Inductive Power Transmission

Inductive power transfer systems have many advantages towards wired solutions, such as the elimination of disturbing wires, the omission of open contacts and the simple overcoming of air gaps. Thus, this technology offers added value in a wide range of applications, for example:

  •    Auxiliary supplies  (e.g. form 48 V to 48 V or 24 V to 24 V)
  •    Wireless plugs for demanding ambient conditions
  •    Energy supply for moved electrical loads
  •    Wireless charging for electric vehicles

We develop and realize complete inductive power transfer systems ranging from the FEM simulation as well as power electronics analysis/simulation and mechanical integration to the realization of complete prototypes.

Inductive Charging

The improvement of user comfort is a crucial point for the success of electric vehicles.

We developed an inductive charging system for battery electric vehicle in order to facilitate an autonomous charging process without any user interaction. This approach improves user comfort and facilitates the necessary technology for an ubiquitary charging concept.


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Not only the increase of electric driving range, but also the improvement of user comfort is a crucial point for the success of battery electric and hybrid electric vehicles. In view of ergonomic and practical aspects of the charging process, wireless charging is a consecutive step for the development of charging infrastructure. We developed an inductive charging system for battery electric vehicle in order to facilitate an autonomous charging process without any user interaction. This approach leads to a tremendous improvement of user comfort and facilitates the necessary technology for an ubiquitary charging concept.

Project Targets

  • Design of a position tolerant wireless charging system
  • Transmission power of 3,7 kW (scalable  up to 11 kW)
  • Charging without user intervention (“autonomous” electric driving)
  • Wireless communication between primary and secondary side


  • Selection of a suitable coil geometry and arrangement
  • Optimization of the coupling coils to reduce the system losses
  • Safe and efficient operation of the charging system


  • extremely compact vehicle side coils (diameter of a CD)
  • 94% system efficiency up to the battery
  • Integration of a low-rate and robust information transmission channel (max.3,5 kW)

Project Partners

Research project in cooperation with the Chair of Electron Devices (LEB) and further chairs of the Universität Erlangen-Nürnberg

Inductive Ball-Bearing

The ability to transfer power in small moving systems is required for a wide range of applications such as wind power systems with electronics integrated in the rotor blades or highly-automated Industry 4.0 production platforms. The goal of the project is to develop a technology for the contactless transfer of power and data in small moving components in harsh environments.


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Project Targets

  • Realization of an inductive energy transfer for fast moving components
  • Transmission power up to 20W
  • Wireless communication of information as well as higher data rates for the transmission of sensor & actuator information


  • High integration level of the coupling coils
  • Realization of a rotating transformer with metal parts in the surrounding
  • High mechanical conditions


  • Demonstration of the functionality of the rotating application (ball-bearing with shaft)
  • Practical robustness tests & simulations of electronic assemblies beyond the normative measuring range
  • Near field transmission at high frequencies including alternative capacitive transmission systems with differential directional coupler
  • High-quality digital modulation and thermoelectric optimization of the crossover

Project Partners


Inductive Plug

Inductive power transfer offers the capability to inductively (contactless) transmit power in moving components. The technology could be used as the basis for robust inductive plugs in food processing facilities or the chemical industry or as a simpler and safer way to provide electricity to agricultural machinery attachments that need robust plug solutions.

Project Targets

  • Realization of an induction plug for special environmental conditions
  • Transmission power up to 1000 W
  • Easy handling
  • High robustness
  • High efficiency


  • Due to the requirement for high compactness only a small power loss can be dissipated (high efficiency necessary)
  • Integration into a small assembly space


  • Demonstration of the functionality
  • System design (across all applications) for magnetics and power electronics with improvement of the performance and simulation methods
  • Practical robustness studies and simulations of electronic assemblies beyond the normative covered measuring range

Project Partners

Wireless Office - Bachmann

A battery and a receiving / transmitting unit for the inductive energy transfer were integrated into a roll container. The battery storage is charged at the socket (optionally inductive). The DC voltage network can be supplied wireless or by cable through the roll container.



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Project Targets

  • Next generation of desks without any visible connections - „Clean Desk“
  • Higher flexibility of the desk


  • Inductive power transmission with medium power (>100W) in the area of protective low voltage leads to high currents
  • Providing a stabilized voltage for the desks DC voltage network


  • Very compact power transmission system (150 mm x 150 mm x 40 mm)
  • Representable air gaps up to 20 mm
  • Transferable power <150 W

Project Partner


Contactless Charging of Hearing Aids

Different coil types and positions were investigated to minimize eddy current in the battery and maximize the efficiency of the electromagnetic transmission. To ensure safe battery charging and discharging, the whole electronics is integrated into the given space and controlled by a tiny microcontroller. As the battery is based on a new chemistry (silver-zink-based), different charging algorithms were implemented and evaluated.

Project Targets

Most hearing aids are powered by non-rechargeable batteries.To improve ergonomics and usability of hearing aids, a inductive chargeable retro-fit battery module for common hearing aids was developed.



  •    Very small physical size of PCB and secondary coil
  •    Battery must supply the hearing aid for at least 18h and be charged again within 6h
  •    Intelligent charging control with battery voltage and charge current monitoring



During this project, a inductive chargeable retrofit battery for hearing aids was developed, integrated and tested. This retrofit module includes a silver-zink based battery, that can be charged inductively and may replace a conventional battery of size 13.


Project Partners



Project Duration

2011 - 2012

HF-Generator for Inductive Heating

The performance and toughness of a CoolMOS™ transistor in high frequency clocked bridges should be shown by the example of a HF-generator for inductive heating.

Project Targets

Development of a HF generator with an extremely high efficiency for inductive heating.



  •     Output power ~ 1 kW
  •     Working frequency 100 - 500 kHz
  •     SMD power transistors
  •     Input voltage 230 Vac
  •     Absolute operational safety under all load conditions


For the generation of an HF-power of 1 kW in the frequency range up to 500 kHz, the generator was realized as a resonant half-bride converter. Each of the both half-bridge switches consist of two parallel connected CoolMOS transistors (type SPB20N60C2 - 190 mOhm, 600 V). Thereby the generator achieves an efficiency of more than 97%. Due to the low power loss, the power transistors could be mounted in SMD technology and heated by the circuit board. A special control method ensures resonant commutation under all conditions (even transits).


Project Partners

Infineon AG


Project Duration

2000 - 2001


Authors Title Talk Paper
Ditze, S.; Heckel, T.; März, M.

Influence of the junction capacitance of the secondary rectifier diodes on output characteristics in multi-resonant converters,

2016 IEEE Applied Power Electronics Conference and Exposition (APEC), Long Beach, CA, USA 2016

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Joffe, C.; Roßkopf, A.; Ehrlich, S.; Dobmeier, C.; März, M.

Design and optimization of a multi-coil system for inductive charging with small air gap,

2016 IEEE Applied Power Electronics Conference and Exposition (APEC), Long Beach, CA, USA 2016

x pdf
Sanftl, B.; Joffe, C.; Trautmann, M.; Weigel, R.; Koelpin, A.

Reliabe data link for power transfer control in an inductive charging system for electric vehicles,

2016 IEEE MTT-S International Conference on Microwaves for Intelligent Mobility (ICMIM)

Roßkopf, A.; Bär, E.; C. Joffe; Bonse, C.

Calculation of Power Losses in Litz Wire Systems by Coupling FEM and PEEC Method,

IEEE Transactions on Power Electronics

Roßkopf, A.; Schuster, S.; Endruschat, A.; Bär, E.

Influence of varying bundle structures on power electronic systems simulated by a coupled approach of FEM and PEEC,

IEEE Conference on Electromagnetic Field Computation (CEFC)

Joffe, C.

Modular Charging Solutions,

ECPE Workshop "Power Electronics for e-Mobility", 22 - 23 June 2016

Ditze, S.

Steady-State Analysis of the Bidirectional CLLLC Resonant Converter in Time Domain,

INTELEC, Vancouver 2014

Joffe, C.; Ditze, S. Rosskopf, A.

A Novel Positioning Tolerant Inductive Power Transfer System,

ETEV, Nürnberg, 2013

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Authors Title Talk Paper
Ditze, S.; Endruschat, A.; Schriefer, T.; Rosskopf, A.; Heckel, T.

Inductive Power Transfer System with a Rotary Transformer for Contactless Energy Transfer on Rotating Applications,

2016 IEEE International Symposium on Circuits and Systems (ISCAS), Montreal, Quebec, Kanada 2016

Gerstner, H.

Inductive Energy and Data Transmission in Novel Industrial Applications,

Embedded Platforms Conference Munich, 10. November 2016


Authors Title Talk Paper
Trautmann, M.; Joffe, C.; Pflaum, F.; Sanftl, B.; Weigel, R.; Heckel, T.; Koelpin, A.

Implementation of simultaneous energy and data transfer in a contactless connector,

2016 IEEE Topical Conference on Wireless Sensors and Sensor Networks (WiSNet)

Ehrlich, S.

Design and Optimization of a Highly Integrated Inductive Power Transfer System for Pluggable Applications,

Wireless Congress: Systems & Applications Munich, 10. November 2016