Anti-Island Strategies Research For Grid-Connected PV System

Economic development issue and environmental issue have always been seemingly contradictory but complementary.To develop the economy quickly,it is inseparable from sufficient energy and good environment.Solar power generation technology has received great attention due to the inexhaustible solar energy and absolute cleanliness in today's rapid economic development.Among many solar power generation technologies,PV generation technology has become the most widely used solar power generation technology due to its good applicability.Compared with off-grid PV system,grid-connected PV system has higher photovoltaic energy utilization rates during operation.However,since the grid-connected PV system directly inverts the electric energy generated by the PV array and feeds it to the power grid,the grid-connected PV system needs to meet the requirements of the maximum power output in addition to the grid connection.The occurrence of the islanding effect will bring a series of serious hazards to the safety of system equipment and staff.Therefore,it is of great significance to study the anti-islanding strategy of grid-connected PV system.In order to provide a basis for the anti-island strategy research of PV systems,this paper establishes a photovoltaic array model in MATLAB/simulink environment and simulates an uneven illumination situation based on engineering mathematical model of PV cells.In order to improve the energy efficiency of photovoltaic power generation systems,this paper proposes a method based on particle swarm optimization and stepwise approximation perturbation observation method.The simulation results show that the method has very good optimization effect under uneven illumination conditions.In order to achieve both GMPPT control and DC/AC conversion,this parper uses a two-stage non-isolated grid-connected inverter.The DC/DC module realizes DC sidevoltage control and GMPPT control.The DC/AC module realizes the grid connection after the direct AC inverter.In ensure the operation efficiency of grid-connected PV system,a method based on particle swarm optimization and variable step size disturbance observation method is designed to ensure the global maximum power output of the PV array.In ensure the grid-connected power quality and DC bus voltage during normal operation of the system,this paper adopts VOC strategy.DC voltage outer loop is used to control the stability of the DC bus voltage.Current inner loop completes no static tracking of active current and reactive current to achieve the purpose of regulating the power quality of the grid point.In ensure the security and stable operation of the grid-connected PV system and efficiently detect the island state while minimizing the adverse effects on the grid,this paper proposes a reactive current disturbance method and O/UVP,O/UFP Mixed islanding detection method.This method detects the relevant parameters in real time and calculates the power output from inverter and the power consumed by the load,and then determines whether to use the reactive current disturbance method according to the Non-Detection Zone judgment of passive method.The reactive current disturbance method,by applying a periodic reactive disturbing current,deviates the frequency of Point of Common Coupling,and further triggers a positive feedback reactive disturbing current to bring the frequency out of limit.The hybrid islanding detection method realizes fast and efficient detection without Non-Detection Zone,and has no harmonic pollution and minor impact of power factor.The simulation results in MATLAB verify effectiveness of the method.