A Magnetic Resonance Wireless Power Transfer System Robust to Distance Variation Using Dual-Matching Scheme

A magnetic resonance wireless power transfer (WPT) system achieves maximum power transfer efficiency (PTE) at the position where critical coupling occurs, but the PTE degrades significantly off this position. In this paper, we propose a new design technique that can achieve high PTE over a wide range by generating critical coupling at two other positions by using a switchless passive dual-matching technique. We present a receiver (RX) and transmitter (TX) configuration implemented with lumped elements for dual-matching and derive the values of each device analytically. A RX part is constructed by connecting parallel LC and C in series to resonate at two frequencies. Considering the mutual inductances between the TX and RX coil at two distances, T-type TX matching is designed to achieve conjugate matching at two resonant frequencies for the source impedance simultaneously. To verify the performance of the proposed technique, a WPT system with critical coupling at 25 and 75 mm for two frequencies of 4 and 6.78 MHz was implemented, and the PTE was measured. The average PTE in the range of 20–80 mm is 70%, and it is verified that the proposed technique can achieve robust WPT system to distance variation.