Research On Modular Energy Storage Technique

With the proportion of electric energy production generated by new clean energy power generation in the whole power network is arising higher and higher,the role of energy storage in the grid is more and more heightened.The increasingly evolving Voltage-Source Converter(VSC)technologies promote the birth and improvement of Modular Multilevel Converter(MMC)technology,which is a most potential converter topology for high-voltage & large-capacity applications.This thesis presents a topology in which battery is added to the MMC sub-module to construct a battery energy storage system(BESS).If it connects to the Grid,the BESS is equivalent to a three-port system through which not only can BESS accomplish AC/DC or DC/AC conversion,but also can the battery be charged and discharge.In this thesis the operation principle of BESS based on MMC is analyzed and its mathematical model in coordinates is deduced in order to discuss the control strategy for the BESS.On the basis of this model,the strategies based on the current flowing at BESS’s AC interface and BESS’s DC interface to achieve the batteries’ charging and discharging control and balance control of batteries’ State of Charge are proposed.Computer simulation in Matlab/Simulink is also carried out,and the results verify the correctness of the mathematical analysis and the validity of the control strategy.In consideration of BESS’s potential capacity expansion,a dual-level hierarchy control architecture in which a dual-core micro-processor with a FPGA chip is to be dominant system and a solution based on a CPLD chip is to be the subordinate system,is proposed and explained.A lot of work on analysis of the prototype machine’s hardware and software design is also conducted.The experiment in the laboratory is carried out as well and the results verified the hardware and software design discussed in this thesis.