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In this paper, the open-circuit dc-winding-induced voltage in a wound field switched flux (WFSFs) machines is analyzed. The phenomenon of open-circuit dc-winding-induced voltage is illustrated and the mechanism is explained. Rotor skewing is proposed to reduce the open-circuit dc-winding-induced voltage, and the optimal skewing angle is analytically derived based on the analytically deduced harmonic orders of the open-circuit dc-winding-induced voltage. Finite-element (FE) analyses show that the open-circuit dc-winding-induced voltages in the analyzed 12-stator-pole partitioned stator WFSF machines having 10-, 11-, 13-, and 14-rotor-pole rotors can be effectively reduced by >94%, while the ac-winding phase-fundamental back-EMFs can be maintained by >95%. Twelve/ten-stator/rotor-pole prototypes with skewed and nonskewed rotors are built and tested to verify the analytical and FE results. [ABSTRACT FROM AUTHOR]

In order to increase the torque density of the five-phase machines, the third harmonic is commonly employed. In this paper, the optimal and critical ratios for the third harmonic current injection are analytically derived and validated by finite element (FE) analyses. It is found that the optimal and critical injection ratios along with the torque improvement are dependent on the ratio of the third harmonic back electromotive force to the fundamental one. In order to improve the electromagnetic torque contributed by the third harmonic component, this paper employs unequal tooth to increase both the fundamental and third harmonic winding factors. Meanwhile, the optimal unequal tooth width combination is deduced and demonstrated by the FE method. When the third harmonic current is injected under the same amplitude constraint, the output torque can be improved. When the third harmonic current is injected under the same RMS value constraint, for the ten-slot/eight-pole equal tooth machine, the output torque can barely be increased, whilst for the unequal tooth machine, the output torque can be increased by 2.1%. Finally, the ten-slot/eight-pole machine with unequal teeth is prototyped and tested to prove the analyses. [ABSTRACT FROM PUBLISHER]

This paper proposes a new partitioned stator flux reversal permanent magnet (PM) (PS-FRPM) machine having integer-slot overlapping windings, i.e., the slot number per pole per phase q is an integer, based on the magnetic gearing effect in stator-PM machines. Compared with the existing PS-FRPM machine with fractional-slot nonoverlapping windings, a more sinusoidal armature reaction magnetomotive force can be achieved in the proposed PS-FRPM machine with integer-slot overlapping windings, resulting in lower iron loss and PM loss. Electromagnetic performance of the PS-FRPM machine, which has q = 1 overlapping windings is analyzed and compared with PS-FRPM machine, which has q = 0.5 nonoverlapping windings by finite element (FE) analysis. FE results show that the proposed 24/10/12-outer-stator/rotor/inner-stator-pole PS-FRPM machine with q = 1 overlapping winding exhibits higher fundamental phase back-electromotive force, higher average electromagnetic torque and lower torque ripple, lower loss and higher efficiency, higher self-inductance but lower mutual inductance, higher d-axis inductance, and potential infinite flux-weakening capability compared with the 12/10/12-outer-stator/rotor/inner-stator-pole PS-FRPM machine with q = 0.5 nonoverlapping windings. Both prototype machines with q = 1 overlapping winding and q = 0.5 nonoverlapping windings are built and tested to verify the FE analyzes. [ABSTRACT FROM PUBLISHER]

This paper first investigates the flux-weakening control performance of two types of partitioned stator-switched flux permanent-magnet (PM) (PS-SFPM) machines and then proposes a novel mechanical flux-weakening technique. The PS-SFPM machine topologies, operation principles, and flux-weakening control method are described. In addition, it is shown that by mechanically varying the relative position of two stators of the PS-SFPM machine, the PM flux linkage can also be varied, and hence, it can provide improvement in the speed range and torque capability. The optimal relative mechanical angle is derived to enable the maximum torque capability and reduce or even avoid the flux-weakening current injected by the inverter. The proposed technique is verified by three-dimensional (3-D) finite-element (FE) analyses and experiments on the prototype machines. [ABSTRACT FROM AUTHOR]

In this paper, a double stator (DS) wound field (WF) switched flux (SF) (DS-WFSF) machine is proposed. In the DS-WFSF machine, field and armature windings are separately placed in two different stators. Compared with the conventional WFSF machine with single stator, in which both field and armature windings are located, nonoverlapping concentrated windings and large slot areas can be obtained in the DS-WFSF machine. The proposed DS-WFSF machine exhibits >19% higher torque than the conventional WFSF machine, with both machines having the same space envelope and being globally optimized. The influence of leading design parameters, such as copper loss ratio between the field and armature windings, air-gap diameter, and rotor iron piece thickness and widths, on the average output torque is investigated for the DS-WFSF machines having 12/10, 12/11, 12/13, and 12/14 stator slots/rotor iron pieces. All the analyses are confirmed by both finite element and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, switched flux permanent magnet (SFPM) machines are analyzed from the perspective of the air-gap field harmonics. It is found that the modulation of the salient rotor to PM and armature reaction fields in SFPM machines is similar to that of the iron pieces to those fields in the magnetic gear and magnetically geared machine. The magnetic gearing effect is analyzed in SFPM machines with different stator/rotor pole combinations, winding configurations, and stator lamination segment types by a simple magnetomotive force-permeance model, and validated by finite-element (FE) analysis. Different from fractional-slot surface-mounted PM machines in which the working air-gap field harmonic generates >95% of the average electromagnetic torque, >95% of the average electromagnetic torque in SFPM machines having \boldsymbol p\boldsymbol {s} stator pole pairs and nr rotor poles are contributed by several dominating field harmonics, i.e., rotating ones with \vert kn\boldsymbol {r}\,\pm \, (\textbf {2}\boldsymbol {i}-\textbf {1})\boldsymbol {p}\boldsymbol {s}\vert pole pair ( \boldsymbol k=\textbf 1, \boldsymbol i=\textbf 1, 2, 3 ) and static ones with (2\boldsymbol i-\textbf 1)\boldsymbol p\boldsymbol {s} pole pair ( \boldsymbol i=\textbf 1, 2, 3 ). The FE predicted average static torques in SFPM machines are validated by measurements on prototype machines. [ABSTRACT FROM AUTHOR]