| Recent years, the permeability of doubly-fed induction generator (DFIG) in the distribution network is continuously improved. Because of the control strategies, fault types, fault locations, access capacity, access modes are different, the transient characteristics of DFIG is polymorphism. It has a great influence on the power flow and the current flow of the distribution network. Traditional relay protection is not suitable for it. Therefore, it is urgent to explore the complex transient characteristics and propose a new scheme of relay protection. This paper in the research of DFIG system mathematical model, established DFIG models based on different control strategies and analyzes the fault transient characteristics. And research the relationship between turn slip and components of short circuit current, as well as the harmonic characteristic of short circuit current. The effect of DFIG on the protection of the distribution network is revealed. A new T line protection scheme is proposed for T-type connection, and the simulation is conducted.In view of the importance and diversity of the control strategy of DFIG’s converter, using vector control and direct power control strategies for mathematical modeling and simulation modeling. Two sets of simulation models based on different control strategies are used to analyze the steady state operation characteristics and the fault transient characteristics. According to the simulation results, the differences and similarities of the steady state operation characteristics and fault transient characteristics under different control strategies are analyzed in detail.There are a lot of factors affecting on DFIG short circuit current characteristics. This paper focuses on the influence of operation of DFIG before fault on each component of the short-circuit current during the crowbar. The analytical expressions of stator and rotor short-circuit current are derived by the mathematical model. Analyze the influence of slip on cycle component, transient DC component and attenuation speed frequency component of short-circuit current. Secondly, different types of faults of DFIG, crowbar whether short-circuit current harmonic characteristics of action has been investigated and simulated. And short-circuit current harmonic characteristics of different types of faults of DFIG, crowbar whether actions has been investigated and simulated. And the effects of the harmonic in the different types of faults on the protection are revealed.For the problem of the DFIG as distributed generations seriously impact on the traditional relay protection, this paper focuses on the impact of T-type connection mode on the protection. A comprehensive criterion is proposed which combinations of the voltage difference criterion and the guarantee of the T junction sensitivity is proposed, and an example is given. The simulation results show that the comprehensive criterion can guarantee one hundred percent correct operation of all types of short circuit fault. |
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