Field Tests Validation of a Mechanical Sensor-less MPPT Control Strategy for Tidal Turbines

The main goal of this paper is to present the experimental evaluation of a novel mechanical sensor-less MPPT control strategy for tidal stream turbines via field tests in a relevant environment. Fluctuations in mechanical loads and generated power, caused by surface waves or turbulence in the water column, pose significant challenges for power conditioning and control systems of instream turbines. In the present work, a simple and robust Maximum Power Point Tracking (MPPT) control method based on an optimal linear relationship between the current and the square of the voltage of the generator outputs is proposed. The MPPT control strategy was developed by a digital model and then implemented on the 1.5 m diameter Tidal Turbine Testing (TTT) device developed at the Queen’s University Belfast (QUB). System validation was performed at the highly energetic QUB tidal test site in the Strangford Narrows, Northern Ireland. Turbine performance results by the proposed methodology were compared with two conventional control strategies: constant speed (RPM) and constant torque control. Field testing in the unsteady inflow environment allowed to investigate hydrodynamic power and Power Take-Off response to the adopted control strategy. The performance of the MPPT control strategy was able to maximize the power coefficient of the turbine and maintain the turbine operation close to its optimal Tip Speed Ratio (TSR) under fluctuations in the stream flow, with improved performance compared to conventional control strategies.