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This article proposes and implements a full-range soft-switching pulse frequency modulated (PFM) wireless power transfer (WPT) system, which not only offers high efficiency but also high controllability, selectivity, and security. Although the phase-shift control (PSC) has been widely used in various WPT applications, the high-frequency hard-switching operation will inevitably degrade the system performances in terms of power losses, and hence, efficiency during power regulation. Thus, a soft-switching PFM is newly conceived to suppress the switching frequency and power losses while maintaining full-range soft switching for effective power control, hence improving the system efficiency. In addition to realizing the controllability, the full-range soft-switching PFM can be further derived to implement the selectivity and security. The system efficiency of a multiobjective PFM-WPT system prototype can reach 86.27% at 220-W output power and 135-mm transfer distance. During wireless power control, it can effectively be improved by up to 5.68% as compared to its counterpart using the PSC. Theoretical analysis, computer simulation, and hardware experimentation are given to verify the feasibility of proposed full-range soft-switching PFM-WPT system.
Liu et al. (2019) studied this question.