## 4 Experimental Results
### Waveform Comparisons with and without Feedforward Compensation  
To further verify the effectiveness of the proposed control method, comparative experiments were carried out on the totem-pole bridgeless PFC prototype. The experimental results with direct input voltage feedforward are shown in Figure 16. It shows that the input current is superimposed with high-order harmonics under direct input voltage feed  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Input Signal Frequency** & **Current Error** & **Voltage Error** & **Power Error** \\ \hline DC & 0.05\% & 0.05\% & 0.05\% \\
0.1–30 Hz & 0.03\% & 0.05\% & 0.08\% \\
30–45 Hz & 0.03\% & 0.05\% & 0.08\% \\
45–66 Hz & 0.03\% & 0.05\% & 0.05\% \\
66 Hz–1 kHz & 0.1\% & 0.1\% & 0.2\% \\
1–10 kHz & 0.15\% & 0.1\% & 0.3\% \\ \hline \hline \end{tabular}
\end{table}
Table 2: Voltage, current, and power measurement error of PA5000H.  
Figure 15: Experimental waveforms of the prototype. (**a**) \(P_{o}\) = 589 W; (**b**) \(P_{o}\) = 784 W; (**c**) \(P_{o}\) = 980 W; (**d**) \(P_{o}\) = 1180 W; (**e**) \(P_{o}\) = 1377 W; (**f**) \(P_{o}\) = 1570 W.  
forward, which is induced by sampling the noise of input voltage, whereas with PLL based feedforward, the sampling noises are almost eliminated as shown in Figures 17 and 18.  
Waveforms of the input voltage, input current, inductor current, and output voltage with proposed control at \(P_{o}=784\) W are shown in Figure 17. With the proposed VAFC, current distortion near the input voltage zero-crossing point is significantly reduced. PF is increased from 98.65% to 99.43%, while THD is reduced from 8.27% to 5.92%. Figure 18 shows the comparative experimental results at \(P_{o}=1570\) W. Current distortion near the zero-crossing point is reduced, which improves the THD from 5.53% to 3.92% and improves the PF from 99.50% to 99.82%.  
Correlations between input admittance and virtual admittance of the PFC converter at 50 Hz under different output power are shown in Figure 19. It shows that the proposed control method can generate virtual admittance to eliminate the imaginary part of the input admittance, achieving a pure conductance input characteristic. Thus, the PF and THD of the PFC converter can be improved.  
Figure 16: Experimental waveforms with direct input voltage feedforward compensation: (**a**) 784 W; (**b**) 1570 W.  
Figure 17: Experimental waveforms when \(P_{o}=784\) W. (**a**) Without feedforward compensation; (**b**) with the proposed VAFC.  
Figure 18: Experimental waveforms when \(P_{o}=1570\) W. (**a**) Without feedforward compensation; (**b**) with the proposed VAFC.  
The input current harmonic analysis at \(P_{o}\) = 784 W and \(P_{o}\) = 1570 W are given in Figures 20a and 20b, respectively. The harmonic distortion of the input current mainly comes from odd harmonic currents. With the proposed VAFC, the odd current harmonic contents, including the third and fifth harmonics of the input current are reduced, which improves PF and reduced THD.  
Figure 19: Correlation between input admittance and virtual admittance of the PFC converter under different output power. (**a**) \(P_{o}\) = 589 W. (**b**) \(P_{o}\) = 784 W. (**c**) \(P_{o}\) = 1180 W. (**d**) \(P_{o}\) = 1570 W.  
Figure 20: Input current harmonic analysis at different power rates. (**a**) \(P_{o}\) = 784 W; (**b**) \(P_{o}\) = 1570 W.