A Traction Substation State Estimator for Integrating Smart Loads in Transportation Grids Without the Need for Additional Sensors

Public electric transport grids tend to be oversized and underutilized. Therefore, they can become sustainable and multi-functional backbones to the city AC grid by integrating smart grid elements into their infrastructures. However, integrating smart grid loads and renewables requires a large array of wirelessly communicating sensors across the traction substations, the smart grid components, and each vehicle of the transport fleet. This can be both costly and technically complex. This paper proposes an analytical state estimator that can predict vehicle traffic count and spare power capacity under a traction substation without the use of any additional sensors. The estimator uses existing, locally available measurements at any power node on the traction section to inform the decision-making of the power management scheme at that node. Validating the results with up to 100000 stochastic test simulations of a verified traction grid model, up to 76% of the monitored conditions were detected, with no false positives, and without the need for additional sensors and wireless communication.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag

Increasing the Braking Energy Recuperation in Electric Transportation Grids Without Storage

When the braking energy in electric transportation grids is not met by another vehicle's demand, it is either harvested by storage systems or wasted in braking resistors. This paper looks at three methods for increasing the amount of harvested braking energy without the use of expensive storage systems: decreasing the substation voltage, decreasing the catenary/rail resistance, and adding smart grid loads such as EV chargers. Compared to the baseline scenario of a presented case study, the first method allowed the recuperation of all the braking energy yet increased the line transmission losses. The second method presented a better performance in both types of losses (23 %), while the third method offered a 66 % reduction in losses in addition to offering more utilities from the same infrastructure. The final paper will go into further detail with a full-day simulation.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag

Toward a Better Estimation of the Charging Corridor Length of In-Motion-Charging Trolleybuses

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. Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag

Increasing the Integration Potential of EV Chargers in DC Trolleygrids: A Bilateral Substation-Voltage Tuning Approach

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%). Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag

A shared PV system for transportation and residential loads to reduce curtailment and the need for storage systems

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.DC systems, Energy conversion & Storag

An Adaptive Battery Charging Method for the Electrification of Diesel or CNG Buses as In-Motion-Charging Trolleybuses

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%.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag

A simple method for sizing and estimating the performance of PV systems in trolleybus grids

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.DC systems, Energy conversion & Storag

Placement and sizing of solar PV and Wind systems in trolleybus grids

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.DC systems, Energy conversion & Storag

Methods for increasing the potential of integration of EV chargers into the DC catenary of electric transport grids: A trolleygrid case study

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.DC systems, Energy conversion & Storag

A Complete DC Trolleybus Grid Model With Bilateral Connections, Feeder Cables, and Bus Auxiliaries

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.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag