The increase in electrified transport has elevated the role of electric buses (e-buses) in addressing urban mobility challenges. Among the types of e-buses, there is the in-motion-charging (IMC) trolleybus, which is powered by DC overhead contact lines and has an on-board battery for traction outside overhead lines. A key challenge for IMC buses is the selection of the optimal on-board-charger (OBC) topology for charging their batteries. Ideally, the chosen OBC should have low weight and volume, in addition to operating with high efficiency levels. Additionally, there is a growing need for isolated DC-DC converter topologies to enhance safety and reduce the risk of electric shocks. However, the isolated topologies tend to have higher volume and weight and reduced efficiency due to the need for a high-frequency transformer (HFT). In this context, this article aims to provide design trade-offs and guidelines for choosing between isolated and non-isolated topologies for OBC in IMC trolleybuses, based on an analysis of their efficiency, weight, volume, and cost. A non-isolated interleaved buck-boost (IBB) and an isolated dual-active-bridge (DAB) converters are taken as the study-case. Results indicate strong potential for the IBB at switching frequencies above 75rm kHz, primarily due to a significant reduction in the weight and volume of the magnetic components, with the weight of IBB being about 0.84 times that of the DAB at 100rm kHz switching frequency. For lower frequencies, the DAB converter presents advantages in terms of magnetic compactness. The efficiency of both topologies remains at similar levels, with a slight advantage for the non-isolated one, achieving an average efficiency of up to 99.07%.

Many DC energy solutions have emerged as potential candidates to enhance the electrical infrastructure in a localized approach, allowing future expansion in the transportation sector despite the congestion of the utility grid. However, the risk of designing large power converter units as controllable substations in complex networks, such as electric railway systems, has encouraged the sophistication of modeling and testing tools. This paper presents a high-fidelity, real-time model implementation of a controllable substation for DC traction power systems. This representative model is developed to facilitate the testing of different upgrading options to understand and quantify how these changes will affect the system and, more importantly, which features are critical to further increasing the sustainability of the railways. This is applied to a case study of the Dutch railway system in Wierden. It is found that while controllable substations can reduce voltage drops from an average of 400 V to only about 230 V, the benefit they bring in regenerative braking harvesting does not outweigh the investment costs, calling for further investigation of energy storage systems as another potential solution.

This paper presents the case against the use of droop control in DC traction grids when integrating third-party users, energy storage, or DC-side renewables. The primary argument is that the voltage behavior and the requirements of traction grids should not be mistakenly compared to those of residential distribution grids or microgrids, as no sufficient control input can be derived from the complex power flow of traction grids. In one example, it is shown that droop control can trigger a traction substation to charge the batteries by 41% of their load demand instead of harvesting the available braking energy. This paper also identifies key directions for traction grid state estimators and warns of the narrow applicability of every estimator to the specific energy supply architecture for which it was designed.

The growth of suburbs is a challenge for public transport, and new tools are needed to electrify suburban and intercity bus lines sustainably. In-motion-charging (IMC) buses combine the advantages of both trolleybuses and electric buses. This paper analyses a case of using IMC buses on a 17-km-long intercity route service between Arnhem and Wageningen in the Netherlands. The analysis covers different traction battery technologies, sizes, and charging strategies to find the economically optimal solution. The study was carried out using a numerical model of an IMC bus, which was validated and tuned based on year-round experimental recordings obtained from Arnhem trolleybuses. The model outputs were next used to analyse the batteries ageing under specific charging-discharging current profiles. The analysis shows that the most long-term cost-effective solution for the considered case consists of using merged IMC and opportunity charging as well as a 90 kWh LTO battery, whose expected lifetime would be more than 14 years.

This paper investigates the feasibility of supplying zero-emissions construction sites directly from traction grids using the metro of Amsterdam, The Netherlands, as a case study. Three construction site sizes are investigated in this paper for either an AC or a DC-side connection and for either a daytime or nighttime energy supply. It is concluded that AC side connections are cheaper, more predictable, and have an abundance of commercial power electronics and protection solutions compared to the DC-side connection, yet they do not allow the harvesting of braking energy, and they can breach the AC grid energy contract limits. Meanwhile, DC side connections have recovered over 25% of the small construction site demand and 18% for medium and large ones from the otherwise-wasted braking energy of the public transport fleet.However, still no solution in this paper is found to be better than the previously investigated construction site mobile batteries, which can supply even the large sites with over a third of their energy from braking energy and offer both the public transport and construction site operators all the benefits of controllability, on-site charging, and logistical flexibility.

DC energy hubs have emerged as suitable candidates to enhance the electrical infrastructure in a localized approach, allowing future expansion in the transportation sector despite the electricity grid congestion. However, a risk in designing such a hub is that the outcome of the optimization can be a mere consequence of the (lack of) sophistication of its generation and load models. In that aim, this paper presents a sensitivity analysis for a power demand profile for a DC railway traction power substation, taking into account traction power parameters and the heating, ventilation, and air conditioning (HVAC) modeling approaches. It is found that the traction parameters such as total mass can be confidently considered using an averaged value. On the other hand, modeling the HVAC system using an averaged power demand can lead to errors over 6%, especially in the recovered braking energy calculations.

This paper proposes a shared multi-stakeholder PV system for traction substations and nearby residential loads to reduce the need for storage, AC grid exchange, and curtailment. The residential stakeholders offer both the base electrical load and the solar panels installation space needed by the traction stakeholder, who brings the peak load and investments to the former. Two case studies were conducted for one year in the city of Arnhem, The cy=Netherlands, using comprehensive and verified simulation models: A high-traffic and a low-traffic substation. The results showed a positive, synergetic benefit in reducing the PV system's excess energy and size requirement for any type of traction substations connected to any number of households. In one detailed example, the multi-stakeholder system suggested in this paper is shown to reduce curtailment by up to 80% in moments of zero-traction load. Generally, the direct load coverage of a PV system is increased by as much as 7 absolute percentage points to the single-stakeholder system when looking at energy-neutral system sizes. This multi-stakeholders system offers then an increase in the techno-economic feasibility of PV system integration in urban loads.

In the presence of a catenary infrastructure, the transition from fossil fuel-based bus fleets to electric-powered ones can be facilitated through conventional trolleybuses or In-Motion-Charging trolleybuses, offering environmentally friendly and cost-effective solutions. However, grid congestion at traction substations (TSs) can limit this transition as the grid operator is incapable or unwilling to provide more capacity. As grid connection contracts are typically tallied and billed in periods of 15 minutes, stationary energy storage devices can prove useful in short-term buffering of the power demand. Consequently, more electrification projects can be rolled out under the same, or minimally extended grid contract. In this aim, this paper looks at validating energy storage as a means of enabling bus fleet electrification. It presents a power management strategy that controls the power exchange between the energy storage system (ESS) within the TS, specifically to manage the 15-minute average power. This strategy also serves as a tool for sizing the ESS with the minimum capacity required for the application. A case study for the city of Bologna, Italy, has been considered to validate the proposed approach. The findings indicate that billing contract power can be reduced by up to 41.7% when a storage device actuates in high-energy-demand substations. Furthermore, different types of Lithium-ion cells, including their second-life versions, are compared to determine the most beneficial options under limited cost and volume constraints. Recommendations are drawn on the exact scenarios where each type of cell is most beneficial.

The decarbonization of urban bus fleets can be made by their electrification as in-motion-charging (IMC) buses which can run as trolleybuses or in battery mode. The benefit is that IMC buses can use the existing trolleygrid infrastructure where their route overlaps with it to charge the battery and operate in battery mode outside of it. Presently, the IMC battery charging power is set conservatively to the minimum of all the spare capacities of the traction substations (SSs) found along the bus route. This can render most electrification projects techno/economically infeasible as not enough energy is picked up for the battery-mode operation and long charging times at bus terminals are required. This article proposes then an adaptive charging approach that uses the locally available spare capacity under any traction SS, taking into account the limitations of the maximum SS power and the minimum line voltage. The method is proven here both theoretically and in a case study over one full year of operation of four electrified diesel/compressed natural gas (CNG) bus lines in Arnhem, The Netherlands, using comprehensive and verified trolleybus and trolleygrid models. The proposed adaptive charging method, as opposed to the present conservative method (here, Regular Charging), is shown to make one bus electrification project completely feasible and reduce the extra terminal charging time for the other lines by up to 64%.

The traction substations of urban electric transport grids are oversized and underutilized in terms of their capacity. While their over-sizing is an unfortunate waste, their under-utilization creates the major hurdle for the integration of renewables into these grids due to the lack of a base load. Therefore, integrating smart grid loads such as EV chargers is not only an opportunity but a necessity for the sustainable transport grid of the future. This paper examines six methods for increasing the potential of EV chargers in three case studies of a trolleygrid, namely a higher substation no-load voltage, a higher substation power capacity, a smart charging method, adding a third overheard parallel line, adding a bilateral connection, and installing a multi-port converter between two substations. From the case studies, the most promising and cost-effective method seems to be introducing a bilateral connection, bringing a charging capacity for up to 175 electric cars per day. Meanwhile, other costly and complex methods, such as smart charging with grid state sensors and communication, can offer charging room for over 200 electric cars per day. Furthermore, using solar PV systems to power the grid showed a more than doubling of the directly utilized energy by installing a 150kW charger, from 19% to 41%. This reduces the power mismatch between the trolleygrid and the PV system from 81% to 59% and thereby reduces the severe economic need for storage, AC grid power exchange, or PV power curtailment while allowing a high penetration of renewables.

Solar PV systems have so far been the source of choice for the sustainable supply of urban electric transport networks—like trams and trolleybus grids. However, no consensus exists yet on the placement or sizing of PV systems at the traction substations, and no method is available for easy estimation of the PV system utilization performance. The latter is crucial for understanding the need for storage, grid exchange, or even power curtailment, and has therefore a direct impact on the technical and financial feasibility of the project. This paper looks at 11 Key Performance Indicators (KPI) that are available to trolleybus operators, in two PV case studies on Arnhem (NL) and Gdynia (PL), using verified and validated bus, grid, and PV models. Through one KPI, namely the here-defined Energy Traffic KPI, a strong trend (R²=0.93) is described that can now allow stakeholders a quick estimation of the PV potential using a simple third-degree polynomial instead of resorting to the complex grid, bus, and PV modelling. A simple placement and sizing method is also presented derived from this KPI, in a way as to increase the technical and economical feasibility of an installed PV system. Despite all efforts, stakeholders are still warned of an intrinsic, upper-performance plateau that exists in transport grids, at around 38% direct PV utilization, caused by the unavoidable mismatch between PV generation and vehicle timetables and schedules. Stakeholders are urged to implement more smart grid loads as a base load to increase the feasibility of their investments in renewables, and to transform the transportation systems thereby to multi-functional grids that can assist the main city grid.

The transport sector has been increasing rather than decreasing its CO2 emissions, and its sustainable electrification faces a number of technical and non-technical challenges. This paper investigates these challenges, namely those of the grid load demand modelling, renewables integration, the present infrastructure limitations, and the policy/non-technical challenges. In synthesis, the suggested vision for the future sustainable urban bus network is presented as a catenary grid running In-Motion-Charging trolleybuses, with integrated PV, EV chargers, and stationary storage systems. The future grid must involve external players such as the DSO/TSO and research/academic institutions, with a dedicated coordination body, from pre-tendering all the way to daily operations.

This paper offers a complete and verified model of DC trolleybus grids and examines the effect of the common modelling assumptions made in literature by using simulations, as well as bus and substation measurements from the grid of Arnhem, the Netherlands. An equivalent model for the overhead line impedance is offered taking into account the single line impedance, the supply and return lines, and the parallel connections between them. A case study shows that the feeder cables from the substations to the sections can be ignored, but only for certain substation power and feeder-line length ranges. On the other hand, the often-neglected regenerative braking, bus auxiliaries load, bilateral connections, and the exact nominal substation voltage are found to be crucial for the correct modelling of a trolleybus grid.

In-Motion-Charging (IMC) buses are destined to become a key player in sustainable urban transport as they combine the advantages of both trolleybuses (overhead supply mode) and e-buses (on-board battery mode). Defining the route ratio of these two modes of operation is a critical task in order to ensure that the IMC battery can complete a full trip once it is out of the charging corridor zone (i.e., out of the trolleybus operation zone). This paper offers a more correct approach to sizing the charging corridor than what is commonly found in literature, by including the effects of both the stopping and moving times of a typical IMC bus and by studying two charging schemes for the IMC bus battery charging. Errors as high as 16.4% and 17.6% were reported for the two charging schemes, respectively, when using the conventional methods found in literature for a case study using measurements of the trolleygrid city of Arnhem, the Netherlands.

Reducing the environmental impact of transportation requires the successful integration of renewable energy sources into the electrical transportation networks. However, the mismatch between renewable generation and the intermittent bus schedules causes temporary absence of loads and creates considerable excess energy, potentially rendering the systems economically infeasible. So far, studies on integration of renewables in transport grids were limited to decentralized solar PV systems (placed at the substation level), using statistical or simplified models, and concerned mainly with increasing the trolleygrid capacity. In this paper, both PV and Wind systems are considered and studied as to maximize their direct utilization by using verified simulation models for six different sizing and placement scenarios. The Dutch trolleygrid of Arnhem is used as a case study. Scenarios I to V looked at a decentralized renewable sources placement and ultimately concluded that PV systems at low-traffic substations are best sized for complete energy-neutrality, with daily storage systems. On the other hand, those at high-traffic substations should be without storage and sized below their energy-neutrality point — ideally, using the Marginal Utilization approach (scenario III). Finally, the Centralized (Aggregated) Energy-Neutral Wind and PV Approach of scenario VI offers the best outcome, with a hybrid solution of 53% PV and 47% Wind. This scenario offers a 54.1% direct bus load coverage. In comparison, scenario I, which had attempted a grid energy-neutrality in a decentralized manner, had only achieved 32.4% direct load coverage. The outcome of scenario VI can even be pushed to values above 80% by installing storage systems.

Light rail networks such as trolleybus grids have the potential to become multi-functional smart grids by using the excess capacity of the grid to implement PV systems, EV chargers, and storage. This paper offers a solution to increasing the potential for integration of EV chargers in the trolleygrid, without additional infrastructure costs, by simply tuning the nominal (no-load) voltages of bilaterally connected substations. This method shifts the load share between the two substations, creating more room for the integration of other utilities in a desired zone of the bus route. A mathematical derivation is presented, followed by a verifying case study using detailed and verified bus and trolleygrid simulation models for the city of Arnhem, the Netherlands. It is shown that by setting a substation nominal voltage from +10V compared to its bilateral substation to -10V, the substation can take, on average, as much as 7.5 percentage points less of the load share (from 45.9% to 38.4%) and see as much as 5 percentage points more of complete zero-load time (84.3% to 89.2%).