Development of a Port-Hamiltonian Model for use in oscillating water column control scheme investigations.

With global energy demand estimated to rise considerably and global warming accepted by the majority of scientists, the pressure to reduce fossil fuel usage is increasing. To this end, the UK government has set a target of generating 50% of electricity from renewable energy sources by 2050. It can therefore be deduced that decreasing the cost of renewable energy by increasing the energy capture is critical. Oscillating Water Columns (OWCs) employing bidirectional turbines coupled with generators can be used to capture energy from oceanic waves and convert it to electrical energy. This thesis includes a study to quantify the potential power smoothing that can be achieved from a wave farm of ideal OWC devices and from auxiliary hardware such as flywheel energy storage systems. Also detailed are the upgrades to the OWC test facility at Cranfield University, including the world-first capability to simulate polychromatic waves. This test facility has been employed to validate turbine characteristics derived from Computational Fluid Dynamic (CFD) numerical results. This thesis contains a literature review of the existing control strategies for OWCs that concludes that the optimization of power capture from individual components in the energy chain forces system-level compromises. This conclusion drove the development of an unique energy-based model of the complete wave-to-wire system utilizing port-Hamiltonian mechanics which mandated two modifications to the port-Hamiltonian framework. The first modification to the port-Hamiltonian framework resulted in a new generalized means of modeling systems where the potential energy is dependent on the momentum variables. The second modification expands the port-Hamiltonian framework to allow the modeling of ow source systems in addition to effort source systems. The port-Hamiltonian wave-to-wire OWC model enables the future development of a control approach that optimizes power capture at a system level. As a first step to achieving this goal an Injection Damping Assignment (IDA) Passivity Based Control (PBC) strategy was successfully applied to an OWC system and an energy storage flywheel system. These strategies pave the way for future developments utilizing optimization techniques, such as the use of cost functions to identify the peak efficiency operating condition.