Thesis

Modelling and optimisation of the dynamic performance of a reversible solid oxide fuel cell system for the grid intergration of renewables

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Awarding institution
  • University of Strathclyde
Date of award
  • 2013
Thesis identifier
  • T13374
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Abstract
  • Along with the increasing concerns on environmental issues, the penetration level of renewable energy is growing fast, e.g. wind, tide and solar energy. However the impact of renewable energy on the conventional power grid is increasing due to their intermittent characteristic of power supply. As a result conventional approaches of energy storage need to be improved or reconsidered. One way to increase the value of intermittent renewable energy is to use high efficiency reversible solid oxide fuel cell (RSOFC) system as an energy storage device. A development of solid oxide fuel cell is being carried out at University of St. Andrews with focusses mainly on material selection and coating technology, etc. This RSOFC system aims to provide effective and flexible power delivery through advances in materials and fuel processing technology. The University of Strathclyde is also a partner of this collaborative research, and this thesis offers comprehensive modelling of this RSOFC system and optimisations proven by simulations to the original design proposed by the Fuel Cell group at University of St. Andrews. The utilization of RSOFC systems within AC power networks requires power electronic inverters with appropriate controls to convert variable DC power into AC power. However it is commonly recognized that power electronic inverters have major impacts on the dynamic behaviour of the fuel cell system, and these effects are highly dependent on the inverter control algorithms. To investigate the performance and stability of the RSOFC system as an energy storage device within the AC power network this thesis also presents the modelling of the integrated system, along with three competing inverter control algorithms developed at the University of Strathclyde. Conclusions include the fidelity of the RSOFC concept and the proposed design improvements proven by simulations. An overheating issue is discovered and solved by an innovative application of a phase-change heat store. This heat store is critical in stabilizing the fuel cell system temperature and increasing the cycle efficiency. This thesis demonstrates that the direct deployment of certain control algorithms may not be appropriate under certain grid scenarios due to excess fuel cell current ripples. Simulations show that appropriate DC bus capacitors effectively reduce the ratio of fuel cell current ripple although potential system cost is implied. Finally it is found that the state of charge (SOC) can in fact have a more negative impact on system efficiency and safety operation than current ripple. The nominal operation range of state of charge is suggested to be constrained according to the ratings of the fuel cell system.
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  • Strathclyde theses - ask staff. Thesis no. : T13374
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Date Created
  • 2013
Former identifier
  • 989132

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