Modeling And Simulation Of Micro Grids Based On Master-slave Control

A microgrid which is able to operate in both grid-connected and islanded mode can increase the reliability of power supply by disconnecting from the network in the case of main grid faults or reduced power quality. The strategy for controlling micro sources in different modes is the basis for stably operating microgrids. This paper studies the master/slave control of microgrids as well as models and simulates the system in PSCAD.Methods to control inverters are comprehensively analyzed in both islanded and grid-connected mode. Then a simulation of microgrids are carried out using PSCAD, including inverter and controller simulation models, Microgrid protection simulation model and so on. Finally the simulation verifies the boundary conditions of switching from PQ control to V/f control. An effective separation of the microgrid from the main grid as well as an immediate alteration of control strategies are both paramount for the microgrid to successfully switch from grid-connected mode to islanded mode.The traditional switch distinguishes considerably from the static switch in the relay protection. Among the effects of the differences on the stability of the microgrid while switching control strategies, this paper mainly discusses the effect of time lag. It is then found out through modeling that under most circumstances when external electric grids break down, micro-grids can be effectively separated from the centralized grids. Furthermore, ensuring immediate reaction of relay protecting devices in micro-girds is the key to switching connected grids to isolated grids. The static switch with delay time of 20ms can make microgrid remain stable after disconnecting from the main grid.