JPH02168813A - Protective circuit for voltage type inverter - Google Patents

Abstract

PURPOSE:To prevent burning reliably by monitoring the voltage across a resistor for suppressing a smoothing capacitor charging current and interrupting the circuit upon continuation of high voltage for a long time. CONSTITUTION:Upon closure of a switch 1, a smoothing capacitor C is charged with the output from a rectifier 2. A contactor 3 is opened by the output from a voltage comparator 4 during when the voltage across the capacitor C is low, and limited current flows through a charging current suppressing resistor R1. At this time, an output is produced from a photo-coupler 8 but a time limit element 9 does not function because it is set to a larger value when compared with the value being set during charging operation of the capacitor C. Upon charging of the capacitor C, the contactor 3 is thrown in the through the voltage comparator 4 and the charging current suppressing resistor R1 is bypassed. Upon occurrence of abnormality in the circuit, output from the capacitor C drops to open the contactor 3 so as to produce output continuously from the photo-coupler 8, and the switch 8 is released upon elapse of time set in the time limit element 9.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a protection circuit for a DC intermediate circuit rectifier of a voltage source inverter and a resistor for suppressing capacitor charging current.

[Conventional technology]

A conventional voltage source inverter device of this kind is known, the circuit diagram of which is illustrated in FIG. That is, an AC power supply switching breaker or contactor 1, an AC input rectifier 2, a capacitor C for smoothing the output of the rectifier, a resistor R1 for suppressing the capacitor charging current, a contactor 3 for shorting the current suppressor, and the contactor coil excitation. A DC intermediate circuit comprising a voltage comparator 4, a braking resistor R2 for suppressing overvoltage of the terminal voltage Ed of the capacitor C, and a transistor 5 for energizing the braking resistor, and an AC motor 7 as a load using the intermediate circuit output voltage as a power source. It is composed of a voltage source inverter 6 for driving.

Here, the current suppression resistor R1 is for suppressing the inrush charging current of the capacitor C during a transient period immediately after application of the AC power supply voltage due to the closing of the breaker or contactor 1, and as the capacitor C is charged, When the terminal voltage Ed rises above a specified value, the voltage comparator 4 excites the coil of the short-circuit contactor 3, and the contact closes, thereby preventing short-circuiting of the current suppressing resistor R1. At this point, the operation of suppressing the charging current of the capacitor C by the resistor R1 ends. Therefore, the resistor R1 is originally energized for a short period of time.

Further, when the AC motor 7 is controlled to decelerate, its rotational energy is regenerated to the power supply side via the inverter 6 and increases the capacitor terminal voltage Ed, but the voltage Ed exceeds a specified value set above its rated value. When this happens, the transistor 5 is controlled to be conductive, and the braking resistor R2 is energized to cause the resistor R2 to consume the regenerated energy as thermal energy, thereby avoiding an abnormal rise in the capacitor terminal voltage Ed.

[Problem to be solved by the invention]

However, in the above conventional system, if the transistor 5 is short-circuited or is erroneously controlled and becomes continuously conductive, the capacitor terminal voltage Ed decreases, and the contactor 3 closes its contact due to the decrease in the coil excitation voltage. Since the circuit is opened, the short circuit of the current suppressing resistor R1 is broken, and as a result, a current exceeding the specified value continuously flows through the rectifier 2 in the series circuit of the resistor R1 and the braking resistor R2. , therefore the normally short-time rated resistance R
There was a risk that the rectifier 2 as well as the rectifier 1 would be burnt out.

In view of the above, an object of the present invention is to provide a state detection and protection circuit when a braking transistor circuit of a voltage source inverter DC intermediate circuit is abnormal.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a breaker or contactor for switching an AC power supply, an AC input rectifier, a smoothing capacitor for the output of the rectifier, a resistance for suppressing the charging current of the capacitor, and a contactor for shorting the suppression resistance. a DC intermediate circuit consisting of a voltage comparator for excitation of the contactor, a braking resistor for suppressing overvoltage of the capacitor terminal voltage, and a transistor for energizing the braking resistor; and a voltage for driving an AC motor as a load using the intermediate circuit output voltage as a power source. In an inverter device comprising a type inverter, a photocoupler connected in parallel to the capacitor charging current suppression resistor and a time element operated by an output signal of the photocoupler are provided, and the voltage period of the voltage across the current suppression resistor is When the time exceeds the set time of the timer, which is determined by taking into account the normal charging time of the capacitor when the power is turned on, the condition is determined to be an abnormality in the DC intermediate circuit, and the AC power supply switching breaker or contactor is opened. It is something.

[Effect]

When the voltage period of the voltage across the current suppressing resistor detected by the photocoupler exceeds the set time of the timer determined by the power-on charging time constant of the capacitor, this state is detected by the short-circuiting contact. Due to the operation of the capacitor, the energization state in the pre-electromotive current suppression resistor, which should normally occur only during a transient period immediately after the application of the power supply voltage to the capacitor, continues for more than a specified time. By disconnecting the device from the AC power source, the rectifier and the charging current suppressing resistor, which is originally used at short-time rating, are protected from burnout due to continuous overcurrent.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and components having the same functions as those in the prior art embodiment shown in FIG. 2 are given the same reference numerals.

Figure 1 shows the capacitor charging current suppression resistor R shown in Figure 2.
A timer element 9 which is connected in series with the photocoupler 8 and the photocoupler current limiting resistor R3 in parallel with the resistor R1 at both ends of the photocoupler 8 and whose input signal is the output signal of the photocoupler 8.
The output signal of the timing element 9 provides a voltage application signal for excitation of the tripping coil when the AC power supply switch 1 is a breaker, and a voltage application signal for excitation of the closing coil when the switch 1 is a contactor. It is designed to give a voltage cutoff signal.

The operation time setting value of the timer 9 is such that when the charging circuit state of the smoothing capacitor C is normal, the terminal voltage Ed will surely close the shorting contactor 3 of the resistor R1 during a transient period immediately after the power supply voltage is applied. The value is set as the time required to reach a sufficient value plus an appropriate margin time.

Therefore, when the circuit shown in FIG. 1 is in a normal state, when an AC power supply voltage is applied to the circuit, the capacitor terminal voltage Ed immediately after the voltage application is lower than the closing voltage of the short-circuit contactor 3, so it is caused by the contactor contact. The charging current suppressing resistor R1 is not short-circuited, and the transient charging current limited by the resistor flows into the capacitor C. As a result, the terminal voltage Ed rises and becomes equal to or higher than the specified voltage of the contactor excitation voltage comparator 4, which is set as the contactor 30 closing voltage, and the contactor 3 operates and its contacts close. A short-circuiting of the resistor R1 is effected by the contact.

At this stage, the capacitor C flows according to the difference voltage between the output voltage of the AC input rectifier 2 and the terminal voltage Ed.
The charging current becomes small, the transient state of the charging current immediately after the AC power supply voltage is applied almost ends, and the voltage source inverter 6
A current corresponding to the load state of the contactor 3 passes through the contacts of the contactor 3, but does not flow through the resistor R1. Therefore, the voltage state with a voltage drop across the resistor R1 occurs only within a short period of time until the end of the transient state, and in the steady state after the end of the transient state, there is no voltage equal to the voltage drop across the contacts of the contactor 3. Become.

However, if the current-carrying transistor 5 of the braking resistor R2 is short-circuited or damaged, or if a continuous abnormal conduction state occurs due to malfunction of the control circuit of the transistor 5, a low-resistance short circuit of the power supply due to the braking resistor R2 is caused, and the terminal voltage Ed
decreases, the contactor 3 is opened due to insufficient excitation voltage, the short circuit of the resistor R1 by the contactor contact is released, and the rectifier 2 is connected to the series circuit of the resistor R1 and the resistor R2.
An abnormal condition occurs in which a continuous current flows due to the output voltage.

Therefore, a voltage drop sufficient to operate the photocoupler 8 occurs across the resistor R1, and when the duration thereof exceeds the set time of the timer 9 which uses the output signal of the photocoupler 8 as an input signal, the timer 9 is activated. The output signal of 9 provides an opening signal for the AC power supply breaker or contactor 1 as described above, and as a result, the continuous abnormal current is interrupted by disconnecting the power supply. Therefore, a burnout accident due to continuous abnormal current in the rectifier 2 and the resistor R1, which normally performs short-time rated operation, is prevented.

〔Effect of the invention〕

As described above, the present invention detects an abnormal conduction state due to short-circuit damage of the braking resistor current-carrying transistor in the DC intermediate circuit of a voltage source inverter or malfunction of its control circuit, and based on the abnormal state (AC input rectifier due to continuous overcurrent) This has the effect that a protection circuit that reliably prevents a burnout accident between the capacitor charging current suppressing resistor and the capacitor charging current suppressing resistor can be provided at a low cost.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram illustrating a conventional technique. In both figures, circuit components having the same function are given the same reference numerals. 1... Breaker or contactor, 2... Rectifier, 3...
... Contactor, 4... Voltage comparator, 5... Transistor, 6... Voltage type inverter, 7... AC motor,
8... Photocoupler, 9... Timing element, C... Smoothing capacitor, R1... Charging current suppression resistor, R2...
・Braking resistance, R3...Resistance for photocoupler, Ed...
Smoothing capacitor terminal voltage.

Claims (1)

[Claims] 1) A breaker or contactor for switching an AC power supply, an AC input rectifier, a capacitor for smoothing the output of the rectifier, a resistor for suppressing the charging current of the capacitor, a contactor for shorting the suppressing resistor, and a voltage comparator for exciting the contactor. An inverter device comprising a DC intermediate circuit comprising a braking resistor for suppressing overvoltage of the capacitor terminal voltage and a transistor for energizing the braking resistor, and a voltage source inverter that uses the intermediate circuit output voltage as a power source to drive an AC motor as a load, A photocoupler connected in parallel to the capacitor charging current suppressing resistor and a timer operated by the output signal of the photocoupler are provided, and the voltage period of the voltage across the current suppressing resistor is the normal charging time of the capacitor when the power is turned on. The voltage type inverter is characterized in that when the time exceeds the set time of the time limit element determined by taking into account, the condition is treated as an abnormality in the DC intermediate circuit and the AC power source switching breaker or contactor is opened. protection circuit.