Author: M.Sc. Ajay Poonjal Pai
Co-authors: Dr. Tomas Reiter, Prof. Martin März
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This paper evaluates the benefits of replacing the Si diodes of a commercial IGBT module for the main inverter application of an electric vehicle with SiC diodes, leaving the other components of the package and the system unchanged. This will give a direct comparison of Si vs SiC, without giving scope for discrepancies arising out of differences in the packaging, gate-driver circuit etc. The IGBT-module chosen for comparison is a low inductance (8nH) HybridPACK Drive module from Infineon, suitable for very high speed switching. The focus of the comparison is the following:  Static and dynamic characterization of the Si and hybrid-SiC modules.  Development of a loss model for the modules based on the above measurements.  Application of the developed loss model to investigate the performance for various drive cycles (Artemis, WLTP, NEDC).  Development of a novel calorimetric loss measurement setup for experimental verification of the results. Motivation Papers that address the topic of SiC for automotive main inverters often have one or more of the following drawbacks: The considered devices are rated for low currents, quite far from the typical application requirements of the main inverter The devices/packages chosen are prototypes, which do not face the same constraints a mass product would. The compared Si and SiC chips are in completely different packages or application conditions In short, a clear investigation of the benefits of using SiC as a plug-and-play replacement for a commercial Si-IGBT module is still missing in literature. This gap is attempted to be filled by the paper Results Fig. 1 shows an IGBT-diode pair of the compared HybridPack Drive module with Si diodes (the module will be referred to as “HPD”) and SiC diodes (the module will be referred to as “HPD-Hyb-SiC”) respectively. Static losses are measured with a curve tracer and the switching energies of both the modules are measured in a double pulse test setup (see Fig. 3). The SiC diodes help reduce E_on and E_rec by around 25% and 75% respectively. A loss model is derived based on these measurements and this model is used to calculate the inverter losses for Artemis, NEDC and WLTP drive cycles. As seen in Fig. 3, HPD-Hyb-SiC offers more than 10% reduction in losses for all the drive cycles. The Artemis Urban cycle with a reduction of around 20% losses sees the most benefit of using SiC diodes. Also, the inverter losses at different rms currents and dc-link voltages are measured in a novel calorimetric setup (see Fig. 2) introduced in the paper and the results are summarized in Fig. 3. It can be seen that there is no benefit of using the SiC diodes at V_dc=100V. At V_dc=300V, the benefits of SiC become prominent and this gap widens as we increase V_dc, and at V_dc=400V, 75A, we can see a reduction of around 7% in the overall losses. Also, the simulated losses are found to be in good agreement with the measured losses, thereby validating the loss model.