2.2.1. Public Transportation Catenary-Supplied Vehicles

This section describes the applications of SCs in urban passenger transport vehicles powered by a catenary. This type of vehicle is usually known by the name of trolleybus [41]. The difference respect to light vehicles is the electrical circuit is not closed by the rail, but the catenary must consist of two poles. The predominant electrical scheme of this type of vehicle is shown in Figure 10. The catenary voltage is usually a direct voltage of 600–900 VDC generated from a three-phase rectifier connected to an electrical substation. The equipment on board the vehicle is made up of the inverter that feeds the traction motor and an electrical braking to avoid overvoltages in the power line (catenary). The trend in this type of transport is to replace the chopper with an ESS to take advantage of regenerative braking energy, save a percentage of energy, and, in a second step for the electrical power system, to place charging points in different sections of the route.

**Figure 10.** Simplified electrical diagram of the traction drive of public transportation catenarysupplied vehicles.

Cignini, F. [42] made a comparison of four prototypes of electric buses with an onboard storage system to fulfill certain speed requirements in a specific time. The study is carried out from the real data taken from the vehicles (energy consumption, acceleration, and maximum speed) in different scenarios. The four storage technologies being compared are a hybrid energy storage system (HESS) consisting of:


An economic analysis is also carried out to complement the previous comparison from a life cycle cost point of view. The paper concludes that the best option (lowest cost) is formed by SCs and lithium-ion batteries followed by option 1 (SCs/AGM batteries). On the other hand, from a technical point of view, option 2 is the best because it is the option that supports the highest charging rates.

Soltani, M. [43] proposed a HESS made up of lithium batteries and lithium-ion capacitor (LiC) as the only power source for a city bus. LiCs complement the use of batteries to extend their useful life by reducing the power peaks in the acceleration and decelaration stages, supplying/absorbing that energy in the LiCs. This study proposes an electrical, thermal and aging model of each ESS is presented and a methodology for the distribution of power requirements. The research concludes the HESS, compared to the ESS made up only of batteries, reduces the size of the energy storage required by 30% and the cost by 16%. The reason for this development is the increase of the battery lifetime and an improvement in the dynamic response and efficiency of the system.
