Electromagnetic Interference and Compatibility within SiC-based Medium Voltage Converters

Abstract

The emergence of silicon carbide (SiC) devices gives rise to more severe electromagnetic interference (EMI) challenges than ever before due to their fast switching capability. Meanwhile, medium voltage (MV) high power converters have been pushed to higher power, higher voltage, and higher power density design requirements in recent years, which makes the EMI management even more difficult. Unlike converter-level noise emissions which can be regulated by certain EMI/EMC standards, the noise inside the power converter has no standard to follow. Moreover, even if a converter complies with certain standards at its terminals, the internal components are not guaranteed to work without issues. Modern power converters consist of numerous auxiliary circuits within the converter to achieve sophisticated functionalities such as sensing, communication, fault detection, signal processing, etc. To ensure reliable operation, these auxiliary circuits are required to achieve electromagnetic compatibility (EMC) to the fast switching of power converters. The existing knowledge for noise propagation inside the converter is limited to the conducted emission caused by the fast switching of the power devices. Although prior research has demonstrated various approaches to mitigate the CM current of the gate driver, the mechanism of the gate driver's false triggering remains unknown. It is of great importance to study the mechanisms by which the noise is induced on low power logic circuitry caused by the switching transient of the high power main circuit power stage, as well as the mechanism of the gate driver's false triggering. The design of the MV gate driver lacks a general guideline to achieve high EMI immunity. The isolated power architecture has gained popularity for the MV gate driver structure, while the double-isolated power architecture is the state-of-the-art structure. When designing the gate driver, the primary design criterion was to mitigate the CM current flowing on the reference planes of the printed circuit board (PCB). However, as discussed above, CM current mitigation is not the final goal; instead, the signal integrity of critical signal traces needs to be strictly ensured to guarantee the reliable operation of the gate driver. Finally, the inductor is a very important element to mitigate EMI. However, its design for MV, high power, high frequency power converters is one of the key challenges of the overall design because MV insulation systems usually have very bulky designs that decrease the overall power density; meanwhile, for high power applications, the large DM current flowing on the inductor windings is the key reason for the total inductor loss. As universal modular units, power electronics building blocks (PEBBs) can be configured into various structures. The inductor is distributed in each individual PEBBs to maintain high power density, while ensuring functional performance.