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

Variable frequency asymmetrical pulsewidth 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, the analysis of WPT systems is based on first harmonic approximation, which only considers the fundamental harmonic signals. This could be inaccurate for variable frequency asymmetrical pulsewidth-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.