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European Association for the Development of Renewable Energies, Environment and Power Quality (EA4EPQ)

International Conference on Renewable Energies and Power Quality (ICREPQ’10) Granada (Spain), 23rd to 25th March, 2010

Control of Hydrodynamic Parameters of Wave Energy Point Absorbers using Linear Generators and VSC-based Power Converters Connected to the Grid
Agustín García Santana1,Dan El Montoya Andrade2 and Antonio de la Villa Jaén3
Department of Electrical Engineering AG Ingeniería Phone:+0034 634 821844, e-mail: agustin.garcia@agingenieria.abengoa.com
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Department of Electrical Engineering Venezuela Central University e-mail: danel.montoya@ucv.ve Department of Electrical Engineering E.S.I., Seville University e-mail: adelavilla@us.es extract energy, springs areattached between the alternator and the foundation to pull the alternator downwards in wave troughs. The direct conversion power take-off (PTO) system provides a simple and robust way of increasing the survival possibilities, reduces the maintenance costs and may reduce the cost of electricity produced from wave energy [2]. The electric energy should be properly injected in the grid. This conditionimplies to keep the right wave quality at the connection point. The available primary energy features are pulsing and thus, it is necessary to use WEC systems that incorporate intermediate energy storage, to reduce the oscillations in the injected power. For this purpose, several systems have been used, such as oil or air pressure circuits. One of the most interesting proposals about connecting theelectricity generated by buoy oscillating systems to the power grid, is based on using linear generators and full-scale back-to-back Voltage Source Converters (VSC) jointly [3,4,5]. Linear generators do not require mechanical linkages to convert the buoy oscillating motion into rotative generator motion [6]. Besides, the power converter enables the use of DC Link capacitor as an intermediate stageof storage. It also enables to adapt electric power output for proper grid connection [3,4]. The hydrodynamic characteristics of the WEC system made up of the buoy and the generator moving parts, largely determine the amount of energy extractable from waves. For regular waves, it is possible to calculate the optimal hydrodynamic characteristics that enable to extract the maximum amount of energy,for each type of WEC and for incident wave [7]. Controlling the auxiliary mechanical systems enables to achieve these optimal hydrodynamic conditions. However, these systems entail

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Abstract. The use of linear generators in offshore wave energy plants is one of the most promising technologies for such facilities. The first power converter stage consists of rectifying the electricitygenerated by the linear generator. Lower cost and easy of assembly are the main diode rectifier advantages, but these devices are not able to control the power extracted from waves. The use of power converters allows control over the instantaneous power flow, and in turn enables both power flow directions. This paper focuses on the control of the first power conversion stage using Voltage SourceConverters, in order to modify the characteristics of the hydrodynamic buoy-translator system and thus, optimize the extracted energy from the waves. Simulation results are presented showing the features and advantages of the use of controlled power converters. Key words
Wave energy converters, linear generators, WEC control, renewable energy, modelling.

1. Introduction
Among the emerging electricalpower generation choices from renewable sources of energy, the energy contained in the seas and oceans is one of the most promising. Research and industry have begun considering Wave Energy Converters (WEC) as the next new alternative energy. A diversity of prototypes has been developed during the last decades. Oscillating buoy systems are one of the systems currently in testing stage [1]....