A contactless slipring (CS) system utilizing inductive-power-transfer (IPT) technology is a good candidate for traditional mechanical slipring assemblies. However

suffering from the high harmonic currents in strong coupling CS systems

the output power will deviate from the theoretical values estimated by the fundamental harmonic approximation (FHA) and its extension method

i.e.

E-FHA

in which the power is transferred by both the fundamental current and the high order harmonic currents. In order to achieve high precise output estimation

a unified analysis is proposed in this paper. First

“Fundamental-harmonic Double Resonance Phenomenon” is revealed via impedance analysis

to address the nature of the high harmonic currents in strong coupling systems. Then

a unified output current expression owning high precision is derived

and followed by a unified fundamental load impedance. Discussions show that both the output and the fundamental load impedance of FHA

and E-FHA are the special cases of the unified expressions proposed. FHA and E-FHA are precise enough for the loose coupling system

whereas the proposed method is indispensable for the strong coupling system with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$k 0.4$. Finally

simulations and experimental measurements of a 1.6kW CS system

as well as the comparative studies related to FHA

E-FHA

and the proposed method

are presented

indicating that the proposed method is effective for high precise output estimation.