JPH08317660A - Protective circuit for power conversion apparatus - Google Patents

Abstract

PURPOSE: To obtain a protective circuit which prevents a charging resistance inserted across a rectifier and a smoothing capacitor for a power conversion apparatus from being overheated and burned out. CONSTITUTION: A protective circuit is provided with a timer circuit 70 by a voltage across both ends of a charging resistance 3, with a comparator 80 which detects and compares the voltage of a smoothing capacitor 5 and with a sequence circuit 20. In a normal operation, both ends of the charging resistance 3 are short-circuited by the contact 4a of a contactor 4 for short-circuiting by operating the comparator 80. In an abnormal operation, under a condition where the timer circuit 70 is operated and that the comparator 80 is not operated, an AC contactor 1 is not excited, and a voltage is made extinct.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for a power converter which converts DC power obtained by a rectifier and a smoothing capacitor into AC power of a desired voltage and frequency by an inverter.

[0002]

2. Description of the Related Art In a power converter of this type, when a commercial power supply is supplied to the input of the rectifier, an excessive charging current flows through the smoothing capacitor to prevent the rectifier from being damaged in order to prevent damage to the rectifier. A charging resistor is inserted between the capacitor and the capacitor, and when the voltage across the smoothing capacitor rises to a predetermined value, the charging resistor is short-circuited.

The charging resistor is a downsized power converter.
It is selected to operate in the short-time overload region of the charging resistor for cost reduction.

[0004]

SUMMARY OF THE INVENTION The charging resistor described above is a commercial power supply for the input of the rectifier when a short-circuit fault or the like occurs due to some trouble on the load side of the DC power obtained by the rectifier and the smoothing capacitor. There is a risk that overheating and burning will occur when the power supply of No. 1 is started, and in the conventional power conversion device of this type, a temperature sensor was installed on the surface of the charging resistor to protect from overheating and burning. It was sometimes difficult to detect the temperature rise above C and within a short time (about 0.5 seconds).

An object of the present invention is to provide a protection circuit for a power conversion device that solves the above problems.

[0006]

According to a first aspect of the present invention, there is provided a protection circuit for a power converter for converting direct-current power obtained by a rectifier and a smoothing capacitor into alternating-current power having a desired voltage and frequency by an inverter. The AC contactor connected to the AC input side of, the charging resistor inserted between the rectifier and the smoothing capacitor, the short-circuiting contactor connected in parallel with the charging resistor, and the voltage across the smoothing capacitor are A comparator that operates when the voltage exceeds a specified voltage, a timer circuit that detects that the voltage across the charging resistor exceeds a specified voltage, and measures a specified time period from when it is detected, and an AC contactor. And a sequence circuit that turns on the short-circuit contactor when the comparator is operated and turns off the AC contactor when the measured value of the timer circuit exceeds a predetermined time period.

In a second aspect of the invention, in the protection circuit for the power converter, an AC contactor connected to the AC input side of the rectifier, a charging resistor inserted between the rectifier and the smoothing capacitor, A short-circuit contactor connected in parallel with the charging resistor, a comparator that operates when the voltage across the smoothing capacitor exceeds a predetermined voltage, and a timer that measures a predetermined time period from when the AC contactor is turned on. And a sequence circuit that turns on the AC contactor, turns on the short-circuiting contactor when the comparator operates, and shuts off the AC contactor when the measured value of the timer exceeds a predetermined time limit and the comparator is not operating. Equipped with.

[0008]

According to the first aspect of the invention, when the voltage across the charging resistor exceeds the predetermined voltage and exceeds the predetermined time limit,
By shutting off the AC contactor, overheating and burning of the charging resistor is prevented. According to the second invention, a predetermined time period is measured from the time when the AC contactor is turned on, and when the time period is exceeded and the voltage across the smoothing capacitor is less than the predetermined voltage, the AC contactor. By shutting off, the overheating and burning of the charging resistor is prevented.

[0009]

1 is a circuit configuration diagram of a protection circuit for a power conversion device according to a first embodiment of the present invention. In FIG. 1, reference numeral 1a is a contact point of the AC contactor 1 indicated by reference numeral Ry1,
Is a rectifier composed of a diode or the like, 3 is a charging resistor, 4a is an a contact of the short-circuit contactor 4 indicated by reference symbol Ry4,
Reference numeral 5 is a smoothing capacitor, 6 is an inverter including a transistor, 20 is a sequence circuit, 70 is a timer circuit, and 80 is a comparator.

The timer circuit 70 applies the voltage across the charging resistor 3 to the zener diode 71, the resistor 72 and the photocoupler 7.
When the zener voltage of the zener diode 71, for example, 5 V is exceeded, the transistor of the photocoupler 73 is turned on, and the timer unit 74 starts measurement. R
It operates so as to excite the relay 75 indicated by y7.

The comparator 80 is a smoothing capacitor 5
Is divided by resistors 81 and 82, and when this voltage exceeds a set value of the setter 83, for example, a voltage corresponding to 70% of the rated DC voltage of the output of the rectifier 2, the comparator section 84
Is operated, and as a result, it operates so as to excite the relay 85 indicated by the symbol Ry8. The operation of FIG. 1 will be described below with reference to the operation waveform diagram shown in FIG.

FIG. 2A shows an operation waveform diagram in a normal state, and the start switch 21 of the sequence circuit 20 at time t ₀ .
When is turned on, Ry7 is in a non-excited state, so that the AC contactor 1 (Ry1) is excited through the contact 7b, the voltage of the commercial power source is applied to the rectifier 2 through the contact 1a, and the smoothing capacitor 5 charges the charging resistor 3 It is charged via the battery and gradually rises ((B) in FIG. 2 (A)).

Next, at time t ₁ , the comparator 80 operates to excite Ry8, the contact 8a of Ry8 is turned on to excite the short-circuiting contactor 4 (Ry4), and the charging resistor 3 is short-circuited by the contact 4a. This completes the startup. Time t ₀
Since the period of time t ₁ is shorter than the set time of the timer unit 74 of the timer circuit 70, Ry7 remains in the non-excited state ((to) in FIG. 2A).

FIG. 2 (B) shows an operation waveform diagram when the inverter 6 is started in a state where some trouble has occurred, and when the start switch 21 of the sequence circuit 20 is turned on at time t ₀ , Ry7 becomes Contact 7b because it is not excited
The AC contactor 1 (Ry1) is excited via the
The voltage of the commercial power source is applied to the rectifier 2 through the charging resistor 3 and the smoothing capacitor 5 is charged through the charging resistor 3, but the voltage rise is slight due to the above-mentioned trouble (see (B) in FIG. )), The comparator 80 does not work and therefore Ry8
Remains unexcited, and the short-circuit contactor 4 (Ry4) remains unexcited ((c) in FIG. 2B).

However, since the voltage is sufficient for the photocoupler 73 of the timer circuit 70 to operate ((D) of FIG. 2B), the set time of the timer section 74 is exceeded at time t ₂ , and Ry7 Is excited and AC contactor 1 (Ry1)
Is de-excited, the commercial power supply is cut off, the voltage across the charging resistor 3 also disappears, and overheating and burning are prevented. FIG. 3 is a circuit configuration diagram of a protection circuit of a power conversion device showing a second embodiment of the present invention. Components having the same functions as those in the circuit diagram of FIG. To do.

The operation of FIG. 3 will be described below with reference to the operation waveform diagram shown in FIG. FIG. 4A shows an operation waveform diagram in a normal state, and when the start switch 31 of the sequence circuit 30 is turned on at time t ₀ , the relay 9 indicated by the reference symbol Ry9.
Is a non-excited state, the AC contactor 1 (R
y1) is excited, the voltage of the commercial power source is applied to the rectifier 2 via the contact 1a, and the smoothing capacitor 5 is charged by the charging resistor 3
It is charged through the battery and gradually rises ((B) in FIG. 4 (A)).

Next, at time t ₁ , the comparator 80 operates to excite Ry8, the contact 8a of Ry8 is turned on to excite the short-circuiting contactor 4 (Ry4), and the charging resistor 3 is short-circuited by the contact 4a. This completes the startup. Time t ₀
And the time t ₁ is shorter than the time set by the timer 10, for example, 0.5 seconds ((e) in FIG. 4A), Ry9
Remains unexcited ((to) in FIG. 4 (A)).

FIG. 4B shows an operation waveform diagram when the inverter 6 is started in a state where some trouble occurs, and when the start switch 31 of the sequence circuit 30 is turned on at time t ₀ , Ry9 becomes Contact 9b because it is not excited
The AC contactor 1 (Ry1) is excited via the
The voltage of the commercial power source is applied to the rectifier 2 via the charging resistor 3 and the smoothing capacitor 5 is charged via the charging resistor 3. However, the voltage rise is slight due to the above-mentioned problem (see (B) in FIG. )), The comparator 80 does not work and therefore Ry8
Remains unexcited, and the short-circuit contactor 4 (Ry4) also remains unexcited ((c) of FIG. 4 (B)).

However, when the set time of the timer 10 operated by the activation switch 31 being turned on exceeds the time t ₂ ((e) in FIG. 4B), Ry9 is excited and the AC contactor 1 (Ry1). Is de-excited, the commercial power supply is cut off, the voltage across the charging resistor 3 also disappears, and overheating and burning are prevented.

[0020]

According to the present invention, it is not necessary to directly detect the temperature of the charging resistor, which becomes high temperature, at high speed, overheating and burning of the charging resistor is prevented, and it is possible to reliably protect the power conversion device at a low cost. For example, it is suitable as an inverter device for driving an electric motor.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a protection circuit of a power converter showing a first embodiment of the present invention.

FIG. 2 is a waveform diagram illustrating the operation of FIG.

FIG. 3 is a configuration diagram of a protection circuit of a power conversion device showing a second embodiment of the present invention.

FIG. 4 is a waveform diagram illustrating the operation of FIG.

[Description of Reference Signs] 1 ... AC contactor, 2 ... Rectifier, 3 ... Charging resistance, 4 ... Shorting contactor, 5 ... Smoothing capacitor, 6 ... Inverter, 9
... relay, 10 ... timer, 20, 30 ... sequence circuit, 21, 31 ... start switch, 70 ... timer circuit, 7
DESCRIPTION OF SYMBOLS 1 ... Zener diode, 72 ... Resistor, 73 ... Photocoupler, 74 ... Timer part, 75 ... Relay, 80 ... Comparator, 81, 82 ... Resistance, 83 ... Setting device, 84 ... Comparator part, 85 ... Relay.

Claims (2)

[Claims] 1. A protection circuit of a power converter for converting DC power obtained by a rectifier and a smoothing capacitor into AC power of a desired voltage and frequency by an inverter, and an AC contactor connected to an AC input side of the rectifier. , A charging resistor inserted between the rectifier and the smoothing capacitor, a short-circuiting contactor connected in parallel with the charging resistor, and a comparator that operates when the voltage across the smoothing capacitor exceeds a specified voltage. And a timer circuit that detects that the voltage across the charging resistor exceeds a specified voltage and measures the specified time period from the time when it is detected, and a short circuit when the comparator operates after the AC contactor is turned on. A protection circuit for a power converter, comprising: a sequencer that turns on the contactor and shuts off the AC contactor when the measured value of the timer circuit exceeds a predetermined time limit. 2. A protection circuit of a power converter for converting DC power obtained by a rectifier and a smoothing capacitor into AC power of a desired voltage and frequency by an inverter, an AC contactor connected to an AC input side of the rectifier. , A charging resistor inserted between the rectifier and the smoothing capacitor, a short-circuiting contactor connected in parallel with the charging resistor, and a comparator that operates when the voltage across the smoothing capacitor exceeds a specified voltage. And a timer that measures a predetermined time period from when the AC contactor is turned on, and a short circuit contactor that is turned on when the AC contactor is turned on and the comparator operates, and the measured value of the timer is set to the predetermined time period. A protection circuit for a power converter, comprising: a sequence circuit that shuts off the AC contactor when the voltage exceeds the threshold and the comparator is not operating.