Analysis and Design of an Air-Gap-Insensitive Hybrid Inductive Power Transfer System With Constant Voltage Output

Inductive power transfer (IPT) systems that are insensitive to air gaps are preferable for wirelessly charging of electric vehicles over different air gaps. To fulfill this need, this paper proposes a six-coil hybrid IPT system that uses particle swarm optimization to maintain constant voltage output over a wide variation of air gap and load. It employs two orthogonal DD coils and one quadrature (Q) coil pad structure on each side to achieve stable and load-independent output voltage with high tolerance to air gap variation. A detailed mathematical model with theoretical analysis is presented for the proposed system, which can be operated safely even under no load conditions. To demonstrate the applicability of the proposed concept, experimental results of a prototype system are presented. The results indicate that the proposed system can operate under simultaneous variations of air gap from 20 mm to 140 mm (the coupling factor varies from 0.1–0.6) and load from 80 Ω to 400 Ω while maintaining the output voltage within 5% and at maximum dc–dc efficiency of 96%.