JPS6039376A - Inverter device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a variable voltage variable frequency PWM control inverter device that uses an AC motor as a load.

[Prior art]

FIG. 1 shows an example of a schematic block configuration of a conventional inverter device. In the figure, (1) is a commercial power supply, (2) is a converter circuit for rows consisting of thyristors, etc., (8)
) is a smoothing capacitor, (4) is an inverter main circuit consisting of transistors, etc., (5) is a load AC motor, (
The names of the regenerative converter circuit (6), the regenerative transformer (7), and other control circuits are shown in each block.

FIG. 2 shows the vicinity of the regenerative converter circuit (6) shown in FIG. 1 and FIG. The regeneration converter circuit (6) is composed of six thyristors R+, S+, T+, R-, S-, and T-.

Next, the operations of these conventional devices will be explained. At the time of operation, the voltage supplied from the commercial power supply (1) in Fig. 1 is as follows:
After being rectified by the converter circuit (2), the capacitor (8
), further converted into alternating current by the inverter main circuit (4), and finally supplied to the electric motor (5). On the other hand,
The speed command circuit outputs a speed command corresponding to the target rotation speed of the electric motor. The reference voltage waveform forming circuit forms a reference voltage waveform having a frequency corresponding to the speed command output and an amplitude matching the output of the voltage command circuit. The PWM control circuit outputs a signal for controlling on/off the transistors of the inverter main circuit (4) depending on the deviation between the reference voltage waveform and the output voltage of the inverter main circuit (4). That is, the output voltage of the inverter main circuit (4) is made to follow the reference voltage waveform, so that the inverter main circuit (4) outputs an AC voltage of the desired frequency specified by the speed command circuit. Then, the electric motor (5) is driven.

On the other hand, during regeneration, the rotational energy of the electric motor (5) is transferred to the power supply (1) via the regeneration converter circuit (6).
) is regenerated. Next, we will discuss the commutation operation during regeneration in the second section.
This will be explained with reference to the figures. The rotational energy of the electric motor (5) is stored as electric charge in a capacitor (3), and the voltage between the terminals of this capacitor (3) is set to Vd.

Now, thyristors R+ and T- are conducting, then R+→
Considering the case where commutation to S+ is performed, R+ cannot be turned off due to the characteristics of the thyristor unless the voltage vR+ applied to R+ is reduced to zero or less.

If commutation is attempted while VR+>Q, thyristor R+ cannot be turned off and remains on.

The same applies to the other six thyristors, and in such a case, a DC bus short circuit occurs.

According to the circuit configuration shown in Figure 2, the voltage applied to each cyrisk is determined by the voltage V (1) of the capacitor (8) and the voltage of the power supply (1), but in such a circuit configuration, the short circuit accident described above can be prevented. As a method, the capacitor voltage d
It has been considered to set the voltage according to the state where the power supply voltage is lowest. According to this, commutation failure does not occur even when the power supply voltage is reduced. However, on the other hand, since the converter output voltage (-capacitor voltage Va) is low, a large amount of current must flow in order to generate the rated output power of the motor even in normal times when the power supply voltage is high, and large elements are required. However, this method has the drawbacks of increasing costs and increasing the size of the device.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and when the power supply voltage drops, the converter output voltage is clamped lower than in normal cases, thereby preventing commutation failure. At the same time, the converter output voltage is set high under normal conditions.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In Fig. 6, (1) is a commercial power supply, (2) is a power converter circuit consisting of silice etc., (3) is a smoothing capacitor, (4) is an inverter main circuit consisting of transistors etc., ( 5) is the load AC motor, (6) is the regenerative converter circuit, (7 is the regenerative transformer, (8)
, (9) are newly introduced circuits, in which (8) is an input voltage detection circuit that detects the input voltage from the power supply (1), and (9) is a voltage correction circuit. The output of the voltage correction circuit is input to the converter voltage command circuit, and the converter output voltage can be controlled according to fluctuations in the power supply voltage.

The other control circuits are the same as those in FIG. 1, and include a speed command circuit, a voltage command circuit, a reference voltage waveform forming circuit, a PWM control circuit, a converter voltage command circuit, and a four-phase control circuit.

The operation of the apparatus shown in FIG. 5 will be explained. When the power is on, the commercial power supply (1) is rectified by the power converter circuit (2), smoothed by the capacitor (3), and then converted into alternating current by the inverter main circuit (4). , and finally drives the electric motor (5). On the other hand, during regeneration, the rotational energy of the electric motor (5) is regenerated to the power source (1) via the regeneration converter circuit (6). As described above, when the power supply voltage is normal, the operation is the same as in the conventional case, but when the power supply voltage decreases, the operation is as follows. That is, a decrease in the power supply voltage is detected by the input voltage detection circuit (8), and the value thereof is input to the voltage correction circuit (9). The converter voltage command circuit receives the output of the voltage correction circuit and
A predetermined clamp voltage is output in order to lower and clamp the converter output voltage (voltage between - capacitor terminals) by a predetermined amount. The phase control circuit causes the converter output voltage to follow the output voltage of the converter voltage command circuit by controlling the gate phase of the converter (6) according to the deviation between the output voltage of the converter voltage command circuit and the converter output voltage. . Thus, by reducing the converter output voltage, the phase control circuit can operate smoothly, and failure in commutation of the sirisk in the converter (6) can be prevented.

FIG. 4 shows an example of the characteristics showing how the inverter output voltage and the converter output voltage are corrected, and the solid line shows the output characteristics when the power supply voltage is at the rated value.

When the power supply voltage decreases, the highest value is clamped in the high voltage region as shown by the broken line, and the converter device can operate stably without commutation failure.

〔Effect of the invention〕

As described above, according to the present invention, when the power supply voltage drops, commutation failure is prevented by detecting this voltage drop and clamping the output voltage of the converter to a predetermined value accordingly. On the other hand, at normal power supply voltage, by setting the converter output voltage high, the inverter output voltage can be increased, and the rated output power of the motor can be increased without increasing the element capacity of the device. It is possible to provide an inverter device that can

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional voltage type PWM control inverter control, FIG. 2 is a regenerative converter circuit and its peripheral circuit diagram, and FIG. 5 is a block diagram of an embodiment of an impark device according to the present invention. FIG. 4 is a diagram showing the characteristics of the inverter output voltage and converter output voltage. (1)...Commercial power supply (2), (6)...Converter circuit (8)...Input voltage detection circuit Note that in the drawings, the same reference numerals indicate the same or equivalent parts. Agent Masuo Oiwa Figure 1 Figure 2

Claims (1)

[Claims] In an inverter device that uses an AC motor as a load and is equipped with a converter circuit that rectifies the power supply voltage supplied to the inverter device, an input voltage detection circuit that detects the power supply voltage is provided, and when the power supply voltage is lower than normal. An inverter device, characterized in that the output voltage of the converter circuit is controlled to be suppressed to a value lower than normal according to the output of the input voltage detection circuit.