Numerical Analysis of the Cooling Performance in a 7.2 kW Integrated Bidirectional OBC/LDC Module

Abstract

To satisfy increasing demands for ecofriendly vehicles, researchers are now studying electric vehicle (EV)-related technologies. In particular, integrated bidirectional onboard battery charger (OBC)/low-voltage DC-DC converter (LDC) modules are being researched to improve the efficiency of onboard chargers for EV charging applications. In this study, a numerical analysis method is proposed that considers the power loss and heat flow characteristics in the design of a 7.2 kW integrated bidirectional OBC/LDC module. The developed module supports four operating modes depending on the service situation: OBC and LDC single operation, OBC/LDC simultaneous operation, and LDC operation. The mode is selected based on the power system flow. The characteristics of the circuit were analyzed in each of the four modes to compute the heat loss from the major heating elements. The results of a numerical analysis of the internal cooling characteristics showed that the internal temperature was higher in the OBC single operating mode than in the OBC and LDC simultaneous operating mode in which the power loss was the highest. The results emphasize the importance of ensuring that cooling designs consider the characteristics of various modes as well as the worst-case power loss.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 ...

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Electro-Thermal Model-Based Design of Bidirectional On-Board Chargers in Hybrid and Full Electric Vehicles

“…In Ref. [3], the authors propose a numerical analysis of the thermal behaviour of a 7.2 kW bidirectional OBC with a DC-DC converter multi-stage output, based on FEM SW. In this study, circuit analysis is simplistic and based on linearity approximation, while thermal analysis is quite comprehensive as it is performed on FEM-based SW.…”