Coaxial Nested Couplers-Based Offset-Tolerance Rotary Wireless Power Transfer Systems for Electric Excitation Motors

In order to improve poor anti-offset capability of rotary transformer in electric excitation motor, a coaxial nested rotary wireless power transfer (CNR-WPT) system has been proposed in this paper. Firstly, considering the spatial geometric relationship of the coils and the power transmission efficiency of the CNR-WPT, the preliminary coil structure has been proposed. Secondly, through theoretical derivation, the specific relationship between the mutual inductance of the coils and the offset have been studied to verify the feasibility of the preliminary design. Thirdly, aiming at the problem that the CNR-WPT is susceptible to steel interference, the magnetic field has been optimized by adding ferrite and introducing a protective casing in this paper. Finally, an experimental platform for CNR-WPT system has been built. The experimental results verify that the power transmission efficiency of the CNR-WPT system can reach 90% when the radial offset and axial offset are below 5 mm, and the angular offset is below 5°. The energy losses can be reduced by adding ferrite and protecting the casing. The CNR-WPT system thereof can also be applied to other rotary power transmission occasions.