Abstract
Wave energy has been identified as an abundant renewable energy resource that could complement other more intermittent renewables like solar and wind power Wave energy converters are designed to harness this resource but must overcome technical challenges to transform the low-speed, high-force wave phenomenon into a usable form for electricity generation or other uses. Within the WEC, the power take-off (PTO) is the component responsible for that transformation. For a PTO to be effective, it must operate reliably and efficiently across a wide range of sea states and be able to survive extreme events.
A PTO concept based on a hypertwisted loop passing through a permanent magnet rotor has been explored by the research team previously. This traditional hypertwist rotor (THR) topology can be integrated with a generator to form a PTO, but the layout requires a number of compromises, including:
- The loop must pass through the center of the generator, limiting the types of generators.
- Without a central shaft, the rotor must be supported by bearings at the outer radius, increasing the cost and losses in the bearings.
To address these shortcomings, the group has devised a double loop hypertwist rotor (DLHR), which consists of a common shaft which supports two endplates. Each endplate engages with a unique loop that twists and untwists in an equivalent manner to the THR. This layout allows the configuration to be agnostic to whatever interfaces are required at the center of the shaft to interface with the rotor. This design freedom opens up a numerous options for generators, easing the eventual integration with a WEC.
The shift from the THR to the DLHR does come with one significant difference in the loading of the system. In the THR, there rotor is not subject to significant axial loading as the loop passes through the rotor. In the DLHR, each endplate is subject to axial loading from the tension of the loop, and must be accounted for to maintain structural integrity.
The operation of the DLHR has been verified experimentally as comparable to the THR. Additionally, scaling analysis has been performed to identify the key factors to consider when scaling up the PTO concept.