, if the proportional + integral calculation output of the speed estimation calculation has a negative polarity, SW30, SW3
2 is ON and SW31 is OFF. In this state,
The proportional + integral operation output is output via the limiter circuit 23 as the speed estimated value ω⌒r with a negative polarity. In this state, when the proportional + integral calculation output has a polarity opposite to that of the speed command ωr * due to load fluctuation, rapid deceleration operation, etc., the SW32 is turned off. As a result, the estimated speed value ω⌒r is calculated by the limiter circuit 23.
Is limited to the upper limit value of 0, '0' is output, and the integration circuit operation is stopped.

The operation of the conventional control system and the control system of the present invention will be described with reference to FIGS. 4 and 5, taking as an example the case where an excessive load disturbance is applied in the low speed region, which has been a problem of the conventional control system. To do.

FIG. 4 shows an operation time chart when an excessive load is applied during low speed operation by the conventional control method. When the load is applied at time t ₀ and the load torque increases, in the speed sensor-less vector control, in the control configuration diagram of FIG. 1, (1) an increase in the torque current component Iq is first detected, and (2) ) Speed estimation calculator 8
The estimated speed value ω⌒r, which is the output of the above, decreases, (3) the speed control circuit 6 operates and the output torque current command It * increases, and (4) the vector output increases the motor output torque. Now, at time t ₁ , when the torque current command It * is limited to the limiter value by the limiting circuit 7, the load torque is excessive, the actual speed of the motor further decreases, and the torque current component Iq increases. Estimated flow and velocity ω⌒r
Is further reduced. At this time, the estimated speed value ω⌒r may decrease more than the actual speed. Estimated speed value ω at time t ₂
When the polarity of ⌒r is reversed, the estimated speed ω⌒r becomes the reverse polarity with respect to the actual speed. In such a state, the direction of change in torque current is opposite to the direction of change in output frequency ω ₁ , the frequency control loop becomes a positive feedback loop, overcurrent occurs, and stable operation continues. There is a problem that you cannot do it.

The present invention has been made to solve the above problems. FIG. 5 shows the operation when the present invention is applied.
The operation time chart will be described. Similar to FIG. 4, FIG. 5 shows the operation when an excessive load is applied during low speed operation. The operation from time t _{0 to} t ₂ is the same as the above-described conventional control method, and the description thereof is omitted. Now, at time t _2, the proportional plus integral operation output estimated speed calculator 8 shown in FIG. 2 - When the polarity, SW30,32 is OFF, the integration operation of the speed estimation calculation is stopped, the speed estimated value ω⌒ r is'
Limited to 0 '. Therefore, while the frequency control loop does not become the positive feedback loop and the overload is applied (time t _{2 to} t _{3 in} FIG. 5), the induction motor ₂ causes the torque of the limiter value of the limiting circuit 7 to rise. It outputs a torque equivalent to the current and stops. Next, when the load torque applied after time t ₃ falls below the torque current limiter value, the torque current component I
q decreases, the estimated speed value ω⌒r is again + polarized, and the actual speed and estimated speed value ω⌒ by the frequency control loop.
r can be automatically restored to the speed command value and stable operation can be continued.

Although the case where an excessive load disturbance is applied in the low speed region has been described, it goes without saying that the same applies to the case where the high speed region is decelerated to an extremely low speed or zero speed.

In the embodiment described above, the actual rotation direction of the electric motor is obtained from the polarity of the speed command, it is detected that a difference has occurred between the rotation direction of the command and the rotation direction of the speed estimation value, and the speed estimation value is calculated. This is to prevent the loop for controlling the output frequency from becoming a positive feedback loop by limiting the value to “0” and stopping the integration operation for calculating the speed estimation value.
This is a case where the polarity of the speed command is regarded as the actual rotation direction of the electric motor, but as another method, an overload exceeding the limit value of the limiting circuit 7 in FIG. 1 is applied and the torque current command is limited by the limiter. When the polarity of the speed estimation value is reversed in the state where the value is a value, even if it is considered that the rotation direction of the actual speed and the rotation direction of the speed estimation value are different, the same function as described above is exerted. In this case, the speed command ωr in FIG.
The limiter value of the torque current command I * may be used instead of *.

[0015]

According to the present invention, stable operation can be performed against severe operation, such as when an excessive load disturbance is applied in the low speed region, or when the high speed region is decelerated to an extremely low speed or zero speed. You can continue. Therefore, the speed control range in the speed sensor-less vector control can be substantially expanded. Since the speed control range is expanded, the merit of speed sensor-less is further expanded, so that the speed control range can be applied to a wide variety of uses. Furthermore, since it is possible to output torque according to the torque current command from the initial stage of startup, it is not necessary to give a margin to the inverter capacity, the minimum inverter capacity can be selected, and the economic effect is significantly improved. To improve.

[Brief description of drawings]

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

FIG. 2 is a detailed circuit of a characteristic part of the present invention in the circuit configuration of FIG.

FIG. 3 is a diagram for explaining the circuit operation of FIG.

FIG. 4 is a diagram for explaining the operation of the device in the conventional control method.

FIG. 5 is a diagram for explaining the operation of the present invention.

[Explanation of symbols]

 1 PWM Inverter 2 Induction Motor 4 Current Vector Component Detector 6 Speed Control Circuit 7 Limiting Circuit 8 Speed Estimation Calculator 11 Two-Phase Sine Wave Generator 13 Voltage Command Calculation Circuit 14 AC Voltage Command Calculation Circuit 16 Switching Circuit 21 Proportional Calculation Circuit 22 Integral arithmetic circuit 23 Limiter circuit 24, 25 Comparator 26 EOR logic circuit 30, 31, 32 Circuit changeover switch element (SW)

Claims (4)

[Claims] 1. A frequency converter that outputs a variable voltage / variable frequency alternating current, an induction motor driven by the frequency converter, and a torque current of a primary current supplied from the frequency converter to the induction motor. Current detection means for detecting a component, speed estimation calculation means for calculating a speed estimated value of the induction motor proportionally and integrally based on a deviation between the torque current command and the detected value of the torque current component, speed command value and the speed estimation A speed control means for comparing the values and outputting the torque current command; and a speed control device for controlling the output frequency of the frequency converter by a frequency command obtained from the speed estimated value and the torque current command. When there is a difference between the rotation direction polarity obtained from the command polarity and the rotation direction polarity output as the speed estimation value, the integration operation of the speed estimation calculation is stopped. A control device for an induction motor, which is characterized by: 2. The speed control device according to claim 1,
Limiting means for limiting the torque current command is provided at the output of the speed control means, and in the state where the torque current command is the limit value of the limiting means, the rotation direction polarity obtained from the polarity of the torque current command and A control device for an induction motor, characterized in that, when a difference occurs in the polarity in the rotation direction output as the speed estimated value, the integral operation of the speed estimation calculation is stopped. 3. The estimated speed value is limited to an upper limit value or a lower limit value by a switching circuit having a limiter circuit, and does not have a polarity opposite to the rotation direction polarity obtained from the polarity of the speed command or the polarity of the torque current command. The control device for an induction motor according to claim 1 or 2, characterized in that. 4. The switching circuit includes a comparator that determines the polarity of the speed command, a circuit switch that switches the limiter circuit to an upper limit value or a lower limit value based on the output of the comparator, and a polarity of the speed estimation calculation value. 4. The control device for an induction motor according to claim 3, further comprising a comparator for judging and a circuit changeover switch for stopping the integration operation based on the outputs of both comparators.