Inductor Based Active Cell Equalization for Ultracapacitor Energy Storages

Abstract

Ultracapacitors, known for their high power density and long cycle life, are widely used in various applications. However, when ultracapacitor cells are connected in series, voltage imbalances can occur, limiting overall energy storage capacity and system performance. This paper presents an investigation into inductor-based active cell equalization techniques for ultracapacitor energy storage systems. The proposed approach utilizes inductors, switching devices, and control circuitry to efficiently balance cell voltages. By monitoring cell voltages and activating switching devices when predetermined thresholds are exceeded, energy is transferred from higher voltage cells to inductors during the charging phase. In the subsequent discharging phase, the stored energy is released, equalizing the cell voltages. This iterative process continues until voltage balance is achieved. Inductor-based active cell equalization offers advantages such as rapid voltage equalization, wide voltage range operation, and electrical isolation between cells. However, challenges include system complexity, cost, and losses introduced by switching devices. Ongoing research focuses on optimizing design and control strategies to improve energy efficiency and address these challenges. The proposed technique shows promise in maximizing energy storage capacity and enhancing the performance and lifespan of ultracapacitor systems. This circuit could balance the capacity of the ultracapacitor in 2.3 seconds with a voltage ripple of 0.0038 V (0.18 %). Further advancements are expected to promote the widespread adoption of inductor-based active cell equalization in diverse applications. (Abstract)