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Design and Implementation of Integrated Common Mode Capacitors for SiC-JFET Inverters

Fig 1. SiC-JFET power module test board. The power module terminals were soldered directly onto the bottom layer of this board.
This paper discusses the issue of electromagnetic interference (EMI) in SiC-JFET inverter power modules, and proposes a solution to limit conducted emissions at high frequencies. SiC-JFET inverters can achieve very fast switching, thereby reducing commutation losses, at the cost of a high level of EMI. In order to limit conducted EMI emissions, this paper proposes to integrate small-value common-mode (CM) capacitors directly into the power module. High-frequency noise, which is usually difficult to filter, is then contained within the module, thus keeping it far from the external network. This approach is in line with the current trend toward the integration of various functions (such as protection, sensors or drivers) around power devices in modern power modules. To demonstrate this concept, the resulting CM noise was investigated, and compared with a standard configuration. Simulations were used to design the integrated capacitors, and measurements were carried out on an experimental SiC-JFET half-bridge structure. A significant reduction was achieved in the experimentally observed CM conducted emissions, with a very minor influence on the switching waveforms, losses, and overall size of the system. The benefits and limitations of this design are discussed in the case of mid-power range inverters for aircraft applications.

Fig. 2. Simulated EMI spectra for different values of the integrated CM capacitors.