Load-Independent Push-Pull Class-Φ2 Inverter With Single Compact Three-Winding Inductor

This article proposes a push-pull class-Phi(2) inverter with a single three-winding integrated inductor. A design methodology is presented to achieve load-independent operation of the proposed class Phi(2) inverter, ensuring consistent soft-switching operation and constant voltage gain under varying load conditions. A compact magnetic structure is proposed to implement the threewinding integrated inductor, which distinctly reduces the number and size ofmagnetic components compared with conventional class F2 inverters. By flux cancellation and core sharing, the magnetic integration not only reduces the inductor's overall volume and losses but alsomaintains the inverter's high efficiency. A6.78-MHzLCC-S resonant wireless power transfer prototype is built to validate the proposed methodology and the magnetic structure. Furthermore, an active push-pull class-Phi(2) rectifier is implemented and demonstrates the load-independent resistive input. The experimental results indicate that the prototype performs robust soft switching over the entire load range, from no load to 320 W output. The voltage gain remains nearly constant, varying within +1%/-3.5%. Moreover, themeasured dc-dc peak efficiency of the system reaches 91% at 170Woutput, whereas the estimated peak efficiency of the class-Phi(2) inverter attains 96.6%. The proposed magnetic structure offers compact dimensions and low loss characteristics for the megahertz inverter.