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 DFIGbased 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.

This study presents an improved super-twisting sliding mode (SSM) approach to a stand-alone doubly fed induction generator (DFIG) for direct current (DC) generation system. By taking the uncertainties into consideration, an improved SSM regulator based on an extended state observer (ESO) is proposed to enhance the robustness of DC-voltage regulation. Moreover, a novel sinusoidal rotor current calculation method is proposed to generate sinusoidal reference of rotor current. A resonant-based ESO (R-ESO) SSM approach is proposed to regulate rotor current. By applying the R-ESO to estimate the model-related part of DFIG, the tracking performance with respect to a sinusoidal reference is improved. Then, the suppression ability to fifth and seventh harmonic currents are enhanced. Finally, both simulations and experiments on a 6-kW DFIG-DC system are provided to show the effectiveness of DC-voltage regulation and harmonic current suppression of the proposed approach. Nomenclature i, u, φ current, voltage and flux R, L, T resistance, inductance, torque ω sl , ω s slip, and synchronous angular frequency C DC-bus capacitance V dc , i dc DC voltage and current i l DC-load current Superscript

No abstract

This study presents a direct voltage control strategy for a stand-alone doubly fed induction generator (DFIG) subject to non-linear loads. The voltage regulator employs a super-twisting sliding mode (SSM) control to directly calculate the rotor voltage reference with the advantage of mitigating the voltage chattering and omitting the current control loops. On the basis of the harmonic-eliminating principle under non-linear loads, an improved extended state observer is proposed and applied to estimate the model-related part in the SSM control law. The advantages are that no extra sequence decomposition operations and machine parameters are required; therefore, enhancing the robustness and simplifying the structure of the controller. Finally, the proposed method is applied to a 6 kW DFIG-based hardware system under varying speed conditions. Both simulation and experiment results are given to validate the harmonic-eliminating performance of the proposed method for the stand-alone DFIG system. Nomenclature i, u, φ current, voltage and flux R, L, R d resistance, inductance, resistance in dc side ω sl , ω s slip and synchronous angular frequency Z L , Z C impedances of inductance and capacitor Superscript

No abstract