Voltage-SOC Balancing Control Scheme For Reconfigurable Equalization Circuit

Since the "outline of the twelfth five-year plan for national economic and social development of the people’s Republic of China" first mentioned "energy storage",China has paid more and more attention to the field of energy storage,electrochemical energy storage,especially lithium-ion battery,develops rapidly with its excellent performance.Since it is impossible to guarantee the consistency of battery in production and use,it is necessary to balance the battery packs in series and parallel to ensure safety,improve the usable capacity and extend the life of the battery pack.The balance index plays an important role in battery balance.The commonly used balance index is the voltage of the battery and the residual capacity of the battery,which is the state of charge(SOC).The voltage balancing control scheme with the voltage of the battery as the index has the characteristics of simple but poor performance,while the SOC balancing control scheme with the SOC of the battery as the index has the characteristics of good performance but complex.Compared with the common balance circuit,the comprehensive performance of the reconfigurable equilibrium circuit is better.Based on the reconfigurable equilibrium circuit,this paper proposes the voltage-SOC balancing control scheme,which has the advantages of simple of the voltage balancing control scheme and well performance of the SOC balancing control scheme.The main works of this paper are as follows:Firstly,the working principle of the reconfigurable equalization circuit is simply analyzed.According to the working principle of the reconfigurable equalization circuit,the advantages of reconfigurable equalization circuits are theoretically analyzed.The reasons for the advantages and disadvantages of the voltage balancing control scheme and the SOC balancing control scheme are analyzed.Because the advantages and disadvantages of the SOC balancing control scheme and the advantages of the voltage balancing control scheme are easier to analyze,the voltage balancing control scheme is used to analyze it in detail while it is applied to the reconfigurable equalization circuit.The existing shortcomings and why the voltage balancing control scheme has these shortcomings are analyzed in detail and verified through experiments.Then,based on the reconfigurable equalization circuit,the principle of the proposed voltage-SOC balancing control scheme is introduced.This balancing control scheme builds a bridge between the voltage balancing control scheme and the SOC balancing control scheme by G and realizes the transition between the voltage balancing control scheme and the SOC balancing control scheme.The advantages of the voltage balancing control scheme and the SOC balancing control scheme are better retained.The error source and magnitude of the voltage-SOC balancing control scheme are analyzed in detail and compared with the voltage balancing control scheme and the SOC balancing control scheme.Finally,an experimental platform is built to verify the performance of the proposed voltage-SOC balancing control scheme.The experimental battery pack consists of five 18650 lithium-ion batteries in series,all made by SAMSUNG,with a nominal capacity of 2200 mAh.The experiment is carried out under the four conditions of the SOC of the battery pack is about 98%,83%,53%,30%,the experimental results show that the voltage-SOC balancing control scheme can more easily estimate the SOC difference between the two cells like voltage balancing control scheme,and the errors of the SOC difference estimated are 0.24%,5.3%,5% and 0.8%,which can be compared with the performance of the SOC balancing control scheme using mainstream SOC estimation methods,which proves its superiority.