Research On Power Quality Control Strategy Of Grid-connected Photovoltaic Power Generation System

Today,new energy is widely used in the world,which greatly reduces the burning of fossil fuels and the emission of greenhouse gases.Due to the depletion of traditional fossil fuels,the increasingly serious air pollution,a greater degree of the use of new energy has become the focus of research in various countries.Solar energy as an environmentally friendly and sustainable new energy is getting more and more attention.With the development of smart grid,more and more solar power systems will be incorporated into the power grid in the future.At the same time,due to the solar energy itself is intermittent and a lot of nonlinear loads are connected to the grid,the power quality become decline seriously,which will bring bad effect to the grid such as voltage sags,harmonics,low power factor,load imbalance etc.In this paper,the power quality problems caused by three phase photovoltaic power generation system are studied,and the effective control strategies are proposed for the harmonic and over voltage problems of power quality.Considering of a large number of nonlinear loads in the power system and photovoltaic power generation system connected to the grid,the paper analyzes the instantaneous reactive power theory used to control grid-connected photovoltaic harmonic,and traditional instantaneous reactive power theory of photovoltaic grid-connected inverter control method is improved.The DC side voltage feedback is used to stabilize the DC side voltage,and improve the effect of harmonic and reactive power compensation;adding the three-phase voltage feedback to adjust the PCC voltage,using PI controller to realize the harmonic static error free tracking,thus effectively reducing the harmonic and stable PCC voltage.The simulation model of photovoltaic grid connected generation system is built by Matlab/Simulink software.Through the experimental verification,it is proved that the improved control algorithm can achieve the desired results in the suppression of harmonic and stable PCC point voltage.In order to solve the problem that large scale photovoltaic grid-connected power systems produce over-voltage of feeder in distribution network,a new method based on BP neural network is proposed to reduce the active power of PV power generation.The strategy uses historical data,such as the solar irradiance and temperature data of meteorological forecast,by which forecasts the active power of the photovoltaic power generation needing to be cut,and control the power output of photovoltaic panels to avoid the occurrence of over-voltage.In this paper,the forecast model is introduced,the prediction models of different types(sunny and cloudy)are presented.Finally,through the analysis of MATLAB simulation software,the results confirm the feasibility and effectiveness of the predictive model.