# Numerical Analysis of the Cooling Performance in a 7.2 kW Integrated Bidirectional OBC/LDC Module
## 3 Results and Discussion
In total, the efficiency of Operating Mode 4 was computed to be 96.75%. Figure 6: Input and output voltages of the integrated module in (**a**) Mode 1, (**b**) Mode 2, (**c**) Mode 3, and (**d**) Mode 4. Figure 7: _Cont._  
inlet, right outlet), and to simulate the exposure of the charger module to air, the convection conditions on the external surface were set to 300 K and h = 10 W/m\({}^{2}\)-K. To confirm the heat flow characteristics for each operating mode, the results of streamline, pressure, velocity, and temperature distributions over a time period of 4000 s were evaluated. The streamline distribution was identified using a top-view drawing. The pressure and velocity characteristics were identified by drawing the cross-section of a cooling channel through which the fluid flows (Section View III in Figure 8). The temperature distribution was evaluated based on the locations of the major devices. In Figure 8, Section View I (a) shows the center position of the cooling water channel, Section Views IV (d) and V (e) show the center position of the inductor, and Section View VI (f) shows the center position of the capacitor. The results of analyzing Operating Mode 1 are shown in Figure 8. The streamline, pressure, and velocity distributions shown in the figures were used to verify the flow characteristics of the cooling water. The streamline distribution shows that the fluid was injected into the inlet, passed through the internal channel, and flowed out the outlet. As the water flowed through the module, the heat from the heat sources was transferred to the cooling water, and then flowed out through the outlet and away from the module. The pressure distribution in the cooling water channel was predicted to be the highest at the inlet and to drop by 11.62 kPa as it flowed through the channel. A high velocity distribution with a small cross-sectional area was seen in the inlet and outlet channels on the bottom of the module with a relatively low velocity distribution in the center where the majority of the heating sources were concentrated. A limitation was identified in this analysis in that the parallel configuration of the cooling water channels introduces variations in the velocity distribution of each channel, depending on the degree of flow distribution. This should be improved by adjusting the channel layout as the current configuration degrades the heat transfer coefficient and heat transfer rate. In the future, we plan to conduct a follow-up study to optimize the cooling performance, based on the results of this study. In terms of the temperature distribution, the highest temperatures in Section View I were observed in N-Mosfet XXI (410.9 K) and XXIII (410.5 K). In Section View II, the highest temperatures were observed in Mosfet II (320.3 K), Mosfet III (319.5 K), Mosfet V (319.6 K), and Mosfet VIII (318.2 K). Figure 8: Streamline, pressure, velocity, and temperature distribution in the integrated module with a cooling water flow rate of 6 LPM over a 4000 s time span in Operating Mode 1. In Section Views III and IV, the highest temperatures were observed in Inductor I (422.6 K) and Inductor II (417.7 K). In Section View V, the highest temperatures were observed in Capacitor I (319.9 K), Capacitor II (326.1 K), and Capacitor IV (318.7 K). These results were produced by the circuit load associated with SRC operation in Operating Mode 1 in which the OBC operates independently. Note that the results varied as the operating mode changed. In other words, the operating circuit domain is affected by the operating mode, which changes the heating elements and the heating value. The internal temperature changes over time in Operating Mode 1 are shown in Figure 9, where it can be seen that for Mosfet and N-Mosfet, which are relatively small devices, the temperature of the circuit after startup quickly rose until it stabilized at around 200 s. However, in the case of the transformer, inductor, and capacitor, which have relatively large volumes, the temperature curve is gentle and it takes a long time to reach steady state.