An EMI-less full-bridge inverter for high speed SiC switching devices

To improve the efficiency of inverters used in hybrid cars and electric vehicles (EVs), SiC-MOSFET transistors are used to minimize the switching losses by high-speed switching. However, as the speed increases, surges and ringing occur in the output voltage, and these can cause electromagnetic interference (EMI). In this paper, we study how this issue can be addressed by using a full bridge inverter to suppress common-mode voltages and cancel ringings currents with opposite phase that are generated when driving at high speed. In most cases, one should assume that transistors that are driven simultaneously have slightly different I-V characteristics. Due to this variation, the ringing cannot be completely canceled, resulting in a common-mode voltage. Although this is liable to cause EMI, we also found that if the two transistors are operated close to the point where the maximum switching current occurs, the common-mode voltage fluctuation can be sufficiently suppressed at any current. We analyzed these characteristics in a simulation using a SiC-MOSFET transistor model, and experimentally verified its behavior in a prototype inverter.