Analysis and Design of the Suboptimum Class-EM/F3 Resonant Inverter

In this paper, the analysis and design method for the suboptimum Class- $\text{E}_{\mathrm {M}}/\text{F}_{3}$ inverter (i.e., only the zero-voltage switching (ZVS), the zero-voltage-derivative switching (ZVDS), the zero-current switching (ZCS) conditions are satisfied) with a duty ratio D =0.5 are presented. In the proposed design method, a new design parameter K called the slope of switch current (when the switch turns off) is introduced for defining the suboptimum degree and the distance from the optimum condition. By using the design method of the soft switching resonant inverter, the third harmonic filter circuit is innovatively introduced to reduce the current flowing through the parallel capacitor of the main circuit, and greatly reduce the peak switching voltage of the main circuit and auxiliary circuit. And the circuit waveforms and design equations can be derived in detail. Compared with the conventional Class- $\text{E}_{\mathrm {M}}$ inverter, the proposed inverter can offer the much lower peak switching voltage and higher efficiency. To verify the validity of the proposed method, a Class- $\text{E}_{\mathrm {M}}/\text{F}_{3}$ inverter operating at 1MHz is designed using the IRFZ24N transistor. The experimental results show that the output power of the new inverter is 15.138W, the efficiency reaches 96.4%, and the peak switching voltage of the main circuit and auxiliary circuit is reduced by 29.3% and 15.6%, respectively. The PSpice-simulation results and the experimental measurement results of the designed inverter are agreed with the analytical results, which verified the effectiveness of the proposed design method.