Fast Calculation Method Research For IGBT Junction Temperature Based On Fourier Transform

Insulated gate bipolar transistors(IGBTs)have higher failure rates than other components in converter failure statistics,therefore their reliability analysis is gradually becoming the focus of power electronics research.Thermal stresses have been demonstrated as one of the most critical factors for the reliability of IGBT modules and systems,junction temperature calculation is important.One of the key challenges for long-term reliability analysis is to quickly estimate extensive junction temperature cycles while fulfilling an accepted accuracy.Therefore,how to address this challenge has important research significance.Either due to un-quantization of junction temperature dynamics,small iteration period is adopted in existing calculation methods,which results in slow calculation speed and requires more storage resources,or although fast calculation is achieved,the estimated accuracy of junction temperature is degraded.Improving the thermal estimation accuracy and reducing computational burdens simultaneously are completely contradictory in the previous research where a trade-off must be taken between them.To address this challenge,this paper proposes a fast calculation method of junction temperature based on Fourier transform.First,combining with the working mechanism of the IGBT,the generation and calculation of each power loss are introduced in detail.And the existing power loss calculation methods are classified,and the reasons for presenting advantages and disadvantages of the existing methods are revealed.Next,according to the unidirectional conductivity of the IGBT module,the relationship between the current flowing in the IGBT and the anti-parallel diode and the phase current is analyzed.And the IGBT conduction current is expressed quantitatively.Morever,combining the modulation strategy and the output characteristic curve of the IGBT module provided in the datasheet,the power loss of IGBT in a single fundamental wave period is quickly represented.Secondly,combining with the Foster thermal network,the details of junction temperature dynamics under each power loss component are quantified by the generic discretizationintegration process and further expressing the junction temperature dynamics within a single fundamental period.Afterward,maximum and minimum junction temperature,which are more concerned,can be only collected through derivation and substitution,and the junction temperature at other time points is calculated selectively according to actual demand.And the fundamental period is chosen as the iteration period in the proposed method.Next,taking a two-level three-phase inverter as an example,the accuracy and rapidity of the junction temperature calculation with the electro-thermal simulation method,the analytical method and the proposed method in this article are compared and analyzed in the wide frequency domain through simulation through MATLAB and PLECS electrothermal simulation.And the results of junction temperature estimation under the changing operating conditions is also expressed.At the same time,the influence of junction temperature calculation accuracy on lifetime evaluation is analyzed.Finally,an experimental platform is built to verify the accuracy of junction temperature estimation.Aiming at the change of heat dissipation condition caused by the opening of the IGBT module,the parameters of thermal network are revised based on the multi-physical field analysis.