Research On IZCT/ARCP ZVT Soft-switching Converter

With the increasing demand for higher power density, lower switching losses and switching stresses, soft-switching technologies are attractive in power converters. In recent years, various soft-switching techniques have been developed, which can be classified into two categories:DC-side resonant topologies and AC-side resonant topologies. In a DC-side resonant soft-switching converter, the whole or part of the auxiliary circuit is inserted between the DC-side and the main bridges, which will increase the conduction losses and voltage stresses. Also, the normal PWM algorithms must be modified in order to achieve soft switching for the main bridge. Usually the AC-side resonant soft-switching converter that offers the advantages of piggyback PWM control and without additional voltage stresses is considered a better contender of high power converters. This dissertation gives thorough analysis on the AC-side ZCT and ARCP ZVT soft-switching technology in considering the impact of non-ideal device and circuit stray parameters. Loss calculation model is established and verified by experiment. Some improved methods and design recommendations are proposed.Firstly, resonant processes of the IZCT soft-switching converter are discussed in considering the impact of diode reverse-recovery. The corresponding resonant state equations are given. The impact of diode reverse-recovery on resonant process is theoretically analyzed. It is noted that the increase in IZCT soft-switching losses is mainly due to the diode reverse-recovery. Subsequently, the research results are validated by experiments.Secondly, the mechanism of diode reverse-recovery is discussed. Effects of resonant parameters on diode reverse-recovery are analyzed. A method for extracting important parameter-carrier lifetime affecting the diode reverse-recovery is introduced. Based on this parameter, the model for calculating diode reverse-recovery charge is established, which is validated by experiments. Then, instantaneous voltage and current waveforms of IZCT soft-switching transition are studied and linearized, and a diode charge-control model is employed to formulate the switching losses equations. The approach of calculating switching losses is basically agreement with experimental test.Thirdly, a total loss model of the IZCT soft-switching converter is established, which is validated by simulation and experiments in different resonant parameters. According to the model, soft-switching key parameters design and device selection can be optimized. A new control method to reduce switching losses of the main bridge devices during turn-on soft-switching transition is proposed. By changing the timing of the main bridge devices’ drive signal during turn-off soft-switching transition, the resonant capacitor can store more energy for the next turn-on soft-switching transition. It is validated by simulation and experiments that the diode reverse-recovery and the corresponding switching losses of the main bridge devices are greatly weakened during turn-on soft-switching transition.Fourthly, resonant processes of the ARCP ZVT soft-switching converter are discussed in considering the impact of stray parameters. The mathematic models of commutation process and power loss in the ARCP are established. Validities of the models are verified by the experimental results.