Abstract
This paper presents a novel direct-drive electric traction system that incorporates a disk permanent magnet (PM) motor, which shows practical potential to urban rail trains. The disk PM motor can be directly mounted on the train wheel, which realizes the direct contact of power and load. First, conceptual structure of the direct-drive system is described. Then, the motor structure and its specifications are presented from the viewpoint of replacing the asynchronous motor of the existing ALSTOM 04A02 urban rail system. Machine parameters are calculated and 3-D finite element (3-D FEM) simulation is carried out to analyze magnetic field distribution. Design results demonstrate that the disk PM motor has distinguished advantages in power density and efficiency over the asynchronous motor in use, which would be more suitable for heavy-load rail trains. At last, the influence of harmonic current from the inverter on the harmonic torque of the disk PM motor is studied, and results demonstrate that the 6 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> harmonic torque is the main factor affecting the torque ripple and could be suppressed by further optimizing the machine parameters. This work can provide some reference for improving the train traction system, and has reference values to other electric traction systems.
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