Analysis of high-frequency IGBT soft switching buck converter with saturable inductors

In this paper a high switching frequency buck converter using IGBTs is presented. This was done by using an auxiliary branch made of an IGBT of the same type as the one used for the main switch and saturable inductors. The proposed topology allows both switches to be fully soft switched to keep the efficiency high over a wide load range. Because of its topology the open loop behaviour of the converter can be unstable. A detailed small signal analysis is presented to explain this behaviour and as a basis for the synthesis of a closed loop controller. Experimental measurements on a laboratory prototype demonstrated the accuracy of the small signal analysis and validated the operation of the auxiliary network. The resulting efficiency is around 92% over a 200 to 800W output power range and at a 80kHz switching frequency.