Research On Condition Monitoring Of Utilization Battery And Control Strategy Of Echelon Energy Storage System

The rapid rise of electric vehicles has brought about the retirement of a large number of power batteries.Battery’s retirement does not mean the end of battery life.Using retired batteries in energy storage system can not only improve the life cycle economic value of the battery,but also reduce the waste of resources and environmental pollution.However,compared with the new battery,the retired battery has serious inconsistency about State of Charge(SOC)and State of Health(SOH).Echelon utilization of battery in energy storage system will bring the problem of low energy utilization.In this paper,the control strategy of the echelon energy storage system based on parameter monitoring is proposed.The main contents and research results are as follows.(1)Two online identification methods of battery equivalent circuit parameters are proposed: discount method and Unscented Kalman filter(UKF).The inconsistency of SOC and SOH in echelon energy storage system will cause the imbalance of system power.Battery parameter monitoring is an important premise to solve this problem.Using the experimental data of dynamic conditions,the online identification of battery equivalent circuit parameters is realized based on the proposed method.Compared with the reference values of battery equivalent circuit parameters obtained offline,the results show that the online identification accuracy of UKF is higher,which can be controlled within 0.3%.Based on this,the on-line identification of SOC and SOH is realized based on UKF.(2)Based on the proposed online identification scheme of equivalent circuit parameters,a SOC and SOH estimation method based on model and data fusion is proposed.The online identification of battery equivalent circuit parameters and the real-time monitoring of battery SOC and SOH status are realized synchronously.Through the theoretical derivation and analysis of the proposed SOC and SOH estimation algorithm,combined with the experimental data analysis of different dynamic conditions,the SOC and SOH estimation error based on the proposed algorithm is controlled within 0.15%,which provides a theoretical basis for the hierarchical control of echelon energy storage system based on parameter monitoring in the next chapter.(3)Based on the above work,a hierarchical control strategy of the echelon energy storage system based on parameter monitoring is proposed to solve the problem of power imbalance.Echelon energy storage system is based on DC-DC cascade topology.Firstly,through the proposed SOC and SOH online monitoring method,the SOC and SOH online identification of each battery power module echelon is realized,and the dynamic power distribution and balanced control of the battery are realized.Secondly,the power distributed by the battery power module is taken as the power reference of each module,and the independent control of each battery power module is realized through the droop link.Finally,the stability,dynamic and steady performance of the proposed control strategy are verified by simulation based on MATLAB / Simulink platform.