Multi Stage Constant Current Charging Strategy Of Power Lithium Battery Based On Optimization Of Energy Loss And Temperature Rise

The strategy of charging power lithium battery is one of the main functions of battery management system of electric vehicle.Up to now,people pay more attention to charging strategy than the requirement of charging time.On the premise of ensuring the shorter charging time,more attention has been paid to the safety of batteries and economic and energy saving.At present,most of the mature charging strategies are optimized for the battery charging time.The common method is to charge the battery with a high rate of current.Although this method can shorten the charging time,it will produce a lot of energy loss and battery temperature rise,which will affect the economic and safety of power battery.In order to solve the above problems,this paper studies an optimal charging strategy which can shorten the charging time of the battery,taking the energy loss and the temperature rise of the battery as the constraint conditions.The specific research contents are as follows:(1)The appropriate lithium-ion battery model was selected.After comparing the advantages and disadvantages of several common battery models,the thesis chooses the equivalent circuit model of Thevenin which the energy loss and temperature rise are most suitable for the research of charging process as the following research.The accuracy and calculation complexity of the model can meet the requirements.The parameters related to charging strategy in the battery model are identified by the model parameter identification method based on genetic algorithm,and the identification results are verified under the constant current discharge condition.The results show that the model selected in this paper can better reflect the charging characteristics of the battery.(2)Based on the Thevenin model,the mathematical models of energy loss and temperature rise of battery during charging and discharging are deduced and analyzed.The mathematical models are verified by experiments in different temperature and SOC state.The results show that the energy loss model and the battery temperature rise model established in this paper have high accuracy,which lays a theoretical foundation for the subsequent research.(3)Based on the above research,an optimal charging strategy is proposed,and the target function aiming at reducing the charging time of the battery is established.The charging process of lithium-ion battery is optimized under the condition of reducing the energy loss and the temperature rise of the battery.The objective function is solved by genetic algorithm,and a two-stage charging method is proposed,which combines SOC segment and voltage segment.Considering the complex environment temperature that the actual lithium battery may face during charging,the optimal charging strategy proposed in this paper is used to simulate and calculate the optimal charging current curve between10℃ and 50℃ at 5℃.In order to verify the charging effect of the optimal charging strategy,this paper designs charging experiments under different ambient temperature and different initial SOC conditions.The results show that compared with the traditional multi-stage constant current charging method,the optimal charging strategy proposed in this paper can effectively reduce the charging time of lithium-ion battery under the two kinds of common charging conditions,and the energy loss and charging temperature rise are optimized.