Research On Maximum Power Tracking Of Photovoltaic Power Generation And Control Method Of Grid-connected Inverter

With the increasing energy crisis and the intensification of environmental pollution,photovoltaic grid-connected power generation technology,as one of the important means of using solar energy,has become a research hotspot for many scholars.Thus,this thesis takes photovoltaic grid-connected power generation system as the research object,and mainly studies the following contents:The principle of photovoltaic cell is described and the mathematical model is established,Aiming at the problems of slow dynamic response and poor steady-state accuracy of INC method when the solar irradiance changes rapidly,a compound MPPT algorithm control strategy is adopted.When the solar irradiance changes,the maximum power point current can be estimated according to the I-U characteristic curve of PV and the INC method is used to quickly locate near the maximum power point to improve the tracking response speed;After reaching a certain accuracy requirement,the fuzzy control is used to search accurately and find the maximum power point.Finally,the simulation verification shows that the composite control can find the maximum power point more quickly and accurately.The topological structure of the three-phase grid-connected inverter is introduced,and the mathematical model of the LCL inverter in the dq coordinate system and the αβcoordinate system is analyzed.Aiming at the resonant frequency of LCL filter,an active damping strategy based on grid-connected current feedback is proposed.By analyzing its resonance peak damping effect,the control strategy is proved to be reasonable.Aiming at the characteristics of insufficient dynamic response of repetitive control,an improved repetitive control current control strategy of grid-connected inverter is proposed.The improved repetitive control is based on the combination of repetitive control and proportional control,and the parameter design method is given in combination with the steady-state requirements and dynamic response of the control system.The feasibility of the strategy is verified by simulation.Aiming at the problem that the control effect of the repetitive control strategy decreases when the grid frequency fluctuates,an adaptive repetitive control based on a power series is proposed.By reasonably designing the fractional delay filter based on the power series,the adaptive repetitive control can obtain better harmonic suppression ability in case of frequency fluctuation.Simulation verification shows that the control strategy can improve the current quality when the power grid frequency fluctuates,and this control strategy makes it immune to frequency fluctuations.