CM & Line-Dm Noise Separation for Three-Level NPC Inverter with Connected Neutral Point for Vehicle Traction Applications

Paper in proceedings, 2019

EMI standards limit the noise level for conducted disturbances on DC power cables of electric vehicles. However, designing the EMI filter requires the information about the CM and DM noise levels. Therefore, a separation of the noise is needed. This paper deals with the separation and quantification of the three-phase DM and CM noise for a three-level NPC inverter with a connected neutral point. A hardware separator, based on HF transformers was developed to separate the noise into CM and line-DM noise. The CM and line-DM noise of the NPC inverter was measured, when operating the inverter with a two-level and a three-level modulation. As expected, the CM noise is dominating, and it is shown that the three-level operation reduces the noise compared to the two-level operation by about 3 to 6 dB.