The Study On Dynamic Voltage Restorer Based On Modular Multilevel Converter Topology

With the development of modern science and technology, a lot of precision equipment relying on computers and microprocessors is used in the power system. Transient interruption of power supply or voltage drop will affect the normal work of the equipment, which leads to great economic loss. At present, dynamic voltage restorer is the most effective method to suppress voltage fluctuations. It can effectively solve the voltage swell and sag, voltage harmonics and other power quality problems.The structure and working principle of the dynamic voltage restorer are analyzed in detail. Three compensation strategies, pre-sag compensation, in-phase compensation and minimum energy compensation are introduced with the comparison of these strategies. Voltage sag detection algorithms of dynamic voltage restorer are researched in depth. The advantages and disadvantages of commonly used detection algorithms and one based on dq transformation are put forward.A new technology is presented, which applies modular multilevel structure to dynamic voltage restorer. Modular multilevel structure is easy to expand and realize. The topological structure and working principle of the modular multilevel converter are introduced and analysed. A mathematical model is established. The modulation method and sub module capacitor voltage control strategy of MMC are researched. The sub module capacitor voltage fluctuation and the interphase circulating current characteristics are analyzed, which prove the basis for the selection of parameters of MMC circuit.The simulation model of dynamic voltage restorer based on MMC topology is built using the electromagnetic transient simulation software PSCAD. Power quality problems such as long term low voltage, the instantaneous voltage sag and voltage harmonics are simulated respectively. The simulation results show that the dynamic voltage restorer based on MMC topology can respond fast and has significant compensation effect. It can effectively suppress the voltage fluctuation and ensure the power quality of the load.