Ripple current and electrical noise characterization of DC BUS capacitors for future power electronics

For automotive applications there is an increasing demand to miniaturize power electronics circuits and operate at higher temperatures. Active SiC-based devices operate at high frequency which decreases circuit dimensions. Passive components, such as the DC-BUS capacitor, must complement new SiC technology. In this study the high frequency performance of DC-BUS capacitors in a DC-DC converter was tested. The relationship between ripple voltage and ripple current were explored as a function of switching frequency (f_s) and total DC-BUS capacitance. The DC-BUS capacitor's charging and discharging current was independent of the capacitance or switching frequency. The calculated necessary capacitance for DC-BUS capacitor was proportional to 1/f_s and 1/f_s ² by assuming constraining condition of ripple voltage and ripple current, respectively. In addition, to minimize the DC-BUS capacitor size, the current density through the capacitor was calculated as proportional to f_s and f_s ² by assuming constraining condition of ripple voltage and ripple current, respectively. Therefore, high current density performance will be important to miniaturize power electronic circuits by increasing switching frequency. DC-BUS current and DC-BUS voltage noise increased with increasing switching frequency over a wide frequency range. The benefit of using a multilayer ceramic capacitor (MLCC) to reduce noise was demonstrated.