Research On Voltage Multiplier Based Multioutput Voltage Equalization Circuit For Series-connected Lithium-ion Battery/Supercapacitor

With the rapid development of electric vehicles and new energy power generation technologies,the applications of energy storage cells represented by lithium-ion batteries and supercapacitors are becoming more and more widespread.However,the cell voltage of lithium-ion batteries or supercapacitors is relatively low.In order to meet the system requirements for voltage and power levels,multiple energy storage cells are often used in series.However,the inconsistency of energy storage cells is likely to cause voltage imbalance.In order to solve this problem,the paper proposes a new type of voltage equalizer.Based on the analyses of voltage multipliers and feasible input cells,a CSI-SVM voltage equalizer composed of Boost full-bridge inverter(current source inverter,CSI)and symmetric voltage multiplier(SVM)is proposed.The working mode of the CSI-SVM voltage equalizer is analyzed;the mathematical model of the CSI-SVM voltage equalizer is established;the comparisons between CSI-SVM voltage equalizer and the existing equalization circuit are made.Based on the established mathematical model of equivalent dc resistance,a design method of the CSI-SVM voltage equalizer is proposed.This method introduces an auxiliary parameter k_i,and the peak charging current,the equivalent dc resistance of the voltage multiplier,and the power loss of the devices are used as design parameters to achieve equalization charging for CSI-SVM voltage equalizer,improving converter efficiency and reducing electrical stress.The design example validates the proposed design method.The CSI-SVM voltage equalizer is simulated and analyzed.In order to verify the correctness of the equivalent dc resistance model of the charging branches,an equivalent circuit of the CSI-SVM voltage equalizer is established,and simulation analysis is performed;In order to verify the voltage equalization performance of the designed CSI-SVM voltage equalizer,the voltage equalization performance of the equalizer is simulated and analyzed under the same and inconsistent charging branch parameters.The experimental research of the CSI-SVM voltage equalizer is carried out.An experimental prototype of the CSI-SVM voltage equalizer is developed.The constant input current(CIC)-constant voltage(CV)charging scheme is adopted,that is,the CIC-CV charging scheme.The characteristics of the CSI-SVM voltage equalizer are analyzed by the key experimental waveforms of the prototype;The efficiency of the experimental prototype is tested and analyzed;Under the condition of initial voltage imbalance,equalization charging experiments are performed for lithium-ion batteries and supercapacitors respectively,and equalization charging experiments are performed for lithium-ion batteries under discharging conditions.The experimental results show that the CSI-SVM voltage equalizer has a good voltage equalization performance,and also verifies the correctness of the theoretical analysis and the effectiveness of the design method.