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Multilevel converters have attracted more and more attention for their advantages over the two-level converters in breaking voltage limitation and multichannel wireless power transfer (WPT), but their switching loss is unbearable due to the lack of an effective soft-switching modulation method. To fill this gap, this article proposes and implements a segmented-vector pulse frequency modulation (SVPFM) of a half-bridge three-level inverter for WPT systems. Moreover, the sigma-delta (Σ-Δ) modulator for the SVPFM-WPT system is proposed, and the modulation range is expanded to 0, 1. It can achieve wide-range zero voltage switching (ZVS) without auxiliary circuits and inverter modification, and it suppresses the power losses, further improving the system efficiency of a three-level inverter-based WPT system. In the meantime, a switching state-based capacitor voltage balancing method is proposed to control the half-bridge three-level inverter for the WPT system. It can balance the capacitor voltage of the flying capacitor at the reference value with a small voltage ripple. Software simulation and hardware experimentation are both given to verify the feasibility of the proposed Σ-Δ SVPFM of the three-level inverter for WPT systems. The system efficiency can reach 95.2% with the wide-range ZVS operation.
Guo et al. (Tue,) studied this question.