Abstract: The drop of grid voltage can cause the stator voltage of double fed induction wind generator （DFIG） to drop rapidly, which can make the DFIGs stator flux vibrate and cause a large oscillating current in DFIGs rotor and stator side, especially to the dual pulse width modulation （PWM ） converter. If we dont take an effective low voltage ride-through （LVRT） control measure, the DFIG may be disconnected from grid which will endanger the safe operation of the power system. This paper presents the DC-side LVRT technology, which installs super capacitor energy storage system on the DC bus capacitor in DFIG back to back converters, and uses its characteristics of high power density, short charging time, long service life and good temperature characteristic to realize short-term high-power charging and discharging; in the period of grid voltage drop and the DC voltage fluctuation, store the energy in the super capacitor, meanwhile can release excess energy to compensate DC voltage, thus can effectively enhance the low voltage fault tolerance of DFIG, and achieve the LVRT of DFIG. Through establishing 3 MW wind turbine simulation model, we determine and configure 7.65 F super capacitor according to the corresponding calculation principles. When the voltage drops 50% and the failure time continues, the super capacitor can maintain stable operation 15 s. The result verifies the effectiveness of super capacitor improving the LVRT capability of wind turbines.

Key words: double fed induction generator （DFIG）, low voltage ride-through （LVRT）, super capacitor, capacity configuration, control strategy