The optimisation of a wave energy converter hydraulic power take-off for sea states of varying wave amplitude, direction and frequency is a significant problem. Sub-optimal configuration can result in very inefficient energy conversion, so understanding the design trade-offs is key to the success of the technology. This work focuses on a generic point absorber type wave energy converter. Previous work by the authors has considered the optimisation of this device for regular waves to gain an understanding of the fundamental issues. This work extends the analysis to the more realistic case of irregular waves. Simulations are performed using an irregular wave input to predict how the power take-off will operate in real sea conditions. Work is also presented on a motor speed control strategy to maintain the maximum flow of electrical power to the grid, assuming the use of a doubly fed induction generator. Finally, the sizing of key components in the power take-off is considered in an attempt to maximise power take-off efficiency and generated power. Using the Pierson-Moskowitz spectrum, the random phase method was applied to create the wave elevation and excitation force profile to represent an irregular wave. Using this input, the behaviour of a point absorber WEC with a hydraulic PTO was examined. As expected, no pseudo steady state is reached and the behaviour of the device is very changeable. Induced body stall occurs but the period of stall is varying. The pressure and volume of the accumulators to continuously vary in an attempt to maintain a relatively constant motor speed. In terms of tuning, a linear trend between optimum PTO damping and peak wave period is observed but values differ from those for a regular wave input. The power captured by the hydraulic PTO is low in comparison to regular waves of the same wave height. Consideration was given to how the mechanical power generated by the PTO would be transmitted into electrical energy. It was assumed that a DFIG would be used, as in wind turbines. It was assumed that power is transmitted if the speed of the hydraulic motor is within the range of ±30% of the generator synchronous speed. A feedback controller is therefore needed to maintain the motor speed within these limits by altering the fraction of motor displacement. The generator load must also be altered to maintain optimum PTO damping and ensure maximum power capture.


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    Titel :

    Optimisation and control of a hydraulic power take-off unit for a wave energy converter in irregular waves


    Beteiligte:
    Cargo, C.J. (Autor:in) / Hillis, A.J. (Autor:in) / Plummer, A.R. (Autor:in)


    Erscheinungsdatum :

    2014


    Format / Umfang :

    18 Seiten, Bilder, Tabellen, 22 Quellen




    Medientyp :

    Aufsatz (Zeitschrift)


    Format :

    Print


    Sprache :

    Englisch