JPS6130991A - Controller of voltage type inverter - Google Patents

Abstract

PURPOSE:To stably start by detecting the attenuation of an AC input current corresponding to the rise of a DC voltage at the start of a motor at the starting time to rise the output frequency. CONSTITUTION:A current variation detector 18 for detecting the variation in the reduction of a starting current by differentiating an input AC current detection value from a rectifier 8 to output an acceleration signal for controlling the DC voltage of a power reactor 1 in a switch circuit 17 at the reduction varying time, and means for performing the increase in the frequency command signal of a frequency control system by applying an acceleration signal to the switch circuit are provided. Thus, the rise of a DC current due to the regenerative energy based on the abrupt variation in the starting current can be suppressed.

Description

Detailed Description of the Invention Field of Application of the Invention The present invention relates to an AC motor (hereinafter referred to as a motor) drive voltage type variable voltage variable frequency ( (AVAF) This invention relates to a control device for an inverter device, and particularly relates to a control device that aims at the stability of an output-side transformer at the time of starting an electric motor.

[Background of the invention]

Generally, when performing acceleration/deceleration control of an induction motor, a voltage type AVAF inverter device that performs frequency control is used. An example of a conventional voltage source AVAF inverter device is shown in FIG.

In FIG. 4, input AC power is converted into DC power by a forward converter 1 composed of a thyristor bridge circuit, etc., ripples are removed via a smoothing reactor 2 and a smoothing capacitor 3, and an inverse converter 4 is supplied to The inverter 4 is configured using power elements such as thyristors, GTOs, power transistors, flywheel diodes, etc., and is connected to a matching transformer 5 for matching AC output at a predetermined frequency.
is supplied to the electric motor 6 via. The main circuit described above is controlled by a control device to be described later, and is configured to control the AC output frequency of the inverter 4. The relationship between the output voltage Vo and the output frequency f0 is generally set as follows: Vo * -fo'' (1). Hikoo K is a constant.

The control device performs control operations based on a speed command v8 separately given from the outside, and is roughly divided into a voltage control system that controls the forward converter 1 and a frequency control system that controls the frequency of the inverse converter 4. It will be done.

First, the voltage control system will be explained. Switch circuit 17
The speed command signal vg given via the command conversion circuit 1
3 is used as a voltage command signal, the output DC voltage of the forward converter 1 is passed through the insulation amplifier 9 as a return signal, and the two are matched and the voltage is controlled by the AVR (automatic voltage controller) 12 from K. This is the control loop. In addition, as a minor looseness, the AC input current IIM is returned through the alternator 7 and the rectifier 8, and the ACR (automatic current controller)
11, current control is performed. 10 is an automatic pulse phase shifter.

On the other hand, in the frequency control system, the inverse converter 4 converts the speed command v11 into a frequency command through the switch circuit 17 and the command conversion circuit 16. Based on this directive, voltage/
A control pulse signal is outputted via the frequency conversion circuit 15 and the frequency divider 14, and frequency control is performed. The switch circuit 17 becomes electrically conductive after a fixed time period (between 1. and t2 in FIG. 5) of the inverter start command generation wave elapses, and the inverter 4
, a command to increase the frequency is given to increase the rotation speed of the electric motor 6.

Next, the operation will be explained. FIG. 5 shows the operating wave numbers of each part when starting and controlling the rotation speed of the AC motor using this inverter device. In FIG. 5, time 1. At point 11, the inverter device is activated, and at point 11, the electric motor 6 starts rotating. After performing constant frequency operation at a low starting frequency for the time up to t2, the engine shifts to acceleration, ends the acceleration at 11 points, and thereafter continues to perform constant speed steady operation. After that, when changing the operating frequency, after decelerating operation as after t4, 1,
Continuous operation at another frequency begins at point. At point 13, by stopping the inverter device, the electric motor also stops rotating.

Now, when the inverter device as described above is used to drive a motor that has a large starting current at startup and a large difference between that value and the current during synchronous operation, the following problem occurs. That is, if we pay attention to the waveforms of the AC input current Its and DC voltage V in Fig. 5, we can see that a very large starting current II for starting flows during the period to-ytl.
Once the motor starts rotating at point IzK, there is a sudden drop in input current. As a result, the DC voltage V cannot absorb the current change and causes a voltage increase Δv1 for a short period of time, and this voltage increase ΔVIK causes magnetic saturation in the transformer and motor on the output side, causing an inverter output overload. There was a drawback that startup failure occurred due to current. In other words, a big start-up electrician!
flows, and the back electromotive force in the motor due to this current is returned through the flywheel diode of the inverter 4, and this regenerated energy causes an increase in DC voltage Δv1. At this time, the transformer 5 has a predetermined capacity. Because of the overcurrent used, magnetic saturation occurs due to overcurrent, and the impedance of the transformer decreases due to magnetic saturation. This results in a startup failure.

[Purpose of the invention]

An object of the present invention is to provide a voltage type A that enables stable starting even when driving a motor whose starting current is rapidly attenuated.
It is an object of the present invention to provide a control device for a VAF inverter device.

[Summary of the invention]

In order to achieve the above object, the present invention provides a current change detector for detecting a decrease in the starting current of the AC motor in a control device for a voltage source inverter device that supplies driving power to an AC motor via a transformer. and a point'VC feature, comprising a control means for suppressing the DC voltage in the inverter device when the starting current changes to decrease. To summarize, at startup, the output frequency is increased (
In other words, the rotational speed is accelerated.

[Embodiments of the invention]

Next, an embodiment of a control device for a voltage source AVAF' inverter device according to the present invention will be described based on the drawings.

FIG. 1 shows an embodiment of a control device according to the present invention.

In FIG. 1, the same parts as in FIG. 4 (prior art) are given the same reference numerals, and detailed explanation thereof will be omitted.

The control device according to the present invention shown in FIG. 1 and FIG. 4 (conventional example)
The difference between the two is that the detection value of the input AC current from the rectifier 8 is differentiated to detect the decreasing change in the starting current, and the switching circuit 17 is used to control the DC voltage of the forward converter 1 at the time of the decreasing change. The current change detection circuit 18 outputs an acceleration signal, and means for increasing the frequency command signal of the frequency control system by applying the acceleration signal to the switch circuit.

FIG. 2 shows a detailed configuration example of the current change detection circuit 18. In FIG. 2, a starting current detection signal from a rectifier 8 is applied to a differentiator 19. The differentiator 19 may be a commonly used so-called CR differentiator circuit or an active filter using an operational amplifier.

When the differentiator 19 detects a decreasing change in the starting current I+, the detection signal is amplified by the amplifier 20 to a signal of a predetermined level. Note that this amplifier 20 is not necessarily necessary as long as the differential output level can drive a switch 21, which will be described later. The switch 21 is used to operate the detection circuit 18 only when the electric motor 6 is started, and to disconnect the detection circuit 18 having a suppressing effect after the electric motor 6 enters an acceleration state (after t1 in FIG. 3).

This switch 21 is configured to open when the starting frequency value of the speed command signal Vl reaches a predetermined value based on a detection signal from the starting frequency detection circuit 22.

Next, the operation will be explained with reference to FIG. When the speed command Vl is given to the switch 17 at time 1o, the starting current If
is input to the forward converter 1. When the starting current 1 reaches its peak and begins to decrease, the decreasing change in current is detected by the differentiating circuit 19 at time 11, and the switch 21
The acceleration signal V is applied to the switch 17 via the acceleration signal V.

The electric motor 6 starts rotating from these acceleration signals v and Ic (
Time 't+No). When the electric motor 6 starts rotating, the starting current suddenly decreases, but in this way, the acceleration signal v
When 1 is given, more AC input current flows, so the starting current It does not decrease to I, but only to the point Δ11. As a result, it becomes possible to suppress an increase in the DC voltage V due to regenerative energy due to a sudden change in the starting current 1. Regarding this point, conventionally (Fig. 5)
In this case, since the acceleration command is given at time t2 and after the starting current Is has once decreased to t2, regenerative energy cannot be suppressed and the above-mentioned problem occurs.

In this way, it is possible to suppress the rise in DC' voltage due to the regenerative energy, prevent magnetic saturation of the transformer, etc., and enable stable motor function.

〔Effect of the invention〕

As described above, according to the present invention, when an AC motor is reversed by a voltage source AVAF inverter device, it is possible to prevent starting failure due to a sudden decrease in starting current that occurs during starting.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a control device for a voltage source AVAF inverter device according to the present invention, FIG. 2 is a block diagram showing an example of a current change detection circuit according to the present invention, and FIG. Waveform diagram showing signal waveforms of each part, 4th
This figure is a block diagram showing the configuration of a control device of a conventional voltage type AVAF inverter device, and FIG. 5 is a waveform diagram showing waveforms of various parts. DESCRIPTION OF SYMBOLS 1... Forward converter, 4... Inverse converter, 5... Transformer, 6... AC motor, 7... Current transformer, 8... Rectifier, 17... Sinch, 18...Current change detection circuit.

Claims (1)

[Scope of Claims] 1. In a control device for a voltage source inverter device that supplies driving power to an AC motor via a transformer, a current change detector detects a decreasing change in the starting current of the AC motor; A control device for a voltage source inverter device, comprising a suppressing means for suppressing a DC voltage in the inverter device when the starting current changes to decrease. 2. Control of a voltage inverter device according to claim 1, wherein the current change detector includes a differentiating circuit that differentiates a current value input to the inverter device. Device. 3. A voltage source inverter device according to claim 1 or 2, wherein the DC voltage suppressing means is constituted by a circuit that provides an acceleration signal to the speed command signal of the control device. control device.