Research On Equalization Circuit And Battery Management System Based On Resonant LC Unit

In recent years,with the rise of the electric vehicle industry,power batteries have received extensive attention as the main energy source for electric vehicles.At the same time,power batteries also have many technical difficulties that need to be overcome.Because the voltage and capacity of the battery cells are usually small and cannot meet the requirements of the vehicle,the batteries are often used in series in groups.However,the parameter difference between the battery cells will lead to a decrease in the usable capacity of the battery pack,and even an explosion accident in severe cases.Therefore,equalization circuit that can achieve the same voltage/capacity/state of charge(SOC)among battery cells has become a research hotspot nowadays.In the thesis,the equalization circuit is deeply studied,and an equalization circuit and control strategy optimization method based on resonant LC unit are proposed.On this basis,a battery management system with complete performance is developed,which can realize non-dissipative equalization with voltage or capacity as equalization variable.To improve the problem of the decrease of the equalization current and the equalization speed when the voltage difference between the battery cells becomes smaller in the direct cell-to-cell(DC2C)equalization circuit based on the two-resonant-state LC unit,a DC2 C equalization circuit based on the three-resonant-state LC unit is proposed.The equalization circuit can not only greatly improve the equalization speed,but also has the advantages of small size and low cost.At the same time,the equalization circuit is simulated and experimentally analyzed using the maximum and minimum equalization control strategies.Finally,the equalization circuit is compared with the DC2 C equalization circuit based on the two-resonant-state LC unit through simulation and experiment.The results show that the equalization circuit has a faster equalization speed.The DC2 C equalization circuit based on the two-resonant-state LC unit and the DC2 C equalization circuit based on the three-resonant-state LC unit have their own advantages and disadvantages.The equalization efficiency of the DC2 C equalization circuit based on the three-resonant-state LC unit may be lower than that of the DC2 C equalization circuit based on the two-resonant-state LC unit in some time periods.On the other hand,when the voltage between the battery cells is seriously unbalanced in the battery pack,the use of the maximum and minimum equalization control strategies in the DC2 C equalization circuit will also result in a long equalization time.In view of these problems,this thesis analyzes the efficiency of the DC2 C equalization circuit based on the two-resonant-state LC unit and the DC2 C equalization circuit based on the three-resonant-state LC unit,based on the topology structure of the DC2 C equalization circuit with two-resonant-state LC unit and maximum and minimum equalization control strategies.Aiming at the relationship between the efficiency and the voltage conversion ratio k of these two DC2 C equalization circuits,a dual-mode hybrid control strategy is proposed to improve the equalization efficiency.And by analyzing the equalization methods of the direct cell-to-cell and direct multicell-to-multicell,a multi-equalization method hybrid control strategy is proposed to improve the equalization speed.The dual-mode hybrid control strategy is applied to the multi-equalization method hybrid control strategy,and finally a multi-mode hybrid control strategy that can improve the equalization speed and efficiency is proposed.It is verified by simulation and experiment,and the results show that the multi-mode hybrid control strategy can improve the equalization speed and equalization efficiency.To ensure the efficient and safe operation of the battery pack,a combination of analog front-end chip BQ40Z50 and microcontroller STM32F103C8T6 is used to design a battery management system(BMS)that can realize the DC2 C equalization circuit based on the three-resonant-state LC unit and improved multi-mode hybrid control strategy.hardware circuit design and software writing are completed,a BMS prototype is developed and an experimental platform is built,data acquisition such as voltage,temperature,and current is completed,and functions such as charge and discharge control,equalization control,SOC and capacity estimation,and communication are realized.Finally,combining with the DC2 C equalization circuit based on the three-resonant-state LC unit,non-dissipative equalization experiment with voltage and capacity as equalization variables is completed,and the experimental results show that the battery management system has a complete equalization function.