A novel reconfigurable supercapacitor system with equalization and surge current suppression to improve energy-utilization in supercapacitor urban transit systems

Abstract

—Supercapacitors (SCs), with their high energy density, long cycle life, and excellent low-temperature performance, have emerged as a highly suitable energy storage devices for the electrification of urban transit systems (UTSs), especially for the fast-charging applications. However, the wide voltage range of SCs results in low energy utilization for the SC UTSs. Reconfigurable SC systems (RSSs) are considered a promising solution to significantly improve energy utilization rate. However, the existing RSSs are unable to maximize energy utilization and lack effective equalization capability. Moreover, the surge phenomenon is common in the RSSs, which will lead to the power device failure. To tackle these challenges, a novel RSS is proposed, integrating series-parallel reconfiguration, reconfiguration equalization, and surge current suppression. This innovative approach enables achieving ultra-high energy utilization of the SCs while significantly improving voltage consistency. Furthermore, the surge current during the mode-switching process can be effectively suppressed. Experimental results demonstrate that the RSS achieves an impressive energy utilization rate of 93.7 %, which is 137.8 % higher than the fixed-connected supercapacitor pack, and 8.8 %–16.7 % higher than the existing RSSs. The voltage difference is reduced from 493 mV to a mere 13 mV, resulting in a further 10.9 % increase in energy utilization. The surge suppression method limits the surge current from 42.3 C rate to nearly zero. The RSS proposed can remarkably enhance the driving range of electric urban rail trains and electric buses, concurrently reducing the cost and volume of the SESSs.