Research On Control Strategy Of Power Conversion System For Microgrid

In recent years,regional power grid blackout caused by natural disasters and partial failure of the grid happens sometimes,which reveals the shortcomings of traditional electric power system.At the same time,due to the growing environmental pollution and energy crisis,the development of clean and renewable energy has become the focus of the world.In order to solve these problems,distributed generation technology is getting more and more attention.As the important issue of the development of the distributed power generation technology,microgrid technology has gradually become the research hotspot of technical personnel.As the distributed power supply in the microgrid is affected by the meteorological conditions,it is intermittent and hard to predict,the output power of the microgrid is changing all the time.Therefore,the microgrid must be equipped with a certain capacity of energy storage system to ensure the safety and stability in operation.According to the research status of microgrid system,the research on control strategy of power conversion technology in microgrid is the main line of this thesis,and themain contributions of this thesis are as follows:(1)Based on the analysis and research of conventional PQ control strategy of power conversion system(PCS)in microgrid interconnection mode,aiming at power quality improvement in microgrid,power quality active compensation technique is proposed in this paper by using redundant capacity of the energy storage system.The technique realized fundamental positive sequence extraction from the AC voltage with serious harmonic wave and the fundamental phase detection based onadaptive notch filter(ANF).Combining with conventional PQ control method,the PCS can either accept the dispatch of superior and determine the output power,or carry out power quality compensation with redundant capacity of energy storage system.(2)According to the analysis and research of traditional droop control strategy,considering the poor adaptability of the droop control with constant droop coefficient in microgrid,improved adaptive droop control strategy is proposed in this thesis.The strategy can adjust the droop coefficient along with the frequency and voltage of microgrid,and ensure the optimal matching between output power of microgrid and frequency and voltage.(3)According to the change of the load power within the microgrid,off-grid integrated control strategy of PCS is put forward to keep frequency and busbar voltage of microgrid in high precision,which combines the V/f control strategy and the improved adaptive droop control.The simulation results verify the effectiveness of the proposed control strategy.(4)Based on the similarity of controller in structure between grid-connection and off-grid,controller structure with double-negative feedback is proposed to realize seamless transfer of output control signal when control strategy is switched,and reduce the unstable factors of the microgrid operation-mode switching process.(5)Through the analysis of the condition of the quasi-synchronization in microgrid,because the risk of voltage oscillation caused by the mutual interference of the two controller in the traditional quasi-synchronization method exists,an improved quasi-synchronization controller is proposed,which is simpler and easier to implement.The simulation resultshows the control effect is satisfactory.