JPS6012854B2 - Inverter protection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to a variable voltage variable frequency inverter (VV
It is abbreviated as VF inverter.

) protection circuit. Generally, an inverter circuit is configured to supply alternating current power to a load by intermittent DC voltage via a main thyristor, a commutation assisting thyristor head, and a group control reactor.

Each arm of the main thyristor and commutation auxiliary thyristor does not cause any problems as long as the commutation is carried out sequentially and accurately in a predetermined order. When the main thyristor or auxiliary thyristor arm short circuit occurs,
The short-circuit condition must be removed immediately. To this end, conventionally, a circuit has been considered in which when the commutation failure is corrected, the thyristor arm whose commutation has failed is extinguished by the resonance current of the reactor interposed between the smoothing capacitor and the thyristor arm. This method is effective for inverters with a constant DC power supply voltage, but cannot be applied when the DC power supply voltage drops, such as in VVVF inverters, because the arc extinguishing energy is insufficient. In addition, when a rectifier circuit or a DC chopper circuit is generally used as a variable DC power supply, the capacitance of the smoothing capacitor inevitably becomes large, which causes the circuit to become non-oscillatory, resulting in large attenuation of the resonant current and arc extinguishing ability. It has the disadvantage of causing a decrease in Furthermore, since the arc-extinguishing ability is influenced by the wiring resistance and the critical resistance becomes small, it is difficult to obtain a constant arc-extinguishing ability. On the other hand, in conventional circuits, if the reversal current is increased to increase the arc extinguishing ability of the thyristor, the half-cycle peak current when a short circuit occurs in the thyristor arm also increases, and the overcurrent rating of the thyristor must be increased. Next, although conventional circuits protect against inverter commutation failure and commutation assist thyristor arm short circuit, in order to obtain a constant commutation capability in the VVVF inverter, a charging assist thyristor is provided independently. The inverter has the disadvantage that it cannot provide protection against a short circuit between the charging auxiliary thyristor and the commutation auxiliary thyristor. The purpose of the present invention is to provide an inverter with
The object of the present invention is to eliminate all of the above-mentioned drawbacks by adding a very simple circuit mainly consisting of thyristors and diodes, and to reliably prevent thyristor arm short-circuiting without increasing the overcurrent rating of the thyristor.

The illustrated embodiment will be specifically described below. The figure is a circuit diagram showing the present invention. In the figure, 1 is a variable DC power supply, which is connected to an inverted L-shaped smoothing circuit consisting of a reactor 2 and a capacitor 3. 4 and 5 are the main thyristors, with one thyristor arm, both ends, group rail actuator 6,
7 is connected, and an anti-parallel circuit consisting of a diode 8 and a thyristor 9 is connected to both ends of the capacitor 3, that is, to the series circuit of the variable DC power supply 1 and the actuator 2, through an anti-parallel circuit consisting of a diode 8 and a thyristor 9. 1 voltage is applied in the forward direction.

At this time, the main thyristors 4 and 6 are responsible for orthogonal conversion for one phase, and although not shown, main thyristor arms and associated elements are provided as many as the number of phases required by the load. It is assumed that there is Feedback diodes 10 and 11 are connected antiparallel to the main thyristors 4 and 5, respectively. Reference numerals 102 and 13 denote auxiliary thyristors for commutation, which are made up of one thyristor arm, each end connected to restraint reactors 14 and 15, and the main thyristors 4 and 5 mentioned above.
The thyristor arm is connected in parallel with the thyristor arm with matching polarity.

16 is a commutation capacitor, 17 is a commutation reactor,
They are connected in series and are connected between the connection point of the main thyristors 4 and 5 and the connection point of the auxiliary thyristors 12 and 13.

Reference numeral 18 denotes an auxiliary power supply provided as a constant voltage DC power supply for supplying commutation energy, and is connected to a smoothing circuit formed by connecting a reactor 19 and a capacitor 20 in an inverted L shape. Reference numeral 21 denotes a thyristor, which is connected to the capacitor 20 through the group control axle 22 with the polarity shown.

Reference numeral 23 denotes an ignition device which supplies a gate signal for the thyristor 21 in response to a signal from a current transformer 24 which obtains a signal proportional to the current flowing in the capacitor 20. That is, when the signal from the current transformer 24 becomes 0, the thyristor 21
It is configured to ignite. At the thyristor 25', the groove and the reactor 26 are connected, and in addition, it is connected between one end of the capacitor 20 and the connection point of the auxiliary thyristors 12 and 13 with the polarity shown.

Reference numeral 27 denotes a load to which orthogonal power converted power is supplied from the connection point of the main thyristors 4 and 5. P is a gate control circuit,
Commutation auxiliary thyristor 12, 13 or main thyristor 47
When arm 5 is short-circuited, the gate of thyristor 9 is cut off as described later, and a gate signal is supplied to thyristors 25 and 13. It is something. This is accomplished by known means such as using a current transformer to detect overcommutation caused by a short circuit in the arms of the main thyristors 4, 5 or the auxiliary thyristors 12, 13 for commutation. In the configuration of the above embodiment, first, when the inverter is normally supplying power to the load, a signal is constantly supplied to the gate of the thyristor 9, and power from the variable DC power source 1 is transferred to the reactor 2 and the capacitor. The main thyristors 4 and 5 are connected through a smoothing circuit consisting of 3
This results in orthogonal power conversion based on phase control.

At this time, the commutation energy stored in the commutation capacitor 6 is reliably supplied from the constant voltage source 18 through the thyristor 25 even when the variable DC power supply 1 is particularly reduced. That is, it is synchronized so that the main thyristor 5 conducts power every time the main thyristor 5 conducts current, and performs a supplementary charging function for the commutating capacitor 16, which is charged by the illustrated gutter as the thyristor 4 commutates. Now, if an arm short circuit of the main thyristor 12 or auxiliary thyristors 12 and 13 occurs due to overload or accidental ignition, an overcurrent etc. based on the arm short circuit will be detected. The thyristors 25 and 13 are fired. Therefore, the charges accumulated in the smoothing capacitors 3 and 20 are discharged through the closed circuit including the thyristors 4 and 5 and the open circuit including the thyristors 25 and 13. At this time, Each thyristor is processed and generates a resonant current with the small cherry blossom and woven actor.

Among the resonant currents flowing in these two closed circuits, the resonant current flowing in the circuit including the thyristors 25 and 13 is constant, whereas the other resonant current is not kept constant depending on the voltage of the variable DC power supply 1. Since the capacitor 20 is charged to a constant voltage state by the voltage power source 18, the voltage is regulated to be constant.
Now, if the resonance current becomes 0 after this resonance half cycle has passed, the input signal from the current transformer 24 to the ignition device 23 will disappear. At this time, the ignition device 23
A pulse signal is supplied from , the thyristor 21 becomes conductive, and the reversal current after the resonance half cycle flows into an open circuit consisting of the capacitor 20 , the diode 8 , the thyristor 21 , and the reactor 22 . This reversal current flows through diode 8
When flowing through the diode 8, the thyristor 9 is reverse-biased with a voltage corresponding to the normal voltage drop across the diode 8, and the thyristor 9 is extinguished since the gate signal has already been lost during the arm short-circuit. Also, this reversal current is determined by the reactor 22 and capacitor 201,
Since it can be designed without regard to the peak current determined by the lj actors 26, 15, and 7 during discharge, it is possible to suppress the discharge current at the time of arm short circuit and to design a large reversal current. A large arc extinguishing capacity can be obtained. The ignition device 23 detects by the current transformer 24 that the current in the capacitor 20 is 0, and ignites the thyristor 21. That is, since it is detected that the voltage of the capacitor 20 is inverted, the charge of the capacitor 20 can be effectively used. In the above description, the arm short-circuit of the main thyristors 4, 5 to the auxiliary thyristors 12, 13 has been described, but the arm short-circuit of the thyristors 25, 13 is extinguished based on exactly the same effect. During steady operation of the inverter, the thyristor 21 is always reverse biased by the capacitor 20', and even if there is a timing when the outflow current from the capacitor 20 becomes zero, the thyristor 21 has no room to operate. As described above, the circuit according to the present invention is a circuit that connects a thyristor and a diode in antiparallel between a DC power supply and an inverter, or integrates these in an inverter equipped with a reactor in series with a thyristor arm for the inverter. Insert the reverse conduction thyristor so that when the inverter current flows from the DC power supply, it flows through the thyristor part, and when it is reversed, it flows through the diode part, and also connects the DC power supply for supplementary charging of the commutating capacitor and its smoothing circuit. In addition, a thyristor that controls supplementary charging from the smoothing capacitor to the commutating capacitor, and a thyristor that receives conduction control when the current from the smoothing capacitor is 0, and a thyristor in an anti-parallel circuit of the thyristor and diode. It is equipped with a resonance control thyristor that turns off the thyristor.

When the voltage of the DC power supply for the isoverter is variable, the thyristor can be reliably protected from arm short circuit due to commutation failure, especially at low voltage.

{〇} Disadvantages that arise due to the large capacity of the smoothing capacitor in VVVF inverters, namely, the critical resistance of the circuit becomes small, so it tends to become non-oscillatory, the attenuation of the resonant current increases, and the arc extinguishing ability decreases due to the wiring resistance. It is possible to solve all the drawbacks of the conventional method, such as the fact that the current is greatly affected, and that the initial half-cycle peak current at the time of an arm short circuit cannot be kept small and the reversal current cannot be increased.

It can protect against all arm short circuits in the inverter circuit.

Short-circuit protection devices such as fast-acting fuses and high-speed circuit breakers can be omitted by simply adding two thyristors and one diode.

Therefore, there is no need to replace a fast-acting fuse or reinsert a burnout switch during loss time when inverter commutation fails, and the entire device can be downsized. Further, even if an arm short circuit occurs, the circuit of the present invention protects the inverter and then automatically restarts the inverter.

[Brief explanation of the drawing]

The figure is a circuit diagram showing an embodiment according to the present invention. 1,18...DC power supply, 3,20...
Smoothing capacitor, 4, 5... Main thyristor, 8... Diode, 9... Thyristor, 12, 13...
・・Auxiliary thyristor, 6, 7, 14, 15, 22, 26
...,．．・Gundo Kick Actor・21. ．．・...thyristor.

Claims (1)

[Claims] 1 Connect the thyristor arms of the main thyristor for orthogonal power conversion and the auxiliary thyristor for main thyristor commutation for each phase, and the reactors for suppressing changes in current and voltage in series with each of these thyristor arms, and An inverter equipped with a diversion capacitor, a variable DC power supply and its first smoothing circuit for supplying power to the input side of the inverter, a constant voltage DC power supply and its second smoothing circuit for supplying commutation energy to the commutation capacitor. a smoothing circuit, a supplementary charging control thyristor that performs supplementary charging to the commutating capacitor from this second smoothing circuit, and its current;
In a circuit configuration consisting of a reactor for suppressing voltage changes, each DC power supply has a reverse conduction control circuit that incorporates a thyristor and a diode separately or integrally between the variable DC power supply, the constant voltage DC power supply, and the inverter. When the current flows from the inverter to the inverter, it flows through the thyristor part, and when the current flows in the opposite direction, it flows through the diode part, and the reverse conduction is inserted in parallel to the capacitor in the second smoothing circuit. A series circuit of a resonance control thyristor and a reactor having a forward polarity with the diode of the reverse conduction control circuit is connected through the control circuit, and the resonance control thyristor is connected to the polarity of the capacitor of the second smoothing circuit. means for igniting at the point when the current is reversed and the current becomes zero;
and when any of the thyristor arms in the inverter is short-circuited, the gate signal of the thyristor in the reverse conduction control circuit is removed, and the thyristor for supplementary charging control and the thyristor in the inverter directly connected to the thyristor arm in the forward direction are removed. A protection circuit for an inverter, comprising: a means for igniting the inverter.