Research On Distribution Network Self-healing Control Based On Contingency Set

China with the largest power grid is the first generated energy and electricity consumption country in the world. However, compared with the developed countries and regions, its power supply reliability is not at the top of the world. According to the statistics, more than 80 percent letting off customer is caused by distribution system fault. With the development of smart grid, self-healing, as an important characteristic of smart grid, plays an important role in improving the power supply reliability. Self-healing control technology on distribution network is still in a developing stage now. The current research achievements mainly focus on the concept, function, structure, and some independent technology fields, and how to organically integrate these independent technologies into achieve the self-healing function lacked adequate research and discussion.Therefore, it is significant to systematically research on the self-healing control of distribution network. The main content and achievements of this paper are as follows:(1) From the perspective of load, this paper proposed an online assessment method on outage risk of load for distribution network. Firstly, the concept of online risk assessment is defined and described in detail. On this basis, an improved k-th shortest path algorithm is proposed to obtain the power supply paths without loop. The feasible power supply paths are obtained by security verification,which they are uesd to calculate the power outage probability and power outage risk. The proposed method can accurately reflect the power outage risk of load, and its high computational efficiency can meet the need of online operation.(2) From the perspective of electrical equipment, this paper proposed an online safety analysis method for distribution network. Firstly, the establishment and ranking methods of contingency set were proposed, and they lay the foundation for the online security analysis of distribution network. Secondly, according to the characteristics of distribution network, the appropriate evaluation criteria and indicators were proposed. Finally, multi-objective optimization algorithm based on decision preferences is introduced to do security scan on the contingency set. The proposed method can effectively reflect the potential weakness of power grid, and it can propose pre-arranged plan for possible fault.(3) The paper proposed a fast service restoration method considering lack of power supply capability of distribution system. Traditional intelligent algorithm cannot solve the problem that distribution system lacks power supply capability, so load shedding strategy based on repeat power flow were proposed. In order to improve convergence ability, rank preference optimal was introduced to evaluate recovery plan. The proposed method can solve the problem that the load cannot be recovered completely, and it can obtain the global optimal solution efficiently.(4) This paper proposed an island partition method for distribution system based on the shortest path algorithm. Firstly, Dijkstra algorithm was used to get the shortest path from DG note to important load note. In order to restore important load’s power supply, these load is preferentially incorporated into isolated island. Secondly, under satisfying constraint of operation in island, the other load is incorporated into island based on the adjacent relation of the island and the load priority. Finally, considering the function of tie switch, the proposed method have a good searching ability and it can ensure power supply of the important load to the maximal degree with full use of DGs capacity.(5) On the basis of the work done, the paper proposed a self-healing control method for distribution network based on contingency set. The proposed method can provide accident early warning information and pre-arranged plan for possible fault with fully using of system resource during normal operation of the distribution system. Power supply can be recover quickly when fault occurs. DGs capacity can be fully used to improve power supply reliability in extreme condition.