Hybrid energy storage system and operational strategy for an electrified trailer unit of a 40-ton truck

Within the evTrailer2 project (“Autarkes elektrisches Antriebskooperationssystem für LKW-Trailer und Fahrzeuganhänger”, funded by BMWK), an electrified trailer is developed. By use of an auxiliary electric axle on a trailer in conjunction with a diesel-powered tractor, a significant reduction in CO2 emissions is in prospect. This paper focuses on a hybrid energy storage system concept specifically designed for a trailer to overcome the drawbacks of standard energy storage systems. Traditionally, energy storage systems for a truck are designed with higher capacity to cope with distance requirements or higher power to cope with power demand. These energy storage systems are typically constructed using high-energy cells for greater energy capacity or high-power cells for improved performance. In the hybrid storage concept, two distinct energy storage systems are developed for the trailer unit to work in tandem with each other. The primary energy storage system made of high-energy cells is larger and provides continuous low-range power to the auxiliary electric axle during the drive. The secondary energy storage system developed with high-power cells is smaller but handles the peak power requirements during acceleration, uphill travel, and regenerative braking. This contribution presents the analysis determination of the hybrid storage specification based on an analysis of power profiles for the trailer along different routes in the European Union as well as an optimized operational strategy to ensure the simultaneous operation of both systems without depleting the energy entirely between recharging intervals. Hybrid energy storage has several advantages regarding energy and recuperation efficiency which directly results in an increased driving range.