Variable Speed Control In Wells Turbine-Based Oscillating Water Column Devices: Optimum Rotational Speed

The effects of climate change and global warming reveal the need to find alternative sources of clean energy. In this sense, wave energy power plants, and in particular Oscillating Water Column (OWC) devices, offer a huge potential of energy harnessing. Nevertheless, the conversion systems have not reached a commercially mature stage yet so as to compete with conventional power plants. At this point, the use of new control methods over the existing technology arises as a doable way to improve the efficiency of the system. Due to the nonuniform response that the turbine shows to the rotational speed variation, the speed control of the turbo-generator may offer a feasible solution for efficiency improvement during the energy conversion. In this context, a novel speed control approach for OWC systems is presented in this paper, demonstrating its goodness and affording promising results when particularized to the Mutriku's wave power plant.This work was supported in part by the University of the Basque Country (Universidad del Pais Vasco UPV/Euskal Herriko Unibertsitatea EHU) through Project PPG17/33 and by the MINECO through the Research Project DPI2015-70075-R (MINECO/FEDER, EU), as well as to the Basque Government through Ph.D. Grant PIF PRE_2016_2_0193. The authors would like to thank the collaboration of the Basque Energy Agency (EVE) through Agreement UPV/EHUEVE23/6/2011, the Spanish National Fusion Laboratory (EURATOM-CIEMAT) through Agreement UPV/EHUCIEMAT08/190 and EUSKAMPUS - Campus of International Excellence. They would also like to thank Yago Torre-Enciso and Olatz Ajuria from EVE for their collaboration and help

Centralized Airflow Control to Reduce Output Power Variation in a Complex OWC Ocean Energy Network

A centralized airflow control scheme for a complex ocean energy network (OEN) is proposed in this paper to reduce the output power variation (OPV). The OEN is an integrated network of multiple oscillating water columns (OWCs) that are located at different geographical sites connected to a common electrical grid. The complexity of the OWC-OEN increases manifolds due to the integration of several OWCs and design of controllers become very challenging task. So, the centralized airflow control scheme is designed in two stages. In control stage-1, a proportional-integral- (PI-) type controller is designed to provide a common reference command to control stage-2. In control stage-2, the antiwindup PID controllers are implemented for the airflow control of all the OWCs simultaneously. In order to tune the large number of control parameters of this complex system, a fitness function based on integral squared error (ISE) is minimized using the widely adopted particle swarm optimization (PSO) technique. Next, the simulation results were obtained with random wave profiles created using the Joint North Sea Wave Project (JONSWAP) irregular wave model. The OPV of the proposed OWC-OEN was reduced significantly as compared to the individual OWC. It was further observed that the OPV of the proposed scheme was lower than that achieved with uncontrolled and MPPT controlled OWC-OEN. The effect of communication delay on the OPV of the proposed OWC-OEN scheme was also investigated with the proposed controller, which was found to be robust for a delay up to 100 ms.This work was supported in part by the Basque Government through project IT1207-19 and MCIU/MINECO through RTI2018-094902-B-C21/RTI2018-094902-B-C22 (MCIU/AEI/FEDER, UE)

Output Power Improvement in Oscillating Water Column-based Wave Power Plants

[ES] Las centrales de aprovechamiento de la energía proveniente de las olas, y particularmente los dispositivos de columna de agua oscilante, resultan una alternativa factible para reducir la dependencia de los combustibles fósiles y frenar el creciente problema del calentamiento global. Así, los nuevos esquemas de control pueden jugar un papel importante a la hora de aportar mejoras de rendimiento y competir de igual a igual desde un punto de vista comercial con las fuentes de energía tradicionales. En este sentido, el presente artículo propone un nuevo método de control basado en el seguimiento de la curva de máxima potencia, mediante el establecimiento de los valores óptimos de los coeficientes de flujo y de par que permiten maximizar la potencia generada en cada instante. El esquema de control ha sido implementado sobre un modelo completo desde la ola hasta la red de potencia a fin de demostrar la viabilidad del método propuesto y la bondad de sus resultados.[EN] Wave energy power plants, particularly Oscillating Water Column devices, become a feasible alternative to reduce the dependence on fossil fuels and slow down the growing problem of the global warming. Thus, new control schemes can play an important role, providing performance improvements to compete from a commercial point of view with the other traditional energy sources. In this sense, this paper proposes a new control technique based on the maximum power point tracking, by establishing the optimal values of the flow and torque coefficients that allow the maximum power generation at each moment. The proposed control scheme has been implemented on a complete wave-to-wire model in order to demonstrate both the goodness and the viability of the proposed method.Este trabajo ha sido realizado parcialmente gracias al apoyo de la Universidad del País Vasco (UPV/EHU) a través del Proyecto PPG17/33 y del Gobierno Vasco a través de la beca predoctoral PRE_2016_2_0193, además del MINECO a través del Proyecto de Investigación DPI2015-70075-R (MINECO/FEDER, EU)Lekube, J.; Garrido, AJ.; Garrido, I.; Otaola, E. (2018). Mejora de la Potencia Obtenida en Plantas de Generación Undimotriz basadas en Columna de Agua Oscilante. Revista Iberoamericana de Automática e Informática industrial. 15(2):145-155. https://doi.org/10.4995/riai.2017.8831OJS145155152Alberdi, M., Amundarain, M., Garrido, A.J., Garrido, I., Casquero, O., De la Sen, M., 2011. Complementary control of oscillating water column-based wave energy conversion plants to improve the instantaneous power output. IEEE Transactions on Energy Conversion 26, 1021-1032. https://doi.org/10.1109/TEC.2011.2167332Amon, A., Brekken, K.A., Schacher, A., 2012. Maximum power point tracking for ocean wave energy conversion. IEEE Transactions on Industry Applications 48, 1079-1086. https://doi.org/10.1109/TIA.2012.2190255Amundarain, M., Alberdi, M., Garrido, A.J., Garrido, I., 2009. Neural control of the Wells turbine-generator module. Proceedings of the IEEE Conference on Decision and Control, 7315-7320.Amundarain, M., Alberdi, M., Garrido, A.J., Garrido, I., 2011. Modeling and Simulation of Wave Energy Generation Plants: Output Power Control. IEEE Transactions on Industrial Electronics 58, 105-117. https://doi.org/10.1109/TIE.2010.2047827Bailey, H., Robertson, B.R.D., Buckham, B.J., 2016. Wave-to-wire simulation of a floating oscillating water column wave energy converter. Ocean Engineering 125, 248-260. https://doi.org/10.1016/j.oceaneng.2016.08.017Correia da Fonseca, F.X., Gomes, R.P.F., Henriques, J.C.C., Gato, L.M.C., Falcao, A.F.O., 2016. Model testing of an oscillating water column spar-buoy wave energy converter isolated and in array: Motions and mooring forces. Energy 112, 1207-1218. https://doi.org/10.1016/j.energy.2016.07.007Cui, Y., Hyun, B., 2016. Numerical study on Wells turbine with penetrating blade tip treatments for wave energy conversion. International Journal of Naval Architecture and Ocean Engineering 8, 456-465. https://doi.org/10.1016/j.ijnaoe.2016.05.009Delmonte, N., Barater, D., Giuliani, F., Cova, P., Buticchi, G., 2016. Review of oscillating wáter column converters. IEEE Transactions on Industry Applications 52, 1698-1710.Falcao, A.F.D.O., 2002. Control of an oscillating-water-column wave power plant for máximum energy production. Applied Ocean Research 24, 73-82. https://doi.org/10.1016/S0141-1187(02)00021-4Garcia, E., Correcher, A., Quiles, E., Morant, F., 2016. Recursos y sistemas energéticos renovables de entorno marino y sus requerimientos de control. Revista Iberoamericana de Automática e Informática industrial 13, 141-161. https://doi.org/10.1016/j.riai.2016.03.002Garrido, A.J., Garrido, I., Alberdi, M., Amundarain, M., Barambones, O., Romero, J.A., 2013. Robust control of oscillating water column (OWC) devices: power generation improvement. Proceedings of the OCEANS-San Diego, 1-4.Garrido, I., Garrido, A.J., Alberdi, M., Amundarain, M., Barambones, O., 2013. Performance of an ocean energy conversion system with DFIG sensorless control. Mathematical Problems in Engineering 2013. https://doi.org/10.1155/2013/260514Garrido, I., Garrido, A.J., Sevillano, M.G., Romero, J.A., 2012. Robust sliding mode control for tokamaks. Mathematical Problems in Engineering 2012. https://doi.org/10.1155/2012/341405Garrido, A.J., Garrido, I., Amundarain, M., Alberdi, M., De la Sen, M., 2012. Sliding-mode control of wave power generation plants. IEEE Transactions on Industry Applications 48, 2372-2381. https://doi.org/10.1109/TIA.2012.2227096Garrido, A.J., Otaola, E., Garrido, I., Lekube, J., Maseda, F.J., Liria, P., Mader, J., 2015. Mathematical modeling of oscillating water columns wave-structure interaction in ocean energy plants. Mathematical Problems in Engineering 2015. https://doi.org/10.1155/2015/727982Lekube, J., Garrido, A.J., Garrido, I., 2017. Rotational speed optimization in oscillating water column wave power plants based on maximum power point tracking. IEEE Transactions on Automation Science and Engineering 14, 681-691. https://doi.org/10.1109/TASE.2016.2596579Le Roux, J.P., 2008. An extension of the Airy theory for linear waves into shallow water. Coastal Engineering 55, 295-301. https://doi.org/10.1016/j.coastaleng.2007.11.003López, A., Somolinos, J.A., Nú-ez, L.R., 2014. Modelado energético de convertidores primarios para el aprovechamiento de las energías renovables marinas. Revista Iberoamericana de Automática e Informática Industrial 11, 224-235. https://doi.org/10.1016/j.riai.2014.02.005Marei, M.I., Mokhtar, M., El-Sattar, A.A., 2015. MPPT strategy based on speed control for ASW-based wave energy conversion system. Renewable Energy 83, 305-317. https://doi.org/10.1016/j.renene.2015.04.039Murakami, T., Imai, Y., Nagata, S., Takao, M., Setoguchi, T., 2016. Experimental research on primary and secondary conversion efficiencies in an oscillating water column-type wave energy converter. Sustainability 8, 756-766. https://doi.org/10.3390/su8080756Murari, A.L.L.F., Sguarezi Filho, A.J., Torrico Altuna, J.A., Jacomini, R.V., 2016. Una introducción al ajuste de parámetros de controladores PI utilizados en el control del generador de inducción con rotor bobinado. Revista Iberoamericana de Automática e Informatica Industrial 13, 15-21. https://doi.org/10.1016/j.riai.2015.11.001M'zoughi, F., Bouallègue, S., Ayadi, M., 2015. Modeling and SIL Simulation of an oscillating water column for ocean energy conversion. International Renewable Energy Congress (IREC). https://doi.org/10.1109/IREC.2015.7110880Rusu, E., Onea, F., 2016. Estimation of the wave energy conversion efficiency in the Atlantic Ocean close to the European islands. Renewable Energy 85, 687-703. https://doi.org/10.1016/j.renene.2015.07.042Rusu, E., Onea, F., 2015. Assessment of the performances of various wave energy converters along the European continental coasts. Energy 82, 889-904. https://doi.org/10.1016/j.energy.2015.01.099Sameti, M., Farahi, E., 2014. Output power for an oscillating water column wave energy conversion device. Ocean and Environmental Fluid Research 1, 27-34.Sevillano, M.G., Garrido, I., Garrido, A.J., 2011. Control-oriented automatic system for transport analysis (ASTRA)-Matlab integration for Tokamaks. Energy 36, 2812-2819. https://doi.org/10.1016/j.energy.2011.02.022Torre-Enciso, Y., Marqués, J., López de Aguileta, L.I., 2010. Mutriku. Lessons learnt. 3rd International Conference on Ocean Energy.Uihlein, A., Magagna, D., 2016. Wave and tidal current energy - A review of the current state of research beyond technology. Renewable and Sustainable Energy Reviews 58, 1070-1081. https://doi.org/10.1016/j.rser.2015.12.284Veigas, M., López, M., Romillo, P., Carballo, R., Castro, A., Iglesias, G., 2015. A proposed wave farm on the Galician coast. Energy Conversion and Management 99, 102-111. https://doi.org/10.1016/j.enconman.2015.04.03

Flow Control in Wells Turbines For Harnessing Maximum Wave Power

Oceans, and particularly waves, offer a huge potential for energy harnessing all over the world. Nevertheless, the performance of current energy converters does not yet allow us to use the wave energy efficiently. However, new control techniques can improve the efficiency of energy converters. In this sense, the plant sensors play a key role within the control scheme, as necessary tools for parameter measuring and monitoring that are then used as control input variables to the feedback loop. Therefore, the aim of this work is to manage the rotational speed control loop in order to optimize the output power. With the help of outward looking sensors, a Maximum Power Point Tracking (MPPT) technique is employed to maximize the system efficiency. Then, the control decisions are based on the pressure drop measured by pressure sensors located along the turbine. A complete wave-to-wire model is developed so as to validate the performance of the proposed control method. For this purpose, a novel sensor-based flow controller is implemented based on the different measured signals. Thus, the performance of the proposed controller has been analyzed and compared with a case of uncontrolled plant. The simulations demonstrate that the flow control-based MPPT strategy is able to increase the output power, and they confirm both the viability and goodness.This work was supported in part by the University of the Basque Country (UPV/EHU) through Project PPG17/33, by the MINECO through the Research Project DPI2015-70075-R (MINECO/FEDER, EU) and by the Basque Government through Elkartek. The authors would like to thank the collaboration of the Basque Energy Agency (EVE) through Agreement UPV/EHUEVE23/6/2011, the Spanish National Fusion Laboratory (EURATOM-CIEMAT) through Agreement UPV/EHUCIEMAT08/190 and EUSKAMPUS - Campus of International Excellence. They would also like to thank Yago Torre-Enciso and Olatz Ajuria from EVE for their collaboration and help. The authors would also like to thank the anonymous reviewers that have helped to improve the initial version of the manuscript

A real time sliding mode control for a wave energy converter based on a wells turbine

Due to the nonlinear dynamics and uncertainties usually present in wave energy conversion systems, the efficiency of these devices can be enhanced employing a robust control algorithms. Wave energy converters are constructed using electric generators of variable velocity, like double feed induction generator (DFIG) since they may improve the system efficiency to generate power when compared to fixed speed generators. The main reason is that this generators with variable speed may adapt the speed of the turbine in order to maintain the optimal flow coefficient values which improves the efficiency of the Wells turbine. However, a suitable speed controller is required in these systems first in order to avoid the stalling phenomenon and second in order to track the optimal turbine reference velocity that optimizes the power generation. In this paper a real time sliding mode control scheme for wave energy conversion systems that incorporate a Wells turbine and a DFIG is proposed. The Lyapunov stability theory is used to analyse the stability of this control scheme under parameter uncertainties and system disturbances. Next, the proposed control scheme is validated first by means of some simulation examples using the Matlab/Simulink software and second using a real-time experimental platform based on a dSPACE DS1103 control board.The authors are very grateful to the UPV/EHU by its support through the projects PPGA18/04 and UFI11/07 and to the Basque Government by its support through the project ELKARTEK KK-2017/00033. The authors also would like to thank the anonymous reviewers who have helped to improve the initial version of this paper

Performance of a U-OWC – PTO coupled system using different control laws

The problem of maximizing the performances of a U-OWC wave energy converter in a variet of environmental conditions is investigated. Specifically, the paper compares two control strategies coupling the U-OWC – PTO system. Two approaches are discussed. The first relies on the tracking of the Maximum Power Points of the system, and empirical relations between the optimal PTO performances and the energy content of the incident sea state are estimated. Secondly, an analytical formulation linking the operational conditions of the turbine to the instantaneous air pressure inside the pneumatic chamber is identified. Results show that a sea state-based controller works better than a wave-to wave fast-acting control

Adaptive Sliding Mode Control for a Double Fed Induction Generator Used in an Oscillating Water Column System

Wave power conversion systems are nonlinear dynamical systems that must endure strong uncertainties. Efficiency is a key issue for these systems, and the application of robust control algorithms can improve it considerably. Wave power generation plants are typically built using variable speed generators, such as the doubly fed induction generator (DFIG). These generators, compared with fixed speed generators, are very versatile since the turbine speed may be adjusted to improve the efficiency of the whole system. Nevertheless, a suitable speed controller is required for these systems, which must be able to avoid the stalling phenomenon and track the optimal reference for the turbine. This paper proposes a sliding mode control scheme aimed at oscillating water column (OWC) generation plants using Wells turbines and DFIGs. The contributions of the paper are (1) an adaptive sliding mode control scheme that does not require calculating the bounds of the system uncertainties, (2) a Lyapunov analysis of stability for the control algorithm against system uncertainties and disturbances, and (3) a validation of the proposed control scheme through several simulation examples with the Matlab/Simulink suite. The performance results, obtained by means of simulations, for a wave power generation plant (1) evidence that this control scheme improves the power generation of the system and (2) prove that this control scheme is robust in the presence of disturbances.This research was partially funded by the Basque Government through the project ETORTEK KK-2017/00033 and by the UPV/EHU through the project PPGA18/04

Rotational Speed Control Using ANN-Based MPPT for OWC Based on Surface Elevation Measurements

This paper presents an ANN-based rotational speed control to avoid the stalling behavior in Oscillating Water Columns composed of a Doubly Fed Induction Generator driven by a Wells turbine. This control strategy uses rotational speed reference provided by an ANN-based Maximum Power Point Tracking. The ANN-based MPPT predicts the optimal rotational speed reference from wave amplitude and period. The neural network has been trained and uses wave surface elevation measurements gathered by an acoustic Doppler current profiler. The implemented ANN-based rotational speed control has been tested with two different wave conditions and results prove the effectiveness of avoiding the stall effect which improved the power generation.This work was supported in part by the Basque Government, through project IT1207-19 and by the MCIU/MINECO through RTI2018-094902-B-C21/RTI2018-094902-B-C22 (MCIU/AEI/FEDER, UE)

Double Fed Induction Generator Control Design Based on a Fuzzy Logic Controller for an Oscillating Water Column System

Oscillating water column (OWC) systems are water power generation plants that transform wave kinetic energy into electrical energy by a surrounded air column in a chamber that changes its pressure through the waves motion. The chamber pressure output spins a Wells turbine that is linked to a doubly fed induction generator (DFIG), flexible devices that adjust the turbine speed to increase the efficiency. However, there are different nonlinearities associated with these systems such as weather conditions, uncertainties, and turbine stalling phenomenon. In this research, a fuzzy logic controller (FLC) combined with an airflow reference generator (ARG) was designed and validated in a simulation environment to display the efficiency enhancement of an OWC system by the regulation of the turbine speed. Results show that the proposed framework not only increased the system output power, but the stalling is also avoided under different pressure profiles.This research was funded by the Basque Government, through the project EKOHEGAZ (ELKARTEK KK-2021/00092), Diputación Foral de Álava (DFA) through the project CONAVANTER, and to the UPV/EHU through the project GIU20/063