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EMI Mitigation for SiC MOSFET Power Modules Using Integrated Common-Mode Screen

Year: 2023 | Author: Taha Moaz | Paper: T3.3
Circuit of the four variations
Fig.1. Four design variations studied.
  The superior material properties of wide-bandgap (WBG) power semiconductors enable them to switch faster, block higher voltages, and have higher current densities compared to silicon devices. With these characteristics, WBG power semiconductors have the potential to improve the efficiency and power density of power electronic converters. However, one of the fundamental roadblocks to fully benefiting from WBG devices is the conducted electromagnetic interference (EMI) associated with the high-speed switching of WBG devices. This work aims to inform EMI mitigation strategies that can be implemented at the power module design stage and that can result in modules with lower noise emissions in the conducted EMI frequency range. The effectiveness of different CM screen architectures is studied by packaging and testing 1.2 kV silicon-carbide (SiC) metal-oxide semiconductor field-effect transistor (MOSFET) power modules.

  Four design variations (Fig. 1) were developed to study the impact of the module architecture on CM noise reduction. A second substrate layer was added into the module architecture to serve as a physical shield to redirect the noise generated by the switching node to the connected DC bus, reducing the current flowing through the baseplate. Two series decoupling capacitors were also included in two design variations to create the midpoint DC Mid. The decoupling capacitors reduce ringing during switching transitions, which results in lower noise being generated.

  A test setup was developed to evaluate the level of noise mitigation introduced by the module architectures. The designed testbed switches each module as a buck converter operating at a switching frequency of 100 kHz, with input/output voltages of 600/300 V, and an output power of ~4.1 kW. The experimental results show that changing the DC node connected to the CM screen and the addition/removal of decoupling capacitors results in different mitigation levels and efficiencies. From the module architectures analyzed, the CM screen (DC Mid) module showed a current noise reduction of up to 26 dB compared to the Baseline (CD) (Fig. 2). The CM screen (DC Mid) module also showed a 0.5% increase in efficiency compared to a conventional module architecture (Baseline module).
Frequency plot of noise current
Fig. 2. Frequency spectra of noise current for the Baseline (CD) and CM screen (DC Mid) modules.

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