Comprehensive Electromagnetic Interference Analysis of Neutral-Point-Less (NPL) Multilevel Inverter with Active Common-Mode Voltage Cancellation

This paper investigates a neutral-point-less (NPL) multilevel inverter (MLI), namely an H-type inverter, and its active common-mode voltage (CMV) cancellation technique to achieve a high-level of common-mode electromagnetic interference (CM EMI) noise reduction in comparison with that of the conventional three-phase two-level and the balanced six-phase two-level inverter topologies. The H-type inverter is proposed to overcome a topological limitation of the conventional MLIs, which have a trade-off relationship between neutral current and CMV, where large and small voltage vectors produce high CMV with low neutral current, whereas zero and medium voltage vectors produce zero CMV with the high neutral current. The proposed H-type inverter topology has no neutral connection with a single dc-link capacitor and generates two equal and opposite CMVs due to the active CMV cancellation. These features enable a significant CM EMI noise reduction while maintaining the neutral current at zero. The single capacitor multilevel operation and active CMV cancellation are validated by simulation as well as the experimental setup where the CM EMI noise magnitude is independent of the various dc-link voltages, switching frequencies, and modulation methods due to the active CMV cancellation.