THERMAL MODELING OF POWER HYBRID MODULES

Accurate prediction of temperature variation of power semiconductor devices in power electronic circuits is important to obtain optimum designs and estimate reliability levels. Temperature estimation of power electronic devices has generally been performed using transient thermal equivalent circuits. In this paper we have developed a simplified thermal model of the power hybrid module. This model takes into account the thermal mutual between the different module chips based on the technique of superposition. Design of power electronics systems involves numerous trade-offs as is common in most engineered systems. It proceeds through a careful selection process for various parameters and technologies starting with the electrical design and culminating in manufacturing process design. The electrical design phase results in the selection of power electronic circuit components, which is relatively mature and well established. However, rendering wellconceived electrical designs into reliable and low-cost products suitable for any application requires a substantial amount of additional engineering effort. The physical design proceeds further beyond the electronic circuit design, accounting for magnetic devices, current densities, dielectric isolation requirements, semiconductor power losses, thermal management methods, thermomechanical stresses, die-attach processes, electromagnetic interference, etc. Aforesaid factors that affect the design are coupled through complex interrelationships. Design activity encompasses several engineering domains including magnetic, electrical, mechanical, thermal, material processing, and manufacturing sciences. In this paper we studied the thermal behavior of the power hybrid modules. The study lead to correct the junction temperature values estimated from the transit thermal impedance of each component operating alone. The corrections depend on the mutual thermal coupling between the different chips of the hybrid structure. It was noticed that the classic analysis of thermal phenomena in these structures, independently of powers dissipated magnitude and boundary conditions, is not correct. In the first part of the paper we have studied the thermal interactions between the module devices. Thermal 3D finite elements simulations have been made to observe the thermal influences between the different components of the module. These results will be compared with those obtained experimentally. An experimental technique, have been developed to estimate the thermal influences, caused by the different chips of the hybrid structure. This technique is based on the measure of IGBT and DIODE thermo-sensitive parameters. In the second part of the paper we have developed a simplified thermal model of the power hybrid module. This model takes into account the thermal mutual between the different module chips based on the technique of superposition. It is obtained by the finite element method (FEM) and implemented in the MATLAB simulator. A 3D numerical simulations were made in order to shows the accuracy of the proposed thermal model.