A Passive Fractional-Order Capacitor to Realize Wide Region ZVS for Improving Efficiency in WPT System

High frequency inverter is essential for wireless power transfer (WPT) system, of which the loss cannot be ignored. Thus, zero voltage switching (ZVS) should be realized to improve the transmission efficiency. The phase shift (PS) control of the inverter can achieve controllable output, while it is under a hard-switching state. Because of their higher degrees of freedom, fractional-order components received attention in WPT system. In implementation, the passive fractional-order capacitor (P-FOC) can adaptively achieve variable capacitance with order of 1 or –1. In this paper, the phase angle of P-FOC is controlled to lag behind the phase-shifting angle of inverter by 90°, which can adaptively maintain the ZVS of the inverter in a wide region. Compared with the switch controlled capacitor (SCC) or variable inductor (VI), the proposed P-FOC has a larger range of impedance matching and a simpler control scheme. Especially, when P-FOC and inverter share the same processor, there is no need for additional feedback circuits. Finally, the system is theoretical analyzed and experimental verified.