The number of wind turbines connected to the grid is steadily increasing in recent years. This situation forced the revision of the electric utilities grid codes requirements, to remain connected during grid faults, i.e. to ride through the faults, especially for those with power electronic converters, such as DFIGs. In fault condition, the voltage at the Point of Common Coupling (PCC) drops immediately and The grid voltage dips imposed at the connection point of the DFIG to the grid induce large voltages in the rotor windings, resulting in high rotor current, which can damage the rotor-side converter and disconnect from grid. In this paper, resistive and inductive superconducting fault current limiter (SFCL) is used to improve the fault ridethrough (FRT) of wind turbine generation system (WTGS). The WTGS is considered as a variable-speed system, equipped with a DFIG. The analytical and simulation studies of the resistive SFCL for improving FRT capability are presented and compared with the inductive SFCL.
Today, synchronous generators are broadly employed in the industry. The thyristor rectifier in the static excitation system of synchronous generators is responsible for supplying the DC voltage of the excitation winding. In these rectifiers, a high-frequency component is generated at the output of the DC voltage, during turning on and off of the thyristor. These high-frequency components charge the generator's parasitic capacitors. The voltage induced in these capacitors induces the voltage in the synchronous generator shaft. In this paper, the induced voltage analysis in the generator shaft is performed. Then, modeling, simulation, and experimental laboratory results of pulse width modulation are performed in the static generator excitation system. The induced voltage of the generator shaft is examined by applying this rectifier and it is compared and analyzed with the results of the thyristor rectifier. The hiring of a pulse width modulation rectifier has had a great impact on reducing the induced shaft voltage.
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