Per Brath

Estimation of effective wind speed

The wind speed has a huge impact on the dynamic response of wind turbine. Because of this, many control algorithms use a measure of the wind speed to increase performance, e.g. by gain scheduling and feed forward. Unfortunately, no accurate measurement of the effective wind speed is online available from direct measurements, which means that it must be estimated in order to make such control methods applicable in practice. In this paper a new method is presented for the estimation of the effective wind speed. First, the rotor speed and aerodynamic torque are estimated by a combined state and input observer. These two variables combined with the measured pitch angle is then used to calculate the effective wind speed by an inversion of a static aerodynamic model.

Estimation of Rotor Effective Wind Speed: A Comparison

Modern wind turbine controllers use wind speed information to improve power production and reduce loads on the turbine components. The turbine top wind speed measurement is unfortunately imprecise and not a good representative of the rotor effective wind speed. Consequently, many different model-based algorithms have been proposed that are able to estimate the wind speed using common turbine measurements. In this paper, we present a concise yet comprehensive analysis and comparison of these techniques, reviewing their advantages and drawbacks. We implement these techniques and compare the results on both aero-servo-elastic turbine simulations and real turbine field experiments in different wind scenarios.

Load reduction of wind turbines using receding horizon control

Large scale wind turbines are lightly damped mechanical structures driven by wind that is constantly fluctuating. In this paper, we address the design of a model-based receding horizon control scheme to reduce the structural loads in the transmission system and the tower, as well as provide constant (or at least smooth) power generation. Our controller incorporates two optimization problems: one to predict or estimate mean wind speed, given LIDAR data, and the other to carry out receding horizon control to choose the control inputs. The method is verified against an existing wind turbine control system, and shows reductions in both extreme loads and power fluctuations by 80% and 90% respectively when compared to a conventional controller.

Gain-scheduled Linear Quadratic Control of Wind Turbines Operating at High Wind Speed

This paper addresses state estimation and linear quadratic (LQ) control of variable speed variable pitch wind turbines. On the basis of a nonlinear model of a wind turbine, a set of operating conditions is identified and a LQ controller is designed for each operating point. The controller gains are then interpolated linearly to get a control law for the entire operating envelope. The states and the gain-scheduling variable are not online available and an observer is designed. This is done in a modular approach in which a linear estimator is used to estimate the non-measured state variables and the unknown input, aerodynamic torque. From the estimated aerodynamic torque and rotor speed and measured pitch angle the scheduling variable effective wind speed is calculated by inverting the aerodynamic model. Simulation results are given that display good performance of the observers and comparisons with a controller designed by classical methods display the potential of the method.

Rate bounded linear parameter varying control of a wind turbine in full load operation

Abstract This paper considers the control of wind turbines using an LPV design technique. The controller design is done by a combination of a method that uses elimination of controller variables and a method using a congruent transformation followed by a change of variables. An investigation is performed to understand the gap between zero rate of variation and arbitrary fast rate of variation for the selected scheduling variable. In particular it is analysed for which rate of variation, the local performance level starts to deteriorate from the performance level that can be obtained locally by LTI controllers. A rate of variation is selected which is expected only to be exceeded outside the normal wind turbine operating conditions. For this rate of variation a controller has been designed and simulations show a performance level over the operating region which is very similar to what can be obtained by LTI designs for the specific operating condition. The LPV controller, however, works for the whole operating range with reasonably fast changes within this.