Independently Modular Control Of Cascaded H-Bridge Energy Storage System

In recent years,with the promotion of new energy power generation,energy storage technology has been widely used in all aspects of the power system.With the characteristic of quick response,higher efficiency and proven technique,battery energy storage system(BESS)has been applied to a certain scale in the grid.Energy storage system based on Cascaded H-bridge(CHB)has several significant advantages,such as lower THD of output voltage,smaller voltage stress of power electronics devices,fault tolerance ability,which make CHB-BESS suitable for high-voltage and large-power energy storage situation.Aiming at CHB-BESS and its control strategy,this thesis conducts some researches as follows.Firstly,the thesis analyzes the topology,modulation strategy and grid-connected control strategy of CHB energy storage system by establishing mathematical models and theoretical derivation to achieve the grid connection requirements of the CHB-BESS.It provides the theoretical basis for the modular independent control strategy of battery energy storage systems.Secondly,the thesis studies the independent control strategy among battery module current and the independent control strategy among three-phase battery power to achieve the independent control of each battery module in the CHB energy storage system.A mixed modulation strategy is proposed to deal with the overmodulation problems that may occur in the battery module current independent control.Simulation results verify the validity of the control strategy.Thirdly,to solve the problems caused by the battery inconsistency,based on the independent control strategy among battery module current and the independent control strategy among three-phase battery power,the thesis studies the SOC balancing control strategy to realize the SOC balance among all battery modules.A SOC balancing control strategy which is suitable for the inconsistent characteristics of the echelon used batteries is proposed to achieve SOC balancing control for the batteries with different capacities.Finally,the thesis conducts experiments on the experimental platform which is a 3-phase 24-module cascaded H-bridge battery energy storage system prototype to verify the above control strategies.The experimental data and waveforms verify the validity of the proposed control strategies.