Simulation Analysis Of The Low Voltage Ride Through Capability Of The Doubly Fed Induction Wind Generator

With the large-scale centralized wind farms in the construction, wind power is with an increasing proportion in the electrical power system, the influence of wind power on the connected power systems is also increased. So the influence to the grid security and stability by wind power can not be ignored. Many Countries have already established the standard of low voltage ride-through according to their own national conditions. The stator of doubly fed induction wind generator is directly connected to the electrical power system, This structure can’t separate the contact between DFIG and the power grid, this leads to some defects in the doubly fed induction wind generators during grid faults. Thus the research to the low voltage ride through technology of DFIG has very important significance.This paper mainly focuses on the doubly fed induction wind generator. First, it has derived the transient mathematical model of DFIG, and analysized the transient performance of the doubly-fed induction wind generator during the voltage drop. Secondly,on the basis of establishing the mathematical model of the wind machine、the double-fed induction generator and the converter in the DFIG system, the stator flux oriented and grid voltage oriented vector control strategies have been studied. Then, this paper researches the improved methods of these control strategies, and builds the DFIG system by using the Matlab/Simulink software platform. The reponse charactetistics of DFIG during the grid voltage drop has been analysized and tested by the simulation. The low-voltage operaating characteristics of the doubly-fed induction wind turbines has been studyed by simulation in the case of the different voltage drop. The results shows that under the conditions of low amplitude voltage drop, the low voltage ride-through can be achieved by itself, but the large amplitude voltage drop will result in over-current and over-voltage, and pose a serious threat to the DFIG system.Finally, in order to improve the low voltage ride through capability of the DFIG, the rotor side crowbar protection circuit has been studyed and the fact that influences the crowbar protection effect is analysed by simulation. The results proved that the rotor side crowbar protection circuit can effectively inhibit the rotor current during the voltage drop, and protect the converter of DFIG, then achieve the low voltage ride through requirements.