Research On Control Strategy Of Hybrid AC&DC Bus Microgrid With Photovoltaic And Storage System

Because of the difficulty to integrate large-scale wind turbines and photovoltaticpanels into grid and the intelligent development of power system, the research onmicrogrid gains increasing attentions now. In the microgrid operation, in order toefficiently control the renewable energy sources, the power electronics converters arecommonly employed as interfacing circuits. In this thesis, the AC-DC hybridmicrogrid is selected as the research subject and the control system for its interfacingconverts is analyzed in detail.An autonomous control is proposed for DC microgrid with photovoltaicgeneration and storage system based on the DC bus voltage control. The operation ofsystem is categorized into several different modes by monitoring the amplitude of DCbus voltage. The DC bus voltage amplitude is employed as an information carrier todetermine the operation mode switching. Hence, each controller operatesindependently without communicating each other. Each power electronic convertercoordinates its control method to maintain the constant of DC bus voltage underdifferent modes. A control strategy for the desalination plant in the system isproposed, which will be switched on when the power is excess and switched off whenthe power is shortage.For low voltage ride through issue of the Micro-grid system, a coordinatedcontrol of low voltage ride-through (LVRT) is proposed for the photovoltaic/batterymicro-grid system. During low voltage of the system, the photovoltaic system tracksmaximum power point of PV panels and the battery system maintains the constant ofthe DC bus voltage. When power output of the battery system has reached its limit thephotovoltaic system adopts the constant voltage control strategy to ensure a stablevoltage. Considering the load fluctuation of microgrid, a current limit control strategywith the function of reactive compensation is proposed. This strategy can providevoltage support for grid side and avoid overcurrent of the converter output. The thesis used the experimental platform of the DC microgrid with photovoltaicand storage system, through increasing or decreasing the load at DC bus terminalsand changing the state of the synchronizing switch to detect the stability andreliability of the system. Experimental results show that this control strategy realizesthe smooth transition between the different modes, which verifies the practicalfeasibility and effectiveness of the proposed control strategy.The simulation results show that the solar energy is fully used, the DC busvoltage is maintained at a constant level, the overcurrent of the converter output isavoided and the system voltage is supported by the reactive power from the inverter.The aim of LVRT is realized and the effectiveness of the control strategy is verified.