SU838975A1 - Series inverter - Google Patents

Description

The invention relates to a converter technique and can be used in thyristor frequency converters for induction heating. Serial stand-alone inverters are known, which allow to regulate the output power, containing a load circuit connected to a power source through an input choke with a coupling capacitor and a thyristor bridge connected in parallel to the load circuit with counter-parallel diodes and a switching Lc circuit, with the switching circuit has two chokes, included in different shoulders of bridge 1, the gates of this inverter are overloaded with currents of the on-bridge discharge of the switching capacitor, which narrows the range p Regulation and stability of work. In addition, this scheme is difficult, because it contains not one, but two commuting Drossel. Closest to the proposed is a series inverter containing load circuits with a coupling capacitor connected to a power source through an input choke and a thyristor bridge with counter-parallel diodes and a commutating L C-circuit in the diagonal of alternating current, as well as an additional choke by thyristors. This inverter has an extended control range and high switching resistance, however, it has a significant drawback - complexity, since the additional choke is connected in series with the LC circuit, and the thyristors that bypass it are connected anti-parallel,; A high-power inverter is known, in which the thyristor bridge is actually made as a parachute, serial or mixed connection of several circuits, which is necessary for a uniform load of all power elements 3. Such inverters are also complex, it becomes necessary to introduce additional chokes for I to the number of bridges. and twice as many shunt thyristors. The aim of the invention is to simplify the device.

To accomplish this goal in inverter 21, an additional choke is connected between the connection point of the load circuit with the input choke and the thyristor bridge, with the thyristors shunting the additional choke being connected in the forward direction. In FIG. 1 is a schematic diagram of the sequential invertor of FIG. 2 - time diagrams.

The circuit contains a load circuit connected to the power source through an input choke 1, consisting of a separate: capacitor 2, protective choke 3 and load 4. Parallel to the load circuit there is a thyristor bridge connected to thyristors 5–8 with counter-parallel diodes 9–12, the diagonal of the alternating current of which is a switching circuit of an LC circuit / consisting of throttles 13 and a capacitor 14. An additional choke 15 is connected between the load circuit and the thyristor bridge and is shunted by thyristors 16 and 17 connected in the same direction, as the thyristors of the bridge.

The scheme works as follows.

At the initial moment of time, the separation capacitor 2 of large capacity is charged up to the voltage by the power supply, and the capacitor 14 of the switching circuit is charged to a certain polarity (Fig. 1). At this moment, control pulses are supplied to the thyristors 16, 5, 8, and the capacitor 14 is oscillatingly recharged along the circuit thyristor 8 - load 4 - choke 3 - capacitor 2 - thyristor 16 - thyristor 5 choke 13. At the moment of time t the current flowing through this circuit, passes through zero, and the thyristors 16, 5, 8 are turned off, after which diodes 9 and 12 begin to conduct, passing the reverse half-current of the recharge of the capacitor 14 (Fig. 2a, current of the thyristor bridge) and instead of the thyristor 16 into the circuit recharge yes an additional choke is turned on 15. During the interval, conduct Bridges of diodes 9 and 12 to the thyristors of bridge 5 and 8 a small reverse voltage is applied, contributing to their recovery. By introducing an additional inductance into the circuit, the recovery time is increased compared to a conventional circuit without additional chokes:

.. ° bf

bl5JlJjl3lbi.

.gss

 recovery time

where are the thyristors of the bridge;

ip (Lc 0j is the recovery time of the bridge thyristors in the circuit without additional throttle; inductance of chokes

15, 13 and 3.

The additional choke also limits the approach current of the counter-parallel diodes to zero, and, therefore, switching voltages. As in the known scheme, in the proposed inverter it is possible to control the output power by changing the time shift of the control pulses of the thyristor 16 relative to the pulses, the control of thyristors 5 and 8. Depending on the magnitude of this shift, the average for the period the impedance of the inverter oscillating circuit determines the power released in the load.

During the next period of the output current, when the thyristors 7 and 6 are first conducted, then the diodes and thyristors work in the same way as in the first period. Then the processes in the circuit are repeated.

As can be seen from the graph of the voltage on the additional thyristor (Fig. 26, the period C-Bd) is the time of the restoration of the thyristor 16, which is about half the time of the restoration of the thyristors, but due to the significant magnitude of the applied reverse voltage and a low voltage rise rate

, quite enough for a reliable com: mutations additional thyristor.

Note that if devices of the same type with bridge thyristors are used as additional thyristors, then the number of additional thyristors connected in parallel is equal to twice the number of parallel connected bridges in the inverter (Fig. 1, shown by dotted lines). At the same time, additional thyristors connected in parallel are turned on alternately, synchronously with the corresponding thyristors of the bridges, skipping the corresponding half-wave current so that the average current load of the additional thyristors is approximately the same as the average current load of the thyristors of the bridges. in the case of using additional thyristors that are more powerful with respect to the allowable current load, it may be sufficient to include one additional thyristor, which is turned on synchronously with each switching on of the thyristors in the bridges. All additional ms thyristors (can be installed on one common cooler

Claims (3)

1. Thyristor frequency converters for induction heating of metals. Proceedings of the Ufa Aviation Institute. Issue 64, Ufa, 1974, p. 5-11. 2. Authors certificate of the USSR. 712911, cl. H 02 M 7/515, 1977. ; 3. Thyristor converters; frequencies for induction heating of metroshells. Works AIM. Issue; XXI1. Ufa, 1971, p. 52-64.