INGINE Inc. developed its own wave energy converter (WEC) named INWAVE and has currently installed three prototype modules in Jeju Island, Korea. This device is an on-shore-type WEC that consists of a buoy, pulleys fixed to the sea-floor and a power take off module (PTO). Three ropes are moored tightly on the bottom of the buoy and connected to the PTO via the pulleys, which are moving back and forth according to the motion of the buoy. Since the device can harness wave energy from all six degrees of movement of the buoy, it is possible to extract energy efficiently even under low energy density conditions provided in the coastal areas. In the PTO module, the ratchet gears convert the reciprocating movement of the rope drum into a uni-directional rotation and determine the transmission of power from the relation of the angular velocities between the rope drum and the generator. In this process, the discontinuity of the power transmission occurs and causes the modeling divergence. Therefore, we introduce the concept of the virtual torsion spring in order to prevent the impact error in the ratchet gear module, thereby completing the PTO modeling. In this paper, we deal with dynamic analysis in the time domain, based on Newtonian mechanics and linear wave theory. We derive the combined dynamics of the buoy and PTO modules via geometric relation between the buoy and mooring ropes, then suggest the ratchet gear mechanism with the virtual torsion spring element to reduce the dynamic errors during the phase transitions. Time domain simulation is carried out under irregular waves that reflect the actual wave states of the installation area, and we evaluate the theoretical performance using the capture width ratio.

This paper presents a novel method of estimating ocean waves by measuring current outputs from the Archimedes Wave Swing (A WS) wave energy converter (WEC). The wave period and height are crucial information to maximize the power output from the A WS. However, since the A WS is installed on the seabed, additional sensors and buoys are required to obtain the ocean wave information. The extended Kalman filter (EKF) is applied to obtain the states of the ocean wave by measuring the generator current in the a -f3 domain. As the EKF requires the Jacobian matrix of the system dynamic equations for the system matrix, simplified hydrodynamics of the floater including the Froude-Krylov excitation force and the a -f3 domain voltage equation of the generator is derived to develop the mathematical model of the A WS. In order to verify the performance of the estimator, a numerical simulation is performed and presented and it shows great agreement with the actual motion.

This paper proposes a new method of estimating incident wave state. This method measures output currents from point absorber type wave energy converter and estimates state of the incident wave such as wave amplitude and wave period. The wave period and height are significant information to maximize the output power or the energy conversion efficiency. However, additional sensors are deployed to measure those information and it always involves cost and maintanance issues. This can be estimated using extended Kalman filter (EKF) by measuring generator output currents in α − β domain which does not require any other equipments. The simplified dynamic equation including the point absorber floater and linear generator inside the floater are derived since the Jacobian matrix of the system is required to perform the EKF algorithm. Finally a numerical example is provided to shoe the effectiveness of the proposed estimator.