# Numerical Analysis of the Cooling Performance in a 7.2 kW Integrated Bidirectional OBC/LDC Module
## 3 Results and Discussion  
A circuit analysis was conducted using the circuit diagram shown in Figure 2. In terms of the system power, power was supplied using CCM. Graphs representing the input voltages applied during the simulation and the corresponding output voltages derived through the analysis are shown in Figure 6a,c. Here, the applied input voltage and current were 85-265 V and 32 A, respectively. The control block ensured that the input/output voltages were similar in every mode. For the PFC circuit, the control block minimized the phase angle to produce a DC output voltage of 400 V. Furthermore, the fixed output voltage in the SRC circuit was predicted to be 470 V when the resonant frequency was aligned to the operating frequency. This value is similar to that predicted using the gain function. The operation of the buck converter varied depending on the high- and low-voltage battery conditions. A simulation was conducted for a state of charge (SOC) of 0%, and the results are shown in Figure 6b,d. In the figures, it can be seen that output voltages of 220 and 13 V occurred at the ends of the high- and low-voltage buck converters, respectively. Furthermore, when the charge state continued, the current was fixed under CC control, and the output voltage increased to 450 V at the high-voltage end. In the discharge state, a fixed voltage was maintained under CV control. Here, the input voltage in Operating Modes 2 and 4 was 450 V. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Condition** & **Value** & **Unit** \\ \hline \multirow{2}{*}{Inlet} & Velocity & 2.17 & m/s \\  & Temperature & 300 & K \\ \hline \multirow{2}{*}{Outlet} & Outlet Pressure & - & - \\ \multirow{2}{*}{Outer Wall} & Temperature & 300 & K \\  & Convection Heat Transfer Coefficient & 10 & W/m\({}^{2}\)-K \\ \hline Heat Source & Uniform Heat Source & variable & W/m\({}^{3}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Boundary conditions used in the numerical analysis model. Figure 6: _Cont._  
The proposed integrated module has four operating modes, and the power loss of each is shown in Figure 7. In each mode, the output power ranged from 2.5 to 7.5 kW, and the MOSFET device generated the largest loss in all modes. First, Operating Mode 1 (Figure 7a) represents the independent operation of the OBC circuit, while the LDC circuit is deactivated when the low voltage battery is in a fully charged condition. In this mode, the total power loss in the PFC, SRC, and buck converter circuits were 94 W, 73 W, and 32 W, respectively. This indicates that the amount of supplied current in each circuit had a significant effect on the power loss. In Operating Mode 2 (Figure 7b), 2.5 kW of power flowed from the high-voltage battery to the low-voltage battery, which necessitated a large amount of power to be allocated to the LDC circuit compared to that in the other operating modes. In the high-voltage buck converter, the voltage remained constant as the circuit was under CV control, while the current decreased somewhat, which resulted in a smaller power loss than in Operating Modes 1 and 3. However, in the low-voltage buck converter, the power supply increased eight times, and the power loss increased relative to that of other operating modes. In Operating Mode 3 (Figure 7c), which denotes OBC/LDC simultaneous charge mode, a power of 7.2 kW was supplied, of which 6.9 and 0.3 kW were allocated to the OBC and LDC circuits, respectively, depending on the load of the controller. Since the power distribution was the same as that of Operating Modes 1 and 4, the loss of each circuit was also similar. In total, an efficiency of 96.99% was realized in Operating Mode 3. In Operating Mode 4 (Figure 7d), 3.3 kW of power flowed backward from the high-voltage battery to the system power and onward to the low-voltage battery. This backward flow produces a different power loss depending on the reverse recovery time of the active devices and the size of the reverse bias voltage, although the loss is smaller than that in the forward direction.