Simulation on the Influence of Square Wave Electric Field on Space Charge Behavior in Polyimide

The polyimide in the inverter-fed motors works under square wave electric field with the periodic variation of voltage polarity and steep rise time. Thus, it is important to investigate the charge behavior under square wave electric field. With the limit of present space charge detection technology under the square wave, this paper focuses on numerical simulations of charge behavior. The multi-mobility mode was introduced into the bipolar carrier model and the simulation of charge transport in polyimide under square wave electric field with different strength and rise time was carried out. It shows that the increase of strength of electric field significantly enhances the accumulation of space charge. When the electric field strength is low, the charge responds rapidly to the change of electric field polarity. However, with the increase of the electric field strength, the heterocharge accumulation becomes obvious, resulting in the distortion of local electric field. The rise time has little effect on the charge distribution. Further, the effect of recombination was used to study the relationship between rise time and charge behavior. When the voltage polarity is reversed, there is a surge in the recombination rate, which is convincing evidence of the coexistence of positive and negative charges. As the rise time increases, the maximum total recombination rate presents a significant downward trend and the mean recombination rate fluctuates accordingly. Spatially, the recombination rate near the boundary is much higher than that inside the specimen. The recombination rate inside the sample slowly raises, while the recombination rate near the boundary has an opposite change with the increase of rise time.