Abstract:

Low voltage ride through (LVRT) capability enables a doubly fed induction generator (DFIG) – based wind farm (WF) to remain online supporting the electric grid during fault condition. This paper proposes a control-based strategy for improving LVRT capability of DFIG, in which by changing active and reactive powers reference values following a voltage dip (VD) condition. Moreover, the direct power control (DPC) method is modified to adaptively change the reference values based on the severity of VD. In the proposed modified DPC (MDPC) method, the parameters of the PI controllers are tuned using the imperialist competitive algorithm (ICA). For activating/deactivating the proposed strategy, a voltage dip index (VDI) is proposed which is updated within a moving time window including samples measured by phasor measurement unit (PMU). In order to evaluate rout mean square (RMS) value of the voltage from the measured values by PMU, the DFT technique is used. For activating/deactivating the control strategy, two threshold values α and β are defined. In the active mode, the active and reactive power are changed to zero and one p.u, while in the deactivate mode theses are changed to one and zero p.u, respectively. Based on the proposed control strategy, during a VD condition, DFIG will be able to smooth the DC-link voltage fluctuations and significantly reduces the oscillations of the stator and rotor currents. The simulation results show the effectiveness of the proposed control strategy for improving LVRT capability of DFIG.<

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