General Device Description
The AquaHarmonics (AH) wave energy converter (WEC) concept is a point absorber style WEC comprised of an axisymmetric floating hull with a “winch style” interior Power Take Off (PTO) which generates electrical power by reacting against the seafloor via an anchor connected to the free end of PTO mooring line.
The PTO operates in a tension only condition with a large operational stroke and an impedance control scheme for matching the WEC’s natural frequency with the frequency of the waves within the deployed wave environment. This particular device topology yields an energy dense device that maximizes electrical power output as compared with a passively operating device of a similar size.
The AquaHarmonics WEC PTO module is comprised of the main PTO drum, which is fixed to a shaft and sealed from the environment with rotary seal and supported by bearings in a sealed compartment. The compartment is integrated with a support structure around a pneumatic return spring assembly used to provide the restoring force, or pre-tension, during operation. The module is bolted and sealed at its base flange into the lower portion of the device hull. The pneumatic return spring connects to the spring return belt, which passes over a return drum and terminates at the spring return shaft. The spring return shaft is connected to the main PTO drum via a synchronous belt. Connected in parallel with the spring return system to the PTO drum is a second synchronous belt, which connects the main PTO drum shaft to the PTO generator which is used to generate electrical power.
The main PTO mooring belt terminates at the PTO drum on one end and is connected at the opposite end to a guided sliding termination assembly (GSTA) which allows the belt to pass tensile loads through the guided sliding termination assembly to an electrical-optical-mechanical (EOM) cable which is connected to the GSTA via a pass thru type connection. The EOM cable passes through and is constrained laterally by a fairlead integrated into the lower spar section, which then connects at standards dive depths to a buoyant EOM connection assembly. This assembly is connected to a second EOM cable that finally connects to the device mooring anchor on the sea floor. A second pass thru type termination allows the electrical and optical part of the EOM cable to continue to a subsea junction box
Mechanical Power Generation
The device is free-floating in 6 degrees of freedom and generates power primarily in the heave DOF, with some power generated in the surge & sway components of device motion. The device generates power on the rise of the wave by reacting against the seafloor via high tensile forces in the main PTO mooring line between the device and the mooring anchor. These tensile forces rotate the PTO drum in its bearings and produces high torque, low RPM power at the PTO shaft. This is then stepped up via the synchronous gear drive to the generator. In parallel to the generator, energy is stored in the pneumatic spring/pre-load system. On the fall of the wave the PTO operates in a “motoring” condition by a combination of releasing energy stored in the pneumatic return spring system and operating the generator as a motor in the opposite direction which reels in the PTO mooring line. The power production cycle is then restarted.
Electrical Power Generation
The PTO couples the electric motor/generator to incident wave forces, generating electrical power at the frequencies of the seastate. An onboard energy storage system provides instantaneous bidirectional power capacity and accumulates the average energy production. The WEC provides continuous and constant power and can support many types of loads, including (micro-)grid or islanded AC loads, low voltage DC for industrial, UAV, IT equipment, or high voltage DC loads found in industrial processses.