JPS62110482A - Inverter protecting apparatus - Google Patents

Abstract

PURPOSE:To facilitate detection of deterioration of electrolytic capacitors constituting a double-voltage rectifier with a simple constitution by a method wherein the operation of an inverter is discontinued and abnormality is indicated when the instantaneous value of the voltage between the terminals of one of the electrolytic capacitors exceeds a certain range. CONSTITUTION:An AC voltage from a single-phase AC source 1 is converted into a DC voltage by a diode bridge 2 and boosting capacitors 3 and 4. The DC voltage is converted into a three-phase voltage by an inverter 7 and supplied to a three-phase induction motor 8. When the voltage between the terminals of the boosting capacitor 4 drops below a certain value, a photocoupler 11 is turned OFF and the abnormal situation is indicated to the outside by an indicating means 16 and all transistors of the transistor bridge are turned OFF through an inverter driving signal generating means 17.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an inverter protection device for driving an induction motor that drives a compressor or the like of an air conditioner.

BACKGROUND OF THE INVENTION In recent years, induction motors are increasingly driven by inverters in order to efficiently control their rotational speed over a wide range.

When configuring an inverter system by receiving a commercial single-phase AC power source, a DC voltage is usually created using a voltage doubler rectification method in order to improve system efficiency. There are various methods for voltage doubler rectification, but it is generally constructed by combining a diode and a capacitor. When the inverter capacity is relatively large, the capacitor needs to have a relatively large capacitance, so an electrolytic capacitor is used.

Problems to be Solved by the Invention In such a conventional inverter drive device, the electrolytic capacitor that constitutes the voltage doubler rectifier has a relatively short lifespan compared to other parts, so it is difficult to perform periodic inspections or periodic inspections. It requires regular replacement and is troublesome in terms of maintenance.In addition, it also has the problem of making the system configuration expensive, such as using an electrolytic capacitor with an excessively large margin in the design. Ta.

Means for Solving the Problems In order to solve the above problems, the inverter protection device of the present invention includes a voltage detection means for detecting the voltage between the terminals of the electrolytic capacitor that constitutes the voltage doubler rectifier circuit, and a voltage detection means for commanding the inverter drive frequency. It consists of a frequency command means to control the frequency and an abnormality display means, and when the instantaneous value of the voltage between the terminals of the electrolytic capacitor exceeds a certain range under the condition that the inverter drive frequency is below a certain value, the inverter operation is stopped and , the abnormal state is displayed externally by the abnormality display means.

According to the inverter protection device of the present invention, when the inverter is operated and the electrolytic capacitor deteriorates, the deterioration state can be detected and replacement can be done within a reasonable period of time. Accidents such as liquid being discharged can also be prevented.

EXAMPLE Hereinafter, an example of the present invention will be described based on FIGS. 1 and 2.

In the figure, 1 is a single-phase AC power supply, which is converted into a DC voltage by a diode bridge 2 and step-up capacitors 3 and 4, which constitute a voltage doubler rectifier circuit. 5 is a reactor, which functions to suppress the peak value of the current of the single-phase AC power supply 1 and improve the system power factor. 6 is a smoothing capacitor. Reference numeral 7 denotes an inverse conversion means composed of a transistor bridge, which converts the DC voltage into a three-phase AC voltage and supplies it to the three-phase induction motor 8. 9 is a frequency command means, which determines the frequency of the three-phase AC voltage. 11 is a photocoupler, a Zener diode 12, resistors 13 and 14
Together with this, it constitutes voltage detection means for detecting the voltage between the terminals of the boosting capacitor 4. When the voltage across the terminals of the step-up capacitor 4 is high, the photocoupler 11 is in the ON state, and conversely, when the voltage across the terminals is low, the photocoupler 1 is turned on.
1 is in the OFF state. Reference numeral 15 denotes an operation command means, and when the inverter driving frequency determined by the frequency command means is below a certain value and the voltage across the terminals of the boost capacitor 4 is below a certain value, an external signal is sent via the display means 16. The abnormal state is displayed and all transistors of the transistor bridge 7 are turned off via the inverter drive signal generating means 17.

Next, the reason why deterioration of an electrolytic capacitor can be detected from the voltage between its terminals will be explained using FIG.

Normally, an electrolytic capacitor will gradually lose its internal electrolyte over time, apart from initial failures. Eventually, the explosion-proof valve will operate and the capacitance will become almost zero, reaching the end of its life.This configuration detects the deterioration of the electrolytic capacitor as a decrease in capacitance before the explosion-proof valve operates. The time when the value becomes constant is determined as the end of life.

FIG. 2 shows the waveform of the voltage between the terminals of the boost capacitor 4 under the condition that the inverter drive frequency is constant in a case where the load torque is almost constant with respect to the motor rotation speed, such as in an air conditioning load.

The same figure (al indicates when the capacitance is the specified value, the same figure (bl indicates when the capacitance is larger than the specified value, and the same figure (cl indicates when the capacitance is smaller than the specified value). When converting to , the smaller the capacitance, the larger the voltage ripple becomes, and the product of capacitance and ripple voltage becomes constant.Therefore, the deterioration of the capacitor, that is, the capacitance decreases. The drop can be detected from the terminal voltage waveform.

That is, when the conditions that the peak value of the inter-terminal voltage waveform exceeds a certain value or the minimum value becomes below a certain value are satisfied, it can be determined that the capacitor has deteriorated.

In this embodiment, the voltage waveform between the terminals of the boosting capacitor 4 is measured, but the boosting capacitor 3 may of course be used. The same thing can be done with the smoothing capacitor 6, but in the case of voltage doubler rectification, the boost capacitors 3 and 4 tend to deteriorate more than the smoothing capacitor 6, so the voltage between the terminals of the boost capacitor 3 or 4 It is more rational to judge deterioration.

As described in detail, the inverter protection device of the present invention converts a single-phase AC power source into a DC voltage using a forward conversion means constituted by a voltage doubler rectifier circuit, and further converts AC power to an induction motor using an inverse conversion device. and a voltage detection means for detecting the voltage between the terminals of the capacitor constituting the voltage doubler rectifier circuit.
If the inverter drive frequency is below a certain value and the peak value of the voltage between the terminals of the capacitor is above a certain value or the minimum value is below a certain value, it is determined that the capacitor has deteriorated and the inverter operation is stopped. When the capacitor stops, an error message is displayed externally, making it easy to replace the capacitor within a reasonable period of time with a simple configuration, and also having the effect of preventing accidents due to capacitor deterioration.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an inverter protection device showing an embodiment of the present invention, and FIG. 2 is a voltage waveform characteristic diagram between terminals of a boosting capacitor constituting a voltage doubler rectifier circuit of the inverter protection device. 1... Single-phase AC power supply, 2... Diode bridge (forward conversion means), 3.4... Boost capacitor (forward conversion means), 7... ... Transistor bridge (inverse conversion means), 8 ... Induction motor, 9 ... Frequency command means, 11 ... Photocoupler (voltage detection means), 12 ... ...Zener diode (voltage detection means), 13.14...
...Resistance (voltage detection means), 16... Abnormality display means.

Claims (1)

[Claims] Forward conversion means comprising a diode and two capacitors for converting a single-phase AC power source into a DC voltage; an inverse conversion means for converting the DC voltage into an AC power source with variable frequency and variable voltage; and operation of the inverse conversion means. The drive frequency is comprised of a frequency command means for commanding a frequency, a voltage detection means for detecting the voltage between the terminals of the capacitor, and an abnormality display means for externally displaying an abnormal state in the event of an abnormality, and a drive frequency output from the frequency command means. is below a certain value and the instantaneous value of the voltage between the terminals of the capacitor exceeds a certain range, the operation of the inverse conversion means is stopped and an abnormal state is displayed externally by the abnormality display means. Inverter protection device.