Research On Three-port DC/DC Converter For Hybrid Renewable Energy Generation System

With the decline of the fossil fuel reserves and the global environmental degradation due to the burning of the fossil fuels, people are focusing on the new energy sources increasingly. New Energy sources are being accepted by more and more people for its non-polluting, recycling, and wide distribution characteristics. This paper leads the necessity and the importance of the new energy hybrid power based on the random fluctuant characteristic of the wind energy and the solar energy. By comparing the relative merits between two-port converter and three-port converter, this paper leads to a conclusion that three-port converter has more advantages in the hybrid new energy generating applications. Based on the requirements of the project, a phase shift controlled bidirectional three-port DC/DC converter which has the advantages of wide input, galvanic isolation, soft-switching operation and small input current ripple is introduced by studying the characteristics of the previous three-port converters.In the second chapter, to facilitate the subsequent circuit analysis, the T/A-equivalent transformation of the three-winding transformer is analyzed detailed. Using the A-equivalent circuit with the condition of wide input, five different operation modes are researched. Then, using the engineering approximation, the power and the transformer RMS current expressions on the five modes are transformed into the unified general expressions in order to simplify the circuit analysis and design complexity. In addition, in the whole operation scope the soft switching operation states of all the switches are analyzed. Then, the soft-switching operating condition, the soft-switching operating area and the method how to expand the area are given in the worst case.In the third chapter, a detailed design and manufacture method of the three-winding transformer and the Boost inductors is described. Moreover the complete control block diagram and a specific control method are proposed. Finally, in the fourth chapter a 2.5kW experimental prototype is made in order to verify the characteristics of five different operation modes, the current flow equalization effect and the soft-switching operation under the condition of wide input.