Control of DFIG Wind Power System Under Unbalanced Grid Voltage

This chapter discusses the control schemes for doubly fed induction generator (DFIG) wind power systems under unbalanced grid voltage. Resonant controllers will be used to resolve the problems caused by unbalanced grid voltage: stator current unbalance and DC voltage fluctuation of the back‐to‐back converter. For the generator side converter (GSC), a capacitor current control method is adopted to suppress the second‐order harmonic current flowing into the DC bus capacitor, also resulting in the suppression of DC voltage fluctuation. The control scheme is performed by the GSC independently not relying on the power information from the RSC, making such a method suitable for large‐scale wind turbine systems adopting a modular design. To enhance the performance of DFIG system under unbalanced grid condition, the following control targets can be adopted: constant output active power, balanced rotor current, balanced stator current and constant electromagnetic torque.

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