Robust control of wind turbines based on fractional nonlinear disturbance observer

Abstract

In order to assure maximum energy conversion, the angular velocity of the wind turbine rotor tracks a nominal profile depending on the wind speed. However, conventionally, wind flows present non‐differentiable components due to turbulence and gust winds, which affect the wind energy management. Thus, a fast and robust controller is required to induce such nominal regime for maximum energy transfer. A fractional‐order nonlinear disturbance‐observer (FNDOB) is proposed in this paper to cancel the non‐differentiable components of the wind speed, as well as dynamic uncertainties and other aerodynamic disturbances. The proposed FNDOB is based on continuous fractional sliding modes, assuring that disturbances and uncertainties are exactly compensated in finite‐time. A representative simulation study for a variable‐speed wind turbine is presented to show the reliability of the proposed scheme, and a comparative analysis with respect to a conventional linear disturbance observer based control is presented.

Wind energy conversion system under asymmetrical voltage failures: Analysis and nonlinear control

“…R is named the circuits mixed potential. According to García-Canseco et al [39], premultiplying (19) by _…”

“…New grid connection codes specifically require that WECS provide grid support in cases of abnormal conditions [5], with special stress in operation under unbalanced grid voltages [6]. In this sense, many interesting contributions about WECS operating under symmetrical and asymmetrical grid failures have been published in the specialized literature during the last years [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. In the particular case of PMSG-WECS, most of these approaches propose, during such grid voltage failures, reducing the wind power extraction at the generator side converter while delivering at the grid side the power required by the net despite the distorted voltage presence [7].…”

“…Besides the previous contributions, other modern control techniques like sliding mode control (SMC) [17] and model predictive control (MPC) [18] have also been proposed for grid connected WECS operating under normal and grid failures conditions. Sliding mode controllers are in general simple to implement and present a high robustness degree against external perturbations and unmodeled dynamics [17,19]. However, first-order sliding mode implementations suffer from the harmful and unavoidable chattering presence and lose its high inherent robustness degree on not unitary relative degree outputs.…”

Robust Mittag‐Leffler stabilisation of fractional‐order systems

“…for a locally integrable flow f(t, x(t)). In addition, for the case of x(t) is differentiable at least almost everywhere, the solutions of systems (6) and 7coincide. Nevertheless, (7) defines a more general class of fractional-order systems, this is, with not necessarily integer-order differentiable solutions.…”

“…Fractional calculus is an old branch of mathematics that dates back since the early foundations of conventional integer-order calculus, three centuries ago. Nonetheless, the very first engineering applications of fractional-order tools were made available in last decades [1][2][3][4][5][6]. Furthermore, the study of nonlinear effects, as well as the implementation of non-smooth techniques in observation and stabilisation of fractional-order systems has been addressed in recent years [7].…”