Aspects of control and system design for hydrokinetic turbines

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Hydrokinetic turbines take energy from flowing water sources, such as rivers, tidal flows, or effluent from industrial processes, and convert this into electricity. As such these turbines are environmentally friendly, involve a renewable energy source and have essentially zero carbon footprint. Thus development of these systems can be considered of very high value to Canada and the world. Moreover, the economic benefit of implementing a hydrokinetic turbine in an existing flow can be significant. A major issue in these type of turbine systems is maintenance of a consistent supply of generated electricity which maximizes the power extracted from the flow source. In order to achieve precisely these results, an optimizing control is needed. The proposed work involves the development and refinement of control techniques for hydrokinetic turbines involving a vertical axis squirrel cage design where the turbine spins perpendicular to the flow and the blades are essentially wing-like surfaces. Advantages of this design are independence of flow direction and ease of start-up. The main control challenges involve maintaining consistent behaviour and performance despite changes in the driving flow (such as in reversing tidal flows), and dealing with varying torque in the blades due to their rotation into and out of the flow. It is proposed to use a type of control that varies according to the external flow conditions (as inferred by mathematical processing) and at the same time limits the torque pulsation. This can be realized with advanced formulations using state of the art optimizing goals and solution techniques, and also using adaptation of the system to the varying factors. The work complements existing results in the wind turbine industry, but has its unique challenges including measuring of the water speed (due to fouling, extreme weather, and debris build-up), much larger forces and torques (due to the energy density of water as compared to air) and limited application volumes (in that rivers and channels are generally small). The results of this project will be a major step forward towards the mainstream muse of hydrokinetic turbines for electrical power generation.