Research On Multi-Module Auxiliary Converter For Decommissioned Battery Energy Storage System

In recent years,with the energy crisis and environmental pollution problems becoming more severe,electric vehicles have attracted widespread attention as clean vehicles.With the development of the new energy automobile industry,a large number of power batteries will reach the decommissioning conditions in the future but still have a certain service life.The decommissioned battery used in the energy storage system can stabilize the fluctuation of renewable energy generation and regulate peak and frequency in power grid.In view of the battery inconsistency in the decommissioned battery energy storage system,a multi-module auxiliary converter solution is proposed and conducts the following research.Firstly,the problems of the use of decommissioned battery in traditional energy storage system are analyzed,and the structure of the decommissioned battery energy storage system using the multi-module auxiliary converter is described.Since the multi-module auxiliary converter circuit structure and principle are based on Voltage-Fed Dual Active Bridge(DAB)converter,the working principle and working characteristics of the traditional phase shift control DAB converter are analyzed.Furthermore,the coupling relationship of the secondary side output current of the multi-module auxiliary converter is studied.Secondly,aiming at the problem of large current stress and reflux power of multi-module auxiliary converter under traditional phase shift control,the extended phase shift control is used to optimize the control,and the working principle and working characteristics of the extended phase shift control DAB converter are analyzed.The Lagrangian multiplier method is used to calculate the minimum current stress and minimum reflux power control strategy of extended phase shift control in the control domain.The working characteristics of multi-module auxiliary converter under extended phase shift control are studied.Thirdly,the SOC estimation method of the battery module of the decommissioned battery energy storage system using multi-module auxiliary converter is studied.Aiming at the problem that the traditional SOC equalization control strategy has steady-state error when the battery capacity is inconsistent,a SOC equalization strategy considering capacity inconsistency is proposed.In order to ensure accurate estimation of the SOC of decommissioned battery module,an online calibration scheme for the SOC and capacity of the battery module is proposed.Finally,the DAB experimental platform of the single side module was built,and the extended phase shift current stress optimization experiment and the re:flux power optimization experiment were completed.The prototype of 50kW decommissioned battery energy storage system was built,and the multi-module auxiliary converter was used to complete the SOC balance when the battery module capacity was inconsistent,and the feasibility of the topology structure and control strategy was verified.The multi-module auxiliary converter effectively improves the capacity utilization of decommissioned battery energy storage system with inconsistent battery module capacity.