An Improved Hybrid Frequency Pacing Modulation for Wireless Power Transfer Systems

Zero voltage switching (ZVS) techniques are widely utilized to increase efficiency and reduce electromagnetic interference of wireless power transfer (WPT) systems. Hybrid frequency pacing (HFP) is an excellent modulation method for WPT systems because it can achieve full-load range ZVS without changing the current frequency or adding auxiliary components. Another advantage of HFP is the average switching frequency reduction as decreasing output voltage so that it further reduces switching losses. This article provides an insight into the characteristics of HFP and points out that a large output ripple occurs under some reference conditions. To improve HFP, this article proposes an improved HFP (iHFP) method to minimize output ripple by optimally arranging the hybrid frequencies pulse sequence, but the implementation process of iHFP becomes more complicated. The reason for the unavoidable complicated calculation of HFP is the quantization error. In this viewpoint, this article proposes a modified sigma-delta modulation method with the quantization noise-shaping property for iHFP. As a consequence, the same pulse sequence can be generated by this simple modulator without complex calculations. Experimental results show that iHFP and Σ-Δ iHFP can reduce more than 60% voltage fluctuations compared with HFP. Under 0.2% input reference resolution, 66%-93% computational time reduction is achieved in going from HFP to Σ-Δ iHFP.