Prediction of dc-link current harmonics from PM-motor drives in railway applications

Depending on the rotor magnet and stator winding configurations, the magnitude of the resulting flux-linkage harmonics in permanent-magnet (PM) motor drives can be substantial. The flux-linkage harmonics result into dc-link current harmonics that can cause the operation of certain track circuits (used to identify the presence of a train on a track section) to malfunction. Predicting the impact of flux-linkage harmonics on the dc-link current is therefore necessary since it may be an important factor to take into consideration when sizing the converter input filter. In this paper, the flux-linkage harmonics from an experimental railway traction PM motor are analyzed using two-dimensional finite element (2DFEM) simulations. Data from the 2DFEM simulations are then used to model the PM motor drive system in a real-time simulator (RTS) model. Output data from the RTS model are compared to experiments with good agreement. Additionally, the impact of resolver eccentricity, typically arising due to bearing wear, on the resulting dc-link current is investigated. A simple analytical model is presented to model resolver eccentricity. The proposed model is then used in the RTS model to analyze the resulting impact on the harmonic content of the dc-link current.