Research On Novel Zero-Voltage And Zero-Current Switching PWM Three-level DC-DC Converter

With the rapid development of the information technology, the research and application of the power electronic technology has been greatly promoted. Meanwhile, high-quality switching power supply systems with high efficiency, small volume, light weight and high precision are also increasing attention. Especially in the high-input voltage and high-power conversion places, it is significant to improve the power conversion efficiency and reduce the electromagnetic interference (EMI) by reducing the voltage stress of power switches and the voltage and current rate of change. Three-level converters are very suitable for high voltage input places because each switch sustains only half of the input DC line voltage, so it has important significance to research three-level converters. In order to reduce weight and size of converters as well as enhance conversion efficiency, many scholars have put forward so ft-switching technology for three-level converters in recent years. Soft-switching technology has the following advantages:improving operating environment and reliability of power switches; reducing power losses and sizes of converters, enhancing efficiency and suppressing the higher dvldt and dildt, and cutting down EMI and system noise effectively.Based on research the three-level converter and its so ft-switching technology widely, several classical three-level topologies and their soft-switching realize conditions and problems have been analyzed in this thesis. Beside, the soft-switching realizing methods have also been classified and summarized. Aiming at the two main disadvantages in conventional zero-voltage three-level converters, that lagging switches realize soft-switching difficulty at light load condition and the converter exists relatively high primary circulating current losses, a novel zero-voltage and zero-current switching TL converter has been proposed.In this thesis, a novel zero-voltage and zero-current-switching (ZVZCS) pulse-width modulation (PWM) half-bridge (HB) three-lever (TL) dc/dc converter with a secondary coupling inductor is proposed. Compared with conventional ZVZCS PWM TL dc/dc converters, this converter doesn't include auxiliary resonant circuits. It can achieve zero-voltage switching (ZVS) for leading switches and approximately zero-current switching (ZCS) for lagging switches with the aid of transformer parasitic inductance, lossless snubber capacitors and tapped-inductor type smoothing filter. This converter can reduce voltage and current spikes of power switches as well as primary circulating current loss effectively. The operation principle of the new type converter and the soft-switching implementation conditions according to different equivalent circuits are analyzed. Besides, the effects of tapped-inductor turns ratio on the current stress of power switches and the output voltage characteristic under open-loop control scheme are discussed. The practical effectiveness of the proposed converter is illustrated by simulation results and experimental results via a 6kW-40kHz prototype using the fast switching insulated gate bipolar transistor (IGBT).