Direct voltage control of stand-alone DFIG under asymmetric loads based on non-singular terminal sliding mode control and improved extended state observer

This study investigates direct voltage control of stand-alone doubly-fed induction generator (DFIG) system subject to asymmetric loads. An improved voltage regulator is designed based on non-singular terminal sliding mode control and an improved extended state observer (ESO). Due to the salient features of the improved ESO, the rotor current transducer is not required and the sinusoidal fluctuation in the sliding surface caused by asymmetric loads is eliminated. As a result, satisfactory balanced stator voltage can be generated under asymmetric loads. The proposed method is characterised by the rapid dynamic response and the elimination of sequence decomposition operations. Finally, the proposed method is applied to a 6 kW DFIG-based hardware system under various loads and varying speed conditions. Both simulation and experiment results are given to validate the effectiveness and robustness of the proposed method for stand-alone DFIG system.