Article Series Dynamic inductive charging in traffic: How does the technology work and where can it be applied?

In recent years, several research projects have been conducted to explore the practical implementation of dynamic inductive charging in the field of electric vehicle charging. This innovative technology enables wireless energy transfer, allowing electric vehicles to be charged while in motion. But how exactly does this technology work, and where do we already encounter induction and inductive charging in our daily lives? What potential does dynamic inductive charging hold for public transportation, and what are its implications for the environment, humans, and energy system? This articles series addresses these and other questions and looks at dynamic inductive charging from various perspectives.

The first article focuses on the functionality and applications of dynamic inductive charging.

This series of articles shows which parameters and methods are used to create reference grids. Furthermore, data from literature is merged and a set of reference grids is created. Specifically, the following topics are addressed:

1. How does the technology work and where can it be applied?
2. What are framework conditions for the technology?
3. What factors influence technology acceptance?
4. How should the technology be evaluated ecologically?
5. What options for action result from the findings?

The low-voltage level

The low-voltage level (LV level) is the lowest voltage level of the electricity grid and supplies households, businesses and small industrial enterprises with electricity. If it is not generated and fed into the LV level itself, it is fed into the LV grid from the medium-voltage grid (MV grid) via the local grid transformer. The LV grids are connected to the MV grid via an loca grid transformer and distribute electricity to the grid connections of the end customers (cf. Figure 1).

In addition to the established conductive charging, however, there are other alternative charging technologies in electromobility. These include inductive (wireless) charging, battery replacement and overhead line systems, which bring their own challenges and opportunities depending on the application [1].

This series of articles focuses on dynamic inductive charging, which represents a possible solution for the energy supply of electric vehicles in the transport sector. DWPT will be considered as a possible charging infrastructure from the perspectives of technology, economic efficiency, regulations, carbon footprint and technology acceptance (cf. Figure 1).

Operating principle of inductive energy transfer

Inductive energy transfer is fundamentally based on the principle of electromagnetic induction and requires two coils. The time-varying current flow in the primary coil generates an alternating magnetic field, which in turn induces a voltage in the secondary coil. The voltage drop creates a current flow [1, 2]. The magnetic field enables energy transfer without a physical connection between the components. However, it is important to ensure that the electromagnetic fields do not exceed certain reference values. The effects of electromagnetic fields and established reference values will be discussed in detail in the next article of the series on the technology environment.

Inductive energy transfer is already being applied in various areas. In the field of medical technology, for example, the technology enables wireless power supply for implants such as pacemakers. Well-known examples in everyday life include induction cooktops or the wireless charging of electric toothbrushes, smartphones, or smartwatches [1, 3], where energy transfer works according to the same principle.

Application of inductive energy transfer in Electromobility

Another significant application of inductive energy transfer is in electromobility, specifically in the wireless charging of electric vehicles. For this purpose, multiple primary coils, also known as transmitting coils, are placed beneath the road surface, while one or more secondary coils are installed on the underside of the electric vehicle [1].

The receiver in the vehicle has an antenna that transmits an radio frequency (RF) signal at a frequency of approximately 13 MHz. Once the vehicle is positioned over a ground antenna, this signal is received. As a result, the contactless power transfer is activated through the coils in a management unit, enabling the vehicle battery to charge. In contrast, conventional vehicles keep the coils inactive since no signals are emitted from the vehicle side. The charging process can occur both while the vehicle parks and while it is moving. During stationary charging, the vehicle is parked over the primary coils, whereas dynamic charging allows for energy transfer while the vehicle is moving [1].

The efficiency of energy transfer depends on various factors. One of these factors is the air gap between the vehicle’s underside and the coils embedded in the road [3]. The smaller the gap, the more efficient the energy transfer can be. Similarly, the alignment of the vehicle plays a role: Optimal energy transfer can only occur when the receiver coils are aligned as accurately as possible with the transmitter coils. However, in road traffic, there may be deviations and efficiency losses due to various factors such as parked cars, overtaking maneuvers, or construction sites [2].

Use cases for DWPT in the transportation sector

Due to the large-scale expansion of electromobility, DWPT presents an interesting charging solution in the transportation sector as it provides vehicles with energy to electric vehicles while in motion. According to the current state of research, various use cases of the technology are conceivable (cf. Figure 4).

The use cases of DWPT in the transportation sector encompass both passenger and freight transportation. In passenger transportation, DWPT technology offers various possibilities for implementation in local public transport, particularly in regular bus services, e-taxis, and trams [1, 4]. Due to repeated usage of the same routes, which may also be shared with other vehicles such as taxis, buses are ideal candidates for integrating DWPT. Similarly, trams could charge on specially equipped tracks, thus eliminating the need for conventional overhead lines [1].

Equipping routes with coils requires careful planning to identify suitable locations. Several factors need to be taken into account when planning routes: High capacity utilization is crucial for economic efficiency. Especially when planning the integration of DWPT to bus routes, it is important to ensure that sufficient energy is transmitted at the designated points during the journey. Otherwise, unplanned charging stops impede smooth operation. In addition, external factors such as road conditions and the transfer capability during the journey influence the possibility of continuous charging. However, according to the study by Schraven et al., dynamic wireless power transmission has the potential to increase the availability of public transport for passengers, as vehicles can spend more time on the road instead of waiting at charging stations [1]. In addition, the study shows that DWPT can also be applied in freight transport on factory premises, airports, ports and transfer stations [1].

The deployment on the motorway poses a use case both for passenger and freight transport. In this setting, cars, intercity buses as well as long-distance trucks could charge using DWPT while driving. The wireless energy transmission enables longer operating times and fewer charging breaks for vehicles.

The combination of DWPT and autonomous driving may also offer potential applications in logistics and public transport in the future. Intelligent e-vehicles can charge without outside interference by driving appropriate routes equipped with inductive charging technology. This is already being researched in Germany in terms of static inductive charging: the Advantage project, funded by BMWK, investigates fully automatic charging of electric vehicles and interoperability with inductive charging systems. The integration of autonomous vehicles into the transport system and into the inductive charging infrastructure will be examined with regard to personnel deployment, energy management and network integration [6, 7]. In the following, an overview of research projects in the context of DWPT is given.

Overview of selected DWPT research projects

The ELINA project is testing the use of DWPT technology for electric vehicles in public spaces. Under the leadership of EnBW, the Stadtwerke Balingen, the Institute for Vehicle Systems Engineering of the Karlsruhe Institute of Technology (KIT) and Electreon Germany GmbH are involved in the project in addition to FfE e.V.. In addition to ELINA, there are other projects in Germany and internationally that are dedicated to testing the technology (cf. Table 1).

Table 1: Overview of selected DWPT research projects [8, 9, 10, 11, 12]

In the following articles of this series, the framework conditions of the DWPT technology and its potentials for public transportation in Germany will be presented, followed by aspects of technology acceptance. In addition to an ecological assessment of the impacts, options for action will also be provided.

More Information

•  ELINA – Deployment of Dynamic Inductive Charging Infrastructure in Public Transport
• Standardization Landscape for Electromobility

Literature

[1] Schraven, S., Kley, F., Wietschel, M. (2016). Induktives Laden von Elektromobilen – Eine techno-ökonomische Bewertung. In: von Weizsäcker, C., Lindenberger, D., Höffler, F. (eds) Interdisziplinäre Aspekte der Energiewirtschaft. Energie in Naturwissenschaft, Technik, Wirtschaft und Gesellschaft. Springer Vieweg, Wiesbaden. https://doi.org/10.1007/978-3-658-12726-8_16 (retrieved on 06.07.2023)
[2] Hisung, M. (2022). Grundlagen und Stand der Technik. In: Detektion von magnetischen Störungen der elektrischen Fahrzeugkomponenten auf Basis einer Mustererkennung am Beispiel eines automatisierten Fahrzeugpositionierungssystems. Wissenschaftliche Reihe Fahrzeugtechnik Universität Stuttgart. Springer Vieweg, Wiesbaden. https://doi.org/10.1007/978-3-658-39947-4_2
[3] VDE ETG (2013): Laden ohne Kabel – Die kontaktlos-induktive Energieübertragung in der Elektromobilität; https://www.vde.com/de/etg/arbeitsgebiete/informationen/ladenohnekabel (retrieved on 22.05.2023)
[4] Viehmann, A., Koschke, B., Rohm, J. et al. Senkung der Infrastrukturkosten für induktives Laden durch fahrzeugseitige Regelung. ATZ Extra 27 (Suppl 3), 22–27 (2022). https://doi.org/10.1007/s35778-022-0534-3
[5] Electreon (2023): The infrastructure to support mass EV adoption; https://electreon.com/media-kit (retrieved on 12.07.2023)
[6] ifak (2023): Automatische induktive Ladung von autonomen Elektrofahrzeugen in Logistik und Verkehr – Advantage; https://www.ifak.eu/de/projekte/advantage (retrieved on 12.07.2023)
[7] Reiner Lemoine Institut (2023): Autonomes Fahren und Laden im ÖPNV; https://reiner-lemoine-institut.de/autonomes-laden/ (retrieved on 12.07.2023)
[8] Smart Road Gotland – Powered by Electreon: The World’s First Wireless Electric Road Charging an E-Bus and an E-Truck; https://www.smartroadgotland.com/ (retrieved on 06.07.2023)
[9] EDAG Group (2023): LaneCharge: Semidynamisches Induktives Ladesystem; https://www.edag.com/de/lanecharge-semidynamisches-induktives-ladesystem (retrieved on 06.07.2023)
[10] Hochschule Hannover (2019): LaneCharge: Das induktive Laden von Elektrofahrzeugen wird zukünftig an der Hochschule Hannover weiterentwickelt; https://www.hs-hannover.de/ueber-uns/organisation/kom/aktuelles/lanecharge-das-induktive-laden-von-elektrofahrzeugen-wird-zukuenftig-an-der-hochschule-hannover-weiterentwickelt/ (retrieved on 06.07.2023)
[11] MILAS Ladesystem (2022): Modulare intelligente induktive Ladesysteme für autonome Shuttles; https://www.milas-ladesystem.de/projekt-idee-vorstellung.html (retrieved on 22.05.2023)
[12] Randeloff, M. (2011): KAIST OLEV: Die Straße als Range Extender; https://www.zukunft-mobilitaet.net/7424/zukunft-des-automobils/elektromobilitaet/kaist-olev-induktion-elektroauto-ladestrom/ (retrieved on 06.07.2023)