## 4 Design Considerations  
The specifications of the battery charger and the solid-state lithium battery pack are listed in Table 2.  
Based on the specifications provided in Table 2, and by substituting \(n_{p}=25\), \(n_{s}=7\), \(V_{i}=400\) V, \(V_{o}=28\) V, \(I_{o}=70\) A, \(k=0.2\), and \(f_{sw}=100\) kHz into (1)-(7), the following component values are obtained: \(L_{\alpha 1}=L_{\alpha 2}=32.65\) uH, \(i_{\Delta(rms)}=6.93\) A, \(i_{\Delta(rms)}=43.87\) A, \(V_{Qur}=112\) V, and \(C_{o}=8.2\) uF (1000 uF in practice).  
The rule table of fuzzy control defined in this study is listed in Table 3. The values of \(e(t)\) and \(\Delta e(t)\) are converted into fuzzy linguistic terms, including the negative big (NB), negative small (NS), zero (ZE), positive small (PS), and positive big (PB). The fuzzy  
Figure 7: The operating flowchart of the proposed current loop controller.  
rule table was established using these fuzzy linguistic terms, with the rule weightings indicating the relative preference between P and PI control strategies. In the steady-state region centered around (ZE/ZE), the control strategy tended to favor PI control to improve accuracy and minimize steady-state error. Conversely, in rapidly changing boundary regions such as (NB/NB) and (PB/PB), P control was preferred to avoid integral saturation and suppress current overshoot.  
As shown in Figure 6, when \(e(t)\) and \(\Delta e(t)\) were input to the fuzzy logic unit, it generated a control preference degree \(\mu\) as the output. Based on the \(\mu\) value, PI control was selected if \(\mu>0.5\), whereas P control was chosen if \(\mu<0.5\). The rule weighting values corresponding to NB, NS, ZE, PS, and PB are listed in Table 4.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(e(t)\) & **NB** & **NS** & **ZE** & **PS** & **PB** \\ \hline NB & 0 & 0.1 & 0.2 & 0.3 & 0.2 \\ \hline NS & 0.1 & 0.3 & 0.5 & 0.4 & 0.2 \\ \hline ZE & 0.2 & 0.6 & 1 & 0.6 & 0.3 \\ \hline PS & 0.3 & 0.4 & 0.6 & 0.4 & 0.2 \\ \hline PB & 0.2 & 0.3 & 0.3 & 0.2 & 0 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Rule weighting value.  
\begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**Single-Phase AC Input**} \\ \hline Input AC voltage & 220 V\({}_{\text{rms}}\) \\ \hline Input AC frequency & 60 Hz \\ \hline \multicolumn{2}{c}{**Phase-Shifted Full-Bridge Converter**} \\ \hline Input voltage, \(V_{i}\) & 400 V \\ \hline Output maximum voltage, \(V_{o}\) & 28 V \\ \hline Output current range, \(l_{o}\) & 0 to 70 A \\ \hline \multicolumn{2}{c}{**Solid-State Battery Pack**} \\ \hline Charging-end voltage & 26.7 V \\ \hline Discharging-end voltage & 18.9 V \\ \hline SOC-dependent & 22 V \(\cong\) 73\% \\ charging voltage & 24 V \(\cong\) 86\% \\ \hline Capacity & 70 Ah \\ \hline \hline \end{tabular}
\end{table}
Table 2: Specifications of the battery charger and pack.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{2}{c}{**Condition**} & **Detection Rule** & **Control Method** \\ \hline Start-up phase & \(\leq\)millisecond & P \\ \hline Large \(e(t)\) & \(\mid e(t)\mid\) \(>\) Error threshold high & P \\ \hline Large \(\Delta e(t)\) and small \(e(t)\) & \(\mid\)\(\Delta e(t)\mid\) \(>\) Slope threshold high & PI \\ \(\mid e(t)\mid\) \(<\) Error threshold low & PI \\ \hline Small \(e(t)\) and steady-state & \(\mid\)\(\Delta e\mid\) \(<\) Slope threshold low & PI \\ \hline \hline \end{tabular}
\end{table}
Table 3: Fuzzy control linguistic rule table.