JPS61273180A - Voltage type avaf inverter - Google Patents

Abstract

PURPOSE:To eliminate a magnetic saturation of an output side transformer by detecting the variation in the DC voltage of the output side of a power inverter when a motor is started to raise an output frequency, and constantly controlling the ratio of an output voltage and the output frequency. CONSTITUTION:A voltage AVAF inverter controls by a power reactor 1 a DC voltage, and controls by a power inverter 4 an AC output frequency. The control system of the reactor 1 AVR-controls a speed command signal through a voltage command signal and a DC voltage feedback signal fed through a command converter 13 and ACR-controls an input current feedback. The inverter 4 frequency-controls a speed command by a frequency command through a command converter through a voltage/frequency converter 15. In this case, a detector 17 is provided to detect the variation in the input DC voltage of the inverter 4, thereby starting the control of the output frequency. Thus, the DC voltage starts rising by the rise of the rotating speed f a motor, and since the AC output frequency is raised, the rise in the DC voltage is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a voltage source AVAF inverter device that supplies appropriate power for stable starting of an AC motor.

(Background of the Invention) Fig. 4 shows a drive system for an AC motor using a conventional voltage-type AVAF inverter device. and inverter 4 (gate turn-on thyristor).

(consisting of flywheel diodes, etc.) controls the AC output frequency. AC output voltage vO and AC output frequency f
Generally, o is set as Vo=Kfo (K: constant).

The control system of the forward converter 1 will be explained below. A by converting the speed command signal into a voltage command signal through the command conversion circuit 13 and matching it with the DC voltage feedback signal through the isolation amplifier 9.
The main control loop performs VR control, and the minor loop performs ACR control of input current feedback.

Further, the inverse converter 4 converts the speed command into a frequency command through the command conversion circuit 16, and outputs a gate turn-off thyristor pulse signal through the voltage/frequency converter 15 and frequency divider 14.

Perform frequency control.

Note that 5 is a transformer for matching the inverter output voltage and the motor voltage. 2 is a smoothing reactor, and 3 is a smoothing capacitor whose purpose is to smooth the DC voltage. 6 is an AC motor.

7 is a current transformer, 10 is an automatic pulse phase shifter, 11 is an automatic current controller, and 12 is an automatic voltage controller.

FIG. 5 shows the operating characteristics when starting and controlling the rotation speed of the AC motor using this inverter device.

In Fig. 5, the inverter device is started at point to, 11
The electric motor starts rotating at the point. After running at a constant frequency at a low starting frequency until I2, the engine starts accelerating.
When acceleration ends at the I3 point, constant speed steady operation continues. After that, when changing the operating frequency, after t4, the engine goes through deceleration operation, and then starts continuous operation at a different frequency at point ts.

At point I6, by stopping the inverter device, the electric motor also stops rotating.

In this inverter device, the following problem occurs when driving a motor with a very large difference between starting torque at startup and steady torque after completion of startup. In other words, if we focus on the AC input current and DC voltage in Figure 5, a very large AC input current flows during the period from tO to t1, and once the conductive machine starts rotating at point 11, the input current suddenly increases. decreases and reaches I2. As a result, the control circuit cannot absorb this current change, and the DC voltage increases (,
, vl), and this voltage increase causes magnetic saturation in the output transformer and motor.

Another disadvantage is that startup failure occurs due to inverter output overcurrent.

In addition, related to this type of device.

For example, JP-A-59-92772. Japanese Patent Publication No. 59-156
No. 190, etc. may be mentioned.

[Purpose of the invention]

An object of the present invention is to provide a voltage type AVAF inverter device that can stably start an electric motor with a large difference between starting torque and steady torque.

[Summary of the invention]

The feature of the present invention is to detect the change in the DC voltage on the output side of the inverter when starting the motor, increase the output frequency, and control the ratio between the output voltage vo and the output frequency f0 to a constant value.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 and 3.

FIG. 1 shows a voltage source AVAF inverter device according to the present invention.

The detection circuit 17 detects a change in the input DC voltage of the inverter 4 and starts controlling the output frequency, which is different from the conventional example, and the starting characteristics of the present invention are shown in FIG. below,
This will be explained with reference to FIG. The differentiator 19 determines the polarity of the change in the DC voltage feedback signal, differentiates it, and transmits it to the amplifier 20.

The signal output through the switch 21 conducts the switch 18 to increase the speed command, and the 0 frequency detection circuit 22 that controls the AC output frequency conducts only the starting frequency state, and when the switch 21 enters the acceleration frequency state, the 21 The detection circuit 17 is disconnected from the control circuit by being made non-conductive. 8 is a rectifier circuit, 12 is an automatic voltage controller.

According to the present invention, the detection circuit 17 generates an output signal at 11 points when the motor starts rotating, increases the speed command to increase the rotational speed of the motor, and ends acceleration at 13 points. As a result, the DC voltage begins to rise at point t□, but in the conventional example, the AC input current decreased to -12, but in the example of the present invention, the AC output frequency is increased when the magnitude of aI is To raise.

Regenerative energy is small, DC voltage rise is suppressed, and stable motor starting characteristics are obtained.

[Effects of the Invention] According to the present invention, magnetic saturation of the transformer and motor on the output side of the inverter device can be eliminated.

[Brief explanation of the drawing]

FIG. 1 is a control block diagram of an AVAF inverter device according to an embodiment of the present invention, FIG. 2 is a starting characteristic diagram of the AVAF inverter device of the present invention, and 3rd rB is a detection block diagram of the present invention.
FIG. 4 is a control block diagram of a conventional AVAF inverter device, and FIG. 5 is a starting characteristic diagram of the conventional AVAF inverter device. l... Forward converter, 2... Smoothing reactor, 3...
・Smoothing capacitor, 4... Inverter, 5... Transformer, 6... AC motor, 7... Current transformer, 8... Rectifier circuit, 9... Isolation amplifier, 10 ... automatic pulse phase shifter, 11 ... automatic current controller, 12 ... automatic voltage controller, 13 ... command conversion circuit, 14 ... pulse distributor, 15 ... voltage/frequency Converter, 16... Command conversion circuit, 17... Detection circuit, 18... Switch.

Claims (1)

[Claims] 1. A forward converter for converting alternating current into direct current, an inverse converter connected to the output side of the forward converter for converting direct current back into alternating current, and the inverse converter. In a voltage source inverter device equipped with a circuit for controlling an output frequency and an output voltage, a mechanism is provided to detect a change in the DC voltage of the inverter at startup, and the output frequency of the inverter is controlled. A voltage source AVAF inverter device characterized by: