Research On The Equalization System With Multiple Equalization Modes And Flexible Equalization Paths

With long cycle periods,low self-discharge rates,and pollution-free materials,the Li-ion battery is widely used in the industrial fields.Some batteries may be overcharged or over-discharged during use,which will affect the actual capacity and energy utilization of the battery pack over time.In some cases,it may even endanger the security of the system.The battery equalization technology is introduced to make every battery's energy remain at the same level,which can improve the working performance of the battery pack.At present,there are many problems in existing equalization topologies,such as fixed energy conversion modes,multiple equalization actions,and single equalization path.Starting from the construction of a new type of equalization topology,this paper carries out the basic research on the application of the equalization system for serial power supplies.The proposed equalization circuit is named after the equalization circuit with multiple equalization modes and flexible equalization paths.The circuit can use adjacent unbalanced cells to form equalization groups,which achieves direct equalization among unbalanced cells or groups in Buck-Boost or flyback mode.The equalization circuit can minimize the paths of energy transfer and improve the flexibility of the equalization system in a great deal.To explore the functional relationships between equalization parameters and circuit parameters,a simplified circuit model is constructed.The expressions of equalization current,equalization power,equalization efficiency and other parameters are obtained through mathematical derivation.Then,the simulation results verify the mathematical results.The influence of the circuit parameters and equalization mode on equalization performance is analyzed.The working status and parameters of the equalization circuit are selected based on the above analysis.To test the basic working modes of the proposed circuit,a Li-ion battery equalization system with a main circuit,an analog front-end circuit,a master-control unit and driving circuits is designed.Based on the basic-operation program,the equalization experiments are performed in different working modes and different working conditions.And the experimental results are compared to the former theoretical analysis results,which provides reference for the design of equalization strategies and the parameter calculations of the equalization experiments.To explore the ability of the equalization system dealing with complicated imbalances of a serial battery pack with four Li-ion batteries,an equalization strategy based on voltage extremes is presented.Then another equalization strategy based on the target voltage is introduced.Two sets of equalization contrast experiments are performed.The experimental results show that the equalization strategy based on the target voltage can significantly improve the equalization speed through forming equalization groups,and can ensure that all the battery voltages change monotonically over the course of equalization.In conclusion,the equalization strategy based on the target voltage and the equalization circuit with multiple equalization modes and flexible equalization paths contribute to dealing with the imbalanced states of the serial battery pack.