JPH01259786A - Frequency controller - Google Patents

Abstract

PURPOSE:To obtain stable control performance, a characteristic error of which is reduced, by changing frequency control into digital control. CONSTITUTION:The number of revolution of an induction machine 2 ls detected by a pulse detector (PLG) 10. A digital slip control circuit 12 composed of a micro-computer circuit receives a setter command from a digital frequency setter 11 for setting the rotational speed of the induction machine 2 and a revolution signal from the pulse detector 10 and comparison-operates the setter command and the revolution signal, and forms a frequency command for controlling a power converter 1. A pulse converter 13 converts an output signal from the digital slip control circuit 12 into the pulses of frequency corresponding to the output signal, and outputs the pulses to a frequency signal forming circuit 8.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) This invention relates to frequency control of a drive device for variable speed operation of an induction motor using a power converter.

[Conventional technology]

FIG. 4 is a block diagram of a conventional control circuit.

In the figure, (1) is a power converter that manually inputs a commercial power supply with a frequency of 50 or 80 Hz and outputs a variable frequency of your choice, (2) is an induction machine connected to this power converter (1) and driven to rotate, (3) is a finger speed generator to detect the rotation speed of the induction motor (2), (4) is a speed setting device to set the rotation speed of the induction motor (2), and (5) is a finger speed generator. (6) is a slip controller for receiving the signal from the machine (3) and No. 43 from the speed setting device (4) to compare and control the rotation speed and the speed setting value, (6) is this slip controller (5) Signal from and finger speed generator (3)
(7) is an adder that receives a signal from the adder and performs an addition operation; (7) is a converter that receives a signal about the calculated value from (6) and converts an analog voltage into a frequency signal; (8) is a converter (7) A frequency signal generation circuit that generates a frequency signal for the power converter (1) according to the number of cabals output from the circuit. (1) This is a signal generation circuit for a power converter that generates a control signal to be applied.

In the conventional control circuit configured as described above, the speed command set by the speed setting device (4) and the finger speed generator (3)
) is compared with the rotational speed signal by the slip controller (5) and fed to the adder (6). This adder (6)
Now let's look at the output of the slip controller (5) and the finger speed generator.
A frequency command is generated by adding and subtracting the rotation speed signal from (3). The output signal of the adder (6) is applied to the converter (7), which converts the analog signal into a pulsed digital signal to generate a clock pulse. Frequency signal generation circuit
(8) generates a frequency signal for the power converter (1) corresponding to the output frequency of the converter (7), and the power converter (1)
Signal generation circuit for power converter (9)
The output frequency of the power converter (1) is controlled by changing the output frequency of the power converter (1).

[Problem to be solved by the invention]

However, in the conventional analog frequency control circuit as described above, due to the nonlinearity of the output voltage with respect to the rotation speed of the finger speed generator (1) and the nonlinearity of the analog adder,
In addition to unstable control, the slip of the induction motor (2) is generally about 1% at rated load, and the slip of the induction motor (3) is generally about 1% at rated load.
) has a problem in that characteristic errors have a large impact on control characteristics.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a frequency control circuit that uses digital control for frequency control and has stable control performance with few characteristic errors.

[Means to solve the problem]

The frequency control circuit according to the present invention is a frequency control circuit that controls an induction machine driven by a power converter, in which a pulse detector detects the rotation speed of the induction machine and outputs a pulse signal, and a digital frequency setter detects the rotation speed of the induction machine and outputs a pulse signal. The rotation speed of the induction machine is set by the
Each signal from the digital frequency setter and pulse detector is received and compared and calculated to generate a frequency command for controlling the power converter.

[Effect]

This invention digitally detects the rotational speed of the induction machine using a pulse detector (PLO), and performs digital calculations using a slip control circuit composed of a microcomputer circuit. It is possible to eliminate changes in characteristics due to temperature changes and temperature changes in the analog control circuit, thereby achieving stable control characteristics.

(Embodiment) The frequency control circuit according to the present invention replaces the conventional finger speed generator with digital detection using a pulse detector.
In addition, the frequency setting device is also a digital setting device, and a slip control circuit using a microcomputer performs calculations to generate a frequency control signal to be applied to the power converter, thereby obtaining stable control characteristics with few errors. It is characterized by the fact that

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, power converter (1), ! Conductor (2), frequency signal generation circuit (8), signal generation circuit for power converter
(9) is the same as the conventional control circuit described above. In the figure, (lO) is a pulse detector (PLO) that detects the rotation speed of the induction machine (2) and outputs a pulse signal, (11)
is a digital frequency setter for setting the rotation speed of the induction machine (2), and (12) is a digital frequency setter that receives the setter command from this digital frequency setter (11) and the rotation speed signal from the pulse detector. A digital slip control circuit (13) that performs comparison calculations and generates a frequency command for controlling the power converter (1) is a digital slip control circuit (12).
This is a pulse converter that converts the output signal from the converter into a pulse with a frequency corresponding to this signal and outputs the pulse to the frequency signal generating circuit (8).

FIG. 2 shows the internal configuration of the digital slip control circuit (12) and the pulse converter (13), and (14)
is a digital input circuit for receiving the set value set and outputted by the digital frequency setter (11) and reading it into the microcomputer circuit of the arithmetic unit (15). The arithmetic unit (15) is connected to the digital input circuit (1
4) and a pulse signal from the pulse detector (lO), performs calculations, and outputs the calculation results to the pulse converter (13). It is composed of a microcomputer and a memory circuit. has been done. The digital slip control circuit (12) is composed of a digital input circuit (14) and an arithmetic unit (15). Further, the pulse converter (13) divides the frequency of the oscillator (16) according to instructions from an oscillator (16) that supplies a fixed frequency to a frequency divider (17), which will be described later, and the arithmetic unit (15). and a frequency divider (17) that generates a corresponding frequency.

Then, the pulse detector (10) supplies a pulse with a frequency corresponding to the rotation speed of the induction machine (2) to the arithmetic unit (15) as an interrupt signal. Then, as shown in Figure 3,
When the arithmetic unit (15) receives an interrupt from the pulse detector (lO) (step 20.27), it calculates the time between interrupt signals and detects the pulse! (10) The time between the pulses is measured (step 28). Using this time, the rotation speed of the induction machine (2) is calculated (step 29), and the time counter is reset (step 3).
0), returns (step 31). Further, following step 20, the input value from the digital frequency setter (11) is sent to the arithmetic unit (
15) (step 21).

Next, the arithmetic unit (15) compares the read frequency setting value and the rotation speed of the induction machine (2), and compares the set value and the rotation speed so that they match. Perform r4 calculation (step 22), when the rotation speed is large, issue a frequency reduction command (step 23), when the rotation speed is small, issue a frequency increase command (step 24), and when the values are the same, issue a command to the effect that the values are the same. A frequency command is generated and the command is output to the frequency divider (17) (step 25). Then the frequency divider (17)
Then, this signal is output to the frequency signal generation circuit (8) as a pulse signal of a frequency corresponding to the frequency command calculated by the arithmetic unit (15). Note that the control is terminated by stopping the induction machine (2), and when the operation is to be continued, the process returns to step 20 (step 26).

Therefore, as described above, in a device that drives an induction machine using a power converter, the present invention provides a circuit that controls the frequency of the induction machine by controlling the pulses of a pulse detector directly connected to the induction machine and separately controlling the slip of the induction machine. Equipped with a digital frequency control circuit that digitally adds and subtracts signals from the finger speed generator, the circuit controls the frequency by analog addition and subtraction using the conventional finger speed generator voltage. It is intended to eliminate control instability caused by linearity and nonlinearity of analog circuits.

As mentioned above, the rotation speed is detected by a pulse detector instead of the conventional finger speed generator, the frequency setter is digitalized, and the conventional analog slip controller is configured with a digital calculator, so the finger speed It is possible to eliminate the control instability of conventional methods caused by the nonlinearity of the generator and characteristic changes due to temperature changes in the analog circuit, and to obtain stable control performance.

〔Effect of the invention〕

As described above, according to the present invention, since the frequency control is digitally controlled, it is possible to obtain stable control performance with few characteristic errors.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block diagram showing a part of FIG. 1 in detail, and FIG. 3 is a block diagram showing a part of FIG.
FIG. 4 is a block diagram of a conventional frequency control circuit, and is a diagram corresponding to FIG. 1. (1)...power converter, (2)...induction machine, (lO)...pulse detector, (11)...digital frequency setter, (12)...
・Digital slip control circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] A frequency control circuit that controls an induction machine driven by a power converter includes a pulse detector that detects the rotation speed of the induction machine and outputs a pulse signal, and a digital frequency setter that sets the rotation speed of the induction machine. and a digital slip control circuit that receives each signal from the digital frequency setter and the pulse detector, performs a comparison operation, and generates a frequency command for controlling the power converter. Frequency control circuit.