Micro-grid Grounding Style Compared And Its Grounding Electrode Design

As the scale and complexity of the interconnected power system keep growing, theproblems of the traditional centralized large power system, such as high-cost, weakness,operation complexity, etc, become more serious. In recent years, large scale blackoutcaused by natural disasters has led to serious economic losses and social impact. Besides,energy shortage and environmental pollution have also made it urgent to pay attention toenergy saving and emission reduction across the world. Meanwhile, distributed generationbased mainly on renewable energy sources develops very fast, providing new ideas forenergy saving and emission reduction, power grid investment saving as well as theenhancement of the security and flexibility of the power system operation. Micro-grid is akind of energy management system that combines and unifies many kinds ofinverter-interfaced distributed generators. It can operate in grid-connected mode and also inislanding mode by disconnecting from the power grid. Its emergence has decreased theimpact to the power grid caused by distributed generation connection, providedconvenience for the access of renewable energy system, realized demand side managementand the maximum utilization of the existing energy. Therefore, it is very necessary to carryout the basic theory research of micro-grid.(1) The background of this thesis and development status of micro-grid technology arepresented. The construction is discussed. And the present research situation of micro-gridprotection and grounding is introduced.(2) The grounding modes of the micro-grid are compared and analyzed theoretically.Different kinds of grounding modes in traditional medium and lower voltage distributionnetwork and the grounding schemes of micro-grid are analyzed. The selection of maintransformers and the grounding modes of micro-generators are analyzed in detail. And thesuggested grounding scheme is proposed.(3) The fault characteristics of micro-grid are analyzed theoretically. The short-circuitcalculation model of direct-access and inverter-interfaced micro-generators are analyzed. The analysis of fault characteristics of inverter-interfaced micro-generators under differentcontrol schemes is conducted. The fault characteristics of micro-grid adopting differentgrounding modes, such as TN, TT and IT, are also analyzed.(4) A400V low-voltage micro-grid simulation model is constructed based onPSCAD/EMTDC. The modeling process of every module in the simulation model ispresented in detail. The simulation of micro-grid grid-connected operation and islandingoperation mode under different grounding modes are simulated.(5) The micro-grid grounding electrode is designed based on CDEGS, and is verifiedthrough grounding electrode experiment. The basic requirements of designing thegrounding electrode are introduced. Three different grounding design schemes arecompared. The experimental principle of grounding electrode is presented and groundingelectrode experiment is conducted.