New ways of inductive charging
Climate change is one of the greatest challenges of our time.
In the transport sector, the electrification of motor vehicles can provide a decisive contribution to the reduction of CO2 emissions.Unfortunately, simple and convenient charging solutions for electric vehicles are not self-evident and there is consequently a correspondingly high demand for convenient charging solutions with significantly increasing numbers of e-vehicles on the road. The way forward is inductive charging, which is not only convenient but also a future-oriented alternative to wired charging. Bidirectional contactless charging of vehicles goes one step further and represents a new and exciting topic in electromobility.
Bidirectional inductive charging solves some of the current difficulties of cable-based charging stations. It eliminates, on the one hand, the plugging in of messy, heavy cables and, on the other hand, the manual registration and starting of the charging process. In order to investigate this topic further, the research project FEEDBACCar (Future Electric Energy Distribution by Aggregated Clusters and Cars with Automated Response) was initiated by a consortium. Zollner Elektronik AG, one of the consortium partners, played a major role in the development and construction of an inductive, bidirectional charging system, including the dimensioning of the power electronics. The software part of the project was successfully implemented by Zollner in cooperation with the specialists from ServiceXpert Gesellschaft für Service-Informationssysteme mbH. The FEEDBACCar project (FKZ: 16EM3129-2) pursued the goal of integrating the electric vehicle as an energy storage device in smart home concepts in order to also form a basis for new business models with the bidirectional contactless charging technology. In this combination with domestic energy management, the purchase of electric vehicles should be made economical in the future and thus the attractiveness of electromobility increased considerably.
The project had particularly high requirements in terms of charging performance, efficiency and safety of the system. For charging and feeding back into the grid, an efficiency of up to 92 percent could be achieved at a charging power of up to 11 kW. Ultimately, this result was achieved through the excellent coil design and the control algorithms that were optimally matched to it.
Another highlight in this research project is the integrated positioning system, which helps the driver to accurately align the vehicle over the ground coil. The positioning of the two coils in relation to each other (on the vehicle and ground side) is regulated by the IEC 61980 standard, which prescribes a positioning window in relation to the centre of the coil. The positioning system thus not only helps to achieve optimum efficiency during charging, but also to comply with the prescribed general conditions for positioning.
To ensure the safety of the system, it is necessary to protect people in the immediate environment of the system from potential hazards due to electromagnetic radiation and to detect metallic objects in the charging field, as these would heat up.
Therefore, two sensors have been integrated that prevent or stop charging if there are metallic objects between the coils or people in the immediate environment. The problem is indicated to the driver so that he can remove the objects and restart or continue the charging process.
The charging system consists of a coil and vehicle electronics on the vehicle side and a coil with wallbox on the infrastructure side, which communicate with each other via WLAN. This controls and monitors the entire charging process. In implementing the wireless communication, the IPv6 procedure was used, which, in contrast to IPv4, has a more comprehensive address range and thus offers greater future security as the number of devices with internet connections increases. By dispensing with manual registration with a charging card and the manual starting of the charging process, the solution was greatly simplified and optimised for the user. The control unit in the vehicle was implemented with fully AUTOSAR-compliant software and is thus prepared for integration into series production. The ServiceXpert engineers also took on the tasks of configuration, implementation and integration of all AUTOSAR elements. Thanks to their many years of experience in embedded software development, with and without AUTOSAR, as well as in the connected areas of diagnostics, integration and testing, the ServiceXpert experts were able to support Zollner AG in a business relationship based on partnership and thus make a significant contribution to the success of the project.
ServiceXpert developed the software design, the software modelling according to the AUTOSAR standard and the configuration of the complete AUTOSAR basic software.
Furthermore, the AUTOSAR experts took over the integration of algorithms for the control and regulation of the power electronics of the DC/DC converter as well as the implementation of the necessary functionality for the connection to higher and lower software layers. Various drivers (complex device drivers) were implemented to generate a total of twelve PWM signals and to control several temperature sensors via an I²C bus. The software modules on the higher software layers were developed according to the current state of the art in order to fully exploit the possibilities and advantages offered by an AUTOSAR 4.2 stack with a currently most advanced automotive multicore microcontroller. For this reason, all state machines within the software were modelled via the AUTOSAR BswM (Basic Software Mode Manager) and communication interfaces (including WLAN) were routed via the AUTOSAR communication stack. This made it possible to achieve maximum abstraction of all signals used in the system to the software components, which contributes to the modularity and maintainability of the software.
In order to be able to test such complex systems and ensure the quality of the software, modern, automated test procedures are important. Here, ServiceXpert draws on its many years of expertise in the areas of classic software development, build and test automation as well as integration tests with Hardware in the Loop (HIL) simulations. For the FEEDBACCar project, a Continuous Integration Server was set up which, in addition to automated software builds and static code analysis (MISRA C, CERT C Secure Coding Standard), was also able to flash the software directly onto the hardware in order to subsequently perform automated integration tests. In addition to the commercially available tools, solutions developed in-house were also used, such as a low-cost HIL to stimulate the hardware and a complete simulation of the WLAN communication. This made it possible to test all states in the system without having a complete system setup on site. The time and effort required to integrate the control unit into the overall system was thus significantly shortened and made a major contribution to the successful completion of the project.
The overall integration was then carried out in cooperation with Zollner Elektronik AG, first on a laboratory setup with all hardware components and finally in three prototype vehicles. The close partnership with ESG Mobility, who established the connection to the vehicle interfaces, proved to be extremely useful. This ensured smooth integration of the laboratory set-up into the vehicles.
The successfully equipped prototypes were presented for the first time at an "Inductive Charging" technology day held by Zollner Elektronik AG on 17 October 2019. Among the participants were representatives of well-known automotive OEMs, who showed great interest in the solution from Zollner and ServiceXpert.
ServiceXpert, an ESG-Group company, employs over 85 staff in Hamburg and Munich. ServiceXpert is a Europe-wide operating system and software house with a focused service portfolio for Lifecycle management of EE information for leading manufacturers of commercial vehicle and their supplier industry.