kQ-product analysis of multiple-receiver inductive power transfer with cross-coupling

This paper investigates maximum achievable efficiency of inductive power transfer (IPT) system with arbitrary number of receivers. We derive the formulas of optimal loads and maximum efficiency based on N-port network model. Via analysis and computer simulations, we show that the cross-coupling among receivers does not affect system efficiency if load resistances and reactances are jointly optimized. We also prove that the maximum efficiency is dominated by a so-called system kQ-product, whose square is interestingly, equal to the sum of squares of kQ-products of individual transmitter-receiver links.