M. L. Buhl

Bio: M. L. Buhl is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 1131 citations.

Definition of the Floating System for Phase IV of OC3

Abstract: Phase IV of the IEA Annex XXIII Offshore Code Comparison Collaboration (OC3) involves the modeling of an offshore floating wind turbine. This report documents the specifications of the floating system, which are needed by the OC3 participants for building aero-hydro-servo-elastic models.

3D simulation of wind turbine rotors at full scale. Part II: Fluid–structure interaction modeling with composite blades

Abstract: In this two-part paper, we present a collection of numerical methods combined into a single framework, which has the potential for a successful application to wind turbine rotor modeling and simulation. In Part 1 of this paper we focus on: 1. The basics of geometry modeling and analysis-suitable geometry construction for wind turbine rotors; 2. The fluid mechanics formulation and its suitability and accuracy for rotating turbulent flows; 3. The coupling of air flow and a rotating rigid body. In Part 2, we focus on the structural discretization for wind turbine blades and the details of the fluid-structure interaction computational procedures. The methods developed are applied to the simulation of the NREL 5MW offshore baseline wind turbine rotor. The simulations are performed at realistic wind velocity and rotor speed conditions and at full spatial scale. Validation against published data is presented and possibilities of the newly developed computational framework are illustrated on several examples.

Control of Wind Turbines

Abstract: Wind energy is a fast-growing interdisciplinary field that encompasses multiple branches of engineering and science. Despite the growth in the installed capacity of wind turbines in recent years, larger wind turbines have energy capture and economic advantages, the typical size of utility scale wind turbines has grown by two orders of magnitude. Since modern wind turbines are large, flexible structures operating in uncertain environments, advanced control technology can improve their performance.The goal of this article is to describe the technical challenges in the wind industry relating to control engineering.

Sliding Mode Power Control of Variable-Speed Wind Energy Conversion Systems

Abstract: This paper addresses the problem of controlling power generation in variable-speed wind energy conversion systems (VS-WECS). These systems have two operation regions depending on the wind turbine tip-speed ratio. They are distinguished by minimum phase behavior in one of these regions and a nonminimum phase in the other one. A sliding mode control strategy is then proposed to ensure stability in both operation regions and to impose the ideal feedback control solution despite model uncertainties. The proposed sliding mode control strategy presents attractive features such as robustness to parametric uncertainties of the turbine and the generator as well as to electric grid disturbances. The proposed sliding mode control approach has been simulated on a 1.5-MW three-blade wind turbine to evaluate its consistency and performance. The next step was the validation using the National Renewable Energy Laboratory (NREL) wind turbine simulator called the fatigue, aerodynamics, structures, and turbulence code (FAST). Both simulation and validation results show that the proposed control strategy is effective in terms of power regulation. Moreover, the sliding mode approach is arranged so as to produce no chattering in the generated torque that could lead to increased mechanical stress because of strong torque variations.

Optimal Control of Wind Energy Systems: Towards a Global Approach

Abstract: Wind is recognized worldwide as a cost-effective, environmentally friendly solution to energy shortages, and wind energy is currently the fastest-growing energy source in the world. Wind power investment worldwide is expected to expand threefold in the next decade, from about $18 billion in 2006 to $60 billion in 2016 [1]. While the cost of wind energy is already very competitive with energy from coal and natural gas, there are still many unsolved challenges in expanding wind power. From bearings under constant friction to blades that must be able to handle gusts, lightning, and constantly changing wind conditions, today’s wind turbines need increasingly sophisticated component designs, sensors, and control systems. Further, better wind forecasting methods are needed to improve site selection, optimize operations, and mitigate load fluctuations on the power grid. Although the United States receives only about 1% of its electrical energy from wind [2], the corresponding figure in Denmark is more than 15% [3]. The integration of more than 20% penetration of wind energy into the grid will require modifications of the grid design and operation, with the possible addition of new transmission lines and energy storage systems. Despite the amazing growth in the installed capacity of wind turbines in recent years, engineering and science challenges still exist. These large, flexible structures operate in uncertain environments and lend themselves nicely to advanced control solutions. Advanced controllers can help achieve the overall goal of decreasing the cost of wind energy by increasing the efficiency, and thus the energy capture, or by reducing structural loading and increasing the lifetimes of the components and turbine structures. Wind energy literature has been similarly expanding with the growing interest in the area. Several tomes cover the subject from a broad perspective, and these tend to blend reference and tutorial material in their presentation [4], [5]. As such they contain large sections that essentially serve as introductions to atmospheric sciences, aerodynamics, structural dynamics, electrical power systems, generator dynamics, power electronics, control systems, and the economics of the power industry. That is the nature of the beast for any book that undertakes the ambitious goal of providing a technical foundation for those interested in the wind industry. Unfortunately, for the controls engineer, the research literature tends to be an expanse of narrowly focused studies with only a few that are tutorial in nature. Further, research is typically focused on control of wind turbines in a particular operating region such as maximizing power in partial load conditions, mitigating loads in above-rated