Thermal Impedance Network Research Articles

On-Site Estimation of Thermal Resistance Degradation of Double-Sided Cooling (DSC) Power Modules Under Power Cycling Conditions

Double-sided cooling (DSC) power modules are increasingly used due to their superior cooling capability and low parasitic inductance. However, the DSC modules have multiple interconnections for heat dissipation, so it is challenging to accurately monitor the thermal resistance degradation of each interconnection under power cycling conditions. An estimation method considering the self-heating and thermal coupling effects of DSC power modules is proposed based on a traditional lumped RC thermal impedance network. The proposed method combining a recursive least squares algorithm with a thermal network model can well evaluate the thermal resistance of each interconnection and their variations on-site during power cycling tests. The lifetime of DSC power modules for power cycling tests could be overestimated if using the 20% increment in overall thermal resistance of DSC modules as a failure criterion.

The Modeling and Simplification of a Thermal Model of a Planar Transformer Based on Internal Power Loss

With the development of high-performance wide-band-gap devices and increasing converter frequency, planar transformers are widely used in high-frequency and high-power-density power conversions. Due to the skin effect and proximity effect, accurate thermal analysis and a simplified thermal model of planar transformers are needed for quick thermal verification as well as system design. This paper proposes two thermal simplification models based on the planar transformer’s thermal impedance network. The internal power loss and thermal coupling between each component are first analyzed. Then, based on thermal radiation theory, the simplified thermal model of the planar transformer is presented. It only requires the input of the total power loss of the planar transformer to calculate the temperature rise, and it does not need the power loss of each component. Finally, the simulation and experimental verification are carried out on a MHz prototype.

Least Squares Method for Identification of IGBT Thermal Impedance Networks Using Direct Temperature Measurements

State-of-the-art methods for determining thermal impedance networks for IGBT (Insulated Gate Bipolar Transistor) modules usually involves the establishment of the relationship between the measured transistor or diode voltage and temperature under homogenous temperature distribution across the IGBT module. The junction temperature is recomputed from the established voltage–temperature relationship and used in determining the thermal impedance network. This method requires accurate measurement of voltage drop across the transistors and diodes under specific designed heating and cooling profiles. Validation of the junction temperature is usually done using infrared camera or sensors placed close to the transistors or diodes (in some cases and open IGBT module) so that the measured temperature is as close to the junction as possible. In this paper, we propose an alternative method for determining the IGBT thermal impedance network using the principles of least squares. This method uses measured temperatures for defined heating and cooling cycles under different cooling conditions to determine the thermal impedance network. The results from the proposed method are compared with those obtained using state-of-the-art methods.

Mission-Profile-Based Lifetime Prediction for a SiC mosfet Power Module Using a Multi-Step Condition-Mapping Simulation Strategy

The reliability analysis and lifetime prediction for SiC-based power modules is crucial in order to fulfill the design specifications for next-generation power converters. This paper presents a fast mission-profile-based simulation strategy for a commercial 1.2-kV all-SiC power module used in a photovoltaic inverter topology. The approach relies on a fast condition-mapping simulation structure and the detailed electro-thermal modeling of the module topology and devices. Both parasitic electrical elements and thermal impedance network are extracted from the finite-element analysis of the module geometry. The use of operating conditions mapping and look-up tables enables the simulation of very long timescales in only a few minutes, preserving at the same time the accuracy of circuit-based simulations. The accumulated damage related to thermo-mechanical stress on the module is determined analytically, and a simple consumed lifetime calculation is performed for two different mission profiles and compared in different operating conditions.

A 3D Thermal Network Model for Monitoring Imbalanced Thermal Distribution of Press-Pack IGBT Modules in MMC-HVDC Applications

In this paper, the impact of a double-sided press-pack insulated-gate-bipolar-transistor (PP IGBT) cooling structure on its thermal impedance distribution is studied and explored. A matrix thermal impedance network model is built by considering the multi-chip thermal coupling effect for the collector side of the PP IGBT. Moreover, a verification has been made by comparing the proposed matrix thermal network model and the conventional lumped RC network model provided by the manufacturer. It is concluded that the collector side has lower thermal resistance and dissipates about 88% of the heat generated by the IGBT chips inside the module. Then, a modular-multilevel-converter high-voltage-direct-current (MMC-HVDC)-based type test setup composed of the press-pack IGBT stacks is established and the junction temperature is calculated with the proposed thermal model and verified by temperature measurements.

Review of Thyristor Junction Temperature Calculation Methods

The thyristor has been widely used in many fields since it has been invented, and has promoted the development of the DC transmission technology rapidly. The increasing temperature of its junction may cause serious hazards. Because of this, a variety of methods that can obtain the junction temperature has been summarized in this paper, such as the indirect measurement method, the direct measurement method, the equivalent thermal impedance network method and the numerical calculation method, etc. Summaries have been made in different occasions which these methods were applied. It also compared the advantages and disadvantages of each method and pointed out the developing trends and researching directions in the future.

Extraction and modeling of self-heating and mutual thermal coupling impedance of bipolar transistors

A measurement system comprised of an ultra-low-distortion function generator, lock-in amplifier, and semiconductor parameter analyzer is used for sensitive extraction of the small-signal thermal impedance network of bipolar devices and circuits. The extraction procedure is demonstrated through measurements on several silicon-on-glass NPN test structures. Behavioral modeling of the mutual thermal coupling obtained by fitting a multipole rational complex function to measured data is presented.

A Fourier transform technique for calculating cable and pipe temperatures for periodic and transient conditions

An underground pipe-type cable system is represented by a thermal impedance network. A ladder network of resistances/capacitances represents the cable out to the outer surface of the pipe. The earth, adjacent pipe-type cables, and cable images are modeled by a frequency dependent thermal impedance found by solving the heat transfer differential equation. The heat input to the system is conductor I/sup 2/R loss. The heat input can be a periodic signal or a transient of up to 300 h. A fast Fourier transform (FFT) is used to obtain heat input in the frequency domain. The frequency domain thermal input at the conductor is divided by the thermal admittance seen by the conductor and an inverse FFT is used to obtain conductor temperature as a function of time. A similar procedure obtains shield and pipe temperature. Iteration is used to model conductor electrical resistance change with temperature. The ambient temperature and temperature due to dielectric loss is added in to obtain final values. >