## 4 Experimental Results
Consequently, a stable DC current must be continuously applied to the bias winding to maintain the calculated inductance value. When the DC current is applied, the operating point of the magnetic core characteristic curve shifts toward the saturation region [30], leading to a reduction in the inductance during actual operation and resulting in a curved waveform for the inductor current. This shift results in the actual inductance value of the variable inductor being lower than the theoretical calculation, thereby causing the inductor current to exceed the theoretically predicted value. Figure 17: Experimental waveforms of \(i_{\text{L1}}\), \(i_{\text{L2}}\), and \(i_{\text{LV}}\) at 110 V input voltage. (**a**) Conventional converter; (**b**) Proposed converter; (**c**) Zoomed in waveform of (a); (**d**) Zoomed in waveform of (b). Figure 19 shows the experimental data of the PF and efficiency. It is obvious that the PF of the proposed converters is improved in the range of input voltage variation, from 0.986 to 0.998 at 110 Vac and from 0.981 to 0.992 at 220 Vac. As illustrated in Figure 19, the efficiency is markedly enhanced with the use of the variable inductor, achieving values exceeding 90% at 90 V input voltage. At the same time, the efficiency of the proposed converter reached 86.8% which is higher than 81.1% of the conventional converter at 240 V input voltage. It can be seen that compared to the conventional converter, the PF and efficiency of the proposed converter are obviously enhanced. The test data of input current harmonic content and THD of the conventional and proposed converter are compared in Figure 20. It can be seen that compared with the conventional one, the proposed converter can more easily meet the requirements of IEC61000-3-2 class D. The proposed converter greatly reduces THD and the harmonic current content, especially the 3 rd harmonic current. Figure 19: Test data of efficiency and PF. Figure 16.0 Experimental waveforms of \(i_{\mathrm{L1}}\), \(i_{\mathrm{L2}}\), and \(i_{\mathrm{LV}}\) at 220 V input voltage. (**a**) Conventional converter; (**b**) Proposed converter; (**c**) Zoomed in waveform of (**a**); (**d**) Zoomed in waveform of (**b**). From Figure 5, it can be seen that the main power losses of the conventional and the proposed converter include the losses of the rectifier bridge, input filter, input inductor \(L_{\text{V}}\) or \(L_{1}\), a power switch \(S_{1}\), a diode \(D_{0}\), a free-wheeling diode \(D_{1}\), and an output inductor \(L_{2}\). The power loss distribution diagram is presented in Figure 16.1 These figures illustrate the power loss of the converters at input voltages of 110 Vac and 220 Vac, respectively. From the figure, it can be seen that the proposed converter mainly reduces the losses of the power switch and input inductor, thereby increasing the efficiency of the converter. Figure 16.2 Power loss analysis. (**a**) 110 Vac input voltage; (**b**) 220 Vac input voltage. Figure 16.3 Test data of input current harmonics and THD. (**a**) Input current harmonics at 110 V input voltage; (**b**) Input current harmonics at 220 V input voltage; (**c**) THD. Table 2 shows that compared to the conventional DCM-DCM Cuk PFC converter, which is mentioned in [19], and the traditional DCM-CRM Cuk PFC converter, the proposed DCM-CRM Cuk PFC converter enhances the PF, reduces the THD, decreases the intermediate capacitor voltage, and improves efficiency.