Sliding-Mode Control of Wave Power Generation Plants

The worldwide demand for energy requires alternatives to fossil fuels and nuclear fission, so renewable resources, particularly ocean energy, are called to play a relevant role in a near future. In particular, the oscillating water column (OWC) is one of the most promising devices to harness energy from the sea, as it is the case of the Nereida project plant, located in the Basque coast of Mutriku. This kind of devices consists of a particular type of turbine and a doubly fed induction generator. The turbogenerator module is usually controlled using a traditional proportional-integral (PI)-based vector control scheme, which requires an accurate knowledge of the system parameters and lacks of robustness, limiting, in some cases, the power extraction. To avoid these drawbacks, a novel sliding-mode-control-based vector control scheme for the OWC plant is presented in this paper. This variable-structure control is intrinsically robust under parameter uncertainties, which always appear in real systems, and presents a convenient disturbance rejection. The stability of the proposed controller is analyzed using the Lyapunov theory. The performance of the control scheme presented is proved by comparing it to the traditional PI-based vector control scheme in a series of representative maximum power generation case studies. Both numerical simulations and experimental results show that the proposed solution provides high-performance dynamic characteristics, improving the power extraction in spite of parameter uncertainties and system disturbances.