Simple starting scheme for a parallel resonance inverter for induction heating

A starting scheme for thyristor-based parallel resonant current source inverters, with particular reference to induction heating applications, is presented. The input stage to the DC-link is a three-phase phase controlled rectifier. It is shown that instead of using the usual startup circuits providing forced commutation, it is possible to start the system by using a single additional thyristor across the DC-link inductor, together with a special timed gating at the input and output converter. The scheme provides startup for a wide range of loads. The paper explains the principle starting concept and derives a simplified model to quantify the important parameters that govern the startup. The theoretical concept is verified by experimental data demonstrating the start of such an inverter