Research On Control Method Of Modular Multilevel Battery Energy Storage System

In recent years,in order to achieve the improvement of the proportion of clean energy and the optimization of energy structure,renewable energy such as wind energy and solar energy have been developed and utilized on a large scale.However,its volatility and intermittent also bring challenges to the stable operation of the power system.The energy storage system consisting of the battery energy storage unit and the power conversion device can effectively suppress the power fluctuation of the new energy power generation,which can produce excellent results.There are many types of power conversion devices,of which modular multilevel converters are widely concerned with its modular structure,flexible expansion,good output power quality and high reliability.Aiming at MMC-ES system and its control strategy,this thesis conducts some researchs as follows:First of all,the topology and operation principle of MMC-ES are analyzed,and mathematic model is built.This thesis derives the transfer relationship among DC port?AC port and battery port.Meanwhile,the modulation strategy for MMC-ES system is discussed.The theory lays a foumdation for the control strategy.Secondly,the DC port and AC port power control based on the power flow analysis of MMC-ES is proposed,realizing the charge and discharge control of the battery unit.The theoretical analysis of the FOPI controller is carried out,and the grid current control strategy based on FOPI control is proposed.The feasibility of the power control strategy and the superiority of the control effect of the FOPI controller are verified by simulation.Thirdly,the theoretical analysis of the circulating current is carried out,and the circulating current suppression strategy based on the quasi-PR controller is studied.This thesis describes the effect of battery accessing on capacitor voltage balance,and proposes a capacitor voltage balance method based on sub-module average power control.Meanwhile,the parameter identification of the second-order RC equivalent model of the battery is carried out,and the three-level SOC balancing control method is studied.Based on this,a phase-to-phase SOC balancing method based on AC power feedback is proposed to improve the adjustment speed of SOC.Simulation results verify the correctness and effectiveness of the overall control strategy of the system.Finally,the software and hardware design of Real Time Digital Simulator is introduced.Combined with the characteristics of small step simulation environment of RTDS,the simulation model of MMC-ES system is built to verify the comprehensive control strategy.