Simulation Research On MMC Based Power Electronic Distribution Transformer

Since twenty-first century, the problems of energy shortage, environmental pollution and climate change have become increasingly prominent, which have seriously threatened the survival and sustainable development of human beings. The global energy structure adjustment, which is characterized by electricity, has become the common choice of the world's leading countries. The growing demand for clean energy has promoted the development of a strong smart grid. It also put forward higher requirements for the security and stability of power system and the stage of its automation. As one of the most important devices in power system, the power transformer needs to be developed to deal with the challenges of modern power system. Development of the modern electric power electronic technology has promoted the innovation of the traditional power transformer to the power electronic transformer. The power electronic transformer, which integrates the functions of electrical isolation, voltage transformation and power quality regulation, is expected to bring its superiority to the smart grid. In this paper, the research of the modular multilevel converter, MMC based distribution power electronic transformer and the simulation research in the hybrid distribution network are studied as follows:The working mechanism of the modular multilevel converter was studied. The modular multilevel converter topologies, the modular multilevel converter simplified equivalent circuit and switch function model were introduced and established. According to the above analysis, the basic working principle of the modular multilevel converter was introduced in this paper. In addition, the multi carrier SPWM technique in MMC were analyzed and compared. Moreover, the MMC operating characteristics were analyzed to explain the generation mechanism of DC capacitor voltage fluctuation and internal circulating current etc..Research on the control method of MMC based distribution power electronic transformer was studied. Aiming at the application of AC/DC hybrid power distribution grid, the topology structure of MMC based power electronic transformer topology with multiple ports including high or low AC and DC voltage was designed. On the basis of the commonly used independent control method, a two stage comprehensive control method was proposed Based on the topological characteristics of this paper, and two control methods were simulated and compared to select a more optimal scheme.The overall design and simulation of MMC based power electronic transformer was researched in AC /DC hybrid application in distribution network. According to the main performance indexes of the application system, main circuit parameters of the MMC based distribution power electronic transformer were designed. Finally, the overall simulation of MMC based distribution power electronic transformer was researched in PSCAD/EMTDC to verify the output performance. Based on the above, varieties of work modes were proposed to adapt to the application of AC/DC hybrid power distribution gird.To sum up, this paper has taken MMC based power electronic transformer as the research object, based on the AC/DC hybrid power distribution network applications, from the aspects of the circuit structure, control method, circuit parameters and working mode, overall design and simulation verification were studied, laying a solid foundation for future practical engineering applications.