JPS6042719B2 - AC power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an AC power supply device that uses DC power as a power source and converts it to supply AC power mainly to equipment such as vehicle air conditioners, indoor lighting lights, and electric fans. It is something.

Conventionally, rotary electric power generators have been mainly used as auxiliary power supplies for vehicles, but in recent years, with advances in semiconductor technology, stationary inverters using thyristors have come to be used.

There are roughly two types of systems used in such static power converters. The first method uses a constant frequency inverter circuit that is energized from a DC power supply through a filter that suppresses harmonic current to the power supply.In this case, phase control is performed to prevent fluctuations in the power supply voltage. We are compensating for
In this method, the DC voltage is controlled at a constant voltage using a power conversion circuit such as a chopper circuit, and an AC output voltage of a constant voltage is obtained using an inverter circuit that operates the DC voltage stabilized at a constant voltage with a fixed phase.

In either method, the control method returns the AC output voltage to be controlled and uses feedback control. A block diagram of the former is shown in FIG. 1, and a block diagram of the latter is shown in FIG.

When driving an induction motor load such as an air conditioner or a blower motor for forced cooling of electronic equipment using a voltage return type AC power supply as described above, disturbances such as fluctuations in power supply voltage or load torque may cause induction A vibration phenomenon may occur at a frequency determined by the control time constant including the dynamic system of the electric motor and the filter circuit constant of the AC power supply.

This phenomenon is due to the load characteristics specific to induction motors.
It can be explained as follows. In other words, the load characteristics of an induction motor are such that as the overburden increases, the input current increases, as shown in FIG. If there is a disturbance such as an increase in load torque or a decrease in power supply voltage,
When the rotational speed of the motor decreases and the slippage increases, the input current increases due to the load characteristics of the induction motor. By the way, the AC power supply that drives this induction motor has a 1-pifilter circuit on the DC side, and there is a reactor with large inductance in series with the DC power supply, so the increase in AC power is accumulated in the filter capacitor. The voltage of the filter capacitor decreases because it is supplied with the charge that was previously stored. The drop in voltage across the filter capacitor causes a drop in the AC output voltage, which further increases the input current of the induction motor and induces electrical oscillations between the filter reactor and the filter capacitor. The above mechanism is repeated to generate a vibration phenomenon.

The state is shown in the flowchart of FIG. In order to suppress the oscillating voltage generated in a power supply device to which such a motor load is connected, it is necessary to reduce the amount of power supply voltage fluctuation due to the load current and voltage, and therefore the filter capacitor capacity must be selected to be large. However, the disadvantage was that the power supply became larger. The present invention has been made to improve the above-mentioned drawbacks, and provides a small and lightweight AC power supply device that is stable even when driving an induction motor load. The present invention will be explained below with reference to the drawings. FIG. 5 shows a block diagram when the present invention is applied to the power supply circuit system shown in FIG. 1, and FIG. 6 shows a block diagram when the present invention is applied to the power supply system shown in FIG. 2.

First, the operation of the case shown in FIG. 6 will be explained.

Voltage feedback to stabilize the voltage changes the AC output voltage to
It is detected by the voltage detection transformer 12, converted to a DC voltage by the rectifier circuit 13, and compared with a reference voltage to control the phase control circuit 24 and the voltage adjustment chopper circuit 7.
On the other hand, the current fluctuation of the induction motor load is detected by the current detection circuit 17
After detecting it and converting it to DC voltage by the rectifier circuit 18,
After ripples in the AC output frequency component are removed by the low-pass filter 19, the output signal is clamped within a certain range by the voltage limiting circuit 20, added to the error signal of the voltage control circuit by the adder 21, and sent to the phase control circuit 24. input. The current signal detected by the current detection circuit 17 is connected to provide positive feedback in consideration of the so-called negative resistance characteristic in which the input power source increases as the input voltage of the induction motor decreases. That is, the setting is made so that when the load current increases, the voltage is increased and the input current of the induction motor is decreased. However, if such a feedback loop is provided, the control stability will deteriorate for general AC loads that do not have negative resistance characteristics, so the above-mentioned voltage limiting circuit 20 is included in this feedback loop to avoid unnecessary I try not to perform these operations. FIG. 7 shows an example of a circuit from the current detection section to the phase control circuit.

Further, FIG. 8 shows waveforms of various parts of the control circuit when the AC load current oscillates.

As explained above, according to the present invention, in an AC power supply device that voltage-controls an inverter connected to a DC power source via a filter circuit consisting of a reactor and a capacitor, the output current is rectified and a low-pass filter and a voltage limiter are used. A small and lightweight AC power supply device that can be used stably even for loads with vibration characteristics such as induction motors by adding the variation of the output current within a predetermined range to the voltage control circuit and feeding it back through the can be obtained.

[Brief explanation of the drawing]

Figures 1 and 2 are block diagrams showing the configuration of a conventional AC power supply, Figure 3 is a diagram showing the general characteristics of an induction motor, and Figure 4 is a diagram showing the general characteristics of an induction motor driven by a conventional AC power supply. FIGS. 5 and 6 are block diagrams showing the configuration of an AC power supply according to the present invention, and FIG. 7 is a diagram showing an example of a current feedback circuit used in the present invention. , FIG. 8 is a characteristic diagram for explaining the present invention in detail. 3... Filter reactor, 4... Filter capacitor, 5, 10... Inverter circuit, 7... Chopper circuit, 12... Voltage detector, 14, 16, 24...
- Gate control circuit, 15... Reference oscillator, 17...
Current detector, 19...Low pass filter, 20...
Voltage limiter.

Claims (1)

[Claims] 1. In an AC power supply device that connects an inverter device to a DC power source via a filter circuit consisting of a reactor and a capacitor, and controls the voltage by feeding back the AC output voltage, the AC output current is detected and rectified, and a low-pass filter is applied. and a voltage limiter, the AC power supply is added to the deviation between the voltage reference value and the feedback signal value of the AC output voltage.