Integration of Electrical Energy Storage in Wave Energy Hardware-in-the-Loop Test Rigs

This paper presents a design methodology for integrating an electrical energy storage unit into a hardware-in-the-loop (HIL) test rig for wave energy converters (WECs). Typically, the power production from WECs is characterised by pronounced fluctuations at low frequency and high peaks compared to the average. Wave energy test rigs should be able to reproduce these variations to impose realistic conditions to the device under test. Thus, the grid connection of the rig must be sized to cope with high peaks, and additional measures may be required to avoid disturbances on nearby loads and negative effects on voltage quality. The integration of electrical energy storage can smoothen power fluctuations and mitigate these drawbacks, while resulting in lower installation and operating costs. The design methodology indicates how to effectively size the storage unit and which technology to favour based on the type and duration of test campaigns. Numerical simulation results are presented for a dual HIL test rig and operational profiles of three different WEC technologies. For designs with energy storage lifetime shorter than the calendar life, sensitivity analyses indicate that the rig's annual utilisation rate and the level of accelerated testing have a significant effect on the storage energy requirements.