Research On Control Strategy Of Bi-directional Isolated DC-DC Resonant Converter

The development of electric vehicles has been listed as a national strategy by the Chinese government.The On Board Charger(OBC)is a core component of electric vehicles,consisting of two stages:a PFC rectifier and a DC-DC converter.The DC-DC converter is used to provide the required voltage and current for each charging process.At present,low conduction loss,low switching loss,bidirectional energy transmission,and wide voltage range are the key points for optimizing DC-DC converters.However,it is challenging to achieve these goals simultaneously.Three aspects(topology,modulation method,and control strategy)are investigated in this thesis to achieve bi-directional energy transfer with low-loss operation over a wide voltage range.A brief introduction of the conventional bidirectional non-isolated DC-DC converter and bidirectional isolated DC-DC converter is given at the start of this thesis.Various topologies of bidirectional isolated DC-DC resonant converters are briefly analyzed.Then,the converter topology,modulation method and control strategy are studied,which is suitable for wide voltage range operation of the converter.Additionally,a new full-half-bridge DC-DC resonant converter topology is proposed in the thesis.A new asymmetric pulse width modulation is proposed and applied to the full-half-bridge DC-DC resonant converter.The power model is obtained and the zero-voltage switching(ZVS)conditions and ranges are solved.In order to get the optimal low-loss control path of the converter,a new voltage matching optimal control strategy is proposed and analyzed in detail in this thesis.Owing to the comprehensive effects of topology,modulation,and control strategy,the full-half-bridge DC-DC resonant converter achieves low-cost,low-complexity,and bidirectional energy transfer.Additionally,all switches operating under ZVS in the voltage gain M range of 0.5～1,and the optimal ZVS region and minimum circulating current can be obtained at M=0.5 and M=1.To verify the effectiveness of the proposed full-half-bridge DC-DC resonant converter,the simulation circuit is built in PSIM software and the simulation results consist with the theoretical analysis.In addition,the power circuit,driver circuit and sampling circuit are designed and the experimental prototype is built.All experimental results are analyzed and summarized,which verify the theoretical analysis successfully.