Soft switching active snubbers fordc/dc anddc/ac converters

Pulse width modulated (PWM) converters are increasingly used in energy conversion because of their control simplicity and their low steady state stress on power semiconductor devices. Among their drawbacks are the high stresses and high losses that occur during the switching transitions (turn-on and turn-off). Soft switching active snubbers are used to alleviate these stresses and to reduce switching losses.; A class of soft switching active snubbers for isolated and non-isolated dc/dc converters is proposed. These snubbers use an auxiliary switch to shape the voltage and the current of the main switching device at turn-on and turn-off. Both zero-voltage (ZVS) and zero-current (ZCS) switching active snubbers are derived and demonstrated. A generic snubber cell is identified for isolated and non-isolated dc/dc converters. A unity power factor three-phase diode rectifier and a buck dc/dc converter are used for verification purposes.; The dc/dc generic snubber cell is used to derive active snubbers for dc/ac converters, since an inverter leg is a combination of a buck and a boost dc/dc converter. The resulting topology is not optimal, hence, a ZVS generic snubber cell is proposed for dc/ac converters. It uses two auxiliary switches and a resonant inductor to achieve ZVS for the main switching devices. A single phase version is demonstrated in square wave and pulse width modulation (PWM) mode. A generic snubber cell is derived and is shown to encompass a large number of resonant inverter topologies.; All of the derived snubber topologies are demonstrated using punch-through (PT) Insulated Gate Bipolar Transistors (IGBTs) as their main switching devices. Since IGBTs (PT and non punch-through (NPT)) have a high current tail at turn-off due to the stored minority carriers in their drift layer, special attention is given to loss reduction at turn-off. The use of ZVS and ZCS allows a net reduction in the switching losses. The effect of these techniques on PT and NPT IGBTs and their effectiveness in improving the overall performance are not completely clear yet. Most of the available devices are optimized for hard-switching applications. The results obtained in this work permit developing physical insights into the behavior of PT and NPT IGBTs under ZCS and ZVS through 2-D simulations and device physics analysis in order to optimize them for ZCS and ZVS applications.