Current Measurements for the characterization of SiC power devices used in electric traction drives

Transient analyses of power devices used in traction motor drives are becoming increasingly challenging because of the use of WBG power switches. Hence, the selection of the sensing plays a key role, as it must be able to accurately measure the critical edges related to the fast transients. A classic method to evaluate the switching losses is the implementation of a double pulse test and computing the energy loss, starting from the measurements of current and voltage waveforms. For this reason, the measurement of the current and voltage should be as accurate as possible to provide good results in this kind of analysis. In this context, the selection of the most appropriate current measurement system can be extremely challenging, since the requirements that must be met are more stringent for SiC- and GaN-based power converters. Indeed, the current sensing system must be compact and non-intrusive to avoid introducing significant parasitic elements, which could influence the transient switching behavior. Furthermore, the current measurement system must guarantee a wide bandwidth, sufficient to capture the fast-switching transient. Moreover, in high power applications such as automotive, current sensing should be characterized by a relevant current range, and it should preferably be isolated to avoid issues in high voltage operations.

This paper aims to investigate the performances of different current measurement systems, considering all the aforementioned requirements. The current measurement achieved by a coaxial shunt resistor, current transformer and Rogowski coil are compared during the performance evaluation of SiC power switches through double pulse tests.

Experimental tests performed on a 1200V – 70A SiC power MOSFET are in progress, and the main goal is to quantify the differences among the current measurement methods under different load and driving conditions, emphasizing their pros and cons. The overall results will be presented in the final presentation.