Research On Maximum Power Tracking And Grid-connection Control Strategy For Photovoltaic Power Generation System

For a long time now,environmental pollution has become increasingly serious as a result of people’s excessive use of fossil fuels.In recent years,therefore,new energy has gradually entered our vision,and solar energy as renewable clean energy has been widely used in real life,where photovoltaic grid technology has become the centrepiece of new energy deployment.However,the output characteristics of PV cells are easily affected by environmental factors,resulting in a reduction in the efficiency of the system’s PV power generation.In addition,with the traditional control strategy at the grid connection stage,the harmonic content of the grid connection current is high,which has a significant impact on the power quality.Therefore,the related gridconnected control technologies of PV power generation,in particular the peak power point tracking and inverter control technologies,are investigated in this work.The main contents are as follows:Firstly,the working principle of PV cells is analysed and their mathematical model is derived.The mathematical model is then simulated with the Simulink module in MATLAB,and the P-U and I-U curves at different light intensities and different temperatures are obtained,and the effects of temperature and light variations on the PV power generation are analysed.At the same time,considering the requirements of the PV grid connection control strategy,a two-stage inverter structure is selected as the basis for further studies.Secondly,the tracking of the maximum power point of PV cells and its improvement method are investigated.After the control circuit analysis,a Boost scheme is applied to the DC-DC converter.Then,the MPPT technology is investigated,and the control effects of some traditional algorithms such as constant voltage method,disturbance monitoring method and conductivity gain method are compared and analysed,but none of them can achieve fast and stable MPPT tracking.Therefore,a novel MPPT control strategy based on the combination of particle family optimization and conductivity gain method is proposed in this work to achieve fast and stable tracking under the changing external environment.Through Simulink simulation,it is verified that the tracking speed and accuracy of the new strategy are obviously improved at the maximum power point,which can ensure the stable operation of the system.Thirdly,the control strategy of grid connection of PV power generation system is investigated.After analyzing the working principle and topological structure of the DCAC inverter unit,it is decided to choose the inverter structure of single-phase full-mile LCL grid as the research object.After the analysis of traditional inverter control methods such as PI control and PR control,it is found that the non-static regulation of the inverter output voltage cannot be realized when the traditional PI control is used for the current inner loop.Therefore,a quasi-PR and PI composite control method based on double closed loop is further proposed in this work.The PI control is used for the voltage outer loop,and the quasi-PR control is used for the current inner loop.Finally,Simulink was used to simulate and verify that this method can achieve the same frequency and phase of grid current and grid voltage compared with the traditional PI control method,and the harmonic content is reduced by 2.54% compared with the previous method,which can ensure the stable operation of the system.The simulation results show that the composite control strategy of quasi-PR and PI based on double closed loop can achieve no static regulation and low harmonic content,which will provide better performance for single-phase PV inverter and create a more stable foundation for the further development of photovoltaic power generation.