A Condition Monitoring Method for the DC-Link Capacitors in the Traction Converter System With an LC Resonant Circuit

This article proposes a condition monitoring method for the dc-link capacitor in railway traction converter systems with an LC resonant circuit. This method applies to nighttime routine inspection procedures in traction systems with the converter power-off state. Different from the existing methods, the proposed method can monitor the capacitance of the dc link capacitor and the resonant capacitor in the traction converter concurrently. It is based on an ac–dc superimposed signal injection with proper excitation frequency and amplitude and a digital twin method based on the BAT algorithm, which is not interfered by circuit parameters other than those on the dc side. Meanwhile, a hand-held test unit with lightweight features is developed, which can generate the required injection signals and collect the responses of the dc-link filter circuit network. Finally, the proposed monitoring method and the developed test unit are validated by a full-size traction experimental platform. Considering multiple scenarios of dc link capacitor and resonant capacitor aging shows that the monitoring error is less than 0.7% (average) and 1.5% (maximum).