The Research On Power Quality Control Strategy In Island Microgrid Bsaed On Virtual Synchronous Generator

The continuous consumption of traditional non-renewable energy such as coal and oil has brought about global environmental pollution and energy crisis,it is widely recognized all over the world that distributed generation as an environmental friendly and flexible power generation methods is being paid attention to and developed.The use of distributed generation can make full use of the abundant and environmentally friendly renewable energy sources and help increase the utilization of traditional fossil fuels and provide green power to users.Microgrid,as an important bridge and link of large power grid and distributed generation,can improve power supply reliability by reducing the impact of distributed generation on the power grid effectively.With the increase penetration rate of distributed power in the microgrid,the stability of the microgrid is greatly reduced,it is difficult for traditional distributed power control strategy to achieve the inertia and damping characteristics of large power grid.By providing inertia and damping characteristics for the microgrid,the distributed generation can be simulated as a traditional synchronous generator by the virtual synchronous generator control algorithm,which improves the stability of microgrids greatly.With the further research on the microgrid,many of its power quality problems such as frequency deviation and voltage harmonics become the focus and hotspot of current research in microgrid.Therefore,based on the virtual synchronous generator control algorithm,this paper studies the power quality of microgrids operating off-grid.Firstly,the background and significance of research on power quality of microgrids are introduced,the research status of microgrid,VSG and microgrid power quality at home and abroad are summarized,and some power quality problems in microgrids are analyzed in detail and summarizing current microgrid power quality governance measures.Then,the research status of the virtual synchronous generator is summarized,and the control principle and parameter tuning method of the virtual synchronous generator are analyzed in detail.Secondly,aiming at the problem of frequency deviation when microgrid runs off-grid in the face of load fluctuation,a strategy of second frequency regulation of microgrid based on virtual synchronous generator is proposed.According to the sampling system frequency deviation,each virtual synchronous generator can allocate load power automatically according to their rated capacity,witch can not only improve the economic operation of the microgrid,but also maintain the microgrid frequency stable at the rated value,and the whole process does not need to rely on the communication between the microgrid central controller and the virtual s ynchronous generator.Then,aming at the microgrid operating off-grid,its AC bus voltage is susceptible to distortion caused by the nonlinear load,a voltage harmonic suppression strategy based on virtual harmonic impedance and multiresonant PR controller is proposed.First of all,the causes of voltage harmonics in microgrid are systematically analyzed by using harmonic load equivalent model,it is found that the output harmonic impedance of virtual synchronous generator is an important factor affecting the voltage distortion.Then the output harmonic impedance of the virtual synchronous generator is analyzed,and the selection method of virtual impedance is proposed.The addition of virtual impedance greatly reduces the output impedance of the virtual synchronous generator at each harmonic frequency,so that the virtual synchronous generator can output a voltage with less harmonic content under nonlinear load.Finally,the control strategy proposed in this paper is applied to the microgrid operating off-grid.the simulation and experiment results show that the proposed control strategy can improve the power quality of microgrid correctly and effectively.