Abstract
This study facilitated the improvement of no-load back electromotive force (back-EMF) wave form, total harmonic distortion (THD) of back-EMF, and torque ripple using a novel skew angle formula, considering the specific order of a no-load THD. In real usage environments, it is taken into consideration for the fully enclosed cooling system and limited inverter switching frequency of urban railway car traction motors. Since the most railway car traction motors use high-withstand voltage rectangular wires in slot-open structure, a no-load back EMF waveform includes large space slot harmonics, which should be smaller as possible. For 6-step control, the no-load back EMF waveform is important because switching for motor control is performed once after the rotor position is determined. To improve the no-load back EMF waveform and THD, two-dimensional and three-dimensional finite element analysis (FEA) were performed using a novel skew angle formula considering specific harmonic order reduction, while the fundamental amplitude was minimally reduced. A prototype with the novel skew was fabricated and verified. In addition, it was designed by calculating a low current density for a fully enclosed cooling system. A temperature saturation experiment was also performed, and successfully verified. Therefore, we suggest that the no-load back EMF characteristics and torque ripple are improved by applying the novel skew angle instead of a traditional skew angle.
Highlights
The global railway market is gradually increasing
The rotating motor type is most commonly used in traditional railway, whereas the linear type is applied to ultra-high speed maglevs [2], or mid-andlow speed maglevs [3]
The induction motor (IM) is less costly and easier to manufacture than permanent magnet synchronous motors (PMSM)
Summary
The global railway market is gradually increasing. There are various railway systems, from low-speed railways operating in cities to high-speed railways connecting countries. In the case of railway car traction motors, many countries require the reliability, stability, and high efficiency for railway vehicle components [6,7,8]. The IM is less costly and easier to manufacture than permanent magnet synchronous motors (PMSM) It has the disadvantage of a low starting torque and a slow response rate, owing to its inherent dynamic characteristics. For the traction motor, it is necessary to design the no-load back-EMF and torque ripple as small as possible so that passengers experience a comfortable ride [25]. The design of a novel skew angle formula that considers the controllability and fully enclosed cooling system, were conducted through a 2-D and 3D finite element analysis (FEA)
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