Modern control strategies of doubly-fed induction generator based wind turbine system

A doubly-fed induction generator (DFIG) based configuration is still preferred by wind turbine manufactures due to the cost-effective power converter and independent control of the active power and reactive power. To cope with stricter grid codes (e.g. reactive power compensation, low voltage ride-through operation, as well as steady and safe operation during long-term distorted grid), control strategies are continuously evolving. This paper starts with a control strategy using the combined reactive power compensation from both the back-to-back power converters for their optimized lifetime distribution under normal grid conditions. Afterwards, an advanced demagnetizing control is proposed to keep the minimum thermal stress of the rotor-side converter in the case of the short-term grid fault. A modularized control strategy of the DFIG system under unbalanced and distorted grid voltage is discussed, with the control targets of the smooth active and reactive power or the balances and sinusoidal current of the rotor-side converter and the grid-side converter. Finally, a bandwidth based repetitive controller is evaluated to improve the DFIG system's robustness against grid frequency deviation.