Adaptive Robust Backstepping Control of the Speed Regulating Differential Mechanism for Wind Turbines

In this paper, a hybrid transmission system equipped with a speed regulating differential mechanism (SRDM) is proposed for grid-connected wind turbines (WTs) to generate constant-frequency electricity. However, the transmission system is subject to pulsating torque from disturbances in the power grid. Coupled with parameter uncertainties, the speed control accuracy of SRDM and the system stability can hardly be warranted by conventional adaptive or robust controllers. Aiming at the proposed WT, this paper presents a discontinuous projection-based adaptive robust backstepping controller (ARBC) with an extended state observer (ESO) for high-accuracy speed control of permanent magnet synchronous motor in SRDM. The designed control approach, whose global robustness is guaranteed by a feedback robust law, can effectively handle both parametric uncertainties and external disturbances together without using the large nonlinear feedback gain and violating any constraints during the transient period. Then, the desired tracking performances of ARBC with ESO are verified through comparative experiments in a built platform of the WT with SRDM. Comparative experimental results show that SRDM equipped with the integrated control method can accurately regulate the power frequency to constant under operating conditions of parametric uncertainties, varying wind speeds, subsynchronous resonance, and sudden load fluctuation in the power grid.