Micro-grid Protection Scheme Based On Regional Pilot Principle

With a series of environmental issues, such as pollution and resource shortage, getting critically serious, achieving sustainable development of energy has already become a consensus of all mankind. Nowadays, wind power, photovoltaic, mi-cro-turbines and other distributed generation (DG) have been widely connected to the distribution system, and then they constitute micro-grid with transmission network and local loads together. However, micro-grid has changed the topology and fault characteristics of traditional distribution network, which means traditional protection methods of distribution network cannot meet the demand of micro-grid protection any more. Therefore, the studies of principles and technologies, which are suitable for mi-cro-grid protection, are of essential theoretical and practical significance to promote high-efficient usage of sustainable energy. This paper proposes a micro-grid protec-tion scheme based on regional pilot after summarizing previous researches, and the main work accomplished in this paper can be list as follow.(1) Distributed generation failure characteristics of double-fed induction motor and the inverter source are analyzed respectively in this paper, based on the different ways they parallel to grid. By analyzing the distributed generation failure characteris-tics and the structure of micro-grid, the impact of DGs on the protection of traditional distribution network is thoroughly discussed. After viewing the micro-grid structures in different countries around the world, this paper proposes a modular analysis to an-alyze the micro-grid structure based on different feeder structures of the micro-grid, which categorizes feeders into simple and complex structures. Finally, this paper proposes different micro-grid protection strategies applied to various possible faults based on a typical micro-grid structure.(2) In order to realize the protection strategies put up above, this paper proposes a micro-grid protection scheme based on regional longitudinal differential principle. In this scheme, fault direction needs to be accurately judged. Consequently, this paper presents a judging element of fault direction based on phase comparison of the com-pensated operating voltage. Besides, some improvements in the criterion of judging element have also been made, in order to get fault direction information by comparing the measuring voltage and measuring phase of the set-point and the relay-point. The specific procedures can be list as follow. Firstly, analyze the methods of protection corresponding to the feeder structures mentioned above. Secondly, take an overall perspective to analyze the protection strategy considering the complex situation of the coordination of feeder protection in micro-grid and the PCC external fault, and then implement the ideal micro-grid protection strategy.(3) To make micro-grid protection more efficient, three micro-grid protection setting conditions are proposed according to the protection methods in this article and protection elements consisted in the micro-grid are classified. One of the features of micro-grid is to provide customers with customized services, such as offering appro-priate power quality as the user demands. This paper considers micro-grid protection as a customized one. Concerning the modular architecture analysis method proposed in this paper, load and all possible failure scenarios, micro-grid protection strategies are customized to fit local conditions.(4) At last, this paper uses MATLAB simulation software to build a double-fed induction machine and a PQ control inverter power source as distributed micro-grid simulation model. The micro-grid simulation model is operated under different fault conditions, so the validity and the rationality of the protection method proposed in this paper have been verified.