Simulation-Based Comparisons of Mobile and Stationary Energy Storage Systems Applied for Electric Transport

Electric public transport infrastructure with its electric trolleybuses plays an important role in large-scale consumption of electrical energy. The most important feature of trolleybuses that are equipped with AC traction drive systems is the ability to generate electrical braking energy. Instead of dissipating in brake resistors, this regenerated energy can be either transferred to other accelerating trolleybus or stored in energy storage system (ESS) for repeated use. However, there are also rather well known technical disadvantages of ESS, for example, mobile ESS causes additional load for trolleybus and stationary ESS might be located so far from trolleybus that most of the energy might be lost in transmission. For this reason, the purpose of this paper was to present a method that compares energy consumptions of trolleybuses unequipped and equipped with mobile or stationary energy storage systems by analyzing the results acquired from simulations of travelling equal distances at equal motion condition cycles. Trolleybus mass increase in case of mobile ESS was considered. Overhead DC line (ODCL) transmission resistance of the portion between substation (SUB) and trolleybus was considered, and ODCL transmission resistance of the portion between stationary ESS and trolleybus was also considered. Losses in both traction drive converter and ESS bidirectional DC/DC converter and also losses in both SUB transformer and SUB rectifier were considered by assuming certain efficiency ratios. Efficiency of regenerated energy storing and substation energy consumption reduction is analyzed and corresponding conclusions are drawn.