An Offline Condition Monitoring Method for the DC-Link Capacitors in Power Electronic Converters

Abstract

Electrolytic capacitors are widely used as DC-link components in power electronic converters such as switched-mode power supplies (SMPSs) and inverters; however, they are also among the most vulnerable components, and their capacitance degradation critically affects overall system lifetime. Condition monitoring is challenging because many converters present complex and inaccessible internal structures, where disassembly or capacitor removal risks equipment damage. To address this, this paper proposes an offline, non-destructive condition monitoring method for DC-link capacitors. The technique limits the input detection voltage to a safe level and injects a small DC detection current into the input terminals while the converter is fully powered down. The DC-link capacitance is then determined from the measured detection voltage and current by utilizing equal-current intervals in which the series resistance terms inherently cancel out. This cancellation mechanism eliminates the influence of front-end circuit components such as input filters, rectifier bridges, varistors, and thermistors without requiring explicit modeling or topology-specific compensation. The method is experimentally validated on multiple converter topologies with consistently high accuracy, confirming its broad applicability.