Partial Discharge Online Monitoring and Localization for Critical Air Gaps Among SiC-Based Medium-Voltage Converter Prototype

As a consequence of higher blocking voltage and power density by using SiC devices, detailed analysis and careful design of insulation are important for future medium-voltage power converters. Because of the insulation or mechanical coordination, air gaps inside the converters cannot be avoided. Moreover, some gaps are more critical than others, since much oversized design or electric shielding there cannot be acceptable. Admittedly, the final design should be partial discharge (PD) free under normal operation with a safety margin. However, due to possible change of air properties and insulation degradation, massive PD can be still initiated from high electric field regions along the gaps and may lead to the damage of devices, through the highly coupled power and driving circuitry. Therefore, with online PD monitoring and localization, insulation health condition of the critical gaps can be provided, which could have great values for converter operation, maintenance, and design. In this paper, after detailed acoustic signal propagation study, a fiber-optic acoustic sensor array has been implemented into a 6-kV H-bridge power electronics building block prototype, in order to realize online PD monitoring along the critical gaps. Finally, from experimental results, the proposed sensor array has good sensitivity, localization accuracy, and high immunity to the electromagnetic interference. It unveils a novel access to insulation online monitoring for future high voltage, high power density SiC-device-based converters.