Research On Photovoltaic Grid-connected Low-voltage Ride-through Based On Hybrid Energy Storage

Fossil energy is decreasing,and environmental pollution is getting worse,There is an urgent need to develop clean and renewable energy,so solar energy has attracted attention as an ideal renewable energy source.However,as the penetration of photovoltaic power generation in the power grid increases year by year,it brings hidden dangers to the stable operation of the power grid.When the photovoltaic grid-connected point voltage drops,a large-scale power failure may occur.Therefore,it is necessary to conduct in-depth research on the low-voltage ride-through technology of photovoltaic grid-connected inverters,enhance the low-voltage ride-through capability of photovoltaic power generation systems,optimize the grid-connected operation performance of photovoltaic power generation systems,maintain system stability,limit grid-connected current,and provide voltage support.Firstly,this paper simulates and analyzes the photovoltaic output characteristics,introduces several maximum power tracking control methods,and select the incremental conductance method based on PI adjustment as the control of the Boost system.The working principle of hybrid energy storage composed of energy storage batteries and supercapacitors is described,and the charge-discharge control method of DC-DC bidirectional converter of energy storage system is designed.This paper introduces the operation control strategy of the inverter under normal conditions.When the voltage of the grid-connected point drops symmetrically,improved and refined the traditional reactive power control and current limiting strategies to effectively suppress the increase of grid-connected current.During low voltage faults,this paper proposes a differential integration method for the input and output power of the inverter to determine the total capacity required by the hybrid energy storage system to ensure the stability of the DC bus voltage.When the grid-connected voltage drops asymmetrically,this article compares and analyzes several common phase-locked loops,and improves the adaptive notch phase-locked loop to reduce the response fluctuation value at the initial moment.Propose asymmetric fault control strategy to prevent the inverter from overloading,while suppressing the negative sequence current and improving theI_abc symmetry.According to the grid’s restrictions on the three-phase current distortion rate and three-phase asymmetry,a suitable filter inductance value is designed.When studying the relationship between the active power output of the inverter and the depth of the voltage sag,this article first considered the duration of the voltage sag.When the low voltage operation time is too long,this paper designs to cut off the photovoltaic system.Finally,the simulation results verify that the improved grid-connected inverter control strategy can achieve low voltage ride-through,and prove that the DC-bus voltage stability of hybrid energy storage is better than single energy storage;At the same time,simulation shows that the photovoltaic system adopts the AC side off-grid removal method,which is conducive to reducing the three-phase current distortion rate and preventing active power feedback.It has important theoretical and practical significance for improving the power quality and improving the stability of the power grid.