Study on Efficiency Enhancement of Resonant Coupled Wireless Power Transmission Using Two-side Impedance Matching

Non-radiant wireless power transmission (WPT) system using high quality factor magnetic resonant coupled coils has been researched for mid-range wireless powering applications, and can provide higher transmission efficiency over a large operating distance than an inductive coupled system. However, the variation in the coupling distance between near-field coils changes the resonant frequency and the overall system impedance which is a serious issue for highly efficient wireless power transmission. In this paper, we proposed a two-side impedance matching technique using self-tuned L-matching circuits implemented at both the transmitting and receiving sides of a 4-coil resonant coupled WPT system to maximize the efficiency at a single frequency. The tuning values of inductance and capacitance for matching networks are derive using the Q-based design principle along with extracted impedance and S-parameters to retain magnetic resonant condition. The feasibility of the conceptual approach is verified by simulation in an electric automation tool. The proposed two-side matching technique improves transmission efficiency of over 90% at small coupling distance and also successfully retains the resonant frequency. Comparing with one-side impedance matching, this technique increases efficiency of 16.3% and 10% at 90 cm and 115 cm respectively.