Low Voltage Ride Through Control Of Photovoltaic Grid-connected Inverter Based On Power Control

Nowadays,the increasing energy crisis and environmental pollution have become a common problem facing all countries,so the development of renewable energy has become the hotspot of global research.Therefore,the clean energy and other advantages have been widespread concern.In recent years,with the high penetration of grid-connected photovoltaic system,it affects the quality of the grid seriously,so the low voltage ride through(LVRT)capability of grid-connected PV inverters under the voltage drops is demand according the new grid codes or standards at home and abroad.In this paper,the LVRT control strategy of three-phase grid-connected inverter is studied.Firstly,the topology of three-phase photovoltaic grid-connected power system is a two-stage structure.Boost circuit has been used in the first stage,after the three-phase bridge inverter is connected to the grid.The double-loop control method of the current inner-loop and DC bus voltage outer-loop is adopted.The mathematical model of the three-phase system is established and the controller parameters are designed.In the normal grid,the three-phase PV grid-connected inverter is simulated by three different control schemes of PI,PR and PCI.The four control targets are the maximum power point tracking control,the stable DC bus voltage,the unit power factor control,and the grid current THD,which lay the foundation for the research of the photovoltaic LVRT technology.Secondly,the method of fast detection of voltage drop type and grid voltage positive and negative sequence separation is studied when the grid faults.The method of this paper is determined.Based on the instantaneous power theory,five power control strategies are analyzed and combined with the three control objectives to realize the coordinated control between current quality and power fluctuation.Switching PR control and PCI control to ensure the precise control of grid-connected current under faulty grid and the relatively fast dynamic response of the grid under normal grid.Based on the research above,the control strategy of LVRT is given.This paper proposed a current-limiting measure,the point of common coupling(PCC)voltage is increased by injecting the reactive power,where the positive sequence voltage was raised and the negative sequence voltage was reduced.The results are verified by simulation software of MATLAB / Simulink,and the results are in accordance with the theoretical analysis.Finally,the experimental results was carried out on dSPACE real-time simulation system experimental platform.It realized three-phase grid-connected inverter and low voltage ride-through control strategy.The results prove that the feasibility and correctness of the adopted strategies in this paper.