Numerical investigation and thermal optimization of low-inductance ring-shaped film capacitors with integrated cooling structure for electric vehicle

Abstract

The advancement of motor controllers for electric vehicles is increasingly focusing on higher power density, efficiency, and miniaturization. Consequently, there is a growing demand for film capacitors that offer not only lower stray inductances but also enhanced high-temperature resistance capabilities. While existing research dedicated to mitigating the stray inductances of film capacitors, studies that address both the capacitors’ stray inductances and the thermal managements remain relatively scarce. Therefore, this paper proposes for the first time a low-inductance ring-shaped capacitor, utilizing an integrated cooling structure to reduce the capacitor’s thermal resistance and enhance its high-temperature tolerance. Firstly, the stray inductances and heat dissipation performances of both ring-shaped and conventional square-shaped capacitors, each with identical capacitances, are compared using Q3D and FLUENT simulations, the results demonstrate that the ring-shaped capacitor exhibits lower stray inductance and superior heat dissipation performance. Then an integrated cooling structure is proposed for the ring-shaped capacitor with the aim of diminishing its thermal resistance and augmenting its tolerance to high temperature. Utilizing FLUENT conjugate heat transfer simulation, the impacts of key factors within the cooling structure such as inlet flow rate, inlet temperature, and ambient temperature on the capacitor’s maximum temperatures are investigated, and the optimal inlet flow rate and inlet temperature are determined by multi-objective optimization. The findings reveal that increasing the inlet flow rate reduces the maximum temperature, although the cooling effect becomes less significant at higher flow rates, leading to increased energy consumption and operating costs. Moreover, the ambient temperature has the largest impact on the capacitor temperature, followed by the inlet temperature. The optimized integrated cooling structure achieves approximately a 73.93% reduction in thermal resistance and lowers the maximum temperature of the ring-shaped capacitor by about 72.24%.