Research On Low-voltage Ride Through Control Of Grid-connected Photovoltaic Power Generation System

With the more and more serious environmental pollution problem caused by traditional petrochemical energy generation,how to develop and utilize the new energy for power generation has gradually become a hot topic.in global research.Grid-connected photovoltaic power generation is a main way to exploit new energy for generation.Compared with the traditional synchronous generator generation system,grid-connected photovoltaic system based on power electronic devices has the disadvantage of time-varying,uncertainty,overvoltage and limited overcurrent capacity,When a fault occurs in the power network that results in a voltage drop at the node,which leads to fault ride through capability reduced.In order to make full use of photovoltaic power generation,focusing the problem of unbalanced fault,we analyze the operational characteristics of the inverter for grid-connected photovoltaic systems and finally improvd its safety and stability with the low voltage ride through technology.Firstly,we make a detailed description of the composition of photovoltaic power generation system and established a mathematical model for photovoltaic inverters with symmetrical and asymmetrical three-phase voltages.And then the influence of the grid on the grid-connected photovoltaic power generation system under symmetric and asymmetrical faults was analyzed.At last,the second-order generalized integrator is used to separate the positive and negative sequence components of the unbalanced voltage and current.Under the premise of ensuring the over-current of the inverter and stabilizing the DC bus voltage,a low-voltage traverse control that suppresses the active power fluctuation is proposed.In the method,a symmetric positive sequence control to ensure the sinusoidal and undistorted grid-connected current is also provided.Based on the fundamental theory mentioned above,the grid-connected photovoltaic power generation system simulation model was built through Matlab/Simulink to verify the low voltage ride through control strategy proposed in this paper.Simulation results show that when an asymmetric voltage drop occurs in the power grid,the low voltage ride through control strategy which suppresses the active power fluctuations can effectively suppress the double-frequency fluctuation of the active power caused by unbalanced grid voltage and keep stable operation of the photovoltaic grid-connected inverter without additional hardware,which provides a more economical and effective solution when the grid is unbalanced.