Multi-Objective Energy Management and Charging Strategy for Electric Bus Fleets in Cities Using Various ECO Strategies

Abstract

The paper presents use case simulations of fleets of electric buses in two cities in Europe, one with a warm Mediterranean climate and the other with a Northern European (cool temperate) climate, to compare the different climatic effects of the thermal management strategy and charging management strategy. Two bus routes are selected in each city, and the effects of their speed, elevation, and passenger profiles on the energy and thermal management strategy of vehicles are evaluated. A multi-objective optimization technique, the improved Simple Optimization technique, and a “brute-force” Monte Carlo technique were employed to determine the optimal number of chargers and charging power to minimize the total cost of operation of the fleet and the impact on the grid, while ensuring that all the buses in the fleet are able to realize their trips throughout the day and keeping the battery SoC within the constraints designated by the manufacturer. A mix of four different types of buses with different battery capacities and electric motor specifications constitute the bus fleet, and the effects that they have on charging priority are evaluated. Finally, different energy management strategies, including economy (ECO) features, such as ECO-comfort, ECO-driving, and ECO-charging, and their effects on the overall optimization are investigated. The single bus results indicate that 12 m buses have a significant battery capacity, allowing for multiple trips within their designated routes, while 18 m buses only have the battery capacity to allow for one or two trips. The fleet results for Barcelona city indicate an energy requirement of 4.42 GWh per year for a fleet of 36 buses, while for Gothenburg, the energy requirement is 5 GWh per year for a fleet of 20 buses. The higher energy requirement in Gothenburg can be attributed to the higher average velocities of the bus routes in Gothenburg, compared to those of the bus routes in Barcelona city. However, applying ECO-features can reduce the energy consumption by 15% in Barcelona city and by 40% in Gothenburg. The significant reduction in Gothenburg is due to the more effective application of the ECO-driving and ECO-charging strategies. The application of ECO-charging also reduces the average grid load by more than 10%, while shifting the charging towards non-peak hours. Finally, the optimization process results in a reduction of the total fleet energy consumption of up to 30% in Barcelona city, while in Gothenburg, the total cost of ownership of the fleet is reduced by 9%.

Smart Integration of Electric Buses in Cities: A Technological Review

“…A significant peak load reduction can be achieved by adding an ESS to an opportunity charger, but the additional space requirements make this solution of course not possible for every charger in the city. The results of Hasan et al [90] are more promising, even though this requires a longer charging time, and thus also a longer waiting time, at the end terminals, while this is not always possible due to delays. Nevertheless, smart charging can become critical for a citywide deployment of high-power chargers.…”

“…Moreover, in [88,89], the authors used an ESS to minimize the total charging cost and reported that it could contribute to a cost reduction of up to 15% and 22%, respectively. A study conducted by Hasan et al [90] for the European project, ASSURED, attempted to determine the impact on the grid due to the deployment of high-power opportunity chargers for public transport networks. The study found that utilizing a pulsed charging method reduced vehicle energy requirements by up to 18% and reduced peak grid loads by 10% or more.…”

Slow and Fast Charging Solutions for Li-Ion Batteries of Electric Heavy-Duty Vehicles with Fleet Management Strategies

“…In some countries like the Netherlands, EV integration reaches the limit in most of the DSO connection points [12][13][14]. In the ASSURED project, among several demos, there are more than 43 HD e-buses integrated in the Eindhoven demo, which will be upscaled to 200 HD e-buses [9]. Smart charging, besides RES, is a promising solution to address the congestion in the DSO grid and maintain the reliability and security of supply with some financial benefits, which could be a motivation to adopt this technology.…”

“…e-buses integrated in the Eindhoven demo, which will be upscaled to 200 HD e-buses [9]. Smart charging, besides RES, is a promising solution to address the congestion in the DSO grid and maintain the reliability and security of supply with some financial benefits, which could be a motivation to adopt this technology.…”

“…Table 2. Overview of ASSURED use cases and demonstrators in work packages 7 and 8 (WP7&8) [9]. * Custom Wireless Power Transfer Unit designed and manufactured by POLITO; ** External to ASSURED.…”