Open Access
Lidar-based feedforward control design methodology for tower load alleviation in wind turbines
(John Wiley & Sons, 2022) Miquélez Madariaga, Irene; Lizarraga Zubeldia, Idoia; Díaz de Corcuera Martínez, Asier; Elso Torralba, Jorge; Ingeniería; Ingeniaritza
Minimising tower loads is a key issue for the optimal operation and cost-effective design of wind turbines. Light detection and ranging (LIDAR) technologies enable the measurement of free wind ahead of the rotor and the addition of new feedforward controllers to the traditional control loops, improving the performance in terms of generator speed regulation and load reduction. This paper presents a design procedure based on plant inversion at a set of key frequencies. Tower base longitudinal bending moment is considered the main output of the system. Although the minimisation of tower base loads is the main objective of the design, good results are obtained in terms of generator speed regulation and pitch actuation as well. The methodology has been tested in the well-known NREL 5MW wind turbine. Results have been obtained for different LIDAR configurations in order to quantify the loss of performance due to measurement errors. In all cases, the feedforward control behaves better than the baseline case.
Open Access
Frequency domain design of a series structure of robust controllers for multi-input single-output systems
(Hindawi, 2018) Gil Martínez, Montserrat; Rico Azagra, Javier; Elso Torralba, Jorge; Ingeniería; Ingeniaritza
The regulation of a disturbed output can be improved when several manipulated inputs are available. A popular choice in these cases is the series control scheme, characterized by (1) a sequential intervention of loops and (2) faster loops being reset by slower loops, to keep their control action around convenient values. This paper tackles the problem from the frequency-domain perspective. First, the working frequencies for each loop are determined and closed-loop specifications are defined. Then, Quantitative Feedback Theory (QFT) bounds are computed for each loop, and a sequential loop-shaping of controllers takes place. The obtained controllers are placed in a new series architecture, which unlike the classical series architecture only requires one controller with integral action. The benefits of the method are greater as the number of control inputs grow. A continuous stirred tank reactor (CSTR) is presented as an application example.
Open Access
Automatic synthesis of feedforward elements in quantitative feedback theory
(Wiley, 2021) Elso Torralba, Jorge; Ostolaza, J. Xabier; Ingeniería; Ingeniaritza; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Recent developments in quantitative feedback theory (QFT) lead to feedforward design problems with both magnitude and phase constraints. In these cases, manual feedforward tuning becomes much more challenging and time consuming than the traditional prefilter shaping taking place on the Bode plot. This article presents a general procedure for the automatic synthesis of such elements. Feedforward bounds in the complex plane are expressed as constraints of a linear programming problem in which the Bode real-complex relation is implicitly considered, ensuring a stable rational solution. The methodology is successfully tested in a well-known benchmark problem.
Open Access
Linear uncertain modelling of LIDAR systems for robust wind turbine control design
(Elsevier, 2023) Miquélez Madariaga, Irene; Lizarraga Zubeldia, Idoia; Díaz de Corcuera Martínez, Asier; Elso Torralba, Jorge; Ingeniería; Ingeniaritza; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Light detection and ranging (LIDAR) sensors measure the free wind ahead of the rotor, enabling the use of new feedforward control strategies. However, there exist some sources of error inherent to the measuring process that should be considered during the design of LIDAR-based controllers. Typically, the coherence function is used for that purpose, but it is not compatible with some robust design methodologies. This paper presents an analytic relation between the coherence function and a non-parametric uncertainty model of LIDAR sensors, suitable for the design of controllers via 𝜇-synthesis or Quantitative Feedback Theory. Such a relation is applied to a realistic LIDAR simulator. First, the linear non-parametric uncertainty model is identified using simulation data obtained from the well-known NREL 5 MW wind turbine. Then, it is validated against the coherence model by comparing linear predictions of the simulation outputs.
Open Access
Multiobjective QFT control as enabler for wind turbines with soft-soft towers
(Wiley, 2025-03-06) Arellano Aguado, Jesús; Elso Torralba, Jorge; Ingeniería; Ingeniaritza
Wind energy tendency towards larger rotors and higher hub heights reach a limit when wind turbine pitch controller bandwidth is constrained by the first tower fore-aft bending moment. While most manufacturers try to find a workaround with alternative nonstandard tower designs, this paper presents a control solution based on quantitative feedback theory (QFT) that provides effective disturbance rejection while maintaining cost-effective conventional tower design for very high hub heights. Frequency domain specifications on measured and nonmeasured variables provide the control designer the insight to make the best use of the available feedback. The new control design procedure is applied to a realistic wind turbine example of 180-m hub height, showing the technical viability of the solution and a profitable business case.
Open Access
Multivariable QFT control of the direction flip problem in wire arc additive manufacturing
(Wiley, 2025-04-25) Masenlle, Manuel; Elso Torralba, Jorge; Ostolaza, J. Xabier; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC
Additive metal manufacturing (AM), particularly Wire Arc Additive Manufacturing (WAAM), offers a compelling alternative to traditional machining methods. While AM presents advantages such as reduced material waste and lower production costs, challenges remain in effectively controlling the process to prevent defects and optimise material deposition. This article proposes a multivariable control system for WAAM utilising Quantitative Feedback Theory (QFT) to maintain the shape of the heat-affected zone (HAZ) during transitions in direction flips during layer deposition. By modelling these direction flips as predictable disturbances, the full potential of QFT to integrate feedback and feedforward actions is exploited. The resulting multivariable control laws seek to minimise temperature variation in two critical points around the welding pool by adequately manipulating the power and speed of the heat source. A benchmark system is established to evaluate the effectiveness of the proposed control system. The results demonstrate significant improvement in temperature control, leading to enhanced layer construction quality and reduced need for height corrections or cooling pauses.
Open Access
Quantitative feedback control of multiple input single output systems
(Hindawi, 2014) Rico Azagra, Javier; Gil Martínez, Montserrat; Elso Torralba, Jorge; Automática y Computación; Automatika eta Konputazioa
This paper presents a robust feedback control solution for systemswithmultiplemanipulated inputs and a singlemeasurable output. A structure of parallel controllers achieves robust stability and robust disturbance rejection. Each controller uses the least possible amount of feedback at each frequency. The controller design is carried out in the Quantitative Feedback Theory framework. The method pursues a smart load sharing along the frequency spectrum, where each branch must either collaborate in the control task or be inhibited at each frequency. This reduces useless fatigue and saturation risk of actuators. Different examples illustrate the ability to deal with complex control problems that current MISO methodologies cannot solve.Main control challenges arise due to the uncertainty of plant and disturbance models and when a fast-slow hierarchy of plants cannot be uniquely established.