Research On Protection Schemes For Micro-grid

Faced with the environmental problems and energy shortages, microgrids has beenwidespread concern, in order to take full advantage of new clean renewable energy.Distributed power can access to the external power grid in an effective way throughmicrogrids. Meanwhile, microgrids can provide efficient, reliable and secure energy supply.With the advantages of distributed energy, microgrids system have been a priority for theresearch and development of electric power.However, microgrids can either operate connected to the grid, or in the case of a gridfault, in an islanded mode. Fault current path will change depending on fault location innetwork leading to mis-operation of protection devices in networks. The converter faultcurrent is limited by the rating of the silicon devices to around2p.u. rated current. It isimpossible for the islanded converter-based microgrids to use traditional overcurrentprotection techniques. It will bring more problems to the grid, if we do not take anytechnical measures to combine microgrids with the grid directly. Further, it will have anegative impact on people’s lives and energy use, so it is necessary to have a research onprotection schemes for microgrids.With the analysis based on PSCAD/EMTDC, this paper describes the main differencesbetween microgrids and the traditional distribution network. Firstly, Microgrid has multiplemicro-power, the trend line can be bi-directional flow, the protection relay of the traditionaldistribution system are considered single-ended power supply, cannot adapt to multiportpower complex working conditions. Secondly, the power electronic devices shut down toofast after the system faults. Moreover, microgrids can operate either interconnected orisolated from the main distribution grid, its protection and control will become verycomplicated. There is a fluctuation to the frequency of short-circuit current for doubly-fedwind power generation system in the first few cycles after the fault.With the analysis the applicability of conventional relay to microgrids, a Wide-areadifferential protection scheme is proposed based on the transient fault characteristics ofmicrogrids. And this paper carries out a detailed protection setting. Finally, a dynamicsimulation test is conducted to verify the transient fault characteristics of microgrids andthe applicability of the protection scheme.