## 5 Experimental Results  
The experimental waveforms in Figures 8-10 were measured using a digital oscilloscope (Model number: HDO4054, LeCroy, Chestnut Ridge, NY, USA). The experimental waveforms of the developed battery charger using conventional PI control and the proposed fuzzy-aided P-PI control are presented in Figures 8 and 9, where \(V_{o}\) represents the charger's output voltage, \(I_{o}\) denotes the charger's output current, \(V_{em}\) indicates the voltage at the inverting terminal of the current-loop error amplifier (EA\({}_{c}\), as shown in Figure 4), and \(V_{anc}\) corresponds to the output voltage of the current-loop error amplifier. In Figure 8, the battery pack was charged at initial voltages of 18 V and 22 V, respectively. When PI control was employed in the charger's current feedback loop, a current overshoot \(I_{o,as}\) occurred during the start-up phase within delay time \(t_{d}\), where \(I_{o,as}\) exceeded the rated constant current of 25 A before the charger transitioned into the constant-current charging mode at 70 A. The charging voltage corresponding to the SOC is shown in Table 2.  
In Figure 9, the battery pack was similarly charged from the initial voltages of 18 V and 22 V, respectively. In Figure 9, the maximum output voltage \(V_{o(\max)}\) was 24.5 V during the transient process. Although the maximum output voltage \(V_{o(\max)}\) was lower than the final charging voltage of 26.7 V, it remained within the acceptable specification range; therefore,  
Figure 8: PI control was employed in the charger’s current feedback loop, when the battery pack was charged at initial voltages of (**a**) 18 V; (**b**) 22 V.  
the battery pack was not adversely affected. The charging voltage corresponding to the SOC is shown in Table 2.  
Figure 10: Input AC current was in phase with input AC voltage. Figure 9: FZ–P–PI control was employed in the charger’s current feedback loop, when the battery pack was charged at initial voltages of (a) 18 V; (b) 22 V.  
However, with the implementation of the proposed fuzzy-aided P-PI control in the charger's current control loop, _Io,os_ was significantly reduced from 25 A to 5 A prior to the transition into the constant-current charging mode at 70 A. Compared to conventional PI control, this result clearly demonstrates the effectiveness of the proposed control strategy in mitigating current overshoot during the start-up phase. The performance of the developed battery charger using PI control and the proposed fuzzy-aided P-PI control in the current control loop was compared as follows:  
* PI control: The current overshoot was 25 A/70 A = 35.71%, with a steady-state error of less than 0.5%. * Fuzzy-aided P-PI control: The current overshoot was 5 A/70 A = 7.14%, with a steady-state error of less than 0.5%. Therefore, the proposed fuzzy-aided P-PI control strategy effectively reduces the start-up current overshoot while maintaining high control accuracy in steady-state operation. P and PI control are widely adopted and effective strategies in many control systems, particularly in stable and linear applications. However, in systems characterized by strong nonlinearity, parameter uncertainties, or significant external disturbances, traditional PI or PID controllers often require extensive tuning, iterative adjustments, and trial-and-error processes to achieve an acceptable trade-off between stability and performance. These limitations can diminish development efficiency and restrict the flexibility of the control strategy in practical implementations. The adoption of fuzzy control is not intended to increase the complexity of control design, but rather to overcome the fundamental limitations encountered by traditional controllers when dealing with complex or poorly defined systems. Fuzzy control offers several advantages, including independence from precise mathematical models, robustness to parameter variations, and the capacity to incorporate expert knowledge and rule-based logic.