# Numerical Analysis of the Cooling Performance in a 7.2 kW Integrated Bidirectional OBC/LDC Module
## 3 Results and Discussion
In other words, as Mosfet and N-Mosfet have a larger heat source or heating value per unit volume (W/m\({}^{3}\)), the temperature rapidly rises until it reaches steady state. In the future, to prevent these devices with large heat sources from reaching their critical temperature, the cooling design should reflect the circuit characteristics and operating mode as well as the required durability of each device. When the charging rate of the low-voltage battery for vehicle control becomes too low, the LDC operates independently (Operating Mode 2). This configuration is shown in Figure 10. When the streamline is examined to identify the characteristics of the cooling water, it can be seen that a streamline formed along a channel shape similar to that in Operating Mode 1 with the same behavior. In addition, the predicted velocity and pressure distributions were similar to those in the previous case. In terms of the numbers, the highest pressure distribution appeared at the inlet, and the pressure drop through the system was predicted to be 11.98 kPa. With regard to the temperature distribution for each section, in Section View I, the highest temperature was observed in N-Mosfet XXII (443.0 K). In Section View II, the highest temperatures were observed in Mosfet XIII (326.2 K), Mosfet XIV (325.6 K), Mosfet XV (327.4 K), and Mosfet XVI (326.5 K). In Section Views III and IV, no device exhibited a particularly high temperature. In Section View V, the highest temperature was observed in Capacitor IV (347.1 K). Figure 9: Temperature profile of the module for a cooling water flow rate of 6 LPM in Operating Mode 1. As explained above, these results were produced using a circuit load consistent with the independent operation of the LDC in Operating Mode 2. Thus, the cooling system design should be based on N-Mosfet XXII, which exhibited the highest temperature. Note that it is important that the cooling system be improved because the predicted temperature of 443.0 K is high enough to affect the durability of the device. The internal temperature changes over time in Operating Mode 2 are shown in Figure 11. As shown, for relatively small devices, such as Mosfet and N-Mosfet (i.e., devices with a large heat source in terms of the heating value per unit volume (W/m\({}^{3}\))), the temperature rises quickly from startup until it converges to steady state at around 200 s. In the case of the transformer, inductor, and capacitor (all devices with a small heat source in terms of the heating value per unit volume (W/m\({}^{3}\))), the temperature curve is relatively gentle. Therefore, in the design of the cooling system for Operating Mode 2, the circuit characteristics and operating mode should be such that the N-Mosfet XXII is prevented from reaching the critical temperature. The results of the analysis conducted in Operating Mode 3 are shown in Figure 6:0 Note that in this mode, the OBC and LDC are simultaneously activated when the low-voltage and high-voltage batteries do not have sufficient energy stored. The predicted streamline, velocity, pressure distributions, and flow characteristics of the cooling water were similar to those in the previous cases. The highest pressure distribution was predicted to be at the inlet with an overall pressure drop of 12.05 kPa through the system. In terms of the temperature distribution for each section, in Section View I, the highest temperatures were observed in N-Mosfet XVII (375.5 K), N-Mosfet XVIII (374.9 K), N-Mosfet XXI (406.7 K), N-Mosfet XXII (407.9 K), N-Mosfet XXIII (399.7 K), N-Mosfet XXV (373.4 K), and N-Mosfet XXVI (372.4 K). In Section View II, the highest temperatures were observed in Mosfet I (330.3 K), Mosfet II (330.1 K), Mosfet III (340.0 K), Mosfet IV (342.4 K), Mosfet IX (331.8 K), and Mosfet X (330.4 K). In Section Views III and IV, the highest temperatures were observed in Inductor I (423.2 K) and Inductor II (418.4 K). In Section View V, the highest temperatures were observed in Capacitor I (320.3 K), Capacitor II (325.8 K), and Capacitor IV (319.6 K).