JPS58103896A - Control system for induction motor - Google Patents

Abstract

PURPOSE:To accelerate the rise of a current when the frequency varies by providing a differentiation compensating circuit which inputs a frequency instruction value at the voltage/frequency constant controller of an induction motor having a frequency regulating loop. CONSTITUTION:A differentiation compensating circuit 20 is provided at the front stage of a voltage regulator which regulates so that the output voltage of an inverter 2 which energizes an induction motor 3 matches the frequency command voltage. This circuit 20 receives the outputs of an adder 31, thereby increasing the input amount of a voltage regulator 10. Even if the deviation between the set value of a terminal voltage and the detected value is small at the frequency varying time, the input of the regulator 10 can be increased by the output of the circuit 20, thereby rapidly increasing the set current value, with the result that the rise of the actual current value can be accelerated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method for an induction motor using a current source inverter, particularly a control method in which the terminal voltage of the motor is controlled in proportion to the applied frequency (hereinafter referred to as V/F). (Also called constant control method.)

11i1 is a configuration diagram showing the basic configuration of the constant V/F control method.

jlE1 In the diagram, 1 is the converter section, 24-1-7
Butter part, 3 is an induction motor (IM), 4 is a current smoothing reactor, 5 is a current detector, 6 is a voltage detector, 7, 13
is a rectifier, 8 is a phase shifter, 9 is a current regulator (ACR), 1
11 is a pulse distributor, 12 is a voltage/frequency (V/F) oscillator, 14 is an acceleration/deceleration calculator, 15 is a frequency setter, 16 is a magnetic flux detector, 1
7 is a magnetic flux adjuster, 18 is a polarity switch, 19 is a magnetic flux setter, and 31 to 34 are adders.

The three-phase terminal voltage of the induction machine IM detected by the voltage detection lI6 is guided to the rectifier 13 on the one hand and used to calculate the magnitude of the terminal voltage, and on the other hand, the magnetic flux calculation consisting of an integrator and a rectifier @ 16 and is used to calculate the magnitude of the magnetic flux. When calculating magnetic flux from voltage, various methods have been known, such as a method that performs compensation using current and a method that does not perform compensation, but the magnetic flux calculator 16 shown here can be used to can also be used. Further, the magnitude of the terminal voltage detected by the rectifier @13 is led to the adder 32 and compared with the voltage setting value,
Its output is directed to a voltage regulator (AVR) 10. The output of voltage regulator lO becomes the current setting value, which is added to adder 3.
3, the magnitude of the current detected by the current detector 5 and the rectifier 7 is compared, and its output is connected to the current regulator (
ACR) 9. The output of the current regulator 9 is the phase shifter 8
The phase shifter 8 outputs a control signal for the converter section l. The output of the frequency setter 15 is sent to the acceleration/deceleration calculator 14.
to one of the addition inputs of the adder 31. The output of the adder 31 is, on the one hand, the set value of the voltage mentioned above, and on the other hand, the output of the V/F oscillator 12 as the frequency command value.
is guided by the input. The output of the V/F oscillator is guided to a pulse distributor 11, and this pulse distributor 11 is connected to an inverter section 2.
outputs a control signal. The output of the magnetic flux calculator 16 becomes a magnetic flux detection value, which is led to an adder 34 and compared with the magnetic flux set value given by the magnetic flux setting device 19, and its output is led to the magnetic flux adjuster 17. The magnetic flux regulator 17 is a one-way FL regulator that outputs a signal of the same polarity as the magnetic flux setting value (or a signal of opposite polarity depending on the configuration) when the actual value of the magnetic flux becomes smaller than the set value. 1. The output of the magnetic flux regulator 17 is guided to the polarity switch 18, and the switch 518 switches the output of the regulator 17 to the same polarity during driving and to the regulator 17 during braking.
The output of the adder 31 is outputted with the opposite polarity. Note that the polarity of the current regulator 90 can be used, for example, as the driving or braking determination signal used by the polarity switch 18, but other methods may be used as long as the desired torque direction can be determined. . In this way, the applied frequency is automatically adjusted so that the detected magnetic flux value does not become smaller than the set value, and therefore the deviation between the set value and the actual voltage value is kept small.

This type of control method is simple and can be configured at low cost, so it has traditionally been used only in cases where strict control characteristics are not required, and it is used to provide quick response to sudden changes in load or set frequency. It could not be applied when one requirement is required. One of the reasons for this is that the large integral constant of the voltage regulator 10 suppresses the rapid rise of the current, so the induction machine is unable to respond quickly and the slip becomes too thick (too much, reducing the magnetic flux of the induction machine). This is because a tax adjustment occurs, but such a tax adjustment can be prevented by a frequency adjustment loop that acts to keep the magnetic flux constant, as shown by the dashed line in Section IV!J.However, if this frequency adjustment loop is provided, As a result, the ratio between the actual value of the terminal voltage and the applied frequency is suppressed within a certain range with respect to the set value of the ratio between the set terminal voltage and the applied frequency. The deviation from the current value is always adjusted to be small, but because the time constant of the voltage regulator 10 is large, the increase in the current command value is slow, and therefore the rise of the actual current value is also slow, which causes transient fluctuations in speed when the load suddenly changes. It has the disadvantage of being large.

This invention was made in view of the above, and is based on the V/F of an induction motor.
It is an object of the present invention to suppress transient fluctuations when a sudden load changes and to improve speed responsiveness of a frequency command value to perform stable operation when constant control is performed.

The feature of this invention is that the ratio (V/P) between the applied frequency (F) and the terminal voltage (V) of the induction motor is controlled to be constant, and when the V/F relationship exceeds a predetermined value, In an induction motor control method that detects the motor magnetic flux and corrects the frequency command value so that the value of V/F becomes a predetermined value, the differential absolute value of the amount corresponding to the modified frequency command is A differential compensation circuit that calculates the value is provided, and when the frequency changes, the output is added to the input of the voltage regulator or current regulator, thereby temporarily increasing the input of the voltage regulator or current regulator, and changing the actual current value. The point is that it has a faster rise.

Embodiments of the present invention will be described below with reference to the drawings.

Figure 2 is a block diagram showing an embodiment of the present invention.

As is clear from the figure, this embodiment is different from the conventional example shown in FIG. 1 in that a differential compensation circuit 20 is provided at the front stage of the voltage regulator (AVR) 10. The differential compensation circuit 20 receives the output of the adder 31 and increases the amount of input to the voltage connecter lO. By doing so, when the frequency fluctuates, even if the deviation between the set value and the detected value of the terminal voltage is small, the input of the voltage regulator 10 can be increased by the output of the differential compensation circuit 20, and therefore the output That is, the current setting value can be quickly increased, and as a result, the rise 9 of the actual current value can be accelerated.

Figure 3 is a diagram showing the main part of an embodiment of the present invention.
2, but is led to the adder 33, and the current regulator 9
By increasing the set value of , the output, ie, the actual operating value, is increased.

FIG. 4 is a block diagram of main parts showing still another embodiment of the present invention.

In this example, the input of the differential compensation circuit 20 is derived from the output of the polarity switch 18. Therefore, in this case, there is no effect on changes in frequency determination, but the above-mentioned Nyodate frequency li! When the regular loop works, the same effect as shown in Fig. 92 can be obtained.

No.! swJ is a circuit diagram showing the configuration of a differential compensation circuit used in Figures -2 to -4.

In the figure, N1-N3 are operational amplifiers, CI is an amplifier, R1-R7 are resistors, and Dl is a diode.

A frequency command voltage is led to the terminal 201, and the calculation amplification aN
1. It is differentially amplified by the capacitor C1 and the resistors R, 1, and R2, and rectified by the subsequent circuit.

Here, the resistances are selected so that R3==R4 and R6=2R5. Therefore, even if the input 201 fluctuates in either the positive or negative direction, a further rectified value (absolute value of the input differential value) of the input differential value is obtained at the output 202, and the voltage is determined by the differential absolute value. The input of the regulator (AVR) or current regulator (ACR) can be temporarily increased to hasten the rise of the actual current value.

As described above, according to the present invention, a differential compensation circuit that inputs a frequency command value is provided in a voltage/frequency (V/F) constant control device for an induction motor having a frequency adjustment loop, and the current when the frequency a changes is Since the rise of the speed is accelerated, when the magnetic flux regulator is activated and frequency 1111 is performed when the load suddenly changes, excessive fluctuations in the speed can be reduced, so the speed can be quickly brought to the normal value. It also has the advantage of providing a fast speed response because the current rises quickly during acceleration/deceleration control.

[Brief explanation of the drawing]

1 Wi is a block diagram showing a conventional example of the induction motor □ V/F constant control system, FIG. 2 is a block diagram showing an embodiment of the present invention,
FIG. 3 is a main part configuration diagram showing another embodiment of the invention, and FIG. 4 shows still another embodiment of the invention. FIG. 5 is a circuit diagram showing a differential compensation circuit according to the present invention. Symbol explanation: 1: Converter section, 2: Inverter section, 3: - Exclusive, 4: Current smoothing reactor, Tor...・Current detector, 6...
...voltage detector, 7. ．． 1B... Rectifier, 8.
... Phase shifter, 9 ... Current regulator, 1G.
...Voltage regulator, 11...Pulse distributor, 12...Voltage/frequency oscillator, 14...
...Acceleration/deceleration calculator, l...Frequency setting device, 16
...Magnetic flux detector, 17...Magnetic flux regulator, 18...Polarity switch, 19...Magnetic flux setting device, 2G... Differential compensation circuit, 31-34・
... Adder, N1 to N3 ... Arithmetic amplifier, CI ... Capacitor, Kl to R - ...
Resistance, Dl...Diode agent Kiyoshi Matsuzaki, patent attorney

Claims (1)

[Claims] A voltage regulator that is composed of a forward and an inverse converter and adjusts the output voltage of the inverter supplied to the induction motor so as to spread it out with the frequency command voltage, and a voltage regulator that adjusts the output current of the inverter based on the voltage adjustment output. forward converter control means having a current regulator and controlling the phase of the forward converter based on the adjustment output; and inverse converter control means controlling the frequency of the inverse converter based on the frequency command voltage. , a frequency control loop that corrects the frequency command voltage value so that the magnetic flux detection value calculated from the terminal voltage of the motor becomes a predetermined value, In the V/F constant control method of an induction motor, which controls the ratio (V/F) to the voltage (V) to a predetermined value,
Provided with a differential compensation means for outputting a differential absolute value of an amount according to the frequency command value corrected by the frequency control loop,
When the motor frequency suddenly changes, the output of the cough compensation means is applied to the voltage regulator or the current regulator, thereby temporarily increasing the input to the voltage regulator or current regulator, thereby accelerating the rise of the actual current value. A control method for an induction motor characterized by the following.