## 4 Discussion  
In Tables 4 and 5, theoretically calculated, simulated and experimental values of important parameters are collected and listed together for comparison. Generally, values from simulation and experiment are quite close and those also match the theoretical calculations with acceptable deviation. The mismatch can be attributed to two reasons: non-ideal values in simulation setup and parasitic parameters in experimental implementation, and the inherent errors from FHA. For example, the existence of necessary dead-band is the main reason of the deviation of phase-shift \(\phi\), while the on-state resistance of switches and threshold voltage of diodes have impacts on actual phase-shift and switching frequency too. In addition, to cope with the wide variation of output voltage and load level, the switching frequency is not quite close to resonant frequency in some operation range. Under such a scenario, the resonant current does not resemble a sinusoidal shape well, which can be easily identified in Figures 8a,b and 9a,b. Therefore, the peak current values from the three sources have relatively large deviations. Comparatively, the rms current values have smaller deviations, and their variation in experiment coincides with that of load level, which implies better partial load efficiency. The peak capacitor voltage in the experiment is clamped below 187 V, which is close to the designed value. The measured efficiency of the two designed converters in the whole charging process is presented in Figure 11. It is seen that the efficiency of Method I is higher than that of Method II in the whole charging process in a range of 0.1\(\sim\)4.29 percentage. The highest efficiency and lowest efficiency of Method I are 93.32% and 77.73%, respectively, while those values of Method II are 92.8% and 72.9%. For both of methods, the highest efficiency is measured at the rated peak power (120 V/5 A), and the lowest efficiency is measured at 70% output voltage in the CC stage (84 V/5 A). The efficiency can be further improved, especially in the CC stage at light load condition. One possible approach is to use more \begin{table}
\begin{tabular}{c c c c c c c} \hline \multicolumn{2}{c}{**Load**} & **70\% (CC)** & **90\% (CC)** & **100\%** & **80\% (CV)** & **50\% (CV)** \\ \hline \multirow{3}{*}{\(V_{cp}\)(V)} & cal. & 165.96 & 172.34 & 180.0 & 139.16 & 84.38 \\ \cline{2-7}  & sim. & 167.3 & 177.67 & 187 & 144.25 & 88.55 \\ \cline{2-7}  & exp. & 171.75 & 178.88 & 187.5 & 144.75 & 88.75 \\ \hline \multirow{3}{*}{\(I_{rp}\)(A)} & cal. & 7.85 & 8.16 & 8.52 & 6.59 & 3.99 \\ \cline{2-7}  & sim. & 7.47 & 7.52 & 7.76 & 5.90 & 3.56 \\ \cline{2-7}  & exp. & 7.48 & 7.63 & 7.81 & 6.19 & 3.48 \\ \hline \multirow{3}{*}{\(I_{rs}\)(A)} & cal. & 5.55 & 5.77 & 6.03 & 4.66 & 2.82 \\ \cline{2-7}  & sim. & 5.54 & 5.73 & 6.04 & 4.62 & 2.80 \\ \cline{2-7}  & exp. & 5.69 & 5.74 & 5.95 & 4.71 & 2.50 \\ \hline \multirow{3}{*}{\(\phi\)(\({}^{\circ}\))} & cal. & 45.6 & 45.6 & 45.6 & 34.9 & 20.9 \\ \cline{2-7}  & sim. & 45.4 & 45.4 & 45.4 & 34.2 & 20.5 \\ \cline{2-7}  & exp. & 52.4 & 52.4 & 52.4 & 41.4 & 22.0 \\ \hline \end{tabular}
\end{table} 
Table 4: Comparisons of parameters using Method I.