Over the past few years, semiconductor technology has come a long way, especially in the fields of power electronics with applications in research and heavy industry applications. Insulated-gate bipolar transistor (IGBT) modules play a crucial role as they are implemented in applications with high operating temperatures, fast switching speeds, higher reliability, etc. In such situations, getting precise results is of utmost importance as there may be several dangerous outcomes to the circuits or even the users operating the circuits if not calculated correctly.

To enable simulation in a multi-dimensional situation, ranging from nanoseconds to seconds and improve circuit performance, a variety of techniques for integrating EM domains to analyse electro-thermal interaction were examined. Research on electro-thermal properties of the IGBT chip has been extensively conducted for a 3-D packaging structure in such chips.

Ⅰ.  Magnetic and Thermal analysis of Power Modules

The experiment conducted presents a simulation wherein, the electrical, thermal and magnetic characteristics of the IGBT are tested during the circuit operations.

Fig 1: Schematics of the proposed EM-electro-thermal analysis method.

The parasitic properties between the chip surfaces (collectors, emitters, and gates) and the module external terminals are represented by this electromagnetic network. The electro-thermal IGBT chip model is constructed in the circuit representing the working point conditions dependency using curve-fitting and weighted interpolation of experimental test results or data sheets. This electro-thermal model acts as an important link between the thermal and EM networks, having to accept Tj s information from each chip and returning power loss values to the former, and accepting existing information and restoring chip on-state voltage drop (Vce(on)) values to the latter.

Fig 2: 1700V/450A half-bridge IGBT power module layout.

The data on the frequency dependant resistance and inductance values between external terminals and chip surfaces, such as from the module's DC+ power terminal to the collector surfaces of the high-side switch IGBT chips is included as shown in Fig 2.

Ⅱ.  Extraction of the Proposed Model

Until recent times, research on the self-consistent interaction between the electrical and thermal characteristics of power modules has been an exciting topic as it includes technologies which can be used in overcoming several obstacles using the ROM method.

While conducting the tests, all thermal characteristics were considered along with an assumption of an intact cooling boundary at the bottom for further simplification and efficiency. Moreover, a baseplate temperature of 90 was set during the simulation of the bottom process.

Fig 3: Temperature distribution when power loss is applied only to U5

As shown above, Fig 3 depicts the thermal behaviour of the entire packaging structure which was recorded to study accurate electro-thermal coupling.

Fig 4: Comparing results of Icepack SVM, Simplorer thermal network and experimentation test

Fig 4 shows the effectiveness of the extraction process to demonstrate its comparison with different results. For instance, the comparison was done among Icepak FVM simulation, Simplorer thermal network simulation and experimental test results to check the thermal resistance of the low side switch. The graph with thermal network topologies shows identical simulation results as that of the standard FVM simulation. The current sharing properties of the IGBT depend on the frequency of the parasitic components of the module packaging which also includes the resistance and inductance of the conduction paths. During its application, each conduction path from the external bus bar terminals to the chip surfaces in the IGBT module application may have an effect on how current is spread among the chips and how each chip switches by itself.  This makes it very important for the modules to characterize the parasitic values from all external terminals to the surfaces of each chip.

Ⅲ.  Simulations and Results

Once the extraction process of the IGBT chip model is complete, simulations for the thermal and EM networks and their analytical representations are taken into consideration for the study of their module performance in chopper circuits. In such chopper circuits, while IGBT modules are operating at high frequencies, a 900V DC power supply is set with a load connected in parallel to the high side switch for three IGBT switches and three FRD chips

Analytical Solution: In a chopper circuit, it is very important to take into account the current sharing and temperature dependency of the power losses due to which the loss can be viewed in an analytic solution.