Research On Non-isolated Bidirectional DC/DC Converter Based On ?-type Resonant Network

In the photovoltaic microgrid,the bidirectional DC/DC converter is connected to the high-voltage side DC bus and the low-voltage side energy storage system.It can realize stable bidirectional flow of energy.It is an important component of the microgrid,so the research of bidirectional DC/DC converter is of great significance.A non-isolated bidirectional DC/DC converter based on a ?-type resonant network is proposed.The proposed converter has the advantages of both isolated and non-isolated bidirectional DC/DC converters.The proposed converter is added to the CLC-? type resonant network and has the characteristics of high efficiency and high power density.For the resonant network,based on the T-? dual principle,the input and output characteristics and structure of the ?-type network and the T-type network are compared.The proposed converter has the advantages of convenient design,small volume,and constant current input constant current output.The theoretical analysis of the working process of the proposed converter is presented,and an optimized parameter design method is proposed.Based on the analysis of the output characteristics and power conversion efficiency of the CLC-? type resonant network,considering the soft switching condition and range of the soft switching,the dominant factor of the soft switching condition is determined and optimized.The correctness of the analysis is verified by simulation.The system has a wide soft switching range when the load changes,which improves efficiency.The Extending Description Function(EDF)method is used to design the parameters of small signal modeling and closed-loop compensation.The system small-signal modeling is used to the Boost and Buck mode of the converter respectively,and the open-loop transfer function of the system is obtained and compensated.According to the compensation function,the difference equation of the digital PI is obtained by the bilinear transformation method,and the control system program is designed to optimize the dynamic performance of the system.Finally,a 300 W experimental prototype was built based on a wide bandgap semiconductor GaN device.Experiments show that the proposed bidirectional DC/DC converter achieves the boost and buck indicators and has a large soft switching range.Under full load conditions,the system efficiency is 97.3% in Boost mode and 96.1% in Buck mode.