Research On Equalization Control For Power Battery Pack Of Electric Vehicle

In the area of new energy automobile,the battery electric vehicle has absolute predominance in technology and market shares,and the momentum is going strong.The power source of every electric vehicle is provided by battery pack,which is composed by hundreds of battery cells.And meanwhile,the maximum available capacity of battery pack depends on the battery with minimum residual capacity.The manufacturing processes of power battery are complicated,there is unavoidable difference among the cells,so that there is discordance among batteries.And also,during the course of using,the degree of discordance among batteries will be stronger,so that the available capacity of battery cells will be weakened in different levels,finally,it will weaken the use ratio of overall energy of the battery pack,and reduce the actual service life.In addition,it is easy to cause the overcharging and under-voltage on the battery,which can make damage on the battery.Thus,it should make balance on the energy of battery back,reform the discordance,and improve the available capacity of battery pack,which is of great significance.In this thesis,the reasons for battery inconsistency production are analyzed firstly.At the same time,the variables which can best show the battery inconsistency: voltage,capacity,charge state(SOC),etc.,be compared and analyzed.Among them,SOC can reflect the battery inconsistency completely and accurately in real time.Therefore,SOC is chosen as the equilibrium variable(evaluation index).Secondly,the equivalent circuit model of the battery is established to reflect the external characteristics of the battery.At the same time,a joint modified estimation method is studied to estimate the battery SOC,which further improves the accuracy of the estimation,and provides the precision guarantee for the equalization.Then,a kind of unit equalization circuit is studied.To achieve two-way fast flow of energy.The relationship among current,voltage and control signal in the circuit is determined by quantitative analysis of the control signal and other parameters.It provides the hardware foundation for equalization.At last,the equalization control strategy is studied.Firstly,a two-stage equalization strategy based on threshold control is studied,and the equilibriumjudgment conditions and equilibrium flow are formulated.Then a strategy based on fuzzy control is studied.Fuzzy control of equalization system is designed.And the fuzzy rules of the equilibrium system are formulated.Finally,the two strategies are compared by simulation.Compared,the effect of the fuzzy control strategy is better.The dynamic adjustment of equilibrium current can be realized.Equalizing is faster.More efficient.The inconsistency of battery pack is improved effectively,and the energy utilization ratio of battery pack is improved.