Harmonic balance design of wireless resonant-type power transfer links

Harmonic-balance (HB) based nonlinear techniques are exploited for the design of a high-efficiency and medium-power switching mode oscillator, used as continuous power source in a wireless power transmission system. The oscillator power is transmitted through resonant coils over variable distances. To account for the resonant frequency variations, which also tune oscillation frequency, a broadband design of the system is carried out with the oscillator load including the resonant coupling and the rectifier. The oscillator efficiency, the RF-to-DC system efficiency and the DC power are then directly optimized for any coupling distance of interest. A Royer-type oscillator is designed and prototyped using the proposed technique. The oscillator exhibits 40 W at 223 kHz with 75% conversion efficiency while the WPT system efficiency, DC-to-DC, is better than 60% for coupling distances of the order of 10 cm.