Research And Design On High Efficiency Non-Isolated Four Switch Buck-Boost Converter

In recent years,with the rapid development of the aerospace and communications,there is an urgent need for a high-efficiency DC-DC converter topology suitable for a wide input voltage range,while can achieve the function of voltage boost and buck.In theconventional non-isolated converters,the buck converter can only achieve buck function,and that maximum efficiency point usually occurs when the input voltage is low,However,the boost converter is the opposite.Compared with the traditional buck-boost converter,the four-switch buck-boost converter has the advantages of the same polarity of input and output voltage,less passive components and low voltage stress of switches,which has become a hot research topic in the academia and industry field.The traditional control strategies for the four switch buck-boost converter have the following drawbacks:(1)Usually needs to distinguish the operation mode of converter,resulting in the complex control structure;(2)ZVS switching of all switches can be achived,which affect the further improvement of the converter efficiency.In order to solve these problems,two fixed frequency modulation strategies for the four switch buck-boost converter are proposed,including the fixed phase-shift modulation strategy and the variable phase-shift modulation strategy.In this thesis,the possible conduction time sequence and the inductor current waveform of the four-switch buck-boost converter are firstly discussed and analysized,respectively.Furthermore,an inductor current waveform,which can realize ZVS of all switches,is proposed.Different from the traddtional modulation strategy,the proposed solution does not need to distinguish the operation mode of the converter.The operation principle and the modulation strategy of the converter are introduced in detail.Then,based on the re-constructed multi-stage inductor current waveform,a fixed phase shift angle strategy is proposed.The operation principle,design consideration and simulation verification are introduced in detail.However,it is found that the fixed phase shift angle modulation strategy has some disadvantages,such as narrow soft switching range,large inductor reverse current under the light load and high input voltage case..Therefore,the modulation strategy is improved and the variable phase-shift angle fixed-frequency modulation strategy is proposed.A prototype of 500 W phase-shifting angular frequency modulation strategy with 200V~400V input and 300 V output is developed in the laboratory.The experimental results show that the converter realizes ZVS of all the switches with 50W~500Wload power,and the conversion efficiency is high as 96.2% at full load.