Research On Resonant Switched Capacitor Converter For Equalization And Charging Of Vehicle Lithium Batteries

The energy balance of lithium batteries in Electric Vehicle is an important part of battery energy management system（BMS）.The voltage regulation of Switched-Capacitor Converter is an important factor that restricts its development.In this paper,the equalization of series lithium battery and the small signal modeling and closed-loop control of Switched Tank Converter with Partial Power Voltage Regulation（PPVR-STC）are studied.Firstly,the existing equalization circuits of series lithium battery are classified and their advantages and disadvantages are summarized.In this paper,a hierarchical equalization scheme is used to balance the cells and the cells in the cell.Aiming at the equalization between batteries,a multi winding CLLC top-level equalization circuit is proposed,which has the advantages of fast equalization speed,simple control,small switching loss and no over-equalization.For the equalization among the single units in the group,the existing bottom equalization circuit of resonant switched capacitor is used.For the top-level and bottom-level equalization circuits,the operation principle and characteristics are analyzed without considering parasitic resistance and parasitic resistance respectively,and the switching frequency conditions of all switches ZCS realized,avoid repeated switching frequency conditions in a switching cycle by the two equalization circuits are obtained.The advantages of the proposed multi winding CLLC top-level equalization circuit and the working characteristics of the two equalization circuits are verified by simulation and experiment.Secondly,PPVR-STC is applied in DC-DC link of vehicle lithium battery charging.In order to achieve better closed-loop control of output voltage and output current,the small signal models of Single-Wing and Double-Wing PPVR-STC are established by combining the average modeling method of switching elements.The accuracy of the small signal model is verified by comparing the Bode diagram obtained by sweeping frequency of simulation circuit through Simplis with the Bode diagram derived from small signal model.Finally,the hardware and control system of Double Wing PPVR-STC for vehicle lithium battery charging are designed in detail.The selection basis and results of specific devices,the design of digital closed-loop controller and the flow chart of software control program are given.According to the design parameters,a closed-loop simulation circuit is built in Simulink to verify the working characteristics and advantages of Double-Wing PPVR-STC.And a 320 W experimental prototype is made,its input is DC400 V and output is DC60 V ～ 84 V.The closed-loop control of voltage and current and the smooth switching between the two loops are realized,and the subsequent improvement suggestions for efficiency optimization are put forward.