Research On Islanding Detection For Fuel Cell Grid Connected And Control Strategy Of Micro-Grid

In order to overcome the problems of energy shortage and environmental protection, as well as the shortcomings of traditional grid, all the world are strongly focus on distributed generation actively, which has the advantages of high energy efficiency, flexible mounting area, low environmental pollution etc. Besides, it can effectively solve many potential problems of large power grid. However, while achieveing peak sharpening, decreasing energy loss and improving power grid reliability, distributed generation has the negative impacts of high cost, controlling difficulty and strong randomness. Hence, the scholars have put forward the conception of micro-grid to decrease its negative infulence. Because of its flexible operation mode and high controllability, it received wide attention from scholars at home and abroad as soon as it is proposed. Micro-grid is a cross technology related to multi-discipline, which has certain key issues to be solved, including model of micro-power, operation and control strategy of micro-grid, power quality, energy distribution, fault detection as well as its influence on traditional power system. Therefore, the study on these key issues of micro-grid, such as seletion of micro source.operation and control of micro-grid, islanding detection and smooth switch, as well as putting forward certain reliable and practical solutions,are of great significance to show advantages of micro-grid and improve grid reliability.This paper introduces key issues of micro-grid from three aspects, including model of micro-grid, islanding detection of micro-grid and on/off-grid smooth switching strategy of micro-grid, and then builds a simulation model of micro-grid. Chief research achievements are as follows:(1) On the basis of the existing fuel cell model, the paper considers factors such as humidity, temperature etc, and builds a proton exchange membrane fuel cell dynamic model relaying on Matlab/Simulink. Then analysis the polarization curve of battery, which verifies the fuel cell characteristics as output voltage, power and efficiency. Through analyzing the process of fuel cell three-phase grid, it develops an inverter control strategy with dq switch, PLL, SPWM to realize unity power factor grid.(2) Faced with the shortage of existing islanding detection method, the paper puts forward a promoted method of timely adding disturbing-an islanding detection method based on half-cycled frequency drift. And it builds an islanding detection model of fuel cell power generation system. The simulation results demonstrate that the method is more effective.(3) Analyzed the principle of PQ. U/f and Droop control strategy and designed fuel cell generation system model to verify the validity of each control strategy. Based on it, the paper builds an on/off-grid smooth switching strategy model of micro-grid. Simulation results demonstrate that the control strategy proposed is yalid in the fuel cell generation system.Simulation results show that the proposed islanding detection has certain advantages in terms of detection time and harmonic content, and it is practicable. Micro-grid control strategy in this paper realizes smooth switching and completes the working conditions of cutting/increasing loads in islanding operation.