Research On Integrated Buck-Boost CLLC Resonant Converter

With the rapid development of renewable energy technology,energy storage technology has been widely used.Bidirectional DC / DC converters in energy storage units have gradually become a research hotspot.However,the unique wide-range voltage output characteristics of the energy storage unit bring great challenges to the research.In recent years,studies have shown that by integrating a bidirectional Buck-Boost converter with a CLLC resonant converter,the wide-range voltage problem of the energy storage unit can be solved.The power of the integrated Buck-Boost CLLC resonant converter can flow in both directions.Resonance makes the soft switching technology simple,reduces switching losses,and improves the power density of the converter.However,when the input terminal is connected to a solar panel with a low voltage level and a large power range fluctuation,the boosted CLLC converter with fixed frequency PWM control reduces the utilization of PV energy,and the synchronization of the secondary and primary drives makes the converter less efficient when the duty cycle is shifted by 0.5.In order to realize the maximum utilization of PV electric energy in the photovoltaic power generation system and improve the conversion efficiency of the converter.A boost-type soft-switching,high-gain CLLC converter with PWM-PFM hybrid control for photovoltaic power generation is studied.By controlling the duty cycle and switching frequency of the primary switch,the converter can track the PV while stabilizing the output voltage Maximum power point.Under hybrid control,the resonant gain of the converter is greater than 1 and the voltage gain is large,the ZVS of the switch is turned on on the primary side,and the ZCS is soft-switched on the secondary side.The overall efficiency is high.In addition,the backflow power phenomenon in the resonant converter is studied.Through the analysis of the converter state trajectory,the relationship between the backflow power and the normalized switching frequency is deeply analyzed.In order to optimize the dynamic performance of the converter,the small-signal model of the CLLLC resonant converter(the excitation inductance participates in resonance under variable frequency control,and the CLLC resonant converter becomes the CLLLC resonant converter)is studied.The design improves the dynamic stability of the converter and improves the power output quality.Finally,through detailed design of the circuit parameters and models,an experimental prototype with a bidirectional power of 500 W was built.20-80 V input at low voltage side,200-400 V output at high voltage side.Through the waveform data of the prototype in the full power range,it can be concluded that the measured maximum efficiency of the prototype is 97.78%,which verifies the effectiveness and feasibility of the converter control strategy.