JPS61189180A - Speed controller of ac motor - Google Patents

Abstract

PURPOSE:To compose a speed controller having high phase resolution with less number and inexpensive parts by converting the output of a differential amplifier into a sinusoidal wave, and sampling it with the detected output of a rotor position. CONSTITUTION:A reverse voltage in polarity to the output of a differential amplifier 9 which differentiates and amplifies a speed command output and a speed detection output is formed by a reverse phase amplifier 10, and the output signal of the amplifier 10 and the output of the original amplifier 9 are converted to rectangular waves of the same frequency as a reference rectan gular wave with zero V as a center. This rectangular wave is converted through a filter 12 into a sinusoidal wave, which is sampled and held by a sample- holding circuit 13 at the rise of the output of a resolver 5. As a result, the output waveform of the circuit 13 becomes a sinusoidal waveform proportional to the rotating speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a speed control device for an AC motor that uses a resolver phase shifter to create a current command and control the AC motor.

[Conventional technology]

FIG. 2 is a block diagram showing a conventional speed control device,
In the figure, 1 is a speed command device that gives a speed command as a reference for the rotation speed of the motor, 2 is an AC motor, 3 is a power amplifier for passing current through the AC motor 2, and 4 is the rotation speed of the AC motor 2. A speed detector (hereinafter referred to as TG) that outputs a voltage proportional to
), 5 is a resolver phase shifter (hereinafter referred to as resolver) for detecting the position of the rotor of the AC motor 2, 6 is a resolver exciter for exciting the resolver phase shifter 5, and 7 is a resolver excitation device. 8 is a waveform shaping circuit for converting the output of the resolver phase shifter 5 into a pulse; 21 is a rising pulse generator that outputs a pulse at the rise of the reference square wave; 22 is a phase difference counter for counting the time difference (phase difference) between the output of the waveform shaping circuit 8 and the output of the rising pulse generation circuit 21 in binary numbers; 23 is a phase difference counter that converts the binary output of the phase difference counter into the rotation speed; A function generator 24 converts the count number into a sine wave with a proportional frequency; 24 a digital/digital converter 24 converting the output of the function generator 23 from a binary number to an analog voltage signal
An analog (hereinafter referred to as D/A) converter 25 is a multiplier for multiplying the output of the differential amplifier 9 and the output of the D/A converter 24.

Next, the operation will be explained with reference to the time chart shown in FIG. The differential amplifier 9 compares the speed command of the speed command device 1 and the output of T0n, and outputs an output so that the difference becomes zero.

The output and the output of the D/A converter 24 are multiplied by a multiplier 25, and the output of the multiplier 25 is amplified in power by a power amplifier 3 and supplied to the AC motor 2.

In the above, as the output voltage of the speed command device 1 increases, the difference with the output voltage of T0n increases, and the AC motor 2
The current flowing through the motor increases and the rotational speed increases. the result,
The output of T0n also increases, the difference with the speed command becomes smaller, and the AC motor 2 is controlled in a certain balanced state.
will rotate. At this time, the current flowing through the AC motor 2 is a sine wave, and its instantaneous value must be synchronized with the position of the rotor of the AC motor 2.

A method for synchronizing them will be explained below. The phase difference between the output of the resolver 5 attached to the AC motor 2 and the output of the reference square wave generator 7 is synchronized with the rotor position of the AC motor 2, and the phase difference between a and b in FIG. If a pulse is generated in this way and its time width is counted by the phase difference counter 22, the value will be a binary number like C in FIG. 3 while rotating, and it will remain stopped at a certain constant value while stopped.

Therefore, the current position of the rotor of the AC motor 2 can be determined from the counted number.

Next, the count output is sent to the function generator 23 as d in FIG.
The signal is converted into a count number of a sine wave-like value such as , and the signal is converted into an analog voltage by the D/A converter 24.

The output of the differential amplifier 9 is proportional to the peak value of the current flowing through the AC motor 2, and the output of the D/A converter 24 has a constant peak and is synchronized with the rotation of the AC motor 2. By multiplying by 25, a signal proportional to the current flowing through the AC motor 2 can be created. Thereafter, the output of the multiplier 25 is amplified by the power amplifier 3 to supply current to the AC motor 2, thereby controlling the rotation speed. As described above, the AC motor 2 can be controlled by the speed command from the speed command device 1.

[Problem that the invention seeks to solve]

Conventional AC motor speed control devices are configured as described above, so there is a large number of parts because analog signals are digitally controlled, phase resolution is limited because it is counted in binary numbers, and 1) /A conversion. There were problems such as the need for expensive parts such as a function generator and a function generator.

This invention was made to solve the above-mentioned problems, and aims to provide a speed control device that can improve phase resolution, reduce the number of parts, and use inexpensive parts.

[Means for solving problems]

The speed control device for an AC motor according to the invention converts the output of a differential amplifier that differentially amplifies the speed command output of the AC motor and the speed detection output of the AC motor into an AC voltage having the same frequency as a reference signal, The input signal of the power amplifier is created by sampling and holding this AC voltage at the rising edge of the output of the resolver phase shifter that detects the rotor position of the AC motor.

[Effect]

The sample hold in this invention converts the output of the differential amplifier, which has been converted into a sinusoidal AC voltage with a constant period, into an AC signal with the same period that is proportional to the current of the AC motor.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1, in which the same parts as in FIG. 2 are denoted by the same reference numerals.

In FIG. 1, 10 is an anti-phase amplifier for inverting the polarity of the output of the differential amplifier 9, and 11 is a reference rectangular wave high (Hl) that connects the output of the anti-phase amplifier 10 and the output of the differential amplifier 9.
gh ) and low (LOW), and 12 is a filter for changing the output rectangular wave of the changeover switch 11 into a sine wave. It consists of

13 is the output of the filter 12, that is, the signal conversion circuit 14
This is a sample hold for sampling the output of the resolver 5 at the rising edge of the output of the resolver 5, that is, the output of the waveform shaping circuit 8.

Next, the operation of the parts different from the conventional example shown in FIG. 2 will be explained. A voltage with a polarity opposite to that of the output of the differential amplifier 9 is generated by an anti-phase amplifier 10, and the output signal of the anti-phase amplifier 10 and the output of the original differential amplifier 9 are set to zero (v) using a changeover switch 11. ) is converted into a rectangular wave with the same frequency as the reference rectangular wave. This rectangular wave is passed through the filter 12 to the third filter.
It is converted into a sine wave as shown in e in the figure, and this sine wave is sampled at the sample hold 13 at the rising edge of the output of the resolver 5.

As a result, the output waveform of the sample hold 13 becomes a sinusoidal waveform proportional to the rotational speed as shown in g in FIG. −
When you look at it, it seems to be the same waveform as d in Figure 3 of the conventional example, but
In reality, the voltage resolution is 1/ω at g in FIG. 3, whereas in the conventional example, it is determined by the number of binary bits.

Then, the signal as shown in Fig. 3g is sent to the power amplifier 3.
The output of the power amplifier 3 is amplified by the AC motor 2.
is supplied to rotate the AC motor 2.

In the above embodiment, the sine wave obtained by switching the output of the differential amplifier 9 with the reference rectangular wave generator 7 was sampled at the rise of the output of the resolver 5, but conversely, the output of the resolver 5 was sampled as a rectangular wave. It is also possible to switch the output of the differential amplifier 9 using the converted signal and sample at the rising edge of the reference rectangular wave. Furthermore, the same sine wave can be created by multiplying the output of the resolver 5 and the output of the differential amplifier 9. - [Effects of the Invention] As described above, according to the present invention, the output of the differential amplifier 9 which differentially amplifies the speed command output and the speed detection output of the AC motor is converted into a sine wave by the signal conversion circuit, Since this sine wave is sampled using the detection output of the rotor position of the AC motor to create a current command for the AC motor, the effect is that a speed control device with high phase resolution can be constructed with a small number of inexpensive parts. There is.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a speed control device for an AC motor according to an embodiment of the present invention, FIG. 2 is a block diagram showing a conventional speed control device for an AC motor, and FIG. 3 explains the operation of the device. FIG. 1 is a speed command device, 2 is an AC motor, 4 is a speed detector, 5
1 is a resolver phase shifter, 9 is a differential amplifier, 13 is a sample hold, and 14 is a signal conversion circuit. In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A speed command device that provides a speed command as a reference for the rotation speed of the AC motor, a speed detector that outputs a voltage proportional to the rotation speed of the AC motor, and a command output of the speed command device and detection of the speed detector. a differential amplifier that differentially amplifies the output;
A signal conversion circuit that converts the output of the differential amplifier into an AC voltage with the same frequency as the reference signal, a resolver phase shifter that detects the rotor position of the AC motor, and samples the AC voltage using the output of the resolver phase shifter. and a sample hold for creating a current command for the AC motor.