Grid-connected/Island Operation Control Strategy For Wind/Photovoltaic/Battery Micro-grid

As an effective method to exploit renewable energy and improve the reliability and flexibility of power supply,micro-grid is a new way to solve environmental pollution and resources shortage problems.Micro-grid has islanded and grid-connected modes.The seamless switching between the two modes has very important research value,because it is the key to provide continous power supply for load,and improve power quality,reliability and flexibility.This paper researches on the control strategy of micro-grid to make the switching process seamless.The micro-grid system based on wind and solar hybrid power generation is studied in this paper,aiming at the voltage fluctuation and current impact of micro-grid operating mode switching,the method of seamless switching control for micro-grid system is studied to improve the stability of micro-grid system.The main research contents are as follows:First of all,the structure of complementary power micro grid system is analyzed,the micro power generation characteristics in photo-voltaic arrays and wind turbines are discussed,and its corresponding MPPT control method.The principle of Buck-Boost circuit for energy storage system is introduced,the working principle and control method of grid connected inverter are studied,established a micro grid system is established.Secondly,this paper puts forward method of operation in each mode based on the structure and characteristics of.Under the grid-connected mode,micro-grid will adopt PQ control.Frequency and phase of micro-grid system is provided by the grid.Under independent mode,the improved droop U/f control strategy is employed to battery,by controlling the energy storage device of the inverter output voltage and frequency,providing frequency and phase for scenery power generation unit.Thirdly,In isolated island operation,the islanding detection technology is adopted to effectively prevent the occurrence of islanding and ensure the power load and personal safety.What’s more,in order to eliminate the impact during switching,a three phase software phase-locked loop(SPLL)based pre-synchronizing unit is designed to track the utility grid voltage by controlling the inverter output.This unit can simultaneously track the amplitude and the phase angle of voltage.Involving this unit,the impact of the reconnecting process is weakened,which makes the process of reconnecting to grid stable and safe.Finally,A model of micro-grid composed of complementary wind farm,solar generation and energy storage system is constructed on PSCAD/EMTDC platform,and the feasibility of the proposed control strategy is verified by simulation results.