Influence of stator/rotor pole combination on electromagnetic performance in all/alternate poles wound partitioned stator doubly salient permanent magnet machines.

In this paper, the influence of stator/rotor pole combinations on electromagnetic performance in partitioned stator (PS) doubly salient (DS) permanent magnet (PM) (DSPM) (PS-DSPM) machines is investigated, in terms of open-circuit flux-linkage, back-EMF, cogging torque, on-load torque characteristics. Analytical deduction shows that by modifying the all poles wound winding to alternate poles wound winding in the 12/11- and 12/13 stator/rotor pole PS-DSPM machines, the fundamental distribution factor and hence the fundamental winding factor can be enhanced, resulting higher torque density. Consequently, among the 12-stator-pole all and alternate poles wound PS-DSPM machines, the 10- and 11-rotor-pole machines exhibit the highest torque density, respectively. However, the 12/10- and 12/14-pole alternate poles wound PS-DSPM machines suffer from higher phase back-EMF even harmonics, resulting larger torque ripple. The 12/10- and 12/11-pole all and alternate poles wound prototypes are built and tested to verify the FE analysis

Investigation of Magnetically Geared Stator Permanent Magnet Machines

Stator-permanent magnet (PM) (Stator-PM) machines include doubly salient PM, flux reversal PM (FRPM), and switched flux PM (SFPM) machines, in which both the PMs and armature windings are placed in the stator, whilst there is neither PM nor coil in the rotor. They have been the subject of much interest over the last 20 years. The operation and interaction mechanisms between the open-circuit and armature excitation magnetomotive forces (MMFs) in stator-PM machines have not been well described, however, which will be explained by the magnetic gearing effect in the first part of this thesis. It is found that similar to magnetic gears and magnetically geared (MG) machines, conventional single-stator-PM machines operate based on the modulation effect of the rotor to the open-circuit and armature excitation MMFs. It is also found that more than 95% of the average electromagnetic torque in SFPM machines is contributed by several dominant open-circuit and armature excitation air-gap field harmonics. The magnetic gearing effect in the partitioned stator SFPM (PS-SFPM) machines, which was proposed recently based on the magnetic gearing effect in the conventional single stator SFPM machines, is also investigated in this thesis. The partitioned-stator-PM machines also operate based on the magnetic gearing effect. Furthermore, over 93% of the electromagnetic torque generated in both the outer and inner air-gaps in the PS-SFPM machines is contributed by the dominant air-gap field harmonics. Consequent-pole PM topology and overlapping armature winding topology for the partitioned stator FRPM (PS-FRPM) machines, based on the magnetic gearing effect in the partitioned-stator-PM machines, are investigated in this thesis. By applying consequent-pole PM topology, about a third of the PM volume can be saved, but the torque density and efficiency are similar. For the overlapping armature winding topology, higher torque density, smaller loss, and hence larger efficiency etc. can be achieved when the machine stack length is relatively long. Finally, the PS-FRPM machines and the conventional MG machines, both of which have surface-mounted PMs, are compared in terms of electromagnetic performance. Compared with conventional MG machines, PS-FRPM machines have a smaller flux-leakage and hence a higher torque density and a larger power factor due to their smaller PM pole-pair number and iron piece number

Comparative analysis of partitioned stator flux reversal PM machine and magnetically geared machine operating in Stator-PM and Rotor-PM modes

In this paper, the partitioned stator flux reversal permanent magnet (PM) (PS-FRPM) machine and the conventional magnetically geared (MG) machine operating in both stator-PM (SPM) and rotor-PM (RPM) modes are comparatively analyzed in terms of electromagnetic performance to provide design guides for a MG machine regarding: (a) a SPM or RPM type machine and (b) a higher or lower gear ratio machine. It is found that a SPM type machine is recommended, since both PS-FRPM and MG machines operating in SPM modes have a higher phase back-EMF and hence torque than their RPM counterparts, respectively, as a result of a similar phase flux-linkage but a higher electric frequency since the iron piece number is larger than the PM pole-pair number. Moreover, a smaller gear ratio machine is preferred from the perspective of a higher power factor and hence a lower inverter power rating, as the conventional MG machines with higher gear ratios suffer from larger flux-leakage, higher synchronous reactance and hence lower power factors, as well as higher iron losses, than the PS-FRPM machines. However, higher gear ratio machines feature lower cogging torques and torque ripples due to the smaller difference between the PM pole-pair number and iron piece number. Both prototypes of PS-FRPM machine operating in SPM mode and MG machine operating in RPM mode are built and tested to verify the FE predicted results

Analysis of coupling between two sub-machines in co-axis dual-mechanical-port flux-switching PM machine for fuel-based extended range electric vehicles

The permanent magnet (PM) field coupling between inner and outer machines of co-axis dual-mechanical-port flux-switching PM (CADMP-FSPM) machines is investigated. Firstly, the relationships between the inner and outer stator teeth are analytically evaluated, with three key stator teeth types defined, i.e. series, parallel, and independent teeth. Secondly, the negative effects of PM field coupling, including high even-order electromotive force (EMF) harmonics, three-phase EMFs asymmetry and DC bias component in flux-linkages, are investigated and verified by two CADMP-FSPM machines, namely, 5/6–12/22, and 5/6–18/42 structures. It is found that for avoiding the negative effects of PM field coupling, all inner and outer stator teeth types should be the same, thus, a 10/12–12/22 structure CADMP-FSPM machine is introduced for analysis. Thirdly, the performance of the 10/12–12/22, 5/6–12/22, and 5/6–18/42 structures, featured by PM field distributions, d-axis flux-linkage ripples, cogging torques, electromagnetic torques, losses and efficiencies, are comparatively analysed by finite element (FE) analysis. The results indicate that the 10/12–12/22 structure exhibits the lowest PM field coupling level and the best performance. Moreover, the 10/12–12/22 structure can avoid all the negative effects of PM field couplings. A prototyped 10/12–12/22 CADMP-FSPM machine is built and tested to verify the FE predicted results.</p

Electromagnetic Performance Comparison between 12-Phase Switched Flux and Surface-Mounted PM Machines for Direct-Drive Wind Power Generation

In this article, the 12-phase switched flux permanent magnet (PM) (SFPM) machine and three surface-mounted PM (SPM) machines designed for direct-drive wind power generation are comparatively analyzed. First, feasible stator-slot/rotor-pole combinations for symmetrical 12-phase winding layout are investigated for both machine topologies. Second, the key design parameters of the PM generators including the split ratio and stator teeth width ratio are optimized by finite element analysis to achieve a high phase fundamental EMF per turn and a low cogging torque, both of which are desired by the direct-drive wind power generator. Third, electromagnetic performances including air-gap field, cogging torque, static torque, inductance, output voltage and its regulation factor, output power, and efficiency of the generators are compared. A 10-kW 24-slot/22-pole SFPM prototype is built and tested to validate the FE predicted results.</p

Dietary patterns and risk for gastric cancer: A case-control study in residents of the Huaihe River Basin, China

AimEvidence linking dietary patterns and the risk of gastric cancer was limited, especially in Chinese populations. This study aimed to explore the association between dietary patterns and the risk of gastric cancer in residents of the Huaihe River Basin, China.MethodsThe association between dietary patterns and the risk of gastric cancer was investigated through a case-control study. Dietary patterns were identified with factor analysis based on responses to a food frequency questionnaire (FFQ). Gastric cancer was diagnosed according to the International Classification of Diseases, 10th Revision (ICD 10). Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated across the tertiles of dietary pattern scores using unconditional logistic regression models.ResultsA total of 2,468 participants were included in this study. Six main dietary patterns were extracted, and those patterns explained 57.09% of the total variation in food intake. After adjusting for demographic characteristics, lifestyle factors, individual disease history, family history of cancer and Helicobacter. Pylori (H. pylori) infection, comparing the highest with the lowest tertiles of dietary pattern scores, the multivariable ORs (95% CIs) were 0.786 (0.488, 1.265; Ptrend &lt; 0.001) for the flavors, garlic and protein pattern, 2.133 (1.299, 3.502; Ptrend &lt; 0.001) for the fast food pattern, 1.050 (0.682, 1.617; Ptrend &lt; 0.001) for the vegetable and fruit pattern, 0.919 (0.659, 1.282; Ptrend &lt; 0.001) for the pickled food, processed meat products and soy products pattern, 1.149 (0.804, 1.642; Ptrend &lt; 0.001) for the non-staple food pattern and 0.690 (0.481, 0.989; Ptrend &lt; 0.001) for the coffee and dairy pattern.ConclusionsThe specific dietary patterns were associated with the risk of gastric cancer. This study has implications for the prevention of gastric cancer

Analysis of Stator Slots and Rotor Pole Pairs Combinations of Rotor-Permanent Magnet Flux-Switching Machines

This paper investigates the influence of stator slots and rotor pole pairs combinations on torque performances in rotor permanent magnet flux switching (RPM-FS) machines. Based on a magnetomotive force (MMF) permeance model, the candidates of stator slots and rotor pole pairs combinations with higher torque capability can be determined by analyzing the PM-MMF and winding factor. Meanwhile, the candidates with a lower torque ripple can be obtained by referring to the cogging torque, which is related to the greatest common divisor of stator slots and rotor pole pairs. In addition, from the field modulation principle, the RPM-FS machines with the same fundamental magnetic loadings and winding factors exhibit identical fundamental harmonic torque, but different modulation harmonic components. Finally, four candidates with attractive torque performance are chosen, and the characteristics are verified by finite-element analysis and experiments.</p