Impact of IGBT behavior on design optimization of soft switching inverter topologies

IGBTs operated under a zero voltage switching scheme exhibit significantly different operating characteristics from specified parameters in manufacturer data sheets. Important differences include an elevated tail current, dynamic saturation and resulting snubber dump, and a significantly higher conduction loss under moderate to high di/dt conditions. Soft switching inverter topologies of various kinds have been reported in the literature including resonant DC and AC link inverters, resonant pole inverters and many variations thereof. Loss characterization of soft switching inverter circuits reported to date is based on manufacturer data sheets, and do not reflect actual losses incurred in the circuit. Including the actual device behavior into the circuit loss calculations has a big impact on the total losses, and more importantly the trade-offs which impact the viability of a given topology at a specified operating point. This paper presents a detailed analysis of the losses in soft switching inverters and the impact on topology choice. A detailed design of a 50 kVA IGBT-based resonant DC link inverter is used as a design example, and it is seen that optimal design points and choices are significantly different from those that have been reported earlier