# Numerical Analysis of the Cooling Performance in a 7.2 kW Integrated Bidirectional OBC/LDC Module
## 1 Introduction  
Until recently, the internal combustion engine was the predominant type in the automotive market. However, the ongoing depletion of fossil fuels and worsening environmental pollution is now causing this market to slowly shift toward an emphasis on ecofriendly cars with high fuel efficiency. Thus, several developed countries, such as the United States, Japan, and Europe, are now taking steps to stimulate the ecofriendly electric vehicle (EV) market and to promote the broad proliferation of charging infrastructure, which is a critical factor in the success of EVs. At the same time, much effort has been focused on improving the stability of renewable energy sources and supporting the decentralization of energy. A major area of focus with regard to EV technologies is to provide components and systems that are high-performance, lightweight, and stable. In particular, development efforts are currently focused on advancing battery technology, such as high-performance, high-density energy storage technologies, and electric drive systems, including high-voltage electrical components, high-power drive motors, and motor control technologies, all of which are core technologies for EVs. Furthermore, to simplify the control and electrical systems in EVs and reduce the overall cost, modules are now being developed that integrate several previously disparate functions into one assembly. One example of this trend is the integration of power conversion devices to increase their efficiency and improve their performance. Researchers currently working in the area of integrated power converters are focusing on a variety of circuit improvements [1; 2; 3]. For example, onboard chargers (OBCs) and low-voltage DC-DC converters (LDCs) are being researched as a way to overcome space limitations and poor fuel economy of systems with connected batteries [4; 5; 6; 7]. These integration efforts are seeking to leverage high-efficiency circuit structures using miniaturized, lightweight components, such as switch-mode power supplies (SMPSs). Studies are also underway to solve the low reverse recovery charge problem using a GaN element with a totem-pole structure in continuous current mode (CCM) operation [8; 9]. Another example is the use of high-frequency switching signals using an insulation-type converter, such as a series-loaded resonant DC-DC converter (SRC) or LLC resonant converter, to minimize power loss in the DC-DC converters commonly used for the auxiliary charging of EVs by applying [10; 11; 12; 13]. In addition, as cooling performance has become an important consideration in circuit improvement, experimental methods of evaluating the cooling performance of heating elements are also being researched [14]. Note that such studies typically employ experimental methods instead of the numerical methods commonly used in battery pack design [15]. Recently, the Buck Converter of the two-way charging system has been proposed as an optimization control method considering the State of Charging (SOC) [16; 17; 18; 19; 20] and the State of Healthy (SOH) [21; 22; 23], and the research is being actively conducted. Among the SOC methods, the CC-CV (Constant Current/Constant Voltage) method, which is the simplest basic model and is controlled according to the determined voltage and current [16], and the CVCC-CV (Constant Voltage/Constant Current/Constant Voltage) and MCC-CV (Multi-Stage Constant Current/Constant Voltage) have been proposed for fast charging and securing cycle stability [17; 18]. On the basis of this, a study has been performed on the converged models. For example, CC-CV and MCC-CV have been converged to consider variables such as charging speed and energy conversion efficiency [19; 20]. In addition, under high temperature conditions, the battery surface may exceed the allowable temperature depending on the state of charge and discharge, resulting in a negative performance such as battery life cycle and charging acceptance.