The increase of power density of Si C-based medium-voltage converters is limited due to external insulation problems

and it is urgent to study its external insulation design and evaluation. First

a novel silicon photomultiplier（SiPM）-based external discharge sensor is proposed. Then

the partial discharge（PD） characteristics of two external insulation structures under PWM excitation are studied using this sensor

and universal high-voltage insulation design recommendations of power electronics are summarized. Finally

by taking the design evaluation of two key insulation components in the SiC-based medium-voltage converters as examples

insulation assessment tests are carried out with the proposed sensor. The results show that SiPM optical sensor has the advantages of small size

high sensitivity

strong anti-electromagnetic interference ability

etc.

which is suitable for power electronic applications under PWM excitation. The PD inception voltages decrease as the switching speed of the device and the frequency increase

under two typical external discharge defects. PD pulses are mainly distributed on the rising and falling edges of PWM excitation for creeping discharge

while for tip discharge

PD pulses mainly exist in the flat area of PWM excitation. The results verify the feasibility that the proposed sensor could be used in offline evaluation of converter insulation system and even future online monitoring applications. The proposed power electronic insulation design recommendations and evaluation method can provide references to the insulation design and evaluation of future medium voltage high power density converters.