Abstract
This paper explores the maximization of tidal energy conversion by adopting hydraulic transformation and through the design of a robust H∞ control scheme. A hydraulic transformation based tidal turbine applicable to realistic tidal states is presented. In this turbine, a hydraulic transformer is developed to have well-adapted characteristics to turbulent tidal stream flows. The dynamics of the tidal turbine is represented as a state space model based on the equations of its main components. The H∞ control scheme is then synthesized by introducing a new state variable that represents the “filtered” of the turbine rotor speed tracking errors. The control problem is formulated as a convex optimization problem with linear matrix inequality (LMI) that is solved to satisfy H∞ performance and obtain good dynamic characteristics. In addition, a robust H∞ observer for estimating state variables along with the online implementations of the robust controller is also designed by using the LMI approach. A case study of a 150 kW hydraulic transformation based tidal turbine system is conducted and detailed analyses of the dynamic behavior of the tidal turbine are presented. According to the test results, approximately up to 40% total power conversion efficiency can be achieved by the proposed turbine under the typical energetic sea state conditions.