A Systematic Approach for Design and Analysis of Electrified Public Bus Transit Fleets

The wide integration of all battery electric buses (BEB) in the operation of public transit services is identified as one of the most promising means toward decarbonizing public transport systems. In response, public bus transit (PBT) and utility grid operators are currently in need of developing analytical techniques that enable them to conduct tradeoff analyses for the many available options of BEBs, charging infrastructure, and their associated system impacts. To that end, this article proposes a systematic and effective technique for feasibility check and configuration design of electrified PBT fleets without the need for the sophisticated optimization toolbox and high performance computing. The configuration design aims at determining the number of BEBs and their on-board battery capacities to meet the PBT prespecified schedule under different sizes of chargers. The proposed model is tailored for BEBs designed to either boost their batteries on-route at intermediate bus stations using fast chargers (opportunity charging) or charge while parked at the depot (in-depot charging). The developed model is also utilized to generate the aggregated power demand profiles of electrified PBT fleets under different charging practices. Based on the generated power demand profile, a lifecycle cost analysis is conducted to compare BEB-based PBT options to their diesel counterparts.

I. Introduction

Public transit operators are under pressure to take serious steps on adopting electric bus technologies to decarbonize their fleets [1]. A zero-emission public bus transit (PBT) fleet can be developed with battery electric buses (BEBs). There are three ways to charge BEBs: on-board, off-board/swapping, and in motion wirelessly. On-board systems provide two different techniques for charging batteries: opportunity and on-site charging [2]. In opportunity charging, BEBs use fast chargers at intermediate bus stops (terminals) to boost their batteries during unloading and loading passengers. As opposed to opportunity chargers, the in-depot charging occurs mostly during overnight hours after the bus has completed its daily schedule and returned to its garage. In off-board recharging, the bus battery is swapped at a designated location on bus routes instead of being charged on-board [3]. Battery swapping offers the advantage of charging the batteries during off-peak periods [4]. However, the robot hands at the swap location lead to high capital costs and new infrastructure. With in-motion wireless charging, the bus battery is charged by coils installed in the pavement during BEB motion and in a wireless manner [3], [4]. In this way, the BEB does not have to stop for charging, but wireless energy transmission reduces the overall charging efficiency. Also, this system requires improvised infrastructure, adding more cost to the PBT budget [5].