Study On SOC Cooperative Control Of Microgrid Multi-energy Storage System

Due to the intermittence and fluctuation of renewable energy sources(RES)in microgrid,RES and energy storage systems(ESS)are usually used together to ensure the reliability and stability power supply of microgrid.The SOC unbalance between battery energy storage systems(BESS)in microgrid will affect the frequency of individual BESS discharge or charge and reduce the service life and capacity utilization.This paper focuses on the SOC cooperative control of BESS in multi-application scenarios,the control scheme of microgrid multi-battery energy storage system based on droop control autonomous control and distributed multi-agent system(MAS)control is studied.The main research contents are summarized as follows:Firstly,the existing droop-based SOC cooperative control schemes for BESS in islanded AC microgrid will cause frequency deviation in the process of SOC cooperative control and can not achieve SOC cooperative control of BESS with different capacities.Therefore,an improved SOC cooperative control scheme based on product factor is studied to eliminate the influence of BESS capacity and SOC balancing factor on SOC cooperative control and frequency respectively.Voltage recovery factor is added to Q-V droop control to recover the voltage deviation caused by load increasing.The small signal model of the control scheme is established,which provides a basis for the selection of control parameters of the proposed scheme.The SOC cooperative control effect of existing droop control and proposed SOC cooperative control scheme on BESS with different capacities under load changing conditions is compared and verified,the effectiveness of the proposed scheme is verified by the simulation and experimental results.Secondly,aiming at grid-connected AC microgrid controlled by single-layer MAS,an energy supply-demand balance and SOC cooperative control scheme of BESS with different capacities is studied.Combined with the demand of energy supply-demand balance in microgrid,a single-layer MAS PQ control scheme is designed,and SOC balance factor and weight coefficient are introduced,the output active power of BESS inverter is regulated by SOC balance factor to realize SOC cooperative control in the process of charging and discharging of BESS with different capacities.The simulation results verify the effectiveness of the proposed scheme under the conditions of load change,plug and play,RES output power change,communication delay and MAS communication structure change.Finally,for grid-connected/isolated AC microgrid controlled by two-layer MAS,the problem of maintaining critical load power supply for a specific time in the extreme case of insufficient power supply energy is studied,and the SOC cooperative control scheme is proposed.Two-layer MAS is used to shedding the non-critical loads in the grid-connected/islanded microgrid reasonably according to the time constraints of BESS,then the output power of BESS can be adjusted and realize supply the specific time of critical load.Meanwhile,the proposed load shedding scheme combines the energy supply-demand balance and frequency constraints of grid-connected/islanded microgrid.The effectiveness of the proposed scheme is studied under the conditions of load change,RES output power change,communication delay,plug and play and critical load power supply time extension.