Firing strategy for bidirectional current switches with unidirectional voltage blocking capability in induction heating parallel resonant inverters

A new firing strategy for a resonant current fed inverter based in switches formed only by IGBTs, without the series diode, is presented in this paper. It is described the behavior of the inverter topology proposed and two different strategies for its reliable operation are explained: control of the switching current level, and control of the over-current through the anti-parallel diodes. Dynamic behavior of the switches defines the frequency limit for the application of one strategy or the other. IGBTs without the series diode are bidirectional current switches with unidirectional blocking voltage capability. This characteristic must be taken into account to define an adequate switching strategy for this converter's topology. Two main advantages are the key issue for the use of this kind of switches: it is a cost-effective solution and the efficiency of the inverter is increased.