Power Quality Research On Solar Photovoltaic Power Generation System

In today's society,with the rapid development of industry and the heavy mining of traditional fossil energy,the shortage of energy and environmental pollution have become an important factor restricting the sustainable development of human society.To find clean and renewable energy has become a focal point in the world.Solar energy has many advantages,such as inexhaustible,clean and pollution-free.Many countries in the world are developing and utilizing it.At present,the photovoltaic industry in the world is developing rapidly,and more and more photovoltaic power sources are merged into the large power grid.But the photovoltaic power generation is affected by the external environment,the output is unstable,and the photovoltaic power system contains a large number of power electronic devices,coupled with a large number of nonlinear,impact load,these factors will bring a lot of new problems to the grid to be incorporated.In this paper,the mathematical model of the photovoltaic cell and the partial occlusion of the photovoltaic array are set up,and the simulation model is built in the Matlab/Simulink to get the output characteristic curve of the single battery and the photovoltaic array under occlusion.According to the characteristics of photovoltaic cells and inverters,the mechanism of harmonic generation in photovoltaic power generation system is analyzed,and the harm of harmonic and the measures to suppress harmonics are outlined.To solve the harmonics of solar photovoltaic power generation system,the similarities and differences between the photovoltaic power system and the active power filter in three aspects of topology,function and control strategy are analyzed.According to the similarity of the two,the photovoltaic power generation and active filter are unified.The design of the unified control system is designed,and the original work is introduced.The unified control system can realize the photovoltaic power generation while filtering the harmonics to improve the power quality and meet the requirements of grid connection.Combined with the basic principle of Maximum Power Point Tracking(MPPT)control,several traditional MPPT control methods are analyzed,and the control flow chart is given.In view of the characteristics of the PV array power output with multiple local maximum points under local occlusion,an improved particle swarm optimization(PSO)method for global tracking is proposed.In the simulation,the superiority of the PSO is verified by comparing with the traditional method.Based on the theory of instantaneous reactive power in three-phase circuit,the method p-q and methodi_p-i _q are analyzed,and the methodi_p-i _q of harmonic current detection is finally determined.The synthesis of the command signal of the unified control system is analyzed and designed.The harmonic current contained in the instruction signal,active current signal of the photovoltaic array and the DC side voltage control signal are analyzed and calculated,and the synthetic structure diagram is given.Several common control strategies are analyzed and introduced,combined with the traditional PI control and the introduction of repetitive controller,this article puts forward a compound control strategy based on repetitive control and PI control.The analysis shows that the strategy meets the design requirements of this paper.Finally,a brief comparison and analysis of two pulse modulation methods of SPWM and SVPWM is made,and SVPWM is used as a pulse modulation method for the post stage circuit of the system.Finally,based on the MATLAB simulation model of the unified control system,the control strategy proposed in this paper is simulated and verified.The simulation results show that the system can achieve the desired goal.It can also compensate the harmonic current in the power grid while the grid is connected to the grid,and proves the correctness and effectiveness of the selected control strategy.