Study On Battery Energy Storage System Based On Module Multilevel Converter And Its Control Methods

Energy storage batteries are increasingly used in applications.It typically requires an external converter to perform the desired AC and DC conversion.The modular multi-level converter(MMC)has the characteristics of flexible structure and AC and DC output ports,which has been widely used in engineering.Considering the structural characteristics of the MMC system,this dissertation integrates battery module into the single-phase MMC structure,and the control algorithm suitable for this structure is proposed to realize the AC-DC power control and the balance between the batteries.The existing battery energy storage system requires a variety of management devices and has poor scalability.In order to improve the system,this dissertation introduces the proposed MMC structure based on battery energy storage first.Compared with the traditional battery power converter and SOC active equalization structure,the MMC battery energy storage system has the functions of AC and DC output and battery SOC equalization.It has certain new ideas and application space.In order to realize the function of the above MMC battery energy storage system,a mathematical model of the MMC battery energy storage system is established.The effects of two kinds of carrier phase-shift modulation methods on the AC and DC output of the system and the multi-terminal power exchange relationship of the system are analyzed.By modeling and analyzing the AC and DC circulating current,the AC/DC current grid-connected control scheme is designed to verify the stability of the system.Aiming at the practical application requirements of battery balancing,a balancing strategy of tracking current is proposed.By adding a current direction tracking operator to correct the DC voltage reference of a single battery module,the battery SOC can be equalized without affecting the AC and DC output.Even when the active power is zero,the battery equalization can be completed as long as the system has current flowing through it.In this dissertation,the MMC battery energy storage system is modeled and time-domain simulated in MATLAB simulation software.Then a hardware experimental platform of low-voltage and low-power MMC battery energy storage system is built and tested.Simulation and experimental results show that the energy control and battery equalization methods are feasible.