Integrated Power Take-Off and Virtual Oscillator System for the VIVACE Converter: V_CK System Identification

The first step in the development of an integrated system encompassing Power Take-Off (PTO) with virtual Mass-Damping-Spring (V_MCK) for the VIVACE Converter (Vortex Induced Vibration for Aquatic Clean Energy) is achieved. VIVACE converts hydrokinetic energy of ocean/river currents to mechanical energy using Vortex Induced Vibrations (VIV). Subsequently, its PTO converts the mechanical energy to electricity. The objective integrated system acts as V_MCK to support the hydro-mechanical component of VIVACE. The second function of the system is to act as PTO to implement the electro-mechanical component converting the harnessed mechanical energy to electrical energy without suppressing the hydro-mechanical energy harnessing mechanism of VIV. Vortex Induced Vibrations (VIV) are motions induced on long elastic bodies with bluff cross-section placed with their long axis perpendicular to a fluid flow due to periodic irregularities in this fluid-structure interaction phenomenon. In this paper, a single cylinder of VIVACE is considered. Even in this simplest case, the underlying physics of this phenomenon is strongly nonlinear. Special care is needed in designing systems that either support or enhance VIV or harvest the energy of VIV oscillations. In the first physical model of VIVACE, a mass-damper-spring arrangement was employed in the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan to transmit mechanically the power to an electrical generator, which converted it to useful electrical power. A Virtual mass-damping-spring (V_MCK) mechanism is intended to substitute the existing physical elements in the MRELab consisting of an electric motor driven by a power electronic converter allowing for programmable mass, stiffness and damping values. The integrated V_MCK system enables improved control of the mechanism originally generating and supporting VIV as well as improved power take-off efficiency and capability. The V_MCK system employs advanced switching control of the power transfer process so that VIV for a given damping is not affected. The first step taken in this paper towards development of the integrated system consists of the identification of the V_CK system. The mechanical transmission system consists of a belt and two pulleys. The cylinder in VIV is attached to one side of the belt causing it to oscillate and in turn drive the pulleys.