Adaptive power tracking control of hydrokinetic energy conversion systems

Khan, Mohammad Jahangir Alam (2010) Adaptive power tracking control of hydrokinetic energy conversion systems. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Hydrokinetic energy conversion systems (HECS) are electromechanical devices that operate in free-stream water channels in a manner similar to wind turbines. The fundamental process of fluid-mechanic energy conversion using a hydrokinetic turbine is manifested through a nonlinear performance characteristics. The problem of maximum power tracking evolves around this nonlinearity and the underlying control objective is to regulate the turbine's operating conditions such that system efficiency is in the neighborhood of the optimum point. Through this research, it has been identified that a power tracking method that is independent of the turbine's characteristics, which can be implemented without using underwater/mechanical sensors would be of significant interest to the emerging hydrokinetic energy technologies. Further to a comparative analysis of various traditional wind turbine control techniques, an adaptive tracking approach termed as 'extremum seeking control' (ESC) approach has been adopted. Detailed mathematical formulations pertaining to this novel control solution has been provided and relevant parameter tuning and implementation procedures are presented. -- In order to provide sufficient insight into the design, operation, and control aspects of a real-life hydrokinetic system, a small-scale vertical axis turbine has been developed in this work. This turbine employs a multi-pole permanent magnet alternator for electromechanical energy conversion. A ac-dc-ac power electronic stage interfaces the asynchronous output of the generator to the utility grid through a single-phase connection. Even though a stand-alone test setup is possible, the grid-tied option has been pursued for ease of implementation as well as to explore broader areas of deployment. In addition to modeling and validating all the subsystems in the laboratory, the turbine rotor system has been tested under controlled environment in a tow tank. Associated numerical models have been validated extensively prior to their use in the power tracking control study. In addition, simulation schemes for hydrological flow fields and rotor fluid-dynamic characteristics have been developed as aiding tools to this research. -- The extremum seeking controller parameter tuning and implementation method developed in this work, has been found to be capable of successfully regulating the system operating condition at the optimum point. This method requires minimal information on the hydrokinetic device's operational characteristics and can be potentially deployed in wide range of devices. Further work within this research track includes, implementation of the ESC method in mid to large-sized hydrokinetic systems and development of multi-objective control solutions. As a continuation of this research, active efforts are currently being made such that the true potential of the extremum seeking control and other advanced power tracking techniques can be realized in near-future.

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