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The Oscillating Water Column concept consists of two key elements, a turbine located in a pneumatic energy collection chamber and a doubly fed induction generator that converts energy extracted by the turbine into a form that can be returned to the network. Since the turbo-generator control requires the rotor angular velocity, removing the rotor speed sensor simplifies the hardware, with the consequent reduction in installation and maintenance costs which is even more relevant in the rough working sea conditions. In this particular case, a Luenberger based observer is considered and the effectiveness of the proposed control is shown by numerical simulations. Comparing these results with those obtained using a traditional speed sensor, it is shown that the proposed solution provides better performance since it allows a more reliable and robust performance of the plant.

There is a worldwide interest in the use of renewable resources for the generation of electrical power. Between all renewable energy sources, ocean energy is the one that still has the furthest to go to achieve commercial maturity. As the most promising ocean energy that can be harnessed in the Basque Country is wave energy, the NEREIDA MOWC project, promoted and led by Basque Energy Board, aims to prove the viability of this technology for future commercial plants. In this paper, an Oscillating Water Column-based wave power generation plant is modeled and controlled by means of a new control scheme that takes into account the influence of turbine damping and the main requirements imposed by new Grid Codes when a grid fault occurs on the transmission system.

One of the main problems arising when dealing with Oscillating Water Column-based wave power generation plants equipped with Doubly-Fed Induction Generator, is the need of an adequate Fault-Ride-Through during voltage drops. In this paper it is proposed an innovative Fault-Ride-Through solution consisting of a control scheme that suitably coordinates the air flow control, the active crowbar and the variable frequency converter, fulfilling the Grid Code. Besides, the variety of cases presented due to different sea states (amplitude and frequency) and characteristics of the grid fault (voltage drop and fault period), makes necessary to adequately modify the references used by the controllers in order to achieve the desired Fault-Ride-Through capability. That is, the application of the same controller references for different sea scenarios, provoke different responses of the plant for the same type of grid fault. In the same way, the application of the same controller references to the plant working under the same sea scenario when a grid fault of different voltage drops occurs on the transmission system, causes different reactions in the wave power plant. In this sense, it has been also implemented a control that adapts the controller references according to the pressure drop and voltage reduction, improving the controllability of the active and reactive power and the Fault-Ride- Through capability during voltage drops.

The control of plasma in nuclear fusion has been revealed as a promising application of Control Engineering, with increasing interest in the control community during last years. In this paper it is developed a control-oriented linear model for the control of plasma current. For this purpose, it is provided a summary of the background necessary to deal with control problems in tokamak-based nuclear fusion reactors as it is the case of the future ITER tokamak. Besides, it is also given a review of the most used simulators and plasma models, with the aim of providing an adequate background for control engineers to derive their own control-oriented model or to choose the appropriate existing one. Finally, the proposed plasma model performance is proven in a current drive profile trajectory tracking problem using a modified anti-windup PID-based control scheme.

The suitability of distributed power generation systems working at medium and high capacity as it is the case of wave power generation plants, requires a reliable Fault-Ride-Through capability. When a grid fault occurs on the transmission system, the speed of the turbo-generator group increases uncontrolled, the induction generator injects large peak currents that can potentially damage the rotor converters and the plant tends to increase the reactive power consumption, so that it might intensify the voltage dip and contribute to the collapse of the power network. A simple solution would be the automatic disconnection of the plant from the grid in response to the power fault, but this policy could lead to a series of chain disconnections that would produce a massive power network failure. This is why new Grid Codes oblige the distributed power generation systems to remain connected to the power network, even in case of balanced voltage dips. In this paper, an Oscillating Water Column (OWC)-based wave power generation plant equipped with a Doubly Fed Induction Generator is modeled and controlled to overcome these balanced grid faults. The improvement relays on the implementation of a control scheme that suitably coordinates the air flow control, the crowbar, the rotor and the grid side converters to allow the plant to remain in service during the grid fault, and to contribute to its attenuation by supplying reactive power to the network. The simulated results show how it is obtained a great reduction in the rotor currents, improving the transient power stability and avoiding the rotor acceleration, complying with new Grid Codes requirements.

Wave energy is one of the most promising forms of ocean renewable sources because of its high availability. The Wells turbine has been one of the defining technologies in the development of wave energy. In this paper a neural control method for the Wells turbine-generator module is presented. For this purpose, a neural control using the backpropagation algorithm has been implemented, based on the addition of external resistances in series with the rotor winding of the induction generator connected to the turbine. The proposed control system does appropriately adapt the rotor resistance according to the pressure drop entry. It will be shown how the controller avoids the stalling behaviour and that the average power of the generator fed into the grid is significantly higher in the controlled case than in the uncontrolled one.

Currently, many visualization methods are used in computer assisted medicine. It is commonly considered that a unique visualization scheme makes difficult the interaction and limits the quality and quantity of the information shown. In this paper we study the specific requirements of a maxillofacial surgery simulation tool for facial appearance prediction. The different stages of the application lead to present medical information in different ways. We propose to adapt visualization techniques to give a more suitable answer to these needs: a hybrid volumetric and polygonal visualization for the planning stage, as well as a scheme for surgery definition in 2D. Finally, we propose the use of mesh visualization for the simulated model, which previously requires the 3D reconstruction of the surface in order to be visualized.

In this paper the performance of the Wells turbine has been improved, studying its stalling behaviour when the flow coefficient reaches a specific characteristic value. The generator increases its velocity when the flow coefficient of the turbine is approaching the critical point at which the turbine losses power.

In this paper the performance of the Wells turbine has been improved, studying its stalling behaviour when the flow coefficient (phy) reaches a specific characteristic value. For this purpose, a control scheme for the flow coefficient is derived based on the addition of external resistances in series with the rotor winding of the induction generator connected to the turbine. Due to the stalling behaviour, the generator increases its velocity as the flow coefficient of the turbine approaches the critical point at which the turbine losses power. The proposed control system does appropriately adapt the rotor resistance according to the entry pressure drop. To do so, the control implements a continuous resistance switching depending on the pressure drop and it will be demonstrated that the proposed control method used for this purpose clearly improves the performance of the system, maximizing the power generated by the turbine.

This paper explores the benefits that can be achieved for stereoscopic visualization when using occlusion culling strategies. The virtual environments analysed in this paper are complex mechanical sets that are not densely occluded. Those which are built up by dense geometric sets like aerospace engines composed of thousands of components and millions of polygons. The algorithm uses occlusion queries and succeeds in improving the frame rate of the stereoscopic visualization with an effective scheduling of the queries. Different coherences, including stereo coherence, are used to achieve this effective scheduling. An aggressive approach has been also validated for inclusion in the proposal. The occlusion culling algorithm can be easily implemented and provides a significant boost in performances.

Occlusion culling proves to be useful for the interactive visualization of environments that are not densely occluded. Those which are built up by dense geometric sets like aerospace engines composed of thousands of components and millions of polygons. In first place the convenience of using occlusion culling is studied with a simple scheme. Then improvements are analyzed. The key points to obtain frame rate speed-ups are: a convenient occlusion query scheduling provides the performance required; depth sorting is performed only when camera orientation changes more than a given threshold; coherence reduces the number of occlusion queries posted per frame. It is possible to select the percentage of occlusion queries that will be performed in each frame, from non-conservative schemes up to a conservative one. Furthermore, we propose a small addition to the GPU occlusion queries to perform faster renderings.