Research On Multi-path Equalization Circuit For Series Battery Pack

The development of new energy technologies is inseparable from the battery,and in some occasions where the voltage level is high,the batteries need to be used in tandem,such as new energy vehicles.There are some problems when the batteries are used in series.For example,due to differences in the parameters among the monomers,some monomers may be overcharged and overdischarged during use,affecting the service life of the batteries.Therefore,it is necessary to introduce battery equalization.technology.In recent years,with the increase in the number of battery series,battery imbalance has become more complex,and the required equalization power has also been increasing,and the requirements for equalizing circuits have also been increasing.In view of the above situation,a series battery pack multipath equalization circuit is proposed.The circuit is based on the fly-through inductor equalization circuit and consists of a switching array near the battery and an inductive energy storage circuit.By controlling the order of the switches in the switch array and the inductor energy storage circuit to switch back and forth between the three processes of inductor energy storage,freewheeling,and energy feeding,the entire equalization process is formed.The idea that neighboring odd-numbered monomer groups can also participate in equalization is proposed,and the equalization path is more flexible.This circuit can realize the equalization function among any single cell,between single cell and small cell,and between small cell and small cell.The working principle of the multi-path equalization circuit of the series battery pack was analyzed.Taking the four typical working paths of singularity odd,even dual,odd dual,and even odd as examples,the circuit was simulated and analyzed.An equivalent circuit model of a multi-path equalization circuit for a series battery pack is constructed,and using this model,the influencing factors of equalization performance such as equalization current,balanced power,and balanced efficiency are analyzed.Based on this,a maximum power control strategy,a maximum efficiency control strategy,and a method of selecting the frequency and inductance of the multipath equalization circuit are proposed.By comparing the equalized power and the balanced efficiency of the maximum power control and the maximum efficiency control in different paths,the advantages and disadvantages of the equalization performance in different paths are obtained.Six series of 20 Ah series lithium battery packs are used to build a series battery pack multipath equalization system and hardware and software design.Through experiments,the system works in the maximum power mode,the maximum average equalization current of the battery side can reach 3.7A,the maximum power can reach 1W,and the maximum efficiency under the maximum efficiency mode can reach 89%.The experiment not only proves that the multi-path equalization system of series battery group can work in discontinuous and continuous mode,but also proves that the circuit can achieve multi-path equalization between any battery cells,between battery packs and cells,and between battery packs.In addition,this circuit can also realize more complicated multi-step path equalization,this function can reduce the pressure difference between any number of cells at any position at the same time.To sum up,the multi-path equalization circuit of the series battery group can effectively cope with the complex imbalance caused by the increase in the number of battery series.