New Modular PV Energy Storage System

In the process of grid upgrading and the construction of smart grid,the proportion of new energy power generation is increasing,and the energy storage system also plays an important role in the operation of power grid.Modular Multilevel Converter(MMC)has the advantages of easy expansion,good output power quality and so on.It is widely used in high voltage and large capacity applications.In this paper,the MMC energy storage system are researched and designed which based on MMC structure and the energy storage batterys are added to the sub-modules.This paper focuses on the MMC energy storage system prototype design and related control algorithms.This article mainly includes the following contents:In this paper,the structure of the traditional MMC is briefly introduced,including sub-module and the working principle of the three-phase MMC,the mathematical modeling is analysized and related modulation strategies are explained.On this basis,the control system is researched.The two-stage and three-level control system architectures of the current mainstream are compared and the two-stage control system architecture is adopted in the designed prototype.The main controller uses DSP + FPGA,the sub-module controller uses FPGA,and the main controller and the sub-module communicate with each other through optical fiber.It also includes the information exchange between DSP and FPGA,and the design of communication between the host controller FPGA and the sub-module FPGA introduced in detail.The implementation process of the main controller FPGA and the submodule FPGA is described.The paper also analyzes the control strategy of MMC energy storage system.The study of MMC energy storage system can be seen as a threeterminal network,DC bus connected PV array,AC side of the grid or load,each sub-module access to storage battery.And through a certain control can achieve the free flow of three-terminal energy.According to the mathematical modeling and analysis of the MMC circuit,the control method of the AC interface current and the interface current of the PV array can be obtained,and the charging and discharging control of the storage battery can be realized by controlling the AC side power and the PV array power.On the basis of power control,the balance control of the energy storage battery is also studied in detail,phase-phase and within phase balance control strategy are tested in Matlab / Simulink.At the end of this paper,the prototype of MMC energy storage system is designed.The hardware design of the prototype is introduced in detail,and the prototype is experimentally tested from the part to the whole.The protection circuit,the system real-time control and the initial operation of the prototype are tested.Experimental results show that MMC energy storage system software and hardware design is reasonable.