Research on Low-voltage Ride-through Technology of Doubly-fed VSCF Wind Power Generation System

Currently, some of the variable speed wind turbine on market have some low-voltage through capacity (LVRT), but do not have dynamic reactive power support capacity under fault.DFIG can't provide dynamic voltage support, in addition, as a result of lower terminal voltage, active power can not be completely output, which has impact on safe and stable operation of power grid. Aimed at this problem, this paper discussed how to improve the reactive power support capacity during grid fault such as three-phase voltage dip fault and presented a improved LVRT technology. First, the paper analyzed the transient responses and characteristics of DFIG under grid voltage fault and introduced several control strategies and protection programs of DFIG under voltage dip existing now; then, based on the traditional control strategy, the paper presented a transient voltage control strategy in rotor-side converter which can make DFIG output more reactive power to participate in the transient voltage control of whole grid during voltage dip in grid fault and during the recovery process after the fault to ensure that the terminal voltage of generator maintain the value before fault; finally, the EMTDC / PSCAD simulation showed that adopted transient voltage control strategy in rotor-side converter, the transient voltage control in rotor-side converter can output a large number of reactive power during fault according to the dip depth of terminal voltage to provide dynamic voltage support and insure the fast recovery of grid voltage.