A New Bi-Frequency Trifunctional Principle for Wireless Power Transfer

Wireless power transfer (WPT) is rapidly transforming industries such as consumer electronics, electric vehicles and robotics by enabling contactless energy delivery. However, a persistent challenge in WPT systems is achieving soft switching across the full operating range of the transmitter power inverter. This is important because emerging wireless charging standards such as the International Telecommunications Union in Europe set new recommendation in late 2024 to use the Mega-Hertz frequency range for WPT. Soft-switching is essential for minimizing switching losses, reducing electromagnetic interference (EMI), and enhancing system reliability—especially in high-frequency (Mega-Hertz) applications mandated by emerging wireless charging standards. Conventional methods often fail under light-load or no-load conditions, leading to degraded efficiency and compromised performance.This research introduces a new Bi-Frequency Trifunctional Principle that exploits the bifurcation (frequency-splitting) phenomenon between a magnetically coupled Transmitter resonator and a Relay resonator as an “integrated” structure. At bifurcation, two resonant frequencies, namely a low bifurcation frequency (f-) and a high bifurcation frequency (f+), co-exist at a specific magnetic coupling coefficient. By carefully designing f- to be the fundamental frequency and f+ to be close to 3f- (i.e third harmonic frequency), this Bi-Frequency Trifunctional principle skillfully allows:(1) WPT between transmitter and receiver resonators at the fundamental frequency.(2) Soft switching of the transmitter power inverter using coupled current at the third harmonic frequency even under no-load condition.(3) Enhanced effective mutual inductance between the transmitter and receiver resonator, resulting in higher WPT capability and energy efficiency.The proposal requires only the addition of a simple relay resonator, making it an extremely low-cost and scalable solution. It can significantly reduce switching losses, thermal stress, and EMI emissions, thereby extending the lifespan of power electronic components. It is compatible with existing inverter topologies and can be seamlessly integrated into modern WPT architectures without substantial redesign. Preliminary simulations have confirmed its feasibility for full-range soft-switching and improved efficiency under various load conditions. This project will investigate various arrangements of the integrated transmitter and receiver resonator structures using discrete components and/or circuit printing technologies, paving the way for mass production.Since this new principle is applicable to both existing wireless charging standards (100 kHz-1MHz) and emerging standards (1MHz-13.56MHz), this innovation could redefine WPT design principles, offering a resilient, efficient, and scalable solution for existing and next-generation WPT systems. The success of this project will place Hong Kong as a leading innovation hub in WPT technology.