Synchronous machines are electric rotating field machines that require a direct magnetic field on the rotor for operation. This can either be caused by permanent magnets or generated by an electrical winding. The permanent-magnetically excited synchronous machine is becoming more and more important in the medium power range (1kW-100kW). However, the disadvantage of this machine is that permanent magnets are temperature-sensitive and difficult to calculate due to the use of rare earth metals. In addition, the noncontrollable magnetic field of the permanent magnets has a negative effect on the efficiency of the machine, especially at high speeds. Therefore, the industry is very interested in finding a reasonable alternative to permanent magnet synchronous machines.
An alternative is the electrically excited synchronous machine. However, since energy is required on the rotor side for the electrical coil/winding, this must be transferred from the stator to the rotating rotor. For electrically excited synchronous machines with high power (>100kW), this is done by means of slip rings. In the medium power class (1kW-100kW), which is used, for example, in electric mobility, hardly any electrically excited synchronous machines are currently used, since the sliding contacts are undesirable, especially in electric vehicles.
In order to create a technically and economically sensible alternative to permanent magnet synchronous machines in this performance class, a technology is required that avoids slip rings. A sensible approach for this is energy transmission via a contactless inductive transmission path.