ABSTRACT

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.

INTRODUCTION

In spite of its TWh-scale potential as a primary renewable source, ocean energy is still largely untapped. According to REN21 (2022), the annual addition of ocean power capacity globally is minimal, at around 0.5 GW in 2021. Additionally, the cost of ocean energy is currently higher compared to established land-based green energy technologies like wind and solar. To make these technologies more cost-effective and sustainable, developers need to increase their understanding of the technology and gain experience in how it performs in the real marine environment.

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