Light Storage Integrated Rural Complex Modular Multilevel Converter

The proposal of the strategic goal of "double carbon" shows China’s firm determination to accelerate the construction of a clean,safe and efficient new energy system.While accelerating the development of cleaner,more environmentally friendly and more economical photovoltaic power generation projects,how to use storage units and converter devices to effectively store and convert these photovoltaic energy is an important and challenging work.Modular multilevel converter（MMC）can decentralize the access of energy storage units,and can improve the direct voltage（DC）input voltage level and converter capacity by increasing the number of sub modules.In this paper,MMC is integrated with photovoltaic cells and energy storage system to realize the two functions of energy storage and current conversion,and it is deeply studied from the following aspects.（1）This paper improves the Carrier Phase Shifted Sinusoidal Pulse Width Modulation（CPS-SPWM）and designs a modified CPS-SPWM method.This method can reduce the amplitude of MMC bridge voltage harmonic,thus improving the waveform quality of alternating current（AC）side output voltage and output current.The simulation verification of the designed method using MATLAB/Simulink software shows that the output voltage and output current of the modified CPS-SPWM method can verify the correctness of the designed method.（2）For decentralized management and efficient conversion of photovoltaic energy,the battery pack is connected to the sub module of MMC through bidirectional DC/DC converter.Using the combination of fixed voltage method and disturbance observation method,the maximum power point tracking（MPPT）of photovoltaic cells is realized by controlling the bidirectional DC/DC converter to change the charge and discharge power of the battery pack.The measured results show that under the designed circuit and control method,the system realizes the MPPT of photovoltaic cells.（3）In order to solve the problem of high hardware cost of MMC applied to rural complex,this paper uses low-cost STM32 single chip microcomputer as the core controller to design a single-phase H-bridge MMC experimental prototype with rated capacity of600V/3KW.The design mainly includes the selection and design of power devices,the design of system control circuit and system program design.The improved CPS-SPWM method,MPPT of photovoltaic cells and circulation suppression strategy are experimentally verified by using the prototype.The feasibility and effectiveness of the circuit and control method of the prototype are verified by testing and spectrum analysis using MATLAB/Simulink software.