Research Of Fault Analysis And Protection Theory Of Distribution System With Inverter-Interfaced Distributed Generator

With increasingly serious energy shortage, environment pollution, and obvious backwards of centralized power supply mode, a large number of inverter-interfaced distributed generators(IIDG) have been connected into the distribution system. Traditional radial system with single source has become complicated system with multiple generators. As a result, the power flow and the fault current level of the distribution system change. Conventional three-step current protection will act incorrectly, which indeed affect the safety and reliability of the distribution system. To solve the problem, the fault characteristic as well as protection scheme of the distribution system with IIDG is studied in this paper.First of all, fault characteristic of a single IIDG with various control strategies is studied. Thus IIDG is considered as a voltage controlled current source. The output current of the IIDG and the grid-connected voltage is not linearized in this model. In order to use traditional fault analysis method which require all the elements in the distribution system is linearized, a linearized model of the IIDG is constructed. A fault analysis method of the distribution system with IIDGs is proposed in this paper. For the positive voltage controlled IIDG which is widely used, a simple fault analysis model is proposed, for study of the fault character of the distribution system.Factors that affect the fault characteristic of the distribution system with IIDG is proposed, based on the fault analysis model. Rules of the effect from each factor is introduced in this paper. Based on the rules, a current protection scheme of the distribution system with IIDG of various capacity is proposed, as well as the limitation of the capacity and connection point of the IIDG due to the violation of the current protection.The theory of wrong action of the traditional directional component in the distribution system with IIDG is introduced. Directional component criteria for distribution system with IIDG of various control strategies is proposed, as well as the characteristic of the criteria. Protection based on the directional component is also proposed in this paper.All the study above including fault model, fault analysis method and protection schemes of the distribution system with IIDG will prompt the further development of the IIDG technology.