Research On The Optimized Charging Strategy In Different Intervals With Maximum Life Of Lithium Ion Battery

As the core components of new energy automotive power system,Lithium-ion batteries have been widely used.Battery charging strategy will affect its charging time,cycle life and safety.Research and select appropriate optimized charging strategy will improve the economy and safety of battery.At present,there are few charging strategies to study how to effectively prolong the cycle life of lithium-ion batteries.In this paper,we take NCM batteries as the research object,and set up an optimal charging strategy for maximizing the life of batteries.The main contents of this paper are as follows:Firstly,the SOC interval characteristics of batteries were analyzed.Pulse experiments were designed for NCM batteries with different charging rates and SOC intervals.The basic parameters of batteries with different SOC intervals were identified by establishing the equivalent circuit model of batteries.A battery cycle life experiment was designed for the same type of battery in different SOC intervals,and the degradation characteristics of the thermodynamic and dynamic properties of the battery in different SOC cycle intervals were obtained.Through the analysis of experimental data,it is concluded that the internal resistance of low-end SOC batteries is large and the dynamic performance is deteriorated seriously,the thermodynamic performance of high-end SOC is deteriorated seriously,and the performance of middle-end SOC is stable,which provides a theoretical basis for the charging strategy in different SOC interval sof batteries.Secondly,a multi-objective function optimization charging strategy considering both capacity degradation rate and energy consumption as penalties is proposed.Based on the experimental data,the capacity degradation speed model of battery in different SOC intervals was established based on the capacity degradationspeed model of battery in full SOC cycle interval.In addition,the relationship model between energy consumption and charge rate and SOC was established.As the energy consumption model is related to the internal resistance parameters of battery,the internal resistance function of battery was established by the incremental method of internal resistance.Then,a multi-objective optimal charging control method for lithium-ion batteries was designed.With capacity degradation speed and energy consumption as optimization objectives,SOC as state variable,and under the constraints of average charging rate,a set of optimal current sequence was calculated by dynamic programming optimization algorithm(DP).In order to preliminarily verify the optimization effect of the charging strategy,the multi-objective optimal charging control of batteries is realized based on model predictive control(MPC)theory.The optimal current sequence is obtained by multi-step predictive control method.The energy consumption simulation results of batteries under the traditional and optimal charging methods show that Under the same average charging rate,the energy consumption is reduced by about 3.68% under the optimized charging strategy,which shows that the optimized charging strategy has a great optimization effect on the temperature rise of batteries.Finally,in order to verify the effect of optimized charging strategy on the cycle life of batteries,a comparative experiment of charging methods was carried out.Four batteries were selected to design the comparative experiment of battery performance and cycle life.The experimental results showed that the optimized charging strategy improved the coulomb efficiency and reduced the energy consumption of batteries.The experimental results showed that after 1300 cycles,the average capacity degradation rates of traditional and optimized charging methods were 7.34% and 5.67%,respectively,which in dicate that the cycle life of the battery has been significantly improved.