Sea-state based maximum power point tracking damping control of a fully submerged oscillating buoy

Abstract

Optimal control has been studied for over two decades in the field of ocean wave energy extraction. However, most algorithms require not only extremely detailed models of the plant but also wave prediction, leading to difficulties when implementing these algorithms in reality. This paper investigates the use of maximum power point tracking (MPPT) control – a simple gradient-ascent algorithm well developed for solar and wind energy – on a novel wave energy converter comprising a fully submerged oscillating buoy and a tether coupled hydraulic power-take-off (PTO) unit. A study of the sensitivity of control to irregular wave fluctuations/variability was proposed to systematically determine the step size and update rate of MPPT controller. The world’s first commercial scale fully submerged wave energy converter (WEC), Carnegie’s CETO system, was used as a test case to assess the proposed methodology under passive damping control. Optimization was done on the CETO system based on typical Australian sea sates in order to benchmark the performance of MPPT control. Simulation results demonstrated that the MPPT damping controlled system is more effective and robust compared to the fixed-damping system with a globally optimized generator damping. The power loss of the MPPT damping controlled system due to tracking and wave/sea state variability is 1.9% of the acausal optimal damping controlled system.