Mahir Al-Ani

A Mechanical Flux Weakening Method for Switched Flux Permanent Magnet Machines

Several switched flux permanent magnet (SFPM) machines with mechanically movable flux adjusting technique are proposed, analyzed, and compared for applications which demand high speed and efficiency. By using ferromagnetic pieces--one per every stator pole or every alternative stator pole, which are named as flux adjusters (FAs) and located on the outside surface of the stator-the airgap flux density can be weakened and therefore the operation speed range and flux weakening capability can be improved. The influence of using all or alternative FAs on the open circuit results, electromagnetic performance, and torque-speed characteristics of the SFPM machine is investigated through three SFPM machines with different stator/rotor pole combinations, i.e., 12/10, 12/13, and 12/14. Moreover, although using FAs in all stator poles can significantly improve the flux weakening capability, alternative FAs can also achieve remarkable improvement although higher torque ripple is observed. Additionally, it has been found that the 12/13 combination is considered to be the most suitable candidate for alternative FAs technique. In addition to 2-D finite-element analysis (FEA) and analytical methods, 3-D FEA results accounting for the end-effect are presented. Furthermore, experiments are performed to validate the results.

Influence of end-effect on torque-speed characteristics of various switched flux permanent magnet machine topologies

Switched flux permanent magnet (SFPM) machines have the permanent magnets (PMs) and armature windings on the stator, and therefore, simple and robust rotor and easy management of the temperature can be achieved. However, the spoke location of the PMs causes not only flux leakages outside the stator but also large flux leakage in the end region, i.e. end-effect, which could result in a large reduction in the electromagnetic performance. Therefore, the influence of the end-effect on the torque-speed characteristics of three conventional SFPM machines having different stator/rotor pole combinations, i.e. 12/10, 12/13 and 12/14 as well as three novel topologies with less PMs, i.e. multi-tooth, E-core and C-core are investigated and compared in this paper. In order to obtain the end-effect influence, 3D-finite element analyses (FEA) results are compared with their 2D-FEA counterparts and validated by experiments. It has been concluded that due to end flux leakage, lower torque capability in the constant torque region is observed in the six machines. However, at high current levels, improved flux weakening capability in the conventional machines can be exhibited, while the large inductance causes lower power capability in the multi-tooth, E-core and C-core machines.

Comparison of alternate mechanically adjusted variable flux switched flux permanent magnet machines

Novel topologies of switched flux permanent magnet (SFPM) machines with mechanically movable flux adjusters (FAs) for either all or alternative stator poles in order to extend the operation speed range are developed and analysed in this paper. Compared with the FAs which are located outside all of the stator poles of SFPM machines (all FAs), the alternative stator pole FA structure (alternative FAs) uses half of FAs. Flux-linkage, cogging torque, static torque waveforms, torque- and power speed curves in 12/10, 12/13 and 12/14 stator/rotor pole SFPM machines with all and alternative FAs are predicted and compared by 2D and 3D finite element analyses (FEA), and partially experimentally validated. Compared with 12/10 stator/rotor combination, the 12/13 and 12/14 SFPM machines have higher maximum speed with both alternative and all FAs.

Novel switched flux machine with radial and circumferential permanent magnets

Purpose – The paper purposes a novel SFPM machine topology with radial and circumferential permanent magnets (PMs). The paper aims to discuss this issue. Design/methodology/approach – In order to reduce the flux leakage in the stator-outer region and consequently achieve higher magnetic material utilization in switched flux permanent magnet (SFPM) machine, a novel topology with radial and circumferential PMs is proposed. This topology (SFRCPM) has the same structure as conventional SFPM (CSFPM) machine except of the additional set of radially magnetized PMs located around the back iron and surrounded by a laminated ring frame. Using finite element analysis (FEA) the influence of the design parameters on the performance is investigated in order to obtain an effective optimization procedure. Internal and external rotor SFRCPM machines with either NdFeB or ferrite magnets are investigated, optimized and compared with the CSFPM machine having the same size, copper loss and stator/rotor pole combination. Findi...

Rotor loss reduction using segmented inverter in surface-mounted permanent magnet drive

In this paper, the influence of different switching modulation arrangements, i.e. current waveform modulation- and phase-shift, on the resultant current waveform of an electrical machine drive consisting of a two segment inter-leaved inverter feeding a surface-mounted permanent magnet (SPM) machine with two identical sets of three phase windings is investigated. The modulation- and phase-shift have been illustrated and the influence of the different modulation and frequency indices have been studied. Furthermore, the torque, and rotor eddy currents and core losses are calculated using FEA when either modulation-shifted or phase-shifted current waveforms are generated and fed to the machine. It is found that using modulation-shift can reduce the current harmonic substantially however the inverter requires two sets of input signals. On the other hand, although the current harmonic reduction is less than that of the modulation-shift, the phase-shift layout can be employed using one set of input signals with a signal delay.

Electromagnetic and mechanical analysis of high speed SPM rotor with copper shield

For high-speed applications, the surface-mounted permanent magnet (SPM) machine is preferred due to its high torque density and efficiency. However, induced eddy currents in the rotor conductive parts result in a loss of efficiency and rotor heating. Therefore, several methods to reduce such losses have been proposed in the literature including copper shielding. In this paper, a high-speed SPM machine rotor with a copper shield is designed and investigated both electromagnetically and mechanically. Several quantitative investigations including placing the copper sheet around the retaining sleeve or magnets, different copper sheet and airgap thicknesses, different retaining sleeve materials, different harmonic contents in the current waveform, i.e. pulse amplitude modulation (PAM) and pulse width modulation (PWM) generated waveforms, and different frequencies and current levels are reported. Additionally, a mechanical analysis investigating possible failure modes of the rotor with the copper sheet is reported.

Integrated electrical machine-turbo machinery

Global warming and climate change due to rising levels of greenhouse gases have placed significant pressure on the automobile industry to adopt more clean fuel, transportation electrification, and waste energy recovery technologies. As a result, several electrically assisted or driven turbo-machines have been proposed such as turbochargers, turbo-compressors, and electrical boosters. Therefore, the electrification of turbo-machinery has been trending for the past decade. All the systems mentioned above consist of a conventional electrical machine connected to the turbo-machinery by a shaft, making the system relatively large, heavy, costly and mechanically complex. In this paper, an integrated electrical machine-turbo machinery concept is proposed. It consists of an electrical machine mounted around a salient rotor that is shaped like an axial flow turbo-machinery wheel. The electrical machine can be used as a motor to drive or assist the operation of the turbo-machine or it can operate as a generator powered by the gas or fluid flow. Compared to the conventional electrically derived or assisted turbo-machine systems, the proposed system is expected to decrease the overall size, weight and complexity. In order to illustrate this concept, an initial multi-physics feasibility study is presented. Electromagnetic and mechanical, performance are calculated and investigated using FEA. Additionally, aerodynamic consideration has been illustrated.