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Abstract-A winding copper loss can be significantly increased due to skin and proximity eddy-current effects. The skin and proximity losses due to fundamental frequency current have been investigated in literature, but the influence of pulsewidth modulation (PWM) on the skin and proximity losses has not been reported. In this paper, a 2-D finite element method is employed to analyze the skin and proximity losses in a permanent magnet brushless ac machine, in which significant proximity loss exists due to high frequency current ripples induced by the PWM, as confirmed by both theoretical calculation and experiment. The analyses should be generally applicable to other machines.Index Terms-Brushless ac machine, eddy-current loss, permanent-magnet machine, proximity loss, pulsewidth modulation, skin effect.

No abstract

No abstract

Abstract-A winding copper loss can be significantly increased due to skin and proximity eddy-current effects. The skin and proximity losses due to fundamental frequency current have been investigated in literature, but the influence of pulsewidth modulation (PWM) on the skin and proximity losses has not been reported. In this paper, a 2-D finite element method is employed to analyze the skin and proximity losses in a permanent magnet brushless ac machine, in which significant proximity loss exists due to high frequency current ripples induced by the PWM, as confirmed by both theoretical calculation and experiment. The analyses should be generally applicable to other machines.Index Terms-Brushless ac machine, eddy-current loss, permanent-magnet machine, proximity loss, pulsewidth modulation, skin effect.

In this paper, the electromagnetic performance of switched reluctance machines (SRMs) with unipolar and bipolar excitations, either sinusoidal or rectangular current waveforms, is investigated in terms of torque capability and torque ripple, iron loss etc. By employing a cost effective standard 3-phase full bridge inverter, both rectangular and sinusoidal bipolar excitations are implemented. Compared with unipolar and rectangular bipolar excitations, the torque ripple and iron loss are significantly reduced with sinusoidal bipolar excitation, albeit with reduced torque capability. Experiments on a prototype 6/4 SRM are carried out to demonstrate the advantages of sinusoidal bipolar excitation.

Abstract-The steady-state performance of Halbach magnetized brushless ac machines when operated in constant torque and fluxweakening modes is investigated both theoretically and experimentally, with particular emphasis on the influence of cross-coupling magnetic saturation on the torque capability.Index Terms-Brushless machines, permanent magnet machines, permanent magnets, torque control.

Vibration and acoustic noise are two critical issues for switched reluctance machine (SRM). The abrupt change of phase current mainly contributes to high vibration and noise under conventional unipolar excitation, sinusoidal bipolar excitation considered in this paper can suppress the vibration in SRM. However, to realize the smooth sinusoidal bipolar excitation, different pulse-width modulation (PWM) strategies can be employed. In this paper vibration and acoustic noise of a prototype 6/4 SRM under different load and speed, which employs hysteresis current control (HCC) and space vector pulse-width modulation (SVPWM), is investigated, together with the conventional unipolar excitation, which is modulated by voltage PWM. It shows that the lowest vibration and acoustic noise are obtained if the SRM excited by the sinusoidal bipolar excitation modulated by the SVPWM, regardless the speed and load. However, the HCC technique exhibits the worst vibration and acoustic noise due to random switching frequencies and mechanical resonances, although less sensitive to the load and speed. In contrast, the acoustic noise with the conventional unipolar excitation is sensitive to both load and rotor speed, when the sinusoidal bipolar excitation modulated by SVPWM is employed it is sensitive to the speed but not to the load.