Three Phase LLC Resonant Converter Improved Hybrid Control Strategy Research

As the core equipment of the power generation system,the power electronic conversion device needs to flexibly adapt to voltage input/output requirements and load characteristics,and its performance directly affects the power generation quality of new energy.In this thesis,the three-phase LLC resonant converter based on Si C semiconductor power devices is taken as the research object.Because of the limitations of the LLC resonant converter’s gain characteristics,it is difficult to adapt to the wide input regulation range of new energy power generation,and the gain characteristic curve distortion in light load causes the high switching frequency,the loss of soft switching conditions and the low efficiency.A hybrid optimal control scheme is proposed,which not only realizes the wide voltage gain control range of the converter but also improves the light load condition efficiency of the converter.Specific research contents are as follows:Firstly,the topology structure of the studied three-phase LLC resonant converter is introduced,and the working principle of the converter under the traditional PFM and PWM modulation strategies is described.The working waveform under the two modulation strategies is obtained by simulation.Then the steady-state equivalent circuit model of the converter is established according to the detailed working mode analysis and the gain characteristic formula of the converter is deduced.According to the theoretical analysis,the method of PFM-PWM hybrid control can effectively broaden the gain range of the converter,which lays a certain foundation for the subsequent control parameter design of the converter.Secondly,according to the existing technical indicators,the resonant parameters of the converter are calculated and the soft switching conditions of the converter are analyzed under the characteristics of a wide input voltage range.Then,the precise small signal dynamic model is established,and the analysis shows that the converter gain and control function is affected by the load conditions.Then the operation characteristics of the converter under light load are analyzed in detail.Based on PFM-PWM hybrid control,intermittent control mode aiming at light load problem is introduced.A PFM-PWM hybrid control method based on intermittent mode is proposed and its parameter is designed and verified by experiments.Then,Based on the analysis in the previous chapter,the main circuit,driving circuit,and sampling circuit of the three-phase LLC resonant converter hardware are designed and the main topology components are selected.The corresponding control program is written in the CCS software development environment,which provides convenience for the construction of the converter experiment platform.Finally,Matlab/Simulink software is used to simulate the wide range gain of the three-phase LLC resonant converter and the control under light load conditions.The experimental verification is carried out based on the 3k W converter experimental test platform.At the same time,the total loss model of the traditional modulation and the optimal control strategy proposed in the thesis are established.The efficiency comparison diagram of different control strategies is obtained,and the feasibility of the design is verified by the theory.Simulation and experimental results show that the proposed hybrid optimization control strategy effectively broadens the regulation range of the converter,reduces the loss under the light load condition,improves the efficiency of the converter,and strengthens the performance.