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

In modular multilevel converters (MMCs) of HVDC systems, metallized film capacitors (MFCs) are commonly used as dc-link capacitors. Based on the unique feature of the self-healing discharge, MFCs can clear internal defects and maintain operation stability. However, self-healing discharge can cause continuous aging of MFCs due to the accumulation of electrode area loss. Although electrical parameters are sufficiently investigated to monitor the operating states of MFCs, the correlation between discharge characteristics and aging states remains unclear based on these parameters. To address this issue, this article provides a novel perspective by proposing a discharge monitoring and aging assessment method based on the acoustic signal. First, an accelerated aging platform is established to obtain MFC samples in different aging degrees. Then, the acoustic signal and the pulse current signal of MFC samples are detected to demonstrate the feasibility of using acoustic signals as characteristic parameters. Furthermore, the processed discharge data are subject to cluster analysis to investigate the relationship between discharge statistic characteristics and the aging states of MFCs. The results indicate that the aging states of MFCs can be assessed using the frequency spectrum characteristics and the cluster ratio of acoustic signals, guiding future research on the monitoring methods of MFCs using nonelectrical parameters.