A novel approach to soft-switching power converters



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Modern power converters operate using PWM (Pulse Width Modulation) and switching their semiconductor switches on and off at a very high rate to achieve a high efficiency. While the losses of the switches are very low in either the on or the off state, the transition times give rise to switching losses, which increase with increasing switching frequency. Soft-switching techniques aim to eliminate this by forcing a zero-voltage or a zero-current condition on the switch during a switching cycle such that the switching losses are eliminated. This is very important to improve the efficiency of power electronics in light of ever-increasing demands to conserve energy and to also allow the power electronics to be made smaller and more compact. While soft-switching has been successfully applied for simpler applications such as DC-DC converters, it has been difficult to apply to general-purpose inverters (such as to drive AC motors). The ARCP (Auxiliary Resonant Commutated Pole) is a topology that is one of the most promising approaches to soft-switching an inverter; however, it has some drawbacks. During the course of my research, I have devised two alternative topologies which aim to address the ARCP's limitations. In addition, I have developed several novel control schemes to more efficiently and reliably gate these ARCP inverters with a minimum of sensor feedback. I have developed my ARCP technology on Simulink models and on a 20kW experimental prototype. I have also implemented and tested some of the control scheme improvements on a 2MW ARCP machine at CEM (UT Center for Electromechanics), which is still the largest ARCP converter ever built. In the process I have also developed techniques to accurately measure the efficiency of high efficiency power converters.