27.12 MHz Bi-Directional Wireless Power Transfer Using Current-Mode Class D Converters with Phase-Shift Power Modulation

Bi-directional power transfer enables new paradigms in how users ubiquitously share and store energy. Increasing switching frequency benefits wireless power transfer (WPT) in miniaturization. Bi-directional WPT at high-frequency (HF, 3-30 MHz) and very-high-frequency (VHF, 30-300 MHz) is challenging, especially with adjustable power and resilience to different loading and coupling conditions. We investigate 27.12 MHz bi-directional WPT using current-mode class D (CMCD) converters. We use a simplified model that is better for design, which we derived from a well-known current-controlled-voltage-source (CCVS) model. A prototype demonstrates a proof of principle and shows that both models predict power and efficiency adequately under different coupling and phase shift. Criteria for maximum power and efficiency are also discussed.