Optimum use of DC side commutation in PWM inverters

Switching losses limit the inverter switching frequency and decrease the overall conversion efficiency. Minimizing switching losses can be effectively achieved by employing soft switching techniques. Specifically, zero voltage switching (ZVS) for a three-phase voltage source inverter (VSI) can be obtained by reducing the switch voltage to zero before main transistor turn-on (switch antiparallel diode conduction) and by keeping the switch voltage to zero during turn-off (purely capacitive snubber). A novel three-phase ZVS PWM VSI topology employing a simple DC bus active snubber subcircuit that provides soft switching commutations is proposed. The main advantage of the proposed inverter commutation scheme is that the DC bus snubber subcircuit is activated only when required, that is when dictated by the respective pulsewidth modulator. Detailed analysis and design procedures are provided and simulation and experimental results are presented to verify the principles of operation of the proposed power inverter scheme