Half-bridge inverters with transformer loads in an alternating current (ac) diagonal are widely used in various electrical installations. Classic variant of such inverters is corresponded the half-bridge of two transistors shunted by two reverse diodes and the half-bridge of two capacitors in-series. A load of the ac diagonal is usually a transformer and the direct current (dc) diagonal is connected to the power source. Main advantages of such inverters are simplicity of the circuit and a default of the constant component in the ac diagonal. The replacement of transistors by thyristors in the half-bridge has own deficiencies: a thyristor half-bridge inverter is operable in restricted load range and his regulation is probable by pulse-frequency method only. Using of the additional switching unit permitting to perform the recharge of the metering capacitor is part of that unit are one of removal variants of that´s disadvantages. Thus a half-bridge inverter control is realized over a wide load range by the instrumentality of the standard time-proportional control system closed on a load current. The hardware form of a realization of the described control system is given in  and the up-to-date form microcontroller-based is given in . But a range extension of regulation of an inverter load is attended by definite problems: 1) the preliminary recharge circuit of metering capacitor contains the circuit composed of thyristors, inductances and the metering capacitor in-series, that increased additional energy losses; 2) transformer windings voltage amplitude and load voltage were vary from zero to supply voltage when the control process is occurred. When voltage amplitude is reduced that an ionization is complicated and an arc excitation is complicated if, for example, electrical arc was a load ; 3) the circuit of the additional switching unit is more difficult.
The solution permitting to eliminate above-listed disadvantages is proposed in . The new respective circuit of the thyristor half-bridge inverter is shown on figure 1.
The device contains the thyristor half-bridge inverter compressed of capacitors 1, 2, thyristors 3, 4, and the additional switching unit. This unit is corresponded the additional thyristor half-bridge inverter compressed of thyristors 7, 8 and capacitors 5, 6 which capacities are far less than capacities of capacitors 1, 2. The dc diagonal of this additional inverter is connected in-parallel with the thyristor half-bridge inverter 1, 2, 3, 4. The primary winding of the transformer 9 is connected with the ac diagonal of the half-bridge inverter 1, 2, 3, 4. And the secondary winding of this transformer is connected to the direct current load 13, which is connected in-parallel with the current sensor 14. In addition, the transformer 9 contains the additional winding 15 that is connected to the ac diagonal of the additional thyristor half-bridge inverter 5, 6, 7, 8 and having the number of loops are less than the number of loops of the primary winding 10. The control system is corresponded the standard system of a pulse-frequency regulation. This system consists of the surge injector unit 16 connected with the one of outputs of pulse-length modulator 17. In addition, the feedback controller is compressed of standard system of a pulse length regulation and the mentioned standard system is closed on a load current by an output signal of the current sensor 14 connected with one of outputs of the feedback controller 18. The secondary input of this controller is connected with the signal of source current U3 and the output of this controller 18 is connected with the secondary input of the pulse-length modulator 17. The output of the mentioned surge injector unit 16 is connected with respective driving points of thyristors 3, 4 and the output of the pulse-length modulator is connected with respective driving points of thyristors 7, 8 included in the additional thyristor half-bridge inverter 5, 6, 7, 8.
The new device permits to exclude the circuit of a preliminary recharge of the metering capacitor together the metering capacitor. Capacitors of the thyristor half-bridge inverter are performed the duties of the metering capacitor thus losses were decreased and circuit was more simplify. In addition, voltage amplitude of the load was not changed and was some more than voltage supply when half-period average voltage of the load was changed in the mentioned device. That made considerably easier the "firing" and the arc stability if arc space was a device load.
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The work was submitted to international scientific conference «Priorities for Science, Technology and Innovation», Egypt (Sharm el-Sheikh), November 20-27, 2008, came to the editorial office оn 06.03.2009.