Eckhard Gauterin

Fault-tolerant control of wind turbines with hydrostatic transmission using Takagi–Sugeno and sliding mode techniques☆

Abstract In this paper, a Takagi–Sugeno Sliding Mode Observer for actuator fault diagnosis and fault-tolerant control scheme of wind turbines with hydrostatic transmission are presented. It will be shown that sliding mode techniques have the advantages that several actuator faults of the wind turbine drive train can be simultaneously reconstructed with one and the same observer and directly applied for fault compensation. Furthermore, a simple compensation approach is implemented by subtracting the reconstructed faults obtained from the (faulty) inputs. These corrected inputs act on the system as virtual actuators, such that the originally designed controller for the nominal, i.e. fault-free situation, can still be used. The fault reconstruction and fault tolerant control strategy are tested in simulations with several faults of different types.

Effective wind speed estimation: Comparison between Kalman Filter and Takagi-Sugeno observer techniques.

Advanced model-based control of wind turbines requires knowledge of the states and the wind speed. This paper benchmarks a nonlinear Takagi-Sugeno observer for wind speed estimation with enhanced Kalman Filter techniques: The performance and robustness towards model-structure uncertainties of the Takagi-Sugeno observer, a Linear, Extended and Unscented Kalman Filter are assessed. Hence the Takagi-Sugeno observer and enhanced Kalman Filter techniques are compared based on reduced-order models of a reference wind turbine with different modelling details. The objective is the systematic comparison with different design assumptions and requirements and the numerical evaluation of the reconstruction quality of the wind speed. Exemplified by a feedforward loop employing the reconstructed wind speed, the benefit of wind speed estimation within wind turbine control is illustrated.

Disturbance Compensation by Wind Speed Reconstruction based on a Takagi-Sugeno Wind Turbine Model

In this work, the nonlinear Tagaki-Sugeno modelling method is utilised to set up an observer-based feed-forward control scheme for wind turbines, which can compensate for the influence of the disturbing wind variation on the rotational speed. The applied scheme leads to a reduced thrust force acting on the rotor.

Analyse der Eingang-Zustand-Stabilität von Kleinwindanlagen mit LMI-Bedingungen

Zusammenfassung Bei Kleinwindanlagen werden zur Leistungsbegrenzung Rotorblattverstellsysteme eingesetzt. Dabei werden aus Kostengründen relativ einfache mechanische Regler verwendet. Die Hauptschwierigkeit liegt in der Exemplarstreuung der mechanischen Komponenten und der alterungsbedingten Änderung der dynamischen Eigenschaften. In dieser Arbeit werden basierend auf der Beschreibung mechanischer Rotorblattverstellsysteme mit Takagi-Sugeno Modellen LMI-Bedingungen und ein Verfahren zum Nachweis der Eingang-Zustand-Stabilität unter Variation der Federsteifigkeit und mechanischen Dämpfung vorgestellt.

Stability analysis of small horizontal-axis wind turbines using Takagi-Sugeno fuzzy models

In modern wind turbines the output power for wind speeds above the nominal wind speed is limited by the adjustment of the rotor blade angles. The adjustment is performed with the pitch system. For cost reasons, in small wind turbines simple mechanical pitch systems are used actuated by centrifugal force and thus depending on the rotor speed and the blade mass. With the help of the converter the generator torque, and as a consequence also the rotor speed, is controlled, so that the constant regulation on nominal power output above the nominal wind speed is enabled. The main difficulty using low cost centrifugal force regulators in pitch systems are determined by a variable structure mathematical description, the manufacturing tolerances, and age-related changes of dynamic properties. The nonlinear dynamics of such systems has not yet adequately been studied. In particular, no stability was verified considering the foregoing model uncertainties.

Nonlinear Quadratic Estimator with selective error state weighting

A new approach for optimal observer design of nonlinear systems, the so-called Nonlinear Quadratic Estimator is proposed. This approach employs the minimisation of a quadratic cost functional, thereby comprising two design parameters: Selective weighting of specific error state components and estimated upper bound minimisation. The new approach works without dual system transformation, achieving significant error state minimisation with optimised error dynamics and enabling a selective error state minimisation. Within this proceeding the observer and estimator design method, respectively, is derived from a Lyapunov stability condition of nonlinear, time-continuous systems in Takagi-Sugeno model structure, solved with linear matrix inequalities. Its capability is illustrated for an academical example of a nonlinear system with observer based stabilisation.

Two-layer observer-based FDI with application to NREL 5 MW wind turbine model

In this paper, a two-layer fault detection and isolation (FDI) scheme with application in wind turbines is presented. Commonly, model-based FDI concepts use a suitable mathematical model of the plant as a redundancy for on-line available data such as measurements and control outputs. In addition, the proposed two-layer concept exploits the redundancy between component and structure models at their common physical interfaces. It is shown by a illustrated example how the FDI problem can be formalized to a two-layer scheme. First, the models of both layers are proposed, a observer is derived for the component-layer and combined with the structure-layer. Applicability is shown by means of the NREL 5 MW reference wind turbine with objective of detection and isolation of parameter faults in the blade slewing bearings and blade structure.

Control Engineering Analysis of Mechanical Pitch Systems

With the help of a local stability analysis the coefficient range of a discrete damper, used for centrifugal forced, mechanical pitch system of small wind turbines (SWT), is gained for equilibrium points. – By a global stability analysis the gained coefficient range can be validated. An appropriate approach by Takagi-Sugeno is presented in the paper.