Adaptive Super-Twisting Sliding Mode Control for Ocean Current Turbine-Driven Permanent Magnet Synchronous Generator

Blue economy industries, such as aquaculture or deep sea mining, are moving further offshore to take advantage of the vast scale of the ocean, but moving further offshore requires access to consistent, reliable power untethered to land-based power grids. With a high potential for low cost power generation in locations otherwise isolated from the grid, marine hydrokinetic turbines could serve to help meet this growing power demand. This paper presents a novel adaptive super-twisting sliding mode control strategy for permanent magnet synchronous generators (PMSG) driven by ocean current turbines (OCT). To ensure robustness and mitigate chattering during maximum power point tracking (MPPT), an adaptive gain adjustment technique is proposed for super-twisting sliding mode control. This technique does not require knowledge of the upper bounds of uncertainties, such as external marine environment variability or unmodeled dynamics. More specifically, the adaptive gain rate can vary with a sliding variable when system states are approaching or on the sliding mode, which constitutes the novelty of this paper. The adaptive dynamic gain enables the rapid establishment of the real 2-sliding mode, and this is accomplished without overestimating or underestimating the disturbance boundary. The Lyapunov function technique is used to analyze the finite time convergence of the closed-loop system. A numerical model of a 720-kW PMSG-based OCT is utilized for validating the effectiveness of the proposed control strategy, with simulated operating environmental conditions based on ocean current data collected from the Gulf Stream off Southeast Florida.