Load-Adaptive Resonant Frequency-Tuned $\Delta$–$\Sigma$ Pulse Density Modulation for Class-D ZVS High-Frequency Inverter-Based Inductive Wireless Power Transfer

This article presents a resonant frequency tuning (RFT) delta–sigma (
$\Delta$
–
$\Sigma$
) signal-transformed pulse density modulation (PDM) class-D converter for inductive power transfer (IPT) applications. The proposed power controller provides a load-adaptive pulse modulation by tuning a zero phase angle and peak-power frequency, i.e., resonant frequency in the primary-side high-frequency inverter. The switching frequency is regulated in accordance with the variations of the load and coupling coefficient between the transmitting (Tx) and receiving (Rx) coils. The output power is controlled by the RFT-
$\Delta$
$\Sigma$
PDM, which is effective for reducing a low-frequency oscillation (subharmonics); thereby, the high-efficiency power transmission can be attained. The essential performances of the proposed IPT power controller are demonstrated in an experiment of a 400 W–500 kHz of prototype, whereby the feasibility is clarified from a practical point of view.