Influence of the Modeling Depth and Voltage Level on the AC Losses in Parallel Conductors of a Permanent Magnet Synchronous Machine

Analysis of ac effects, such as skin and proximity effect as well as the circulating currents and corresponding losses are usually done by finite-element analysis, while mostly only a single slot is considered, neglecting the influence of neighboring phases on the flux density of the stator iron and thus the resulting slot leakage flux. As the simulation of single stranded finite element (FE) models is computationally very demanding and time consuming, this paper compares different levels of detail of two-dimensional FE models and investigates the impact of the modeling depth on the resulting copper loss to find a computation time optimized modeling setup. It is shown that the use of single slot models is sufficient in case of distributed windings. Moreover, the potential increase of ac losses is assessed for two machines that are identical except for the stator winding, so that one and the same machine is investigated at two different voltage levels, namely 400 and 800 V. The reference machine is a 160 kW nominal power and 9000 r/min maximum speed permanent magnet synchronous machine. Since the magnetic circuit has to remain constant, both designs share the same overall winding scheme and total number of strands within a slot but differ in the number of parallel and serial connected strands. Due to the increased bundle cross section of the lower voltage winding, it is more susceptible to ac effects and thus tends to increased winding losses.