## 4 Experimental Results  
To verify the correctness of the analytical results of the proposed DCM-CRM Cuk PFC converter utilizing variable inductor control, a 108 W experimental prototype was constructed. Comparative experimental results between the conventional and proposed converters were obtained. Detailed specifications and key circuit parameters are provided in Table 1. Figures 14 and 15 depict the experimental prototype and the experimental setup respectively. Figure 14a-c show the main board, control board, and digital control board for variable inductor calculation of the experimental prototype. As the control board shares the same control board with other CRM isolated converter prototypes, some components on the control board were not soldered when used for this DCM-CRM Cuk PFC converter. The digital control board for variable inductor calculation in Figure 14c uses STM32F103 RCT6 as the controller, the main program code for variable inductor calculation unit is shown in Appendix A. The experimental results for the input voltage \(V_{\text{in}}\), input current \(i_{\text{in}}\), intermediate capacitor voltage \(V_{\text{c1}}\), and output voltage \(V_{\text{o}}\) of both the conventional Cuk PFC converter and the proposed converter are presented in Figure 16. These figures illustrate the performance of the converters at input voltages of 110 Vac and 220 Vac, respectively. Figure 12: The relationship between \(f_{\text{s}}\) of the conventional converter and \(V_{\text{in}\text{,RMS}}\) at different inductance of \(L_{2}\). Figure 13: The relationship of \(f_{\text{s}}\) and \(V_{\text{in}\text{,RMS}}\). Figure 16: Experimental waveform of \(V_{\rm in},I_{\rm in},V_{\rm o}\), and \(V_{\rm C1}\). (**a**) Conventional Cuk PFC converter at 110 V input; (**b**) Proposed Cuk PFC converter at 110 V input; (**c**) Conventional Cuk PFC converter at 220 V input; (**d**) Proposed Cuk PFC converter at 220 V input. Figure 14: Experimental prototype picture. (**a**) main board; (**b**) control board; (**c**) digital control board for variable inductor calculation. Figure 15: Experimental platform. As illustrated in Figure 16a-d, the output voltage of both the conventional Cuk PFC converter and the proposed converter is stable at 72 V. However, under conventional control, the input current exhibits harmonic distortion at 110 V and 220 V input voltage. In contrast, the proposed converter effectively mitigates this harmonic distortion, the input current of the proposed converter is closer to sinusoid wave. Furthermore, the intermediate capacitor voltage of the conventional converter is around 270 V and 500 V at 110 V and 220 V input voltage, respectively; the intermediate capacitor voltage of the proposed converter is reduced to around 230 V and 400 V at 110 V and 220 V input voltage, respectively. This demonstrates that the proposed converter effectively reduces the intermediate capacitor voltage. The experimental waveforms for the input inductor current and output inductor current at 110 V and 220 V input voltage are presented in Figures 17 and 18. From Figure 17, it is noted that the peak current of the input inductor is reduced from 6 A in the conventional converter to 4.8 A in the proposed converter at 110 V input voltage. From Figure 18, it is illustrated that, at 220 Vac, the peak current value of the input inductor decreases from 5 A of the conventional converter to 3.4 A of the proposed converter. The peak output inductor current remains consistently at 3 A. Consequently, the proposed converter effectively reduces the current stress on the switch and enhances the overall efficiency of the converter, which is the same as the theoretical analysis result. As depicted in Figures 17d and 18d, the current through the variable inductor \(i_{\text{LV}}\) exhibits slight distortion. This distortion arises because the inductor design includes a margin for variation, and the actual operational range of the variable inductor is narrower than anticipated.