Design and Assessment of External Insulation for Critical Components in a Medium Voltage SiC-Based Converter via Optical Method

Exposed metal or insulator to air interfaces widely exists in medium voltage SiC-based converters. To effectively address external insulation along such interfaces, a large insulation distance in the air is applied. However, such insulation tends to significantly impair converter power densities and performances. Targeting the external discharge free design approaches that reflect the relationship between insulation structures and square wave excitation parameters is highly demanded. Moreover, due to possible fabrication issues and insulation degradation, massive external discharges may still occur, even that they should be eliminated by the design. Therefore, insulation assessment for the entire system, or at least for critical components, is necessary. In this article, silicon photomultiplier (SiPM)-based external discharge detection solutions are introduced. Then, for a self-designed SiC-based medium voltage converter, the SiPM sensors enable both its external insulation design and assessment. By using SiPM sensors, two types of external discharges are characterized under square wave excitation, and thus, general design suggestions are developed. Moreover, as shown by two examples, SiPM sensors can be used to assess the external insulation for converter applications. Based on the experimental data, analysis, and real examples, the results of this study can be used to design and assess the external insulation for future medium voltage, high-power density SiC-based converters.