Design and Implementation of a Power Smoothing System for Cross-flow Current Turbines

Abstract

Previous studies optimizing control strategies for cross-flow (i.e., "vertical-axis") current turbines found that sinusoidally varying rotor speed within a single rotation can increase mechanical power output by up to 59%. However, this control strategy, known as intracycle control, comes with a cost: for a two-bladed turbine, electrical power output associated with a 1 kW average is estimated to fluctuate between producing 16 kW and consuming 11 kW twice per rotation. This power quality is incompatible with direct use. Here, we describe a power smoothing system that reduces the root mean square of fluctuating output power by 99% with 96.7% efficiency, using a simple LC filter and bi-directional DC-DC converter. A small-scale simulation of the system is validated using a comparably sized experimental set-up to increase confidence in the full-scale simulation and demonstrate practical implementation.