Circuit topologies for inductive power transfer systems

Reactive power compensation and system behaviour of the contactless inductive power supply

System overview of an inductive transformer

The structure of a contactless energy transfer system (CET system) is shown in Figure 1. Inductive energy transmission is technically possible with high efficiency and a low coupling factor of the coil system, provided the reactive power of the system is compensated. In inductive transmission, the inductances of the transmission coils are compensated by capacitors. The capacitors can be arranged either serial (s) or parallel (p) to the coils. Basically, the following compensation topologies can be distinguished when using one capacitance each for the primary side (1) and the secondary side (2):

  • 1s2s topology
  • 1s2p topology
  • 1p2p topology
  • 1p2s topology

The selection of the topology used to compensate for the CET system depends on the desired system behavior. For example, a voltage or a current source behaviour can be realized by a suitable selection on the load side. Figure 2 shows the system behavior in terms of voltage transfer function and input impedance for the 1s2s system.

The compensation of the inductive energy transmission path results in several resonance frequencies. The CET system is always operated at one of the resonance frequencies. Based on these foundations, various development and research projects are carried out at the IEW.

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Institute of Electrical Energy Conversion