Research On Fault Location Method And Protection Configuration Scheme For Microgrid

Accompanied by the emergence of global fossil energy crisis, the increasinglyserious environmental pollution, and the shortcomings exsiting in ultra-large-scalegrid, distributed generation technologies based on renewable energy play anincreasingly important role in electric construction and development to effectivelycomplement traditional centralized power generation. As a form of effective use ofdistributed generation, microgrid has become an important global technology inelectric power development with its smart, flexible and efficient controlcharacteristics. However, because of microgrid’s multiport power structure and thelimited output characteristics of microsource, the direction of power flow inside thenetwork is no longer single, and short-circuit current differs greatly betweengrid-connected and islanded operation bringing new challenges to traditional relayprotection theory and configuration program. Therefore, the microgrid protectiontechnology research has important theoretical and practical value.Firstly, this paper introduces the components of microgrid and analyzes thecharacteristics of microgrid topology, neutral grounding, operation mode andmicrogrid power transmission, as well as their impacts on normal and accidentoperations of microgrid.Then, two typical control strategies of distributed sources are emphasized, and theoutput characteristics of distributed sources in both constant power and constantvoltage and frequency strategies are presented. In the case of normal operation ornon-serious fault, the output of the two types of distributed sources maintains therespective control target. Meanwhile, the distributed sources behave like a constantcurrent source in the case of a serious fault.Moreover, a novel fault location method for microgrid based on current faultcomponent is proposed. Based on the policy that the static switch operates first in caseof internal fault, the significant differences of current changes in the two prosesses offault happening and switch operating between faulted lines and non-faulted lines canbe applied to locate the fault zone and determine the protection judgement.Finally, a microgrid model is built based on the microgrid laboratory of TianjinUniversity, through which the microgrid failure characteristics are analyszed. Microgrid comprehensive protection configuration is proposed in order that thefaulted element is disconnected and a mini-microgrid is formed with the restmicrosourecs and loads continuously running without affection of failure, improvingthe reliability of power supply in microgrid. The effectiveness of the program isverified through failure simulation in the microgrid model.