Development Of Sub Module Controller On The MMC-HVDC Physical Simulation System

With the problems of global energy shortage and environment pollution, the growing capacity of renewable energy source and the demands of transmitting power to isolated islands and offshore drilling platforms and expansion of city’s power capacity make the old methods of using AC transmission system and traditional HVDC transmission very uneconomical. In the late1990s, a new generation of DC transmission technology using VSC(Voltage Source Converter)based on full-controlled turn-off power electronic devices IGBT is a new technology for power transmission which is more flexible, more economical, more environmentally friendly and could solve the above problems.The most important part of VSC-HVDC is Voltage Source Converter, which can be separated into two-level converter and multilevel converter. With lower IGBT switching frequency and better output voltage waveform, the modular multilevel converter is widely used in VSC-HVDC, called MMC-HVDC. Compared with the traditional HVDC using thyristor converter technology, MMC-HVDC has the advantages when applied in connecting offshore wind power and distributed sources to the grid and sending power to isolated islands. Therefore, it is a hot issue in the current academic research. But most current research is based on theoretical analysis and digital simulation. Consequently, building a MMC-HVDC physical simulation, has a significant meaning for further researches of MMC-HVDC. The MMC-HVDC physical simulation system is a part of the "Hybrid HVDC transmission platform" key construction project in the State Key laboratory of Alternate Power System with Renewable Energy Sources(NCEPU). Based on MMC-HVDC physical simulation system, the system topology, the controller architecture, the system control strategies and sub-module controllers are studied.By connecting the AC side outlets of the two MMC-HVDC converters, a ring network is formed to reduce the capacity of laboratory supply source. According to the different functions, each converter is divided into four cabinets called power supply cabinet, charging cabinet, modular cabinets and DC cabinet. A three-level structure is used by the system controller, namely Pole Control&Protection system(PCP), Valve Basic Controller(VBC), Sub Module Controller(SMC). The function of each level and the coordinating strategy are introduced. Sub Module Controller(SMC) is the research priority of the paper. Firstly, the hardware structure is introduced by different function parts. Then, the serial communication protocol and the coordinating strategy between the SMC and VBC are designed. Finally, Sub module faults and the protection after faults are described. Including the hardware design and software design, a Sub module steady-state test platform is designed to be the type test and quality inspection program.