Electromobility: Wireless charging in everyday life Inductive charging station in use at the Automotive Research Centre Niedersachsen (NFF)
Inductive charging of electric vehicles is an innovative charging technology that enables convenient wireless charging. In addition to increased safety due to the elimination of visible cables, it offers great potential in terms of automating the charging process. Technische Universität Braunschweig, in collaboration with partners, has developed and extensively tested a stationary inductive charging system. The system has been installed at the NFF. It is used by the TU Braunschweig’s facility management team, which has integrated inductive charging into its operations.
In the LISA4CL research project, two institutes of Technische Universität Braunschweig and INTIS GmbH have developed a stationary inductive charging system for electric vehicles with a charging capacity of 22 kW. Component tests for the inductive charging technology were carried out at the elenia Institute for High Voltage Technology and Energy Systems and the Institute for Electrical Machines, Drives and Traction Drives (IMAB) at TU Braunschweig. At INTIS GmbH, the inductive charging system was set up and a light commercial vehicle test vehicle was modified. Subsequently, the entire system was extensively tested in collaboration with TU Braunschweig in preparation for the field tests. This included both functional and safety testing of the system to ensure its suitability for practical use.
The German Federal Ministry of Digital Affairs and Transport (BMDV) is funding the LISA4CL project for four years until March 2024 with around €1.6 million as part of the Electric Mobility funding programme. TU Braunschweig has received more than €1.3 million for the implementation of the project, divided between the elenia Institute for High Voltage Technology and Energy Systems and the Institute for Electrical Machines, Drives and Traction (IMAB). In addition to the project partner INTIS GmbH, Fairsenden, the Berlin Agency for Electric Mobility eMO and VW Commercial Vehicles were associated partners. PtJ (Projektträger Jülich) was the project management organisation. The implementation of the funding guideline was supported by NOW GmbH (National Organisation Hydrogen and Fuel Cell Technology).
Daniela Kluckert, Parliamentary State Secretary at the Federal Ministry of Digital Affairs and Transport:
“The LISA4CL research and development project opens up the possibility of using wireless charging, which is already part of everyday life for mobile phones, for electric vehicles in urban logistics. In particular, inductive charging promises to significantly improve accessibility by making access to the charging infrastructure much easier. The BMDV supports technology transfer and innovation to accelerate the decarbonisation of the transport sector and at the same time support Germany’s competitiveness as a business location. The funding of LISA4CL is part of this effort.”
Professor Bernd, Head of the elenia Institute at TU Braunschweig:
“Intelligent charging concepts are essential for the grid and system integration of electric vehicles. They enable the ecologically and economically optimised operation of electric vehicle fleets.”
During the field test phase, the inductive charging system was initially used at Fairsenden in Berlin in inner-city logistics operations. A field test with conductive charging points was already underway at Fairsenden for a practical comparison with a wired charging infrastructure. In the final phase of the project, the inductive charging technology was installed at the Automotive Research Centre Niedersachsen (NFF) in Braunschweig. The TU Braunschweig’s Facilities Management Department is using the prototype vehicle to investigate inductive charging in regular practical use. The charging system will continue to be operated beyond the end of the project to enable a long-term study of inductive charging technology.
About the technology: An inductive charging system consists of a road-side component and a vehicle-side component. Using magnetic coils, energy is transferred from the road surface to the parked vehicle via an air gap in a non-contact process. Inside the vehicle, the electrical energy is transferred to the high-voltage battery via power electronic circuits.
Findings from the development and testing of an inductive charging system
The 22 kW inductive charging system developed was built as a prototype. The system can be divided into a power path for energy transfer and a communication path for controlling the individual components of the system. The implemented charging communication between the roadside components of the system and the vehicle is based on existing standards in this area. Hardware and software components for communication and control have been developed and integrated into the infrastructure and vehicle side of the inductive charging system.
The system efficiency of the developed system is consistently high and is not significantly reduced even by inaccurate parking. A prerequisite for these properties is the optimisation of the inductive transmission system, in particular with regard to the specific requirements of the application. It has been shown that, in addition to the consideration of the overall system, the optimisation of all individual components is of great importance for maximising the overall efficiency. When interpreting the results, it is also necessary to take into account the vehicle-specific boundary conditions.
Light commercial vehicles offer sufficient installation space to install efficiency-optimised systems that can tolerate the coil misalignment that can occur during manual parking. The smallest possible space requirement in the usable area of the vehicle is desirable. Space-saving integration of the system is possible in this vehicle class. “Seamlessly integrated inductive charging systems with high efficiency are an essential key to the widespread use of contactless charging technology in the automotive sector. At the same time, inductive charging technology offers great potential for autonomous driving,” says Prof. Markus Henke of the Institute of Electrical Machines, Drives and Traction (IMAB) at TU Braunschweig.
For future series production, such systems must be interoperable. For this reason, standardisation bodies are also currently working on inductive charging systems. It is planned to incorporate the results of the developed system, such as the coil design, into the ongoing standardisation of inductive charging systems in the 22 kW power class. To this end, recommendations from the project will be developed in standardisation committees. The developed charging system will be adapted to the current test vehicle. In further development processes, optimisation for the passenger car sector is also conceivable.
Real-life operation of the inductive charging system in field tests
The field tests showed that the inductive charging technology is technically feasible and functional in real-life operation. The inductive charging system was integrated into the operating procedures of both Fairsenden and the TU Braunschweig facility management. The system has been positively evaluated by the users. In addition, practical experience to date has shown that the maintenance requirements for the technology are low.
The charging data recorded during the field test in Berlin show that the inductive charging system was used in everyday life. Overnight charging at the end of the day was common, as were occasional charging stops throughout the day. The inductive charging technology offers a simple and user-friendly integration of opportunity charging. Charging can be initiated directly from the driver’s seat at the end of a journey. This simplified operation demonstrates the potential of contactless charging to optimise operational processes.
Advantages over wired charging
In order for inductive charging technology to gain market acceptance, it must offer practical benefits to the user compared to conventional charging technology. For commercial users of the vehicles, simplification of the operating process and a high utilisation rate are crucial.
In order to assess these factors and compare them with conductive charging, information from the real operation of the charging technology is required. Both the wired charging points in the conductive field test in Berlin and the inductive charging station are connected to a central charging management system, also known as a backend, which records data from the charging processes. Power meters were also used to record the necessary charging data from the charging processes. This showed that in practice, wireless charging can achieve efficiencies comparable to those of wired charging.
The field test in Berlin shows that opportunity charging with the inductive charging system was chosen as a charging option significantly more often than conductive charging. Opportunity charging mostly took place when the vehicle was being charged at the depot. The advantage of the simple and user-friendly start of the charging process is evident here. A positive effect of the additional charging processes is that the range of vehicles in operation increases. The advantage of user-friendliness also reduces the risk of charging processes being forgotten during operation. Another advantage of contactless charging is that there is no need for a charging cable, which can be a disruptive factor when loading and unloading vehicles. Furthermore, the test vehicle was only charged inductively, although conductive charging was still possible. This demonstrates the reliability and acceptance of inductive charging technology.
Impact on the power grid and intelligent charging concepts
As with conductive charging, the grid and system integration of inductive charging infrastructure is a key consideration in the context of grid and generation-oriented operation. In order to investigate the grid feedback of the inductive charging system, a grid analysis measurement device was integrated at the interface between the charging point and the electricity grid.
The data analysis shows that the grid feedback of a single inductive charging system is low. In view of the increasing number of battery-powered electric vehicles and charging points in the future, negative effects on the quality of the power grid cannot be ruled out. Simulations carried out as part of the project show that a high penetration of electric vehicles will pose challenges in terms of voltage stability and resource utilisation. The grid-oriented charging concepts investigated offer a way to minimise grid feedback and maintain grid stability. This was validated by simulations and laboratory tests. Inductive charging points also provide a technical means of implementing grid-oriented charging processes.
From a system perspective, the targeted integration of renewable energies in the charging of electric vehicles is crucial. Studies conducted as part of the project have also shown that generation-oriented charging concepts can increase the economic efficiency of electric vehicle fleets and improve their carbon footprint.
