Sizing, optimization and control of a hydraulic converter for wave energy devices applications

In the last few years, following the increased sensitivity of public opinion and public administrations to clean energy issues, the use of renewable energy sources has strongly increased. Among these, wave motion energy is still not widespread with respect to solar and wind sources, yet there are many active studies focused on the development of the technology. The aim of this work is to analyze the operation of the ISWEC device, which exploits the gyroscopic effect of flywheels enclosed within a hull in order to generate electric power. The heart of the device is the Power Take-Off system (PTO), which converts the mechanical energy produced by wave motion into electrical energy. The hydraulic PTO is therefore deeply analyzed in this work, and two control strategies are compared. The first method, called “Declutching Control”, exploits a valve in order to allow a pump to accelerate. The second control strategy is based on the use of multiple pumps which are connected in series with a variable displacement, thus canceling the need for a valve. This work also analyzes the sensitivity to the control parameters, in order to evaluate how the phase shift of the flywheels can cause a decrease in the electrical energy that can be produced. Finally, a preliminary sizing of the generator and inverter electrical connection to the grid is performed.