Analysis of Influence Factors for Heat Generation Minimization of DC-Link Capacitor

Abstract

With the rapid development of ecofriendly cars, various inverters are also being developed depending on the performance of motors. The DC-link capacitor is used as an inverter component; however, there are several limitations on its size, such as the requirement for wide films. Film width is a major factor that affects the capacitor’s equivalent series resistance (ESR) and is closely related to heat generation. When the temperature of the capacitor increases, the dielectric breakdown due to high voltage causes a reduction in capacitance, which leads to a decrease in inverter power and causes vehicle defects; this needs to be addressed to minimize the heat of the capacitor. Recently, genetic films that can be used at high temperatures have been developed. However, producing such films is difficult because of their 5 µm thickness; thus, the size increases when they are designed and they consequently cannot be used in practical applications. Based on a film width of 50 mm, this study analyzed the factors that can reduce ESR, set the level for each factor, and conducted experiments using the Box–Behnken design. The variables (thermal conductivity, film thickness, and capacitance) were set to three levels for each factor, and the ESR, thermal flux, and temperature characteristics were analyzed through finite element analysis. Based on the temperature results, optimized conditions for film thickness of 3.15 μm, capacitance of 390 μF, and thermal conductivity epoxy of 4.5 W/m·K were derived using Minitab, and samples were made for verification tests. A capacitor was installed in the chamber and was saturated for 2 h at 85 °C and current of 50 A rms was applied at 16 kHz frequency. The K Type sensor attached to the film surface was connected to a temperature recorder to measure the temperature change in the film over time after applying the current. The experimental results confirmed that the temperature of the genetic film with a 50 mm film width was similar to that with a 35 mm film width, and this confirmed that the set factors were similar to that of the genetic film with 35 mm film width. It was confirmed that increased film width can reduce ESR and minimize heat generation.