Analysis and Control of Acoustic Emissions from Marine Energy Converters

TL;DR

This paper addresses the licensing bottleneck caused by underwater acoustic emissions from tidal current converters. It develops an acoustic-aware control framework using a MATLAB/Simulink model to compare drivetrain architectures and operational strategies for noise mitigation. Baseline results show a total SPL of $124.2$ dB re $1 \mu$Pa at 50 m with gearbox tones, which are reduced by roughly $10$ dB to $109.2$ dB when using a direct-drive PMSG, effectively removing tonal noise; switching-frequency adjustments offer negligible acoustic benefit, while MPPT coefficient de-tuning provides a practical transient mitigation with a $3.58\%$ energy yield loss. A tiered mitigation framework is proposed, prioritising design-phase direct-drive topologies and transient MPPT-based derating during sensitive biological periods to enable regulatory approval and broader deployment of marine renewable energy.

Abstract

Environmental licensing related to underwater acoustic emissions represents a critical bottleneck for the commercial deployment of marine renewable energy. This study presents a control engineering framework to mitigate acoustic risks from tidal current converters without compromising project viability. A MATLAB/Simulink model of a tidal current converter was utilised to evaluate two distinct mitigation tiers: (1) architectural modification, comparing a geared induction generator against a direct-drive permanent magnet synchronous generator, and (2) operational control, analysing the impact of switching frequencies and maximum power point tracking coefficient tuning. Results indicate that lowering switching frequencies is ineffective, increasing power electronic losses by over 2000% with negligible acoustic benefit. Conversely, the direct-drive permanent magnet synchronous generator architecture reduced sound pressure levels, effectively eliminating mechanical tonal noise. For existing geared systems, de-tuning the maximum power point tracking coefficient by a factor of 1.2 reduced the probability of exceeding temporary threshold shift limits for marine mammals, with a quantified energy yield reduction of 3.58%. These findings propose a hierarchical mitigation strategy: selecting direct-drive topologies for acoustically sensitive sites, and utilising maximum power point tracking coefficient based power curtailment as a transient operational mode during critical biological migration periods.

Figures (9)

• Figure 1: The SeaGen tidal turbine, a commercial-scale horizontal-axis TCC deployed in Strangford Lough, Northern Ireland turbines2011seagen.
• Figure 2: Audiograms of target marine mammal species and the derived generic hearing threshold (GTV) used as the baseline for acoustic impact assessment.
• Figure 3: Baseline operational characteristics of the simulated TCCS: (a) power coefficient $C_p$, (b) tip speed ratio $\lambda$, (c) mechanical torque, and (d) power output. The simulation demonstrates the dynamic response of the control system to turbulent inflow.
• Figure 4: Time-series of SPL components for the reference geared TCC at 50 m distance.
• Figure 5: Spatial propagation of acoustic emissions at rated power ($T=7340$ s) from 10 m to 200 m.