JPS62260564A - Protective circuit for damping resistor of inverter - Google Patents

Abstract

PURPOSE:To prevent the abnormal overheat of a damping resistor positively by detecting the abnormal conduction of a switching element connected in series with the damping resistor and stopping the operation of an inverter. CONSTITUTION:An inverter has a smoothing capacitor 3 smoothing an output from a rectifier circuit 2 and an inversion circuit 4, and supplies a motor 5 as load with an AC output. A damping resistor 6, a switching element 7 connected in series with the damping resistor and a damping control circuit 8 are mounted, and a voltage over-rise by regenerative energy on the deceleration of the motor is inhibited. A photo-coupler 9, a limiting resistor 10 for primary side currents and a load resistor 11 are fitted as conduction detection means to the damping resistor 6 at that time. Accordingly, when regenerative energy is consumed by the control resistor 6, the actual conduction of the switching element 7 and the state of the actual load of the damping resistor 6 are monitored by the damping control circuit 8, and the conduction of the switching element 7 is inhibited when conduction more than a specified value continues.

Description

[Detailed description of the invention] f Kankei L, 411 1fl n M&
'1 This invention relates to a protection circuit for a braking resistor of an inverter whose load is an electric motor.

[Conventional technology]

Figure 3 is a circuit configuration diagram showing a conventional inverter that uses an electric motor as a load. 5 is a load motor connected to the AC output side of the inverse conversion circuit 4;
7 is a braking resistor, 7 is a switching element such as a transistor connected in series with the braking resistor 6, and 8 is a braking control circuit for the switching element 7.

Next, the operation will be explained. It is well known that the AC output from the commercial power supply 1 is converted to DC by the rectifier circuit 2 and the smoothing capacitor 3, and then converted back to AC at a desired frequency by the inverter 4 and supplied to the motor 5. .

On the other hand, when the motor 5 decelerates, the regenerated energy from the motor is stored in the smoothing capacitor 3 via the inverter 4, and the voltage Vdc at the DC IJ link increases. As regeneration from the motor continues, the voltage Vdc will further rise, eventually damaging the inverter components.
This voltage Vdc is detected, and when it rises above a certain value, the braking control circuit 8 causes the switching element 7 to conduct.

By doing this, the regenerated energy from the motor 5 is consumed by the braking resistor 6, and an increase in the voltage of the DC link portion is suppressed. Then, when the voltage Vdc of the DC link section returns to a specified value or less, the switching element 7 is controlled to be turned off.

In this way, the braking resistor 6 is connected to the DCI connector only during braking and when the regenerated energy is large, so the capacity of the braking resistor 6 is selected according to the usage conditions of the load, making it economical and economical. For this reason, the capacitance is such that if it is continuously connected to the DCI connector, it will overheat abnormally.

Therefore, as a protection against unexpected continuous regeneration from the motor 5, the conduction signal applied from the braking control circuit 8 to the switching element 7 is limited in accordance with the capability of the braking resistor 6.

[Problem that the invention seeks to solve]

The protection circuit for the braking resistor of a conventional inverter is configured as described above, so if the switching element 7 is damaged for some reason and becomes uncontrollable and becomes conductive, the braking resistor 6 is continuously connected to the DC1772 section. There was a problem in that if it was connected to a power supply, it would overheat abnormally and damage other components.

That is, there is a problem in that an abnormality cannot be detected when the switching element 7 is damaged, and the braking resistor 6 cannot be protected.

This invention was made to solve the above-mentioned problems, and provides a protection circuit for an inverter braking resistor that can prevent abnormal overheating of the braking resistor even if the braking switching element is damaged. With the goal.

[Failure to solve the problem]

A protection circuit for a braking resistor of an inverter according to the present invention includes a continuity detection means for detecting the conduction state of a switching element for braking, and a continuity detection means for controlling on/off of the switching element and based on the detection signal of the continuity detection means. and a brake control circuit that detects abnormal conduction of the switching element.

[For production]

The braking control circuit according to the present invention detects abnormal conduction of a switching element based on a detection signal from a continuity detection means that detects a conduction state of a switching element connected in series with a braking resistor, thereby generating an abnormal continuity detection signal. Based on this, the operation of the inverter is promptly stopped, thereby preventing abnormal overheating of the braking resistor.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1, in which the same parts as in FIG. 3 are given the same reference numerals.

In Fig. 1, reference numeral 9 denotes a 7-oto coupler as a continuity detection means, 10 a 7-oto coupler 9 connected to the positive electrode side of the DC link part,
A limiting resistor 11 for the primary current of the photocoupler is connected to the primary anode of the photocoupler 9, and 11 is a load resistor connected to the output side of the photocoupler 9.
An on/off signal of the photocoupler 9 is inputted to the brake control circuit from one end of the point -IDA.

Next, the operation of the embodiment configured as shown in FIG. 1 will be explained. Energy is regenerated from the motor 5, and the voltage Vd
When c rises above a certain value, a conduction command signal is output to the switching element 7 by the action of the braking control circuit 8 as in the conventional case, making the switching element 7 conductive, and causing the braking resistor 6 to become conductive.
The above regenerative energy consumption is performed.

At the same time, the primary side current of the photocoupler 9 also flows through the switching element, and the photocoupler 9 becomes conductive, and the '2' level of the point A changes from the "L" level to the 1H" level.

That is, the level at point A represents the actual conduction of the switching element 7, and the braking control circuit 8 monitors the "H" level period and the "L" level period to determine the actual load on the braking resistor 6. The state can be monitored, and when the conduction continues beyond the specified value (more than the capability of the braking resistor 6), it is reflected to suppress the conduction of the switching element 7.

If the switching element 7 is damaged for some reason and becomes permanently conductive, the signal at point A will always be at the 1H'' level, so the conduction command signal to the switching element γ will command non-conduction. Even though the signal at point A is “H”
“By detecting the level, it is possible to easily detect an abnormality in the switching element 7.

If an abnormality can be detected as described above, it becomes possible to cut off the supply from the commercial power source 1, and it is possible to prevent abnormal overheating of the braking resistor 6.

Here, if a microcomputer is used as the brake control circuit 8, the above-described control can be easily achieved.

In the above embodiment, an example was shown in which the 7-digital coupler 9 was connected to the positive side of the DC link part, but as shown in FIG.
Even if it is connected to the negative side of the CIJ link section, the level at point A is only inverted, and the same effect can be obtained.

In addition, in the illustrated example, a photocoupler that can insulatedly detect the conduction state of the switching element is used as the continuity detection means, but a current transformer that detects the current flowing through the switching element or an excitation coil connected in series with the switching element is used as the continuity detection means. A relay or the like can also produce the same effect as above.

〔Effect of the invention〕

As described above, according to the present invention, since abnormal conduction of the switching element connected in series with the braking resistor is detected, the operation of the inverter can be promptly stopped based on the abnormal conduction detection signal. This has the effect of reliably preventing abnormal overheating of the braking resistor.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a protection circuit for a braking resistor of an inverter according to one embodiment of the present invention, FIG. 2 is a circuit diagram showing another embodiment, and FIG. 3 is a conventional protection circuit for a braking resistor of an inverter. It is a diagram. 5 is a target, 6 is a braking resistor, 7 is a switching element, 9
is a photocoupler. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Procedural amendment (voluntary)

Claims (2)

[Claims] (1) A braking resistor and a switching element are connected in series between the positive pole side and the negative pole side of the DC link part of the inverter, and the regenerative energy from the motor connected to the AC output side of the inverter is consumed by the braking resistor. In the inverter, the inverter is configured to include a continuity detection means for detecting a conduction state of the switching element, and a continuity detection means for controlling on/off of the switching element and detecting abnormal conduction of the switching element based on a detection signal from the continuity detection means. A protection circuit for a braking resistor of an inverter, comprising a braking control circuit for detecting. (2) A protection circuit for a braking resistor of an inverter as set forth in claim 1, wherein the continuity detection means is a photocoupler.