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Low-cost high-voltage power oscillator for inductive energy transferertragung


This further development of a Royer converter allows a reliable, wireless power transfer of energy at high switching frequency and voltage. It is thus possible to implement wireless power transfer systems that can operate with mains voltage without using an additional buck converter


In the wake of new forms of mobility and further technical achievements, the focus is also shifting to new, more flexible charging technologies. Wireless charging offers many benefits. However, there are no low-cost, high-voltage components available. In the industrial environment, Royer oscillators are already used for inductive heating. Until now, however, they could only be operated with a low input voltage and were therefore not suitable for high-power applications.


Today, systems with serial compensation on the primary side are predominantly used for high power ranges. However, these are not no-load proof, or require additional components. There is currently a lack of a cost-effective, reliable solution for an efficient charging infrastructure in the mains voltage range.


By adding at least one more power switch/transistor (Q3, Q4...Qn) in series to the existing power switches (Q1, Q2), a commercially available Royer converter with MOSFET transistors becomes a high-voltage converter compensated in parallel on the primary side; the dielectric strength is thus significantly increased. The additional elements are located above the lowest switching elements to ensure a low potential at the pick-off (Qs1 and Qs2). To balance the voltage, additional capacitors (Cs) and resistors (Rs) are used in parallel to the circuit breakers Q1 to Qn. The control is galvanically isolated by transformers or combined with transformers and active driver circuits. This allows DC link voltages of 600 to 800 V to be processed while enjoying the benefits of a Royer converter.

Fig. 1: Power path of the oscillator circuit according to the invention with additional power switches Q3 and Q4.
Fig. 1: Power path of the oscillator circuit according to the invention with additional power switches Q3 and Q4.
Fig. 2: Detail of the circuit with capacitors and resistors used in parallel [Image material: University of Stuttgart)


  • cost-effective optimization of proven components
  • high dielectric strength
  • no additional buck converter required
  • designed for high power applications with DC link voltages of 600-800 V

Fields of application

Inductive energy transmission in the range of the line voltage, such as charging infrastructure for electromobility.
But also other products could benefit from this wireless energy transfer technology in the future, such as medical devices (e.g., VAD systems).

Publications and references

D. Maier, J. Noeren, N. Parspour and C. Lauer, "A Novel Power Electronics for Contactless Inductive Energy Transfer Systems," 2018 IEEE 18th International Power Electronics and Motion Control Conference (PEMC), Budapest, 2018, pp. 40-45;

Dipl.-Ing. Emmerich Somlo
Ettlinger Straße 25
76137 Karlsruhe | Germany
Phone +49 721-79004-0
somlo(at) |
Development Status
Patent Situation
DE 102017208111 A1 pending
Reference ID
Technologie-Lizenz-Büro GmbH has been entrusted with the exploitation of this technology and assists companies in obtaining licenses.