JPS644436B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method for a squirrel cage induction machine driven by a thyristor converter, and more particularly to a control method for preventing a decrease in the gain of a current control circuit due to induced electromotive force of the motor.

Recently, a control method for induction machines called vector control has been studied. Since this control method can independently control each of the excitation current component and the secondary current component, it is possible to make the speed response performance equivalent to that of a DC machine.

FIG. 1 shows a conventional example to which this control method is applied.

In the figure, 1 is an AC power supply, and 2 is a cycloconverter that generates variable frequency AC. 3 is a squirrel cage induction machine, 4 is a speed generator that detects the rotational speed of the induction machine 3, 5 is a speed command circuit that commands the rotational speed of the induction machine 3, and 6 is the output of the speed command circuit 5 and the speed generator 4. A speed control circuit that operates according to signal deviation.
The output signal becomes a signal that commands the secondary current component of the induction machine 3. 7 is an excitation current command circuit that commands the excitation current component of the induction machine 3; 8 is a slip frequency calculation circuit that calculates the slip frequency of the induction machine 3 in proportion to the output signal of the speed control circuit 6; 9 is a slip frequency calculation circuit 8 and the output signal of the speed generator 4, and an adder 10 that commands the primary frequency of the induction machine 3.
is an oscillator that outputs a sine wave signal (a two-phase signal with a phase difference of 90 degrees from each other) with a frequency proportional to the output signal of the adder 9, and the output signal is
This becomes the position reference signal for the secondary magnetic flux linkage. 11 and 12 are multipliers for multiplying the output signal of the oscillator 10 by the secondary current component commands from the excitation current command circuit 7 and the speed control circuit 6; and 13 is a multiplier for adding the output signals of the multipliers 11 and 12, 3, which commands the primary current, and its output signal is an alternating current sine wave signal which commands the instantaneous value of the primary current. 14 is induction machine 1
A current detector that detects the next current, 15 is an adder 13
16 is an automatic pulse phase shifter that controls the firing phase of the thyristor circuits U _P and U _N in accordance with the output signal of the current control circuit 15; Reference numeral 17 denotes a gate output circuit that alternately supplies a gate signal to _{UP or UN of} the thyristor circuits depending on the positive or negative direction of the output current of the thyristor circuits UP or _UN . Note that the figure only shows the control circuit for the thyristor circuits _UP and _UN , and the other thyristor circuits _VP , _VN , _WP ,
Although the same control circuit is used for _WN , the explanation thereof will be omitted.

This circuit is characterized in that it controls the secondary current component and excitation current component of the induction machine in correspondence with the armature current and field current in the DC machine, respectively. Calculate the instantaneous value command signal of the primary current of the induction machine based on the sine wave magnetic flux reference signal from the secondary current component command signal and the excitation current component command signal, and control the instantaneous value of the primary current according to this signal. do. Controlling in this manner enables highly responsive and accurate torque control.

However, the current control circuit composed of part numbers 14 to 17 has the following problems. That is, the command signal of the current control circuit changes continuously from zero to the rated frequency (16Hz). At this time, the induced electric power of the induction machine is added to the control system as a disturbance, so as the operating frequency becomes higher, the deviation of the feedback signal (primary current) from the command signal becomes larger. This results in a decrease in the gain of the primary current with respect to the current command, making it impossible to cause the primary current to accurately follow the command signal. A possible solution to this problem is to detect the terminal voltage of the induction machine and apply it to the current control circuit. However, this method has a large waveform distortion of the detection signal, so if it is added to the current control circuit, the control signal of the automatic pulse phase shifter will pulsate, the thyristor will not fire properly, and the pulsation of the primary current will increase. There is a problem.

An object of the present invention is to provide a control method that is free from the above-mentioned problems and can prevent a decrease in the gain of a current control circuit.

A feature of the present invention is that the induced power of the induction machine is calculated and determined from the excitation current command, the primary frequency command, and the magnetic flux reference command signal, and is applied as a bias signal to the current control circuit.

FIG. 2 shows an embodiment of the present invention. Part number 1
Items 1 to 17 are the same as those shown in FIG. 18
19 is a multiplier for multiplying the primary frequency command signal of the induction machine 3 and the excitation current command signal, 19 is a multiplier for multiplying the output signal of the oscillator 10 and the output signal of the multiplier 18, and 20 is a multiplier 19 is an adder for adding the output signal of the current control circuit 15 to the output signal of the current control circuit 15.

Next, the operation of the circuit will be described.

The primary angular frequency ω ₁ of the induction machine 3 is determined by adding the slip angular frequency ω _s and the signal ω _r (corresponding to the electrical rotation angular frequency) of the speed detector. Based on the added signal, the oscillator 10 controls the electric motor. Generates a two-phase sine wave signal synchronized with the rotational phase of the magnetic flux. Therefore, a command in phase with the voltage of the induction machine can be detected from the output signal (Asinω ₁ t) of the oscillator 10.
On the other hand, the magnitude of the voltage is proportional to the magnitude of the excitation current command and the primary frequency command. Therefore, by multiplying the above two signals, a signal whose phase matches the induced electromotive force and whose magnitude is proportional to the induced electromotive force is extracted.

By applying this signal to the current control circuit, the decrease in gain of the current control circuit is compensated for in the following manner. That is, since the decrease in the gain of the current control circuit occurs because the induced power of the induction machine is added to the control system as a disturbance, multipliers 18 and 19 detect signals that cancel this disturbance. By adding it to the output signal of the current control circuit 15, the decrease in gain of the current control circuit can be compensated for.

Further, since the signals detected by the multipliers 18 and 19 are obtained by faithfully calculating and detecting the induced electromotive force, gain compensation is performed with high precision.

As described above, according to the present invention, the induced power is calculated faithfully, so that the gain compensation of the current control circuit is performed with high accuracy.

In addition, although the method for calculating the magnitude of the induced electric power from the excitation current command and the primary frequency command was described above, when the slip frequency is small, it can be calculated from the excitation current command and the signal of the speed detector.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional induction motor control device.
FIG. 2 is a configuration diagram showing an embodiment of the present invention.
1...AC power supply, 2...cycloconverter, 3
... Induction machine, 4 ... Speed generator, 5 ... Speed command circuit, 6 ... Speed control circuit, 7 ... Exciting current command circuit, 8 ... Slip frequency calculation circuit, 9 ... Adder, 10 ... ...Oscillator, 11, 12...Multiplier, 1
3... Adder, 14... Current detector, 15... Current control circuit, 16... Automatic pulse phase shifter, 17...
...Gate output circuit.

Claims (1)

[Claims] 1. In a method for controlling an induction machine driven by a converter capable of controlling voltage and frequency,
Current control that calculates induced electromotive force based on a signal proportional to the next frequency and exciting current or magnetic flux, and a signal that is synchronized with the magnetic flux phase of the induction machine, and uses this calculation result to control the output voltage of the converter. A method for controlling an induction machine, characterized by adding the signal to an output signal of a circuit.