Research On Control Strategy Of Three-phase Non-isolated Photovoltaic Grid-connected Inverter

With the rapid growth of economy and population,people’s demand for and dependence on energy is increasing day by day.Social and environmental problems caused by the non-renewability and pollution of traditional energy sources have become more prominent.Under this background,the clean and effective green energy solar energy emerges as the times require,and it soon becomes a hot topic in the world.This paper mainly studies the photovoltaic inverter system,analyzes the photovoltaic inverter system,and establishes the corresponding mathematical model.Based on the mathematical model,focus on the PR plus repeated photovoltaic grid-connected inverter compound control strategy,And the design of phase-locked loop under three-phase unbalanced state.First of all,this article analyzes and models the photovoltaic array,which is one of the important components of the photovoltaic power generation system.Based on the mathematical model,through simulation in MATLAB/Simulink,the output characteristic curve of the photovoltaic array under different light conditions and different temperatures is obtained.On this basis,the maximum power point tracking method of the photovoltaic array: the perturbation observation method(P&O)and the conductance increment method(INC)are analyzed,and the two methods are simulated and compared.The simulation results verify that the conductance increment method can In the case of sudden changes in the external environment,the MPP can be tracked accurately and quickly,so the conductance increment method is selected as the maximum power point tracking method of this system.Secondly,the mathematical models of voltage-type photovoltaic grid-connected inverters in different coordinate systems are established and analyzed,and relevant parameters are designed.In terms of photovoltaic grid-connected inverter control,SVPWM is first selected as the inverter modulation method.Then,in order to solve the problems of the traditional PI and PR control as the current inner loop control,such as the inability to track the sinusoidal signal without static error and the poor harmonic suppression,a composite control strategy of quasi-PR plus repetition is given to improve the quasi-PR dynamic performance Combining with the advantages of repetitive control that it can suppress periodic disturbances and is suitable for harmonic occasions,it can achieve complementarity between different algorithms.Finally,it is simulated in Matlab/Simulink environment to verify that the composite control strategy can effectively suppress harmonics in the power grid.The dynamic response is fast,which effectively improves the grid-connected power quality and system stability.Under the three-phase unbalanced state,how the photovoltaic grid-connected inverter can accurately obtain the phase frequency information of the grid voltage,so as to realize the unit power factor grid-connected problem.Carried out the research and design of the three-phase phase-locked loop,first introduced the design of DSOGI-PLL and DSOGI-FLL,and simulated the possible unbalanced operating conditions of the power grid.Different from the slow response speed of DSOGI,in the case of three-phase imbalance,such as when the system contains harmonics,the phase and frequency detection have the disadvantages of errors.Choose a PLL designed based on the SDFT method and target the possible unbalanced conditions of the grid The simulation results show that the PLL designed by the SDFT method can quickly lock frequency and phase,suppress harmonics and reduce errors,which verifies the feasibility of its theory.Figure [84] Table [2] Reference [72]...