Research On Topology And Control Strategy Of Resonant DC-DC Converter

Resonant DC-DC converters are widely used in DC power distribution,energy storage and new energy vehicles because of their advantages of high efficiency,high power density and wide gain.CLL and LCC resonant converters are one of the popular topologies of unidirectional/bidirectional DC-DC converters at present.In this thesis,to solve the problem that the voltage gain range of CLL resonant converters is narrow and the bidirectional power transmission cannot be realized under variable frequency or phase shift control mode,the converter topology is improved and a variable frequency phase shift hybrid control strategy is proposed.In order to solve the problems of narrow soft switching range and high voltage and current stress of resonant elements in phase shift control mode,a LLCC resonant converter with low voltage and current stress and wide soft switching range was proposed.The specific work carried out in this thesis is as follows:1.The operation principle of CLL resonant converter under variable frequency and phase shift control mode is analyzed.It is pointed out that the voltage gain range of CLL resonant converter is narrow and the bidirectional power transmission cannot be realized under variable frequency or phase shift control mode.Further,the research idea of improving CLL resonant converter is given.The operation principle of LCC resonant converter under phase shift control mode is analyzed,and the problems of narrow ZVS range and large voltage and current stress of resonant element are pointed out.Further,the research idea of improving LCC resonant converter is given.2.By adding a parallel inductor to the input end of the resonant groove of the CLL resonant converter,a CLL resonant converter with bidirectional power transmission capability is formed.The operating principle of the bidirectional CLL resonant converter in variable frequency and phase shift control mode is further analyzed,the advantages and disadvantages of variable frequency and phase shift control are summarized,and a hybrid control strategy of variable frequency and phase shift and voltage reduction is proposed.Under the hybrid control strategy,the converter not only has the ability of bidirectional operation,but also has excellent buck-boost voltage capability and soft switching characteristics.The correctness of the theoretical analysis and the effectiveness of the control strategy are verified by simulation.3.Aiming at the problem of high voltage and current stress of resonant elements in bidirectional CLL resonant converter,a LLCC resonant converter with four elements is studied.The resonant tank of the converter is composed of an auxiliary inductor,a resonant inductor,and a low voltage side series-parallel resonant capacitor.The operating principle of LLCC resonance under phase shift control mode is analyzed,and the model of LLCC resonant converter is modeled by using the improved fundamental wave approximation method.The principle that the parallel inductance structure can widen the range of the converter ZVS and reduce the current stress of the resonant inductor is analyzed.The voltage stress of series parallel resonant capacitor on the low voltage side is analyzed.Finally,combined with the specific parameters of LLCC resonant converter,the advantages of wide ZVS range and low voltage and current stress are verified by simulation.4.The experimental prototype of a 500 W resonant converter is designed,and the feasibility of the proposed converter topology structure and the effectiveness of the control strategy are verified by experiments.Figure [64] Table [2] Reference [54]...