Abstract: To extract maximum power from the available wind energy, it is necessary that the doubly-fed induction generator (DFIG) based wind energy conversion system (WECS) outputs that maximum power at each instant of time for different wind speeds. This can be achieved by controlling the rotor voltage of the DFIG. To make it possible, a novel maximum power point tracking (MPPT) controller in combination with state and disturbance observers and fixed-time stability notion is proposed in this paper. The sliding mode control (SMC) method is used to design the observer-based controller and ensure the robustness. The sliding mode state observer is designed while only the measurement of the stator reactive power and rotor speed is required. The modelling uncertainties and external disturbances are estimated by the sliding mode disturbance observer without information about their upper bounds in advance. Then, the combinatorial effect of uncertainties and disturbances are fully compensated by the designed controller. The fixed-time convergence issue is addressed where the bound on the settling time is user-defined using design parameters regardless of initial conditions. The elimination of chattering issue is considered in the design of the SMC laws. The stability analysis of the closed-loop system is obtained via the Lyapunov stability theory. The validity and robustness of the proposed method is tested in Simulink/MATLAB for a DFIG under two different scenarios of wind speed modelling. The proposed fixed-time method is also compared with a classical finite-time method. Comparing the results demonstrate that the proposed method outperforms the other method.
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Elsevier
Keywords: DFIG, sliding mode, Fixed-time, WECS, observer, MPPT