Abstract
This paper is concerned with the thermal models which can physically reflect the heat-flow paths in a lightweight three-phase half-bridge two-level SiC power module with six MOSFETs and can be used for coupled electrothermal simulation. The finite-element (FE) model was first evaluated and calibrated to provide the raw data for establishing the physical resistor–capacitor (RC) network model. It was experimentally verified that the cooling condition of the module mounted on a water cooler can be satisfactorily described by assuming the water cooler as a heat exchange boundary in the FE model. The compact RC network consisting of 115 R and C parameters to predict the transient junction temperatures of the six MOSFETS was constructed, where cross-heating effects between the MOSFETs are represented with lateral thermal resistors. A three-step curve fitting method was especially developed to overcome the challenge for extracting the R and C values of the RC network from the selected FE simulation results. The established compact RC network model can physically be correlated with the structure and heat-flow paths in the power module, and was evaluated using the FE simulation results from the power module under realistic switching conditions. It was also integrated into the LTspice model to perform the coupled electrothermal simulation to predict the power losses and junction temperatures of the six MOSFETs under switching frequencies from 5 to 100 kHz which demonstrate the good electrothermal performance of the designed power module.
Highlights
The high performance of SiC power devices at high frequency, high power and high temperature applications make them attractive in avionic industry
The finite element (FE) thermal simulation using a proper heat exchange coefficient to simplify the interaction between the power module and the water cooler can still provide good predictions though a much more computation resource demanding co-simulation of thermal and computational fluid dynamics may provide better predictions
By contrast, ignoring the 32% voids in the Sn-3.5Ag solder joint to attach MOSFET M5, the junction temperatures of this MOSFET are underestimated about 3 C during the early stage. These results are probably related to the resolution of the transient thermal test and relative small contribution of thermal capacitance and resistance from the Sn-Ag solder joints in the module system, which could hardly reveal the virtual effect of relatively low percentages of the voids in the Sn-3.5Ag solder joints
Summary
The high performance of SiC power devices at high frequency, high power and high temperature applications make them attractive in avionic industry. The FE model is especially calibrated with experimental data and can be used to calculate the temperature field for further thermo-mechanical design and optimization, and collect the temperature data for extracting the R and C parameters of the compact RC thermal network model. The latter can be used to rapidly calculate the junction temperatures of the power devices for further electro-thermal design, thermal management, reliability and lifetime prediction of the power module
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