A Powerless Fractional-Order WPT System With Extended Zero Voltage Switching Region

The inverter is crucial for a wireless power transfer (WPT) system, wherein its losses cannot be overlooked. For wide output voltage regulation in the WPT system, the phase-shifting (PS) control is often adopted without dc-dc converters, which results in the hard-switching of the inverter. To address this issue, in the implementation, the powerless fractional-order capacitor (P-FOC) is proposed for the WPT system based on PS modulation, which can adaptively achieve variable capacitance with an order of 1 or −1. Where the system can maintain a wide region of zero voltage switching (ZVS) while minimizing the current in the resonant tank. Meanwhile, the inverter could realize its soft-switching. Hence, the system efficiency has been significantly improved compared with traditional PS control, especially under light loads. Compared with conventional switched-capacitors (SC) or variable inductors (VI) based WPT system, the P-FOC and inverter need only one feedback loop simultaneously to regulate two variables. Fewer signal requirements and simplified control strategies bring greater convenience. Finally, a 180W prototype with 72V input voltage and 24V to 60V output voltage is built. Experimental results show the peak efficiency is 92%, and the overall efficiency is superior to traditional system, verifying the effectiveness of P-FOC.