New soft switching high frequency converters with current freewheeling control of DC - link

Abstract

Several types of DC/DC and AC/DC/AC converters based on a new high frequency link, which has good performance by high frequency operation, are proposed. Low losses by zero voltage switching(ZVS) and/or zero current switching(ZCS) enables the high frequency link to be viable technique due to the reduction of switching losses. The high frequency operation provides the merits of high frequency link converter such as high efficiency. Since the resonant ac like converter impresses both polarities of ac voltage and current, it requires bidirectional switches realizable by anti-parallel connection of two unidirectional switches, which makes it uneconomical. The proposed converters employ dc link so that the circuits have a only unidirectional switch and no snubber. An LC tank circuit of the resonant converter is always present near the power switch and is used not only to shape the current and voltage waveforms of the power switch but to store and transfer energy from input to output, thus the peak switch voltage and current stresses are substantially increased by the resonance. Therefore, high power application of resonant converter is hampered by the stresses of switches and reactive elements. In the proposed converters, however, the reactive elements serve as waveshaping or snubbing function around the switching operation and they are minimally involved in the power transfer so that the VA ratings of the reactive elements and switching devices are reduced and the losses due to ESR (Effective Series Resistance) of reactive elements are decreased. The proposed AC/DC/AC converter topologies exhibit unique operating characteristics which synthesizes sinusoidal voltage at the output terminal. The introduction of current freewheeling circuit separates the main power flow from the resonating LC circuit so that the voltage and current peak generated by the resonant circuit is dramatically minimized. Not only these converter operates well on four quadrants but also it could...