The Microgrid Fault Characteristic Analysis And The Study On Protection Principle

With the energy and environmental issues become increasingly prominent,the issue how to increase the utilization of wind, solar and other renewable energy and to achieve the sustainable development of society and the environment, has become a top priority in the development of power industry. For the coordination of utility and distributed resource and to fully exploit the benefits which the distributed generation can bring to the users, the microgrid has received widespread attention as a valid form of distributed resource.Microgrid is a regional power systim which combines the micro-source, energy storage, load and control devices together to form a single controllable unit. Microgrid supplies electricity, heat and other products to users at the same time. Different from the traditional distribution network, the structure of microgrid is no longer radical sources of single form. The distribution of power and current in microgrid has changed a lot. In this case the use of traditional protection such as over current protection in the fault identification and fault location has encountered many difficulties. Therefore, the study of the new protection strategy for microgrid is of great practical significance.This paper studies microgrid consisting of micro-sources with inverter interface. Firstly, a common micro-source equivalent model has been proposed, then the simulink modal of microgrid is established using Matlab and the fault characteristics of microgrid in islanding and grid-connected mode is analyzed to provide guidance to the study on microgrid protection princeple and characteristic analysis. .Microgrid connects with utility through the tie line, so the protection of microgrid can be divided into two parts through theoretical analysis: the protection for tie line and the protection for internal microgrid. For the protection of tie line, we first explores the impact factors of microgrid islanding mode and fault ride through mode when fault occurs, then Summarize the common isolation strategy of microgrid and utility. On this basis, we propose corresponding tie line protection principles and programs for different isolation strategies.For the protection of internal microgrid, the existing microgrid protection strategy is collated and summarized in this paper. Then this paper focuses on the low-voltage protection and current differential protection. The protection principle and Implementation is anglicized and the protection performance is evaluated. On this basis, the paper presents a protection scheme based on the current phase comparison which can be applied in both islanding microgrid and grid-connectting microgrid; the protection scheme consists of two parts: microgrid feeder protection and micro-source protection. The ordination mechanism between feeder protection and micro-source protection is studied. Next, we verified the protection scheme using Matlab/Simulink and evaluated its protection performance.At the end of this dissertation, a systematical summary is given and further work to be studied is pointed out.