Control Strategy For Complex Inequalization Of Series Batteries

With the growing awareness of environmental protection, people begin toaccelerate the pace to research and develop new energies. The rapid development oflithium-ion technology conforms to the trends of the era which has been widely usedin electric vehicles、distributed generation、UPS uninterruptible power supply andsome other related technical fields. Because of the low voltage level of lithium-ion,it is usually connected in series when applied in high-power applications.Aslong-term use, the inconsistencies between monomers in the series connectedbattery pack emerge and they will be aggravated with the continuous charging anddischarging of the batteries. That’s why the research on series battery equalizationtechnique has become a hot issue.This paper focuses on analysis of the existing equilibrium topologies andevaluates them from the equalization speed、efficiency and circuit complexity，andthen indicates their respective applicable occasions. The overall design of atwo-layer equalization system is proposed. The low-layer is a four-monomerequalizer which is based on the centralized flyback transformer balanced topology,and the top-level is a bidirectional distributed Buck-Boost converter. This paperanalyzes the principles of the circuit operation、the way of energy transfermationunder complex inequalization and its influences on efficiency. Complete thedesign of parameters and hardware circuit.The control strategy for the two-layer balancing system which is based on stateof charge of the battery is established and then use open circuit voltage method tomake estimation on it. This paper sets condition-action rules for the two-layerequalizers and logic switch control table for the low-layer equalizer and realizes it inMAPLAB compiler environment in software implementation.A two-layer equilibrium experiment system is built and the waveforms of thetop-layer and low-layer equalizer are tested respectively. Experimental results showthat the design of two-layer system is able to achieve the requirements of rapidequilibrium and high efficiency.