Numerical Simulation Study of Power Electronic Transformer Insulation System Based on Space Charge Characteristics Under Combined Electrothermal Stress

Numerical simulation of space charge dynamics under DC has been commonly used in the area of high voltage insulation, and with access to power electronic equipment in renewable power systems, the complex stress environment faced by multi-energy conversion equipment has led to traditional numerical simulation models of space charge no longer being applicable. In this research, a high-frequency heating model is constructed on the base of dielectric loss mechanism, and a bipolar charge transport model with coupled temperature factors is further proposed to form a space charge numerical simulation model adapted to complex combined thermal and electrical stresses. From the developed model, the effects of the coupled temperature-frequency dual factor on space charge are investigated and the space charge evolution mechanism under combined electrothermal stresses is analyzed. The results indicate that the accumulation of space charge inside the insulation is more significant under combined electrothermal stress than under DC, and massive hetero charges accumulate near the electrodes, resulting in more severe distortion of electric field close to electrodes. This study is helpful to understand the mechanism of space charge production of complex stresses and provides assistance in the design of high voltage insulation in renewable power systems.