Control Strategy Of Grid-connected PV System During Asymmetrical Grid Faults

Photovoltaic power generation rely on zero pollution, low cost, abundant solar energy resources, etc, to save conventional fossil energy, relieve stress of environmental protection and played an important role in promote the economic development of global. With increasing grid-connected photovoltaic systems, the interaction of between photovoltaic systems and the grid has become more and more apparent. A fault takes place in a network, especially asymmetric fault, lead to the grid current imbalanced and DC side voltage instability, and feed into the grid power causing oscillation, even burned PV inverter, influence safe operation of grid-connected PV system and the grid. Therefore, research on operation control technology of grid-connected PV system during the asymmetric grid fault has practical value for engineering application.In this thesis, to increase performance of continuous operation for Grid-Connected PV System under the asymmetric grid fault, power output power quality and DC side voltage stability of grid inverter as optimization control target. from theoretical research to analysis of simulation results, the further study of control technology PV grid inverter under the asymmetric grid fault.Firstly, the mathematical model of photovoltaic cells is established, and the appropriate MPPT control methods is selected. Based on incremental conductance method of PV array maximum power tracking control system is established. Secondly, mathematical model of PV inverters is established under ideal conditions grid, and design PI control strategy, demonstrated the effectiveness and feasibility of PI control strategy. Lastly, the mathematical model of the PV inverter is established under asymmetric grid fault. Power flow of PV inverter, and the mechanism of voltage fluctuation in DC bus is analyzed. In order to maintain the DC bus voltage stability, using resonance characteristics of notch filter, the positive-negative sequence dual current control strategy with notch filter in DC voltage is proposed. In order to eliminate the negative sequence component of grid current, According to the relationship of the inverter output power and the positive and negative sequence component of grid current, suppression of negative sequence component of grid current control strategy is established. The control strategy for the photovoltaic system is simulated in thne Matlab/Simulink platform. The results proved that the proposed control strategy is correct ad effective.