Mate Jelavić

Individual pitch control of wind turbine based on loads estimation

The use of wind energy for generating electricity has been constantly and rapidly increasing over last few decades and this growth is expected to continue. In order to enable even greater role of wind energy in power production wind turbinespsila sizes and rated powers must increase. As wind turbines grow in size they are subjected to extreme loads and fatigue caused by uniform turbulent winds. This prevents further growth of wind turbines. Therefore control methods that assure loads reduction become a necessity. In this paper methods for wind turbine loads reduction based on individual pitch control are explored. To overcome problems related to needed measurements of blade loads a method for their estimation based on loads measured on the fixed parts of the structure is proposed.

Estimation based Individual Pitch Control of Wind Turbine

The use of wind power for generating electricity has experienced an uninterrupted and accelerating growth over last few decades and this growth is likely to continue. In order to enable even greater role of wind energy in power production it is necessary to increase the size and unit power of wind turbines. As wind turbines grow in size they are subjected to extreme loads and fatigue caused by nonuniform turbulent winds. Therefore, control algorithms that can assure load and fatigue reduction become a necessity. In this paper the individual pitch control for reduction of the periodic blade and hub loading is explored. To avoid problems related to the required blade loads measurements a method for their estimation based on other process variables is proposed. The performance of the individual pitch controller that uses such load estimations instead of measurements is tested and compared to the collective pitch control and the individual pitch control based on measured loads.

Linear parameter varying approach to wind turbine control

Design of linear parameter varying control (LPV) for wind turbines is considered in this paper. Multivariable, robust control law, which can guarantee stability and desired performance in the whole operating region of the wind turbine, is obtained LPV controller is compared with a classical controller.

Identification of wind turbine model for individual pitch controller design

The use of wind power has been increasing rapidly over last few decades and according to all predictions this trend is likely to continue. At the same time need for better cost effectiveness of wind power plants has stimulated growth in wind turbinespsila size and rated power. As wind turbines grow in size they are subject to extreme structural loads and fatigue. In order to reduce such loads advanced control methods are explored among which individual pitch control has demonstrated very promising results. To design an individual pitch controller suitable wind turbine model is required. Derivation of wind turbine model for individual pitch controller design is addressed in this paper.

Identification of Wind Turbine Model for Controller Design

Wind power increases rapidly with increase of wind speed. In order to keep wind turbine running even at strong winds wind power capture has to be constrained. Efficient way for constraining wind power capture is the use of pitchable blades. For pitch controller design a suitable wind turbine model is needed. Finding mathematical model that would be a good representation of wind turbine system and at the same time suitable for controller design is very difficult task since wind turbine system is strongly nonlinear. Description of wind turbine system using many linear models identified at particular operating points is explored in this paper. Effects occurring when switching between models are examined and their repercussions on controller design are discussed. Use of fuzzy logic is proposed as possible solution for avoiding negative effects caused by switching between models

Estimation of wind turbulence model parameters

Simulation of wind turbine system is a key step during its design. To be able to simulate realistic behavior of wind turbine system and reliably predict its ultimate loads a suitable wind model is necessary. Modeling only wind time variations proved to be insufficient for quality simulations, so its spatial variations have to be modeled as well. Today there are methods that allow modeling of a 3D turbulent wind fields that proved to be a good description of realistic turbulent winds. All of them assumes use of certain turbulence parameters that denote nature of turbulence generated by those models. Those parameters are difficult to measure and today their values are prescribed as standard recommendations or are obtained using various assumptions based on site geography. A method of determining suitable turbulence model parameters based on wind speed measurement made on site is proposed in this paper. The aim of the paper is not to model atmospheric phenomena but to be able to simulate turbulence with the similar properties as of those observed on site.

Explicit model predictive control for reduction of wind turbine structural loads

In many instances it is desirable for wind turbine to produce less power than is available in the wind. In such instances, one can balance between the strictness of the wind turbine power reference following and the reduction of the wind turbine structural loading. This paper investigates how wind turbine structural loads may be reduced through appropriate changes (i.e., small deviations) in wind turbine power references. An explicit model predictive controller - a closed form, parametric solution to the optimal control problem - is designed for the problem at hand. The extensive, realistic simulations have shown that the optimal controllers, which allow variation of the wind turbine power references, significantly reduce structural loads and fatigue.

Estimation of lube oil viscosities on a vacuum distillation column

The key product specifications on a vacuum distillation column side draw products are viscosity, density, flash and color, although viscosity is usually the most limiting quality. There are online viscosity analyzers available on the market, but their prices are quite high and their reliabilities could be quit low. Possible solution to this problem is development and application of so-called soft sensors, which estimate lube oil viscosities based on available easy-to-measure variables. In this paper we consider the application of neural networks for viscosities estimation of lube oils on the vacuum unit at INA Rijeka lube oil refinery. The proposed soft sensors, based on neural networks, are of nonlinear finite impulse response structure, where their inputs are temperatures and flow-rates of the distillates. Although developed soft sensors do not demonstrate high accuracy they can be used to track trends of the output viscosities, and based on that information plant operators can take proper actions with more certainty. It is to expect some improvements in sensors behavior with arrival of new input/output data.

Reduction of wind turbine structural loads caused by rotor asymmetries

To enable further growth of wind turbine dimensions and rated power, it is essential to decrease structural loads that wind turbines experience. Therefore a great portion of research is focused on control algorithms for reduction of structural loads, but typically wind turbine rotor is considered to be perfectly symmetrical, and therefore such control algorithms cannot reduce structural loads caused by rotor asymmetries. In this paper, the reduction of wind turbine structural loads caused by rotor asymmetries is discussed. To this aim, suitable transformation of structural loads and control algorithm based on such transformation are proposed. Simulation results show that proposed control algorithm is capable of reducing structural loads caused by rotor asymmetries.