A Research On Protection System Of Distribution Network Including Inverter-based Distributed Generation

Considering the present energy shortage and large grid exists prominent problems, there is great significance to the development of distributed power. Distributed energy has features of green, high efficiency, and decentralized near load. However, short circuit current is impacted by the capacity of the distributed power; control mode and access point. As a result, it will brings relay protection new problems and challenges. In general, distributed power is connected to the grid through an inverter. They are called inverter distributed power (Inverter-Interfaced Distributed Generators), referred to as IIDG.A model of IIDG is established in this article and three IIDG control approaches are analyzed. With PQ control and Vf control, the fault current of three-phase short-circuit and asymmetric short-circuit fault is analyzed in detail, obtaining the result that IIDG fault current has a multi-state characteristics.Since the fault current of IIDG is polymorphism, the traditional methods of protection may refuse to move or misoperation. The power frequency variation distance protection program based on the combined sequence component is given in this dissertation. Then, a comprehensive sequence components phase relay and a comprehensive sequence component grounding relay are designed. The comprehensive sequence components phase relay uses positive and negative sequence components as operation component; the comprehensive sequence components grounding relay uses zero sequence components as operation component and negative sequence components as restraint component. The method which has a adaptability to polymorphism of IIDG is verified by simulation. It can be employed in IIDG grid and island operation, possessing the ability of resistance to transition resistance.Finally, a new protection whose main protection is Multi-Agent regional protection and backup protection is comprehensive sequence components power frequency variation distance protection is designed. When the communication of system is normal, Multi-Agent regional protection can accurately locate and resect faults. When communication of Agent unit is faulty, Agent unit will start the comprehensive sequence components power frequency variation distance protection and then it will act to resect the fault. The protection program is verified through case analysis. The results demonstrate that the main protection and backup protection coordination can resect the failure to ensure the normal operation of the faulty-free components.