Comparison of methods for current measurement in WBG systems

One of the biggest challenges faced in the characterization of wide-band gap (WBG) semiconductors is the accurate measurement of the current through the device. Most measuring techniques available do not have the necessary bandwidth to capture the high-frequency current content in such systems. Many of the solutions that do have the necessary bandwidth introduce a “choke-point” into the system by requiring the DC bus to pass through the small sensor aperture, which is not ideal due to the attendant increase in the bus inductance. Many designers use a coaxial shunt resistor when performing WBG device characterization due to the high bandwidth of this approach. In this study, an alternative method was considered using an array of parallel SMT resistors as a custom shunt. This method was evaluated against other measuring techniques in respect to accuracy and found to be in good agreement. This solution was found to have a lower parasitic inductance than competing methods, while reducing the cost of the components by two orders of magnitude. In addition, this paper demonstrates that a limited bandwidth (20 MHz) current transformer (CT) can be used with reasonable results when evaluating SiC multichip power modules (MCPMs); this is not the case with discrete SiC devices, which require a high-bandwidth current shunt for accurate measurement.