One special current waveform of toothed pole doubly salient permanent magnet machine for marine current energy conversion system

Abstract

Marine current energy becomes more and more attractive because of its remarkable advantages. In this paper, one toothed pole doubly salient permanent magnet (DSPM) machine is proposed for marine current energy conversion system. This kind of machine has a simple structure, good fault tolerance, reliable operation, and high power density, which make it very suitable for marine tidal current applications. However, DSPM machine is conventionally operated by means of current chopping control and angle position control in a different region due to the trapezoidal back electromotive force (EMF) waveform. While for this toothed pole DSPM machine, the PM flux-linkage, inductance, and back EMF have more sinusoidal waveforms, which make the sinusoidal current be possible. Unfortunately, the classic sinusoidal current generates a relatively large torque ripple owing to the special inductance. Consequently, the primary purpose of this paper was to design one special current waveform to further reduce the torque ripple. Firstly, the model of the toothed pole DSPM machine is presented. Secondly, the torque distribution theory is proposed without taking into account mutual inductance effect. The mathematic expressions of the currents are deduced subsequently. Thirdly, several fitting currents are analyzed and compared based on the theoretical currents. Moreover, the simulation results verify the torque distribution theory and allow proposing the optimal current waveform (fundamental and second harmonic) in comprehensive consideration of the voltage, powers, and torque ripple. Finally, some robustness analysis is also presented to show the good performances of this current.