Comparison of inner and outer rotor flux reversal machines using an efficiency-based metric for wave energy converters

Wave Energy Converters operate at low speeds and so require the power take off systems to react large torques to generate meaningful power. For a direct drive power train, this naturally leads to generators with a large active radius. For mass reduction, the machines will be hollow, and all the active material will form a rim. This configuration is a long way from conventional shaft mounted rotors which can be used for more moderate sized machines.This paper compares inner and outer rotor flux reversal machines developed for direct drive wave energy converters. The machines are modelled using validated FEA models and optimized using a bespoke algorithm with an objective function focusing on efficiency. As the machine topology has the permanent magnets and the coils on the stator, having an external rotor variant is an easy way of maximizing the active radius for a fixed outer dimension.