Battery Equalizer For Series-connected Batteries Based On Half-bridge LLC Topology

Limited by the developmental level of science and technology,series battery pack,as the power source of electrical velchels,has the drawbacks of energy imbalance,which affects people’s travel safety and battery service life seriously.In order to solve this problem,this thesis proposes a voltage equalizing circuit based on the half bridge LLC topology with multi-port transformer.Researches on the circuit topology,key parameters and control strategy are carried out.The following works are mainly completed:Firstly,four voltage equalizing paths and their working principles of the proposed topology are analyzed.The expression of equalizing current of each path is derived.According to the analysis of the energy transfer directions,the suitable voltage equalization path is selected,and the equalizing principle of this path is defined.Secondly,the influence of circuit parameters,including variable ratio,resonant inductance,damping resistance,and the influence of voltage parameters,including average voltage and target battery voltage,on the voltage equalizing current in the module and the bus are analyzed for the selected equalizing path.Furthermore,the influence of voltage equalizing current on reliable control is analyzed when parasitic parameters are considered.On this basis,the key parameters of the circuit are designed.Then,based on the characteristics of the circuit,the voltage equalizing control strategies with fixed number of open groups and variable number of open groups are proposed.The flow charts of two control strategies are presented respectively.The effects of the number of open groups and the maximum number of open groups are analyzed.The feasibility of the equalizing circuit and the two control strategies are verified by simulation in Simulink.The equalizing time and efficiency of the two strategies are compared.Finally,an experimental prototype of 12-output half-bridge LLC voltage equalizing circuit for 24-series battery pack is designed based on GaN transistors.Two voltage equalizing control programs are designed based on Verilog HDL.The static equalization,charge equalization and discharge equalization experiments are carried out under the two control strategies and the switching details waveform are given.In addition,the experiment for the charger application is also conducted based on the topology.The experimental results show that the LLC voltage equalizing circuit has the advantages of flexible path,high speed of equalizing and high efficiency.