Research On Multi-mode Equalization Circuit For Series Battery Pack

As an energy storage unit,the battery pack is widely used in the field of n ew energy power generation and electric vehicle technology.The battery pack usually adopts a series connection of cells in the group to increase voltage and capacity.During the series use of the monomers in the group,due to the inevitable difference between the cells,such as the internal resistance and other parameters are different,it will cause overcharge or overdischarge of some cells,which will endanger the performance of the series battery pack and affect the life of battery pack.Therefore its required to introduce a series battery balancing technique.Based on the Buck-Boost series battery pack equalization circuit,a series multi-mode energy storage equalization circuit is proposed.The equalization circuit belongs to a multi-inductance equalization circuit,which makes it flexible to configure multiple inductors as energy transfer intermediate links.It is one of three states of access,short circuit and disconnection,so that the adjacent cells or groups form a Buck-Boost converter.The series multi-mode energy storage equalization circuit proposes a group-to-group equalization mode,an intermediate unit or a group-to-side simultaneous equalization mode.The series multi-mode energy storage equalization circuit has the advantages of a typical Buck-Boost class equalization circuit,and multiple adjacent equalization processes can be performed simultaneously.In order to improve the power and efficiency of the equalization process,an equalization circuit model is established,and the factors affecting the equalization power and efficiency are analyzed.The relationship between battery voltage,loop resistance,switching frequency,inductance value,duty cycle,equalization power and equalization efficiency is studied.Based above theoretical analysis,the duty cycle,switching frequency and inductance parameters are optimized,and the selected circuit parameters are simulated and experimentally verified.Taking six-cell series battery pack as the object,the switch tube drive circuit and data acquisition circuit were designed,and the series multi-mode energy storage equalization system was built.Combined with the four basic equalization modes of the series multi-mode energy storage equalization circuit,the underlying basic equilibrium motion process is studied.Six equalization sub-functions are designed and analyzed,and the typical equilibrium process of the bottom layer is experimentally verified.The top-level equalization strategy is formulated,and the imbalance is identified based on the pressure difference between adjacent cells.The underlying basic equalization process is called according to the imbalance type to complete the equalization of the entire series of battery packs.Taking the six-cell 2900 mAh series lithium battery pack as a typical imbalance,the equalization control strategy of the series multi-mode energy storage equalization system is used to complete the equalization of the entire battery pack.In the experiment,some of the cells were charged and redischarged first,and the equilibrium strategy was improved and the improved experiment was completed.Finally,an equilibrium experiment during discharge and charging was performed.The experimental results show that the series multi-mode energy storage equalization system has a fast equalization speed and high equalization efficiency.