Pneumatic Power Regulation by Wave Forecasting and Real-Time Relief Valve Control for an OWC

The shore mounted “Pico” OWC has a relief valve mounted in parallel to the turbine which connects the chamber to the atmosphere. The aperture of this valve is adjustable and can be used to regulate the pneumatic power exposed to the turbine. Here we develop an algorithm to actively control the relief valve aperture so that the peak pneumatic power of each wave cycle approaches but does not breach the turbine stall threshold, thus providing the maximum pneumatic power possible without the turbine stalling. The relief valve aperture is slow to adjust so the hydrodynamic and pneumatic behaviour is forecasted to allow enough time to achieve the correct aperture before the wave reaches the chamber. The chamber hydrodynamics are forecasted using a neural network that considers hydrodynamic measurements made 60 meters up wave and other operational, environmental and preceding wave, parameters. Turbine stalls were identified approximately by the gradient in turbine vibration and the angular velocity dependent pneumatic power threshold for turbine stall is found empirically. The relationship between the forecasted chamber hydrodynamics, relief valve aperture and the resultant pneumatic behaviour, is also found empirically and this is used to select the relief valve aperture that the control algorithm targets.