Adam Pride

Analysis of electromagnetic performance of flux-switching permanent-magnet Machines by nonlinear adaptive lumped parameter magnetic circuit model

A nonlinear adaptive lumped parameter magnetic circuit model is developed to predict the electromagnetic performance of a flux-switching permanent-magnet machine. It enables the air-gap field distribution, the back-electromotive force (back-EMF) waveform, the winding inductances, and the electromagnetic torque to be calculated. Results from the model are compared with finite-element predictions and validated experimentally. The influence of end effects is also investigated, and optimal design parameters, such as the rotor pole width, the stator tooth width, and the ratio of the inner to outer diameter of the stator, are discussed.

Influence of PWM on the Proximity Loss in Permanent-Magnet Brushless AC Machines

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.

Eddy Current Loss in the Frame of a Flux-Switching Permanent Magnet Machine

In flux-switching permanent magnet machines, a significant leakage flux exists at the outer surface of the stator core. Since the leakage flux varies as the rotor rotates, a significant eddy current loss may be induced in the nonmagnetic frame. The leakage flux and the associated eddy current loss in a representative flux-switching machine are investigated by finite element analysis, on both open-circuit and at rated load, predicted results being validated experimentally. In addition, the effectiveness of introducing slots in the frame to reduce the eddy current loss is investigatedThe leakage flux and resultant eddy current loss in the frame of a flux-switching permanent magnet (FSPM) motor was investigated by 2D time-domain finite element analysis and validated experimentally. This paper presents predicted and measured results for eddy current loss in the frame during both low speed, constant torque operation and high speed, constant power (flux-weakening) operation.

Influence of PWM on the Proximity Loss in Permanent Magnet Brushless AC Machines

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.

Performance of Halbach magnetized brushless ac motors

In this paper, an anisotropic bonded NdFeB Halbach magnetised ring magnet, which is oriented in powder alignment system during injection moulding and subsequently impulse magnetised, is employed. The features of such a Halbach magnetised machine, in terms of the airgap field distribution, and the back-emf and cogging torque waveforms, etc. have been compared with those which result with a Halbach magnet having discrete magnet segments have previously been compared.

Performance comparison between unipolar and bipolar excitations in switched reluctance machine with sinusoidal and rectangular waveforms

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.

Performance improvement in Flux-Switching PM machines using flux diverters

Several schemes for mechanical (as against electrical) flux weakening in permanent-magnet (PM) machines have been proposed in recent literature. Although the detailed arrangements differ depending upon whether the magnets are mounted on the rotor or the stator, the principle remains broadly the same. A movable piece of magnetic steel is used to “short” or divert the magnet flux such that the amount of flux crossing the airgap can be varied between a maximum and a minimum level. While previous work on mechanical flux weakening in flux-switching PM machines has emphasized performance improvement achieved mainly through enhanced operating speed range, this paper, based on both analytical and experimental results, demonstrates performance improvement in three other areas, namely, reduction in electromotive force at maximum speed, reduction in open-circuit loss, and enhancement in efficiency under light load.

Dc-link capacitance requirement and noise and vibration reduction in 6/4 switched reluctance machine with sinusoidal bipolar excitation

Although different drive topologies have been developed for switched reluctance machine (SRM), the inherent disadvantages, including high dc-link voltage and current pulsations and low drive efficiency, in addition to relatively high torque ripples and acoustic noise and vibration, have limited their application to many applications. To solve this problem, the SRM may be operated as a synchronous reluctance machine but with concentrate winding, and the vector control strategy can then be employed. Compared with conventional unipolar excitation in SRM, it has the advantages of significant reduction of dc-link capacitance, moreover, lower noise and vibration and higher efficiency are also achieved. In this way, it is possible to replace the electrolytic aluminum capacitors with the film ones, which results in much lower cost and higher reliability of the whole drive system, which is very attractive for many applications. Experimental results on a prototype 6/4 SRM validate the effectiveness of sinusoidal bipolar excitation.

Vibration and noise in novel variable flux reluctance machine with DC-field coil in stator

The vibration and acoustic noise are investigated in a novel variable flux reluctance machine, which utilizes a DC-field coil in the stator to achieve on-line adjustment of air-gap flux density. The capability of adjusting air-gap flux density is expected to improve the efficiency and extend the speed range. The doubly salient structure in switched reluctance machines (SRM) is employed in the variable flux reluctance machine, together with the non-overlapping concentrated windings to reduce the copper loss. The 2D and 3D-finite element analyses are employed to predict the radial force and vibration modes in the variable flux reluctance machine, respectively. With the aid of vector control, which employs space vector pulse-width modulation, the vibration and acoustic noise in this novel machine are experimentally investigated, together with the comparison with SRM, which has the same stator/rotor pole combination. Compared with SRM, under the same load condition, the variable flux reluctance machine significantly reduces the vibration of mode 2, which is dominant in the SRM.

Design Method and Experimental Verification of a Novel Technique for Torque Ripple Reduction in Stator Claw-Pole PM Machines

Although relatively small in size and power output, automotive accessory motors play a vital role in improving such critical vehicle characteristics as drivability, comfort, and, most importantly, fuel economy. This paper describes a design method and experimental verification of a novel technique for torque ripple reduction in stator claw-pole permanent-magnet (PM) machines, which are a promising technology prospect for automotive accessory motors.