The Impact On Power Quality Of Microgrid By Circulating Current

AC micro-grid gradually becomes a research hotspot because it uses more renewable energy, and has characteristics of modularization and easy maintenance. AC micro-grid is a micro source inverters paralleled system in the structure, all of micro source inverters are connected to the micro grid in AC bus for providing power to load. When the output voltages of inverters are different, AC micro-grid system will appear circulating current, the power quality will be affected.At first, the thesis describes the different control strategies of micro-grid. From the comparison, we get that AC micro-grid is most prone to circulating current under peer-to-peer control strategy. So the thesis chooses peer-to-peer control strategy for the system which is studied. The thesis takes two micro sources paralleled system for instance to analyze AC micro-grid’s circulating current, then designs droop controller and establishes a AC micro-grid simulation model in Matlab/SimulinkThe reason is analyzed in theory why circulating current will have an effect on power quality of micro-grid. The result is that circulating current will consume the power provided by micro sources, it must break the power balance of AC micro-grid and cause power quality problems. The simulation verifies the correctness of the theoretical analysis. Aiming at circulating current, the current-limiting inductance method and AC bus voltage feedback droop control method are chose. The simulation shows that current-limiting inductance method has good effect on inhibitory but has bad impact on bus voltage, voltage feedback droop control method has good effect on circulating current inhibition and will keep the AC voltage in the normal range.