JPS60113666A - Controller of pulse width modulation type inverter - Google Patents

Abstract

PURPOSE:To stably operate a pulse width modulation type inverter even if a carrier frequency is increased by correcting an output voltage command in a range that the control range of the inverter is low, and correcting the output frequency command in a high range. CONSTITUTION:The output frequency/voltage command VN of an inverter is inputted to a voltage control amplifier 1 and a voltage/frequency converter 2. The output of the amplifier 1 is used for the output voltage command of an inverter, and the output of the converter 2 is used as the output frequency command of the inverter. A control range discriminator 6 compares a command VN with a reference voltage to discriminate the low and high ranges of the output frequency of the inverter. Analog switches 4A, 5A complementarily become ON state by the output of the discriminator 6, the output voltage range is corrected in the low range of the output frequency of the inverter and the output frequency command is corrected in the high range.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a pulse width modulated (PWM) inverter, in particular an open loop control device.

[Prior art]

In a PWM type inverter, if the frequency of the carrier wave is too high, it will cause unstable operation during acceleration/deceleration, so the fundamental frequency (inverter output frequency) is 30 to 30 times per cycle.
It is often set in a stable region of about 15 pulses. On the other hand, if the carrier frequency is lowered, the current ripple becomes larger, and the problem remains that vibrations occur in the electric motor serving as the inverter load and noise increases. For this reason, countermeasures have traditionally been taken such as increasing the carrier wave frequency to reduce current ripple and incorporating a current minor control system into the control system to suppress the occurrence of unstable regions. The frequency was approximately 100 to 500 pulses, and ripples were not sufficiently reduced. For example, in order to reduce the vibration of the motor to 5 microns or less and the noise to 75 phon or less, it is necessary to increase the carrier frequency to about 2 to 3 pulses, and in this case, even if a current minor control system is provided, it will still be in the unstable region. becomes very large. However, if GD' on the load side is 0.
If it is larger than 5 batatapi, speed fluctuations can be suppressed on the load side, but if it is smaller than that, it becomes unstable and the carrier wave frequency cannot be increased.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a control device that allows stable operation while increasing the carrier wave frequency.

[Summary of the invention]

The present invention corrects the inverter output/voltage command and the output frequency command in proportion to the amount of change in load current, and in the low range of the inverter control range, this correction is made to the output/voltage command, and in the high range, the output frequency command is corrected. It is characterized by an amendment to the directive.

〔Example〕

The drawing is a main circuit diagram showing an embodiment of the present invention. The inverter output frequency/voltage command VN, which is the speed command of the motor as the inverter load, is the operational amplifier AI + AM.
It is input to a pressure control amplifier 1 and a voltage-frequency converter (V/F) 2, which are comprised of the following.

The output of the amplifier 1 is set to the inverter output kick pressure command V, the output of the converter 2 is set to the inverter output frequency command F, and the inverter output is controlled to have a constant V/F, and the output of the carrier wave frequency (not shown) is It is used for PWM control of the inverter main circuit by sub-processing or adjusting the frequency command by converting the voltage command to forward converter control.

In such a control circuit, in this embodiment, the voltage command 79 and the frequency command F are corrected in proportion to the amount of change in load-flow by the correction circuit shown below.

The diode 3 rectifies the load/torque current detection signal and takes it out as a unipolarity signal. Differentiator circuits 4 and 5 are diode 3
The differential circuit 4 obtains a differential signal of the detection signal, that is, a signal proportional to the rate of change.
F is obtained, and the differentiating circuit 5 obtains a correction signal ΔV of the voltage command V. These differentiating circuits 4 and 5 include analog switches 4A and 5A in their signal paths, and complementary output control of signals ΔF and ΔV is performed by turning on and off the switches 4A and 5A.

Correction signals ΔF and ΔV are inverter output frequencies.

・This is done by matching resistors R1 and R2+R3 and R4 together with the voltage command (■).

The control range discrimination circuit 6 discriminates between a low range and a high range of the inverter output frequency by comparing the command (2) with a reference voltage, and 6A is an operational amplifier with hysteresis characteristics provided by an external resistor. Ru. The driver 7 is connected in series with logic inverters 7A and 7B, and the output of the discrimination circuit 6 turns on the analog switch 4A or 5A in a complementary manner. The control mode is such that in the control range where the command VN is at a low level and low output frequency, a high level is obtained in the discrimination circuit 6, and the analog switch 5A
, 4A is turned off, and switch 5A is turned off in the control range of high N force frequency sand where the command ■ is high and becomes 6L.

Turn on 4A.

Note that the differentiating circuit 4.5 generates a correction signal, that is, a correction voltage Δ, individually for the current detection signal using variable resistors 4B and 5B.
Change F, Δ■ and time constant b] is enabled.

In such a configuration, the carrier frequency l number is 1 to 3 Kf
The vibration frequency of iz is reduced by fl K'), thereby reducing the vibration and noise of the electric motor that acts as a load. Further, the unstable operation that becomes wider when the carrier wave frequency is increased can be eliminated by frequency F and voltage correction. As this correction, voltage correction is performed in a control range where the output frequency is low, and frequency correction is performed in a high control range.

This is based on the fact that in acceleration/deceleration in a low control range, changes in pressure become a cause of unstable operation, and in acceleration/deceleration in a high control range of $1, frequency changes tend to be a cause of unstable operation. It was confirmed that acceleration/deceleration control becomes stable when pressure is corrected within a high control range, and stable acceleration/deceleration can be achieved when frequency correction is performed within a high control range.

For example, in the embodiment, if only heavy pressure correction is applied over the entire control range, stable operation can be achieved at a fundamental frequency of 24 H7 or less, but becomes extremely unstable when it exceeds 24 Hz. Conversely, if only frequency correction is applied over the entire control range, stable operation can be achieved at a fundamental frequency of 21 flz or more, but becomes unstable below that.

In this experimental example, in order to operate stably in the entire control range, in the low control range below 22 Elz, it is necessary to set ΔV on the voltage control side.
ΔF is corrected on the frequency control 111 side in the high control range exceeding 22 Hz. All that is required is to set the comparison base i+8 of the control range discriminating circuit 6 so that n+ is positive. In addition, α flow (correction star Δ for changes in I-output signal work)
■, ΔF is adjusted depending on the conditions such as the city engine, load GD t, carrier frequency, etc. For this purpose, the time constant and level of both differentiating circuits 4 and 5 can be adjusted individually. .

〔Effect of the invention〕

According to the present invention, in order to obtain a PWM waveform using oven loop control, stable operation is possible even though the collection wave frequency is increased, and stable operation is possible by reducing ripple and torrent flow to reduce vibration and noise. There is an effect that can be done.

[Brief explanation of drawings]

The drawing is a main circuit diagram showing an embodiment of the present invention. ■ Pressure control amplifier, 2...pressure-frequency converter,
4.5...Differentiating circuit, 6...Control range discrimination circuit, 7...
・Driver, AI + '4*6 A...Operation amplifier, 4A, 5A...Analog switch.

Claims (1)

[Claims] In a pulse width modulation type inverter that obtains a voltage command V and a frequency command F from the inverter output frequency and voltage commands and modulates them with a carrier wave to obtain a pulse width modulation signal, the above voltage commands are adjusted in proportion to the amount of change in the inverter output current. A pair of differentiating circuits that can individually correct V and frequency command F, and a pair of differentiating circuits that determine the high and low of the inverter control range, and in the lower control range, one of the differentiating circuits is used to correct the voltage command (■),
In a high control range, the frequency command F is
1. A control device for a pulse width modulation type inverter, comprising a control range discrimination circuit and a driver.