Research On Modular Multi-level Resonant DC-DC Converter

With the development of power electronics technology,DC medium/high voltage and high-power conversion technology has been applied in many fields such as DC distribution network,train auxiliary power supply and so on.However,in the current high-voltage and high-power applications,the existing DC-DC converters have many shortcomings,such as large number of switching devices,large volume,high hardware cost,and complex voltage and current sharing control strategy.In this paper,a modular multi-level resonant DC-DC converter(MMRC)is proposed,which is suitable for DC medium/high-voltage and high power applicationsMMRC is mainly composed of DC-link capacitors and auxiliary resonant equalizing circuits.It has the advantages of high efficiency,modular structure,low voltage ripple,zero current switch mode and self-balancing capacitor voltage.In this paper,the working principles and modes of MMRC,the zero current soft switching characteristics of switching devices and the self-equalizing characteristics of DC support capacitors are analyzed.On this basis,three connection topologies of MMRC circuits are proposed,and the variation of voltage/current stresses on switching devices in three connection topologies are compared and analyzed.The minimum ripple control strategy of nine-level MMRC is analyzed.The optimal control strategies for realizing minimum input current ripple and minimum DC capacitor voltage ripple are summarized,and the correctness of theoretical analysis is verified by simulation.In addition,the parameter design of MMRC circuit is studied.The current of switching devices,resonant current and capacitive current of DC side are quantitatively analyzed.The equivalent model of MMRC is established.The capacitive voltage difference and converter efficiency caused by circuit loss are estimated and deduced when parasitic parameters exist.Finally,a nine-level MMRC experimental platform is built to verify the above theory and simulation analysis.The experimental results are in good agreement with the theoretical analysis and simulation results in this paper,which effectively proves that MMRC has good application value in DC medium-high voltage high-power power conversion.