Loss reduction potential of electrically excited synchronous traction machines using three-level inverters

While two-level voltage-source inverters have been the norm in variable speed drives including traction drives, an increasing focus on system efficiency makes the consideration of multi-level inverters necessary. In this context, this paper analyzes the efficiency advantages of a system using a T-type three-level inverter in combination with an electrically excited synchronous machine (EESM). Based on the consideration of advantages of using a three-level inverter, and the unique loss characteristic of the considered machine type, the need for a separate consideration of inverter-based machine losses is laid out. Consequently, a time-efficient transient numerical calculation approach is presented, that enables a comparison of machine losses throughout the operating range. Finally, the resulting losses are separated into sinusoidal and inverter-based components and are compared for driving cycle relevant operating points. In conclusion, the expected advantages of the multi-level inverter on machine losses are discussed for the considered EESM.