Multi-Variable Thermal Modeling of Power Devices Considering Mutual Coupling

• Main Authors: Kaixin Wei, Tian Cheng, Dylan Dah-Chuan Lu, Yam P. Siwakoti, Chengning Zhang
• Format: Article
• Language: English
• Published: MDPI AG 2019-08-01
• Series: Applied Sciences
• Subjects: thermal modeling; mutual thermal coupling; thermal resistances; power converter; case temperature
• Online Access: https://www.mdpi.com/2076-3417/9/16/3240

In relation to power converter design, power density is increasing while the form factor is decreasing. This trend generally reduces the rate of the cooling process, which increases the mutual thermal coupling among the surrounding power components. Most of the traditional models usually ignore the mutual effects or just focus on the conduction coupling. To deal with these factors, the thermal modeling for a boost converter system has been built to compare the junction temperatures (<i>T_j</i>) and the increments under different working conditions in order to consider the conduction coupling. A multi-variable thermal resistances model is proposed in this paper to incorporate the convection thermal coupling into the mutual thermal effects. The coupling resistances, MOSFET to the diode (<inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>R</mi> <mrow> <mrow><mi mathvariant="italic">cp-</mi> </mrow> <mover accent="true"> <mrow> <mi mathvariant="italic">MD</mi> </mrow> <mo stretchy="true">⇀</mo> </mover> </mrow> </msub> </mrow> </semantics> </math> </inline-formula>), and the diode to MOSFET (<inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>R</mi> <mrow> <mrow> <mi mathvariant="italic">cp-</mi> </mrow> <mover accent="true"> <mrow> <mi mathvariant="italic">DM</mi> </mrow> <mo stretchy="true">⇀</mo> </mover> </mrow> </msub> </mrow> </semantics> </math> </inline-formula>) have been calculated and the relationships between coupling resistances and their impact factors (separation distances and working currents) have been discussed. New case temperatures (<i>T_c</i>) obtained by calculation and additional measurements at other separation distances serve to verify the efficacy of the proposed model. This model enhances the current thermal models and provides an effective method to calculate the thermal coupling resistances which can be used to estimate the <i>T_j</i>. As the coupling resistances are distance dependent, the model also helps to optimize and fine-tune the placements of components in high-power density converters.