Research On Equalization Control Strategy For Lithium-Ion Battery Pack Based On SOC

The multiple unit cells are connected in series into the battery pack to meet the requirements of power and voltage in electric vehicle, energy storage power station and other energy storage systems. However, the inconsistency of the battery can lead to the reduction of the capacity utilization, which seriously affects the cycle life and using cost of the energy storage equipment. In the battery management system, the balance control module can effectively improve the performance of the battery pack. Battery equalization control technique with great research significance can eliminate the inconsistency between the battery monomer, and slow down the attenuation of energy storage battery pack.On the basis of further understanding and research of the inconsistency of the battery pack, an active equalization control strategy based on SOC was proposed, the balance system is designed and the feasibility is verified by experiments. The specific research contents are as follows:1、In this study, Lithium-Ion battery was selected as the object to research battery characteristics. Experiment took advantage of battery monitoring system to discharge the battery at different current and obtained the real-time measurement of voltage and current. This study selected SOC as balance criterion of control strategy by analyzing the characteristics of battery.2、When considering of the complex computation and long learning time for traditional neural network method to estimate for state of charge of the LiFePO4 battery, a new method based on ELM(Extreme Learning Machine) was proposed to achieve it. The model was trained and predicted by the data obtained from experiments, and the feasibility and advantage of ELM in SOC estimation was verified by compared with BP(Back Propagation) neural network.3、In this study, a comparative analysis of equalization circuit was carried out and the bi-directional Buck-Boost topology was selected as the main circuit of the active balance control system. A new active equalization control strategy, SOC was employed in the strategy as balance criterion, was proposed to balance the lithium-ion battery pack under different working conditions combined with ELM technology. The balance control system was built in Matlab/SimPower to verify the high accuracy and efficiency of bi-directional active equalization control method.4、Hardware circuit of the system was designed by using main - slave balance structure. The experimental results showed that the balance performance of Buck-Boost circuit was well behaved. In addition, the design and PCB fabrication of a balance auxiliary power supply was completed.