Ripple Current and Temperature Distribution in Ceramic Capacitors for DC Link Applications

The relationship between high-frequency ripple currents and thermal stresses in DC link circuits containing multiple parallel ceramic capacitors is analyzed. The capacitors under consideration are specifically intended for DC link applications and have advantageous properties for high-temperature and high-frequency applications. However, the devices’ effective capacitance varies with both bias voltage and temperature. This creates the possibility of both desirable operating regimes, in which changes in capacitance with temperature balance stresses between the parallel elements, and undesirable operating regimes, in which stresses are magnified for a subset of devices. The analysis presented here focuses on the development of accurate predictive models and experimental observations from a hardware prototype. In the latter, individual ripple current magnitudes and temperatures are measured in a custom 4 kW synchronous boost converter which emulates the conditions of a typical application while enabling extensive device-level instrumentation.