Study On The Performances Of Earthing Program And Its Fault Characteristic For Micro-grid

With the rapid development of society, people’s demand for electricity is growing. Inthe power grid environmental pollution, energy shortages and a cascading failure occursfrequently, that is an inevitable problem for the electric power production and powersystem. In recent years the international community attaches great importance to tides,wind, and solar, geothermal and other new energy. So the DG has been widely applied.However, due to the limitation and Instability of the DG, so the micro grid is the solution.Micro grid is a new type of power system network configuration. Through the control andmanagement of distributed power supply, this can reduce the negative impact of the microsource to the main grid. There still exist a series of problems; the micro grid will still havebad effect on the operation of the power system scheduling and relay protection.Firstly, this paper analyzes the low-voltage distribution system earth grounding type.Introduce the three typical grounding methods TN, TT and IT and its applications. Microgrid is usually access to main power grid through the low-voltage distribution system, andthe earth grounding types of the micro grid need reference of the low voltage distributionsystem. The earth grounding types have better matching.Secondly, analyzes the mathematical model of the micro source and its modelingmethod. Micro source output characteristics and the characteristics of the inverter areclosely related. A method of micro source can raise neutral line is realized by inverter.This paper analyses the method of inverter by three-phase three-wire system into threephase four wire system, the method of three-phase inverter with four bridge arms chosenas the final solution, and design the corresponding control strategy. Research the voltagecurrent characteristics in different fault conditions, and the inverter adopts PQ and VFcontrol mode.At last, this article put forward the micro grid earth grounding scheme. Compare theTN, TT and IT three solutions, and combine with the simulation and specific engineeringprojects. The TN earth grounding system is more suitable for micro grid. When the systemhas faults, the TN earth grounding scheme, and has a lower contact voltage and larger fault current, that can simplify the configuration of protection device.