ZCS high frequency inverter using SIT for induction heating applications

A ZCS high frequency inverter with a fixed frequency voltage regulation scheme regulated by an instantaneous current-vector control is presented. Its total conversion efficiency reaches 90% owing to its soft switching operation. It is based on a conventional voltage-fed series-resonant half-bridge inverter, which incorporates reverse-blocking two-terminal quasi-resonant ZCS cells and utilises B-SITs as switching power devices. Thus, high conversion efficiency is attained. Its maximum voltages across active switching power devices are clamped to the DC source voltage so that the voltage rating of the switching power device can be suppressed at a lower level. Since the output power of the inverter depends on the value of impedance of the resonant load circuit, it should be determined at the most suitable value, which is, however, relatively low. Consequently, a working coil with a low inductance is required. On the other hand, its Output power is decreased considerably for a working coil with a high inductance. To solve this problem, a dual-resonant load circuit topology is introduced into the inverter circuit so that it can meet various loads. Next, the reverse-conducting ZCS inverter topology incorporating the reverse-conducting two-terminal quasi-resonant ZCS cells with its circuit operation and performance is described. In addition, a breadboard of this inverter is prepared and operated at 200 kHz for induction heating of an aluminium vessel with a sufficient efficiency. Note that induction heating of nonmagnetic material such as the aluminium vessel has been considered technically difficult.