Analysis on DFIG Wind Power System Low-Voltage Ridethrough

Due to the double fed induction generator’s (DFIG) advantage of controlling active and reactive power independently and partial power converter, DFIG is becoming a popular type of wind power generation system. Nowadays, the grid code demands that the wind power generator possesses the ability of riding through the grid voltage sags, only when the grid voltage drops below the specific curve, the wind turbine is allowed to disconnect. DFIG wind power system has serious problems with the corresponding voltage sag as its partly power converter: depending on the depth and the conditions at the start of the sag, current, power and reactive power peaks may exceed rated values and may lead to a system shut down.  The experiment system includes a DC motor, a DFIG, a 3-phase diode rectifier, a converter, a crowbar and a voltage sags generator. The DC motor simulates the behavior of wind turbine, the 3-phase diode rectifier and the converter controls the DFIG, the crowbar is connected to the rotor of DFIG and the converter. The voltage sags generator provides the voltage sags event for the experiment system. The controller of the converter and crowbar includes DSP and FPGA. It judges the moment of voltage sags and trigs the crowbar, so is the key part of the LVRT system. The simulation and experiment result shows that the dynamic response of inner current loop of rotor side converter is important for damping the transient current during voltage sags. The converter in the rotor side with crowbar using the dq transfer voltage measure method could reduce the transient current in rotor and stator. The DFIG system with crowbar could quickly recover from the voltage sags and provide reactive power to support the grid. So crowbar is important for improving LVRT capability of DFIG. The converter with crowbar in the rotor side implement the LVRT of DFIG, it could send reactive power during voltage sags.