Research On Distributed Online Active Balancing Control System For Power Battery Pack

The increasing energy crisis and environment pollutions make electrical vehicl es,with large penetration become developmental tends of automobile industry generally.As the power source of electric vehicles,power battery pack is one of the most expensive parts of electric vehicles,due to the influence of the manufacturing process and working environment of the single battery,the inconsistency of the monomer gradually increases during the cycle charging/discharging process,which leads to a reduction in the service life and usable capacity of the power battery pack,which in turn shortens the range of the battery pack,in order to reduce inconsistency and improve the service life and cruising range of the power battery pack,the power battery must be balancedly managed.Therefore,this paper takes ternary lithium-ion batteries as the research object,based on the reasons for the inconsistency of power battery packs,theoretical research and experimental analysis of online active balance control of power battery packs are carried out.Firstly,aiming at the problem of low estimation accuracy of the remaining capacity(State of Charge,SOC)of the power battery pack,this paper proposes a SOC estimation method based on unscented Kalman filter,establishes the battery space state equation using Thevenin model,and then focuses on the analysis of the unscented Transform ideas and the principle of SOC estimation by unscented Kalman filter,and finally build a simulation model.Under the conditions of NEDC(New European Driving Cycle)and HWFET(Highway Fuel Economy Test),unsold Kalman filter is used to perform SOC estimation.The estimation and simulation results verify the effectiveness of the algorithm for SOC estimation.Secondly,focused on the shortcomings of the traditional active equalization method and the problem that the SOC inconsistency of the power battery pack gradually increases during charging and discharging,the “battery cells decoupled and distributed converter series-connected overall system architecture” is presented firstly,designed double closed-loop control system of voltage outer loop and current inner loop,realize the precise adjustment of the output voltage and discharge current.Then,through the real-time regulate of bus voltage regulation coefficient and balancing acceleration coefficient during the discharging process,the linear and dynamic discharge rate regulation of each cell is achieved,and meanwhile,the DC bus voltage is stabilized.In charging mode,through the real-time regulation of the balancing acceleration coefficient during the charging process,the linear and dynamic charge rate regulation of each cell is achieved.Aiming at the problem of slow balanced rate of power battery pack,an adaptive adjustment method of balanced acceleration coefficient is proposed.During the equalization process of charging/discharging mode,the balanced acceleration coefficient is adjusted in real time according to the SOC of the power battery pack,and the charging/discharging current is adaptively adjusted,to achieve dynamic and efficient balanced management of power battery packs.Finally,in order to effectively verify the theoretical analysis,based on the Freescale digital signal processor MC9S12XET256 processing chip,the hardware and corresponding software of the distributed online active equalization control system were developed and designed,a test platform for the balanced control of the power battery pack was built,and the balanced experiment in the charge and discharge mode was carried out.Experiments show that the designed distributed online balanced control system and balanced control method,it realizes the online active balance of the power battery pack during the charging/discharging process,avoids the invalid charging and discharging cycle and the monomer overcharging and undercharging.by adjusting the bus voltage arbitrarily,it can adapt to the working voltage requirements of different load,the balance accuracy and rate are improved,and the utilization efficiency and life time of the power battery pack are extend.