Dielectric model of polarization mechanisms in time domain FEM simulation

Abstract

The presented study describes a method to model dielectrics including their polarization mechanisms in time domain FEM simulation to analyse field stresses occurring at pulse voltage. The transition to renewable energies accelerates the development of power modules with higher power density and efficiency. Components close to switched power supplies are stressed with repetitive pulse voltage. Especially SiC and GaN based switched power sources allow for high efficiencies together with steep pulse rise time causing accelerated ageing of insulating systems or triggering partial discharges. FEM simulation allows to understand the field stresses inside an insulating system at pulse voltage and may help to identify design weaknesses. In this paper, there is presented a method to model a material including its polarization mechanisms in FEM simulations suitable for pulse voltage excitation. Dielectric spectroscopy measurements were performed to investigate different materials depending on excitation frequency and temperature. Collected data is post-processed to identify the Debye relaxation equations in both the time and frequency domains. The equations are transferred to COMSOL to model the materials in time-dependent simulations. Identified equations and the resulting COMSOL model are both tested against measured spectroscopy data. Measured dielectric spectroscopy data indicate that several materials pass a dispersion region during the transition from rising flank to voltage plateau during pulse voltage excitation. This effect can lead to electric field distributions different from those considering constant permittivities when combining multiple materials in an insulating system. The application of the model shows mentioned challenges in designing insulating systems for pulse voltage that require attention to modelling Debye relaxation mechanisms for specific materials. This modelling approach can be used for further research helping to set up test objects to investiga.