Operation modes of series inverter 400 kHz for induction heating

A series inverter for induction heating applications working with MOSFETs is presented. Two different operation modes of a MOSFET inverter are discussed. The presented concepts are verified with measurements resulting from a prototype inverter running at 10 kW/400 kHz. In the operation above at the resonance frequency of the series load circuit it is important to protect the switches from overvoltage stress. This paper identifies the cause of the stress and works out options to tackle the overvoltage amplitude. It is shown that the parasitics of the MOSFET with a suitable gate drive may be utilized to aid lossless turn off. In operation below resonance, the high switching speed imposes heavy stress on the MOSFETs. For this operation mode, a novel gate drive circuit is presented that dynamically enables switching in this mode