Research On Voltage And Frequency Stability Of Islanded Microgrid Based On Droop Control

In recent years, the contradiction between energy and the environment has become increasing outstanding due to economic development, therefore, the countries all over the world gradually increase the development and utilization of the clean energy. The clean energy mainly includes wind energy, solar energy,biomass energy and so on. Converting clean energy into electricity by using of power electronic technology in islanded operation of the microgrid promotes the energy utilization rate, provides a new way to solve the difficult problems of electricity consumption for remote mountainous areas and islands, improve the reliability of power supply, which become a new trend in the future. However, the islanded microgrid cannot get reference voltage and frequency from the distribution network,and the load demand is diversified, which the power quality is reduced. Therefore, it is great practical value to study the voltage and frequency stability of island microgrid.The thesis analyzes and compares the existing master-slave control,peer-to-peer control and hierarchical control in order to realize microgrid system stability on the basis of consulting a large number of domestic and foreign literatures. Thanks to"plug and play" and little dependency on communication, the peer-to-peer control is widely used. In the peer-to-peer control mode, the microsource is usually used droop control strategy. Through the analysis of the traditional droop control strategy, it is known that due to the influence of transmission line impedance difference and droop control coefficient fixed, the traditional droop control strategy in the load power changes, the microsource output voltage amplitude and frequency will be deviated,while the load power allocation is unreasonable. In this thesis,fuzzy control is introduced to carry out fuzzy reasoning on droop control, and optimize the droop coefficient, but the steady-state accuracy of fuzzy control is low, which improves the control precision and reduces the steady-state error by increasing the proportion integral. The voltage amplitude and frequency fuzzy PI droop controller are designed to reduce the voltage amplitude and frequency deviation. Finally, the simulation model of island microgrid system is built by MATLAB/Simulink simulation software,and the simulation and comparison of load power increases and decreases are carried out on the two control strategies.The simulation results show that: the improved droop control strategy can not only realize the stability of the voltage amplitude and frequency, but also improve the dynamic response speed of the islanded microgrid, steady-state error is smaller; and achieve accurate and reasonable distribution of load power, the output power of the microsource is more smooth when the load power mutation. The validity and correctness of the improved droop control strategy based on the fuzzy PI control proposed in this thesis are verified by simulation.