Multiple Harmonics Analysis for Variable Frequency Asymmetrical Pulse-Width-Modulated Wireless Power Transfer Systems

Abstract

Variable frequency asymmetrical pulse-width-modulation (VFAPWM) is widely used in wireless power transfer (WPT) systems to control the amount of power transferred. This control scheme is also adopted in Qi, one of the world's most well-known wireless charging standards. Conventionally, analysis of WPT systems is based on first harmonics approximation (FHA), which only considers the fundamental harmonic signals. This could be inaccurate for variable frequency asymmetrical pulse-width-modulated WPT systems because VFAPWM inherently produces multiple harmonics. In this paper a new analytical technique, called multiple harmonics analysis (MHA), is developed to analyze series-series compensated WPT systems. The MHA technique is a comprehensive design foundation and provides a set of closed-form solutions to predict quantities such as zero-voltage switching (ZVS) and voltage gain. New phenomena in ZVS and voltage gain are discovered. The accuracy of MHA is also confirmed by both simulation and experimental measurements.