Discharge Monitoring and Aging Assessment Method for Metallized Film Capacitor Based on Acoustic Signal

In modular multilevel converters (MMCs) of HVDC system, metallized film capacitors (MFCs) are commonly used as DC-link capacitors. Based on the unique feature of the self-healing discharge, MFCs can clear the inner defects and realize the operation stability. However, the self-healing discharge can cause a continuous aging of MFCs due to the accumulation of the electrode area loss. In recent years, although electrical parameters have been sufficiently investigated to monitor operating states of MFCs, the correlation between discharge characteristics and the aging states is still not able to be clarified based on these parameters. To address the issues, this paper provides a novel perspective by proposing the discharge monitoring and aging assessment method based on the acoustic signal. First, an accelerated aging platform was established to obtain MFC samples in different aging degrees. Then, the acoustic signal and the pulse current signal of MFC samples were both detected to demonstrate the feasibility in terms of using acoustic signals as characteristic parameters. Further, the processed discharge data were subject to cluster analysis to investigate the relationship between discharge statistic characteristics and aging states of MFCs. The results indicate that the aging state of MFC can be assessed using the frequency spectrum characteristics and the cluster ratio of AE signals, which would instruct the future research on the monitoring method of MFC using non-electrical parameters.