Modeling of DFIG wind turbines considering fault-ride-through grid code

Abstract

In modern power systems, wind energy is one of the most important among the various renewable sources. Recent grid codes require wind farms to remain dynamically stable during a voltage dip and to supply active and reactive power into systems. Fault ride through (FRT) refers to the capability of generation plant to remain connected and to offer network support throughout a serious voltage disturbance on the power system. Doubly fed induction generator (DFIG) technology is the dominant technology in the growing global market for wind power generation, due to the combination of variable-speed operation and a cost-effective partially rated power converter. However, DFIG is sensitive to dips in supply voltage and risks damage to its power converter without specific protection to ride-through grid faults. The induction generator very quickly loses internal magnetization in proportion to the reduced voltage. The demagnetization produces large currents on both stator and rotor circuits. Since this rotor current is typically far greater than the ratings of the converter's power electronic devices, specific protection measures should be provided to avoid damage to the rotor-side converter devices and dc-link capacitors. Generally, this protection is achieved by rotor crowbar applications that temporarily connect the rotor circuits through a resistor, diverting current from the rotor-side converter and rapidly de-energizing the rotor. In this paper, a DFIG wind turbine with a rotor crowbar is modeled in order to investigate its dynamic responses to ride-through grid faults. PSCAD/EMTDC is used to simulate various fault conditions. In the simulations, the behaviors of the model are presented and analyzed such as the response of the pitch controller, the voltage of the DC-link, voltages and currents related to the stator and rotor. To assess the validity of the modeling, the simulation results are compared to a DFIG wind turbine without a rotor crowbar.