Abstract
Wave power conversion systems are nonlinear dynamical systems that must endure strong uncertainties. Efficiency is a key issue for these systems, and the application of robust control algorithms can improve it considerably. Wave power generation plants are typically built using variable speed generators, such as the doubly fed induction generator (DFIG). These generators, compared with fixed speed generators, are very versatile since the turbine speed may be adjusted to improve the efficiency of the whole system. Nevertheless, a suitable speed controller is required for these systems, which must be able to avoid the stalling phenomenon and track the optimal reference for the turbine. This paper proposes a sliding mode control scheme aimed at oscillating water column (OWC) generation plants using Wells turbines and DFIGs. The contributions of the paper are (1) an adaptive sliding mode control scheme that does not require calculating the bounds of the system uncertainties, (2) a Lyapunov analysis of stability for the control algorithm against system uncertainties and disturbances, and (3) a validation of the proposed control scheme through several simulation examples with the Matlab/Simulink suite. The performance results, obtained by means of simulations, for a wave power generation plant (1) evidence that this control scheme improves the power generation of the system and (2) prove that this control scheme is robust in the presence of disturbances.
Highlights
During the last decade, the use of renewable energy sources have gained increasing attention for several reasons such as the reduction of pollution caused by traditional sources of energy and the removal of dependence on exhausted resources
The performance of the proposed adaptive sliding mode control (SMC) scheme designed to regulate the turbine speed in an oscillating water column (OWC) wave power generator system is analyzed by means of some simulation examples
It is assumed that the OWCs use Wells turbines and doubly fed induction generator (DFIG)
Summary
The use of renewable energy sources (mainly wind and solar) have gained increasing attention for several reasons such as the reduction of pollution caused by traditional sources of energy (mainly fossil fuels) and the removal of dependence on exhausted resources. The doubly fed induction generator (DFIG) is used at many renewable power generation plants (e.g., wind turbines and wave energy plants) since they are able to adapt to sudden changes [12,13,14,15,16] In these machines, the stator is connected directly to the grid, but the rotor is connected to the grid by means of a variable frequency converter (VFC). This work presents an SMC scheme aimed at improving the generation of power in an OWC system that incorporates a Wells turbine in order to transform the pneumatic energy into mechanical energy. The design of the traditional SMC scheme requires calculating an upper bound for the system uncertainties since the value of the sliding gain used must be higher This value is directly related to the control effort, so a high sliding gain value implies a high control effort possibly causing the chattering problem.
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