Control Models for an Oscillating Water Column Device

Abstract: The primary focus of this manuscript is to advance wave energy converter (WEC) devices. Having this aim in mind, a power take off (PTO) system with novel rotational speed control strategies will be presented. The chosen take off system is an oscillating water column converter (OWC), a device that uses a Wells air turbine as the primary energy converter. The secondary of the device is a generator that has been chosen to be a Doubly Fed Induction Generator with novel control strategies. This set up aims to improve the performance by increasing the efficiency, as a result of an increment in the power captured, and providing quality power to the grid. The proposed control scheme is due to be implemented on the NEREIDA MOWC demonstration project, a breakwater wave plant located in the Basque location of Mutriku, using Wells turbines and induction generators. The difficulty lies in finding an efficient variable control speed operation able to smoothly convert the peak-to-average power ratio, even more when this ratio presents a broad bandwidth that relates to the diverse input wave periods. By controlling the slip of the generator, it is possible to determine the behaviour of the whole turbo-generator set so as to maximize the output power. At the same time, the Wells turbine contributes to the robustness of the system because it requires no additional parts to produce unidirectional rotation from the reversing oscillating flow, but its performance is hindered by the stalling behaviour. However, this stalling phenomenon is s non-uniform response that may be avoided by controlling the rotational speed. Therefore, the presented novel control and switching avoidance techniques, will greatly contribute towards an improved PTO for the wave energy sector.