Validating a Wave-to-Wire Model for a Wave Energy Converter—Part II: The Electrical System

The incorporation of the full dynamics of the different conversion stages of wave energy converters (WECs), from ocean waves to the electricity grid, is essential for a realistic evaluation of the power flow in the drive train. WECs with different power take-off (PTO) systems, including diverse transmission mechanisms, have been developed in recent decades. However, all the different PTO systems for electricity-producing WECs, regardless of any intermediate transmission mechanism, include an electric generator, linear or rotational. Therefore, accurately modelling the dynamics of electric generators is crucial for all wave-to-wire (W2W) models. This paper presents the models for three popular rotational electric generators (squirrel cage induction machine, permanent magnet synchronous generator and doubly-fed induction generator) and a back-to-back (B2B) power converter and validates such models against experimental data generated using three real electric machines. The input signals for the validation of the mathematical models are designed so that the whole operation range of the electrical generators is covered, including input signals generated using the W2W model that mimic the behaviour of different hydraulic PTO systems. Results demonstrate the effectiveness of the models in accurately reproducing the characteristics of the three electrical machines, including power losses in the different machines and the B2B converter.This material is based on works supported by the Science Foundation Ireland under Grant No. 13/IA/1886