# Numerical Analysis of the Cooling Performance in a 7.2 kW Integrated Bidirectional OBC/LDC Module
## 4 Conclusions  
A numerical analysis methodology for the circuit and heat flow characteristics of a 7.2 kW integrated bidirectional OBC/LDC module with different operating modes was presented, based on which the following conclusions were obtained. First, a numerical analysis model for the loss rate of an electric circuit was proposed, and the calculated loss rate was adjusted based on the heating value. This value was supplied as an input to the heat flow analysis process to determine the equilibrium state of the temperature distribution. When analyzed, the electrical circuit and heat flow characteristics of the module were changed based on the operating mode, which affected which circuits were activated. The power losses in the operating modes were approximately 142 and 196 W, respectively, when the LDC and OBC were operated independently. However, in a high-voltage/low-voltage charging mode in which both the OBC and LDC were activated, the power loss was the highest at approximately 216.36 W. Furthermore, in Operating Mode 4, in which the power flows from the high-voltage battery to the system power and LDC, the power loss was the lowest at approximately 107 W.  
To examine the thermal characteristics, in Operating Mode 1, where the OBC operates independently, the highest temperatures were observed in N-Mosfet XXI (410.9 K), XXIII (410.5 K), Inductor I (422.6 K), and Inductor II (417.7 K). In terms of the changes in the internal temperature over time, in the devices with a large heat source in terms of the heating value per unit volume (W/m\({}^{3}\)), such as Mosfet and N-Mosfet, the temperature rose quickly until it reached steady state (around 200 s). However, in the case of the transformer, inductor, and capacitor, it took much longer to reach steady state because the temperature rise curve was gentle. In Operating Mode 2, in which the LDC operates independently, the highest temperature was predicted in N-Mosfet XXII (443.0 K). In Operating Mode 3, where the OBC and LDC are activated simultaneously, the highest heating value was generated in many devices. However, as the power was distributed, the heating temperature in the circuit decreased to 442.6 K, compared to 448.3 K in Operating Mode 1. Thus, it is essential that the cooling design for the integrated module consider the cooling characteristics in different modes as well as the characteristics of the mode with the largest power loss.  
Conceptualization, [PERSON]-H.N. and S.-i.S.; Methodology, J.-H.N.; Software, J.-H.N. and S.-i.S.; Formal Analysis, J.-H.N. and S.-i.S.; Investigation, J.-H.N. and S.-i.S.; Data Curation, J.-H.N. and S.-i.S.; Writing--Original Draft Preparation, [PERSON]-H.N. and S.-i.S.; Writing--Review and Editing, J.-H.N.; Visualization, J.-H.N. and S.-i.S.; Supervision, J.-H.N.; Project Administration, D.-J.H.; Funding Acquisition, D.-J.H. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Korea Evaluation Institute of Industrial Technology (KEIT), Ministry of Trade, Industry, and Energy (MOTIE), and Daewoo Electronic Components Co. Ltd. via Grant Number No. 10077362.  
The authors declare no conflict of interest.