Advanced Rotational Speed Control in Ocean Energy Doubly Fed Induction Generators

This article covers research into rotational speed control for oscillating water column converters (OWC). The primary focus is the improvement of the Wells turbine performance by controlling its rotational speed. In this sense, the proposed control scheme has been implemented based on the NEREIDA MOWC demonstration project, a breakwater wave plant located in the Basque location of Mutriku, using Wells turbines and induction generators, so as to advance wave energy converter (WEC) devices. The variable control speed operation involves the use of the Doubly-fed Induction Generator (DFIG) as the main element of the WEC system. By controlling the slip of the generator it is possible to determine the speed of the turbo-generator set. The primary aim of the speed control is to maximize the efficiency of the Wells turbine due to its non-uniform response in the performance, since it mainly depends on the rotational speed. Furthermore, by means of the speed control it is possible to avoid the stalling phenomenon, and therefore the efficiency drop in Wells turbines.