On Control of a Pitching and Surging Wave Energy Converter

The paper presents a model of a pitching and surging wave-energy converter, investigates the tuning problem in regular seas, and presents a practical tuning technique for time-domain studies in irregular seas. The proposed tuning technique is evaluated on a specific device with defined features in irregular seas where the capabilities of the proposed control approach are assessed. Realistic performance analysis of the proposed technique is performed in time-domain studies where the proposed adaptive technique and some other passive and adaptive tuning methods are used. The passive tuning methods are based on tuning the device's natural frequency to peak and energy frequencies and use fixed power takeoff settings. The proposed adaptive tuning approach employs sliding Discrete Fourier Transform for wave properties estimation. The approach then utilizes the estimated wave properties in optimizing the power capture of a pitching and surging device by adjusting the power takeoff system parameters. The paper also presents details of a comparative study on power capture performances of a pitching-and-surging device with that of a heaving device in the same sea states. The practical implications of the results and recommendations are also presented.

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