Estimation Techniques for Supercapacitor Parameters in Uninterruptible Power Supplies

Abstract

The recent social shift towards sustainable energy has brought substantial changes in the energy storage field. Supercapacitors have emerged as a promising alternative to traditional lithium-ion batteries for short-term energy storage, especially in applications such as electric vehicles and uninterruptible power supplies (UPS). Supercapacitors offer unique benefits for UPS in telecommunication systems that cannot be replicated by lithium-ion batteries, such as their small size and long lifespans. Particularly, lithium-ion batteries cannot be used in remote outdoor applications due to their frequent maintenance needs. Further, they are often not desirable in outdoor applications in general due to a limited temperature range and their large size. Supercapacitors also offer faster charge speeds and high power densities, which other energy storage technologies cannot match. This study introduces a novel estimation technique for monitoring the dynamic parameters of a supercapacitor within an uninterruptible power supply system. The estimator is able to extract these parameters in real time and quickly adjusts to the supercapacitor's parameters as they change throughout its life cycle. This technique has impressive accuracy, maintaining less than 1% error at 120ms from start-up and virtually zero error after this time. The estimator's high performance remains consistent with changes in power demands and supercapacitor parameters. The designed UPS system demonstrates robustness and versatility, providing up to 160 seconds of backup time at lower power levels and 30 seconds at its maximum 500W output. Its modular design allows scalability for larger power needs or extended backup durations, making it adaptable to varying supercapacitor types and aging effects. The system is also flexible to changes in the supercapacitor type and aging effects over the supercapacitor lifespan. Currently, low energy density is the most significant limiting factor for supercapacitor applications; however, with soon anticipated advancements in commercially available supercapacitor technology, there is great potential for future widespread use in high-power UPS systems.