Load-Independent Push-Pull Class \Phi2 Inverter with Single Compact Three-Winding Inductor

This paper 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 three-winding integrated inductor, which distinctly reduces the number and size of magnetic components compared with conventional Class \Phi_2 inverters. By flux cancellation and core sharing, the magnetic integration not only reduces the inductor's overall volume and losses but also maintains the inverter's high efficiency. A 6.78-MHz LCC-S resonant WPT 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 watts output. The voltage gain remains nearly constant, varying within +1/-3.5% Moreover, the measured DC-DC peak efficiency of the system reaches 91% at 170 watts output, while 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.