Analysis and suppression of current oscillations in wireless power transfer system using multilevel pulse magnitude modulation

Abstract

Pulse density modulation (PDM) enables continuous output power regulation and zero-voltage switching (ZVS) in wireless power transfer (WPT) systems. However, abrupt voltage transitions inherent to PDM often induce severe current oscillations, critically threatening system stability and operational safety. This paper systematically analyzes the theoretical mechanisms underlying current oscillations, and a multilevel pulse magnitude modulation (ML-PMM) method based on a three-level full-bridge inverter is proposed. The ML-PMM can achieve wide-range flexible power regulation and ZVS operation while effectively suppressing current oscillations across most pulse density ranges. Furthermore, to address persistent oscillations at specific critical pulse densities, a hybrid modulation strategy integrating ML-PMM with asymmetrical voltage cancellation is developed. This hybrid asymmetrical ML-PMM can mitigate severe current oscillations during continuous power adjustment while preserving ZVS without requiring frequency control. Meanwhile, a switching-state-based multi-flying-capacitor voltage balancing method is proposed, ensuring stable capacitor voltage balancing for both modulation schemes. Experimental validation on a hardware prototype of 1.06 kW proves the efficacy of the proposed methods.