This paper proposes a control strategy of doubly fed induction generators (DFIGs) with new protection schemes for enhancing fault ride through capability of wind farms composed of DFIGs and induction generators (IGs). Since the DFIGs will be stressed or overloaded in the process of stabilizing the wind farm during a grid fault, it is paramount to consider a protection scheme for the DFIG, in order to protect its power converters. Two schemes, the DC-link chopper-controlled braking resistor with the supplementary rotor current (SRC) control of the rotor side converter of the DFIG and series dynamic braking resistor (SDBR) connected to the stator of the DFIG, are proposed and compared. Merits and drawbacks of both schemes are highlighted as well. The simulation results in PSCAD/EMTDC show that the two proposed schemes can eliminate the need for an expensive crowbar switch in the rotor circuit, because both could limit the rotor current of the DFIG within its nominal value during a grid fault. Finally, considering the overall system performance, the latter is recommended.

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Transient operations are very crucial for high power insulated‐gate bipolar transistor modules, because high current and voltage are applied during this period for several microseconds. Therefore, the ability for doubly fed induction generator (DFIG) variable speed wind turbine power converters to withstand abnormal conditions is strictly imperative in order to achieve its lifetime specifications and also fulfil the grid codes. This study presents a new control scheme for DFIG wind turbine having parallel interleaved converters (PIC) configuration and a series dynamic braking resistor (SDBR) connected at its stator side. Interleaving the wind turbine converters in parallel configuration could help to increase the current capability, while the SDBR helps in post fault recovery of the wind turbine. The coordinated control analysis of the scheme was implemented in power system computer aided design and electromagnetic transient including DC simulation environment for a severe three‐phase to ground fault. Results obtained were compared with the conventional DC chopper and crowbar rotor circuit protection scheme for the wind turbine. A better performance of the wind turbine variables were achieved using the proposed control scheme of the PIC and SDBR because the space vector modulation of the PIC results in maximum value of the change in common mode voltage, leading to improved switched output voltage of the voltage source converter leg.

-Wind farm grid codes require wind generators to ride through voltage sags, which means that normal power production should be re-initiated once the nominal grid voltage has been recovered. Doubly Fed Induction Generator (DFIG) based wind farm is gaining popularity these days because of its inherent advantages like variable speed operation and independent controllability of active and reactive power over conventional Induction Generator (IG). This paper proposes a new control strategy using DFIGs for stabilizing a wind farm composed of DFIGs and IGs. Simulation analysis by using PSCAD/EMTDC shows that the DFIGs can effectively stabilize the IGs and hence the entire wind farm through the proposed control scheme by providing sufficient reactive power to the system.

-This paper proposes an application of series dynamic braking resistor (SDBR) connected to the stator side of a doubly fed induction generator (DFIG), for enhancing fault ride through (FRT) capability. Two schemes were investigated; the first scheme uses a bypass switch to show the effect of the SDBR magnitude, while the second one uses a circuit breaker to determine the best insertion time and duration of operation of the SDBR, considering the best SDBR resistance obtained in the first scheme. The proposed schemes were then applied to stabilize a DFIG. Simulation analysis by using PSCAD/EMTDC shows that the SDBR can substantially improve the FRT of the DFIG. It also shows that the size of the SDBR should be determined carefully because large value may worsen the system performance during a grid fault.

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Recently, the grid codes require taking into account the reactive power of the wind farm in order to contribute to the network stability, thus operating the wind farm as active compensator devices. This paper presents a comparative study of stabilizing a wind farm using (Doubly Fed Induction Generators) DFIGs or using a (Static Synchronous Compensator) STATCOM during wind speed change and grid fault. Simulation results show that the wind farm could be effectively stabilized with both systems, but at a reduced cost with the DFIGs system because it can provide reactive power through its frequency converters without an external reactive power compensation unit like the STATCOM system significant.