Abstract
Our previous studies showed that geometrical techniques including (1) metal layer offset, (2) stacked substrate design and (3) protruding substrate, either individually or combined, cannot solve high electric field issues in high voltage high-density wide bandgap (WBG) power modules. Then, for the first time, we showed that a combination of the aforementioned geometrical methods and the application of a nonlinear field-dependent conductivity (FDC) layer could address the issue. Simulations were done under a 50 Hz sinusoidal AC voltage per IEC 61287-1. However, in practice, the insulation materials of the envisaged WBG power modules will be under square wave voltage pulses with a frequency of up to a few tens of kHz and temperatures up to a few hundred degrees. The relative permittivity and electrical conductivity of aluminum nitride (AlN) ceramic, silicone gel, and nonlinear FDC materials that were assumed to be constant in our previous studies, may be frequency- and temperature-dependent, and their dependency should be considered in the model. This is the case for other papers dealing with electric field calculation within power electronics modules, where the permittivity and AC electrical conductivity of the encapsulant and ceramic substrate materials are assumed at room temperature and for a 50 or 60 Hz AC sinusoidal voltage. Thus, the big question that remains unanswered is whether or not electric field simulations are valid for high temperature and high-frequency conditions. In this paper, this technical gap is addressed where a frequency- and temperature-dependent finite element method (FEM) model of the insulation system envisaged for a 6.5 kV high-density WBG power module will be developed in COMSOL Multiphysics, where a protruding substrate combined with the application of a nonlinear FDC layer is considered to address the high field issue. By using this model, the influence of frequency and temperature on the effectiveness of the proposed electric field reduction method is studied.
Highlights
Due to the trend toward replacing heavy mechanical, pneumatic, and hydraulic actuators and systems with electrical alternatives with lower weight, higher efficiency, and fewer operational and maintenance costs, a higher electrical demand is needed
This is the case for other papers dealing with electric field calculation within power electronics modules, where the permittivity and AC electrical conductivity of the encapsulant and ceramic substrate materials are assumed at room temperature and for a 50 or 60 Hz AC sinusoidal voltage
The insulation materials of envisaged wide bandgap (WBG) power modules are exposed to square wave voltage pulses with a frequency up to a few kHz and temperatures up to a few hundred degrees
Summary
Due to the trend toward replacing heavy mechanical, pneumatic, and hydraulic actuators and systems with electrical alternatives with lower weight, higher efficiency, and fewer operational and maintenance costs, a higher electrical demand is needed. They are the most promising solution for reducing the size and weight of power conversion systems In this regard, in addition to the trend toward a higher breakdown voltage capability, known as the blocking voltage, for WBG power modules, their volume reduction and their power density increasing have been targeted. The relative permittivity, εr , and AC electrical conductivity, σac , of aluminum nitride (AlN) ceramic, silicone gel, and nonlinear FDC materials were assumed to be frequency- and temperature-independent in [26,27,28,29,30,31,32] This was the case for other papers dealing with electric field calculations within power electronics modules [16,17,18,35,36,37,38,39,40,41,42].
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