Multiphase flux-switching permanent-magnet (FSPM) machines inherit the merits of conventional FSPM machines and the common advantages of multiphase machines, e.g., low torque pulsations, a high torque density, and a high fault-tolerant capability. When a hybrid excitation is applied, postfault armature currents can be reduced by applying a positive field current (PFC). Hence, in this paper, based on both 2-D and 3-D finite-element analyses (FEAs), two six-phase hybrid-excited flux-switching (HEFS) machines with E-core and C-core stator laminations are designed, respectively. Iron bridges are adopted in each machine, and the influences on the performance are investigated. In addition, alternative-tooth-wound armature windings are employed in the C-core machine to obtain physical and magnetic isolations between armature phases. A comprehensive comparison of the two designs is carried out. Then, more attention is paid to fault-tolerant operating capabilities when an open-circuit fault occurs to only one phase and two phases of armature windings, respectively. The PFC can be applied in the C-core machine under fault-tolerant operating conditions; thus, the postfault armature current can be reduced while maintaining the torque output. Overall, the torque output can be effectively maintained in each HEFS machine during postfault operations. Finally, the FEA-based studies are validated by experimental measurements on two HEFS machine prototypes.

The flux-switching permanent magnet (FSPM) machine has aroused wide interest recently due to high-power density, favorable PM cooling capability, and essentially sinusoidal electromotive-force (EMF) waveform per phase. Previously, the phase back-EMF generation mechanism of FSPM machines is exposed from a flux-switching perspective, however, which is rethought from the viewpoint of air-gap modulation magnetic field in Part I as in this article, and electromagnetic torque generation mechanism of FSPM machines will be reported in Part II as another sister paper. With the aid of magnetic field modulation theory, the air-gap PM magnetic field and back-EMF of the FSPM machine are modeled based on modulation and winding functions. Their characteristics are analyzed in detail and consequently, principles concerning FSPM machines on arbitrary stator-slot/ rotor-pole combinations can be obtained, including the basic feature of FSPM machines, the principle and necessary conditions for the back-EMF generation, the fundamental reason of sinusoidal back-EMF waveform, and the contributions of modulation harmonics to phase back-EMF. Finally, experimental verification on a 12s/10p prototyped machine is conducted.

Based on the back electromotive force generation principle in part I of the series papers, the electromagnetic torque generation mechanism of flux-switching permanent magnet (FSPM) machines is rethought in this article as part II from the perspective of air-gap modulation magnetic field. By magnetic field modulation theory, the air-gap armature magnetic field due to winding currents is modeled. Considering the unipolarity of the stator core, a novel concept of ‘fictitious modulation reluctance (FMR) rotor’ for FSPM machines is proposed. Then, by combining with the air-gap permanent magnet (PM) field and the FMR rotor, generation mechanisms of harmonic PM torque and reluctance torque are investigated. The requirements for FSPM machines to produce a stable electromagnetic torque are determined, i.e., |mP_w ± vP_r | = P _pm , m_rvM_fm ≠0, and ω_e = P_rω_r . Besides, the harmonics operation states and harmonic torque characteristics of FSPM machines are analyzed and calculated based on the Maxwell stress tensor method. Further, the average torque versus current density predicted by finite element is validated by testing on an exampled 12s/10p FSPM one.

In this paper, based on 2-D finite-element analysis (FEA), the hybrid-excitation principle of a hybrid-excitation flux-switching (HEFS) machine is analyzed, and consequently, an improved topology is proposed to enhance the flux-regulation capability. These two machines are termed as the basic HEFS machine and the improved HEFS machine, respectively. In the basic HEFS machine, each permanent magnet (PM) is located at the middle of the corresponding slot and wound by a field winding coil. When field excitation is applied, it is found that the currents in the two field slots adjoining each PM exhibit reversal excitation functions, thus reversal flux-regulation functions. Hence, to improve the flux-regulation performances, an improved HEFS topology is proposed based on the basic one by reversing current direction in one of the field slots. Therefore, the improved topology shares identical structure with the basic one but has different field current directions in some field slots and thus different field winding accommodations. Comparisons of the FEA predictions indicated that both armature no-load flux-regulation capability and armature load torque capability in the improved HEFS machine are much better than those in the basic one. Finally, the FEA results are validated by experimental measurements on two prototyped HEFS machines.

Brushless modular spoke type permanent magnet (MSTPM) machine has exhibited prior electromagnetic performance over conventional surface-mounted PM machines for in-wheel traction system in electric vehicles (EVs). However, analysis of thermal behavior of MSTPM machines is rather insufficient, even accurate thermal analysis is of significant importance due to poor heat dissipation condition inside the wheel hub. Conventionally, the losses produced in electrical machines by EM prediction is equivalent to the heat source in normal thermal analysis, and only the resultant thermal behavior is investigated. However, the reaction of temperature rising on the EM performance is neglected. In this paper, a bi-directional coupled electromagnetic-thermal analysis method is proposed and carried out by a combination of lumped parameter thermal network (LPTN) model and finite element method (FEM), where both steady-state temperature distribution and transient-state temperature rise are investigated for MSTPM machines. By finite number of iterations between magnetic and thermal fields, the electromagnetic performance and thermal behavior can be predicted more accurately due to the coupling effect considered. The coupled model-predicted results are verified by 3D-FEM and experimental measurement, which shows that the proposed method has advantages in both computational efficiency and accuracy as well as can be applied to other electrical machines.

In field-oriented vector control of permanent magnet synchronous machine (PMSM) drives, the dead time will cause the 5th and 7th current harmonics in the stationary reference frame. They are mapped to the negative and positive 6th harmonic current in the synchronous reference frame (SynRF), resulting in torque ripple and deterioration of control performance. To solve this problem, a new dead-time compensation method is proposed in this article. First, a multiple complex coefficient filter is modified with a low-pass filter being paralleled to extract positive and negative sequence components of 6th harmonic from dq -axes currents. Then, based on the extracted harmonics, a voltage feedback path with variable gains is designed in SynRF to eliminate the dead-time effect. Finally, the proposed method is implemented in a prototyped PMSM drive to verify its effectiveness. Both the simulations and experiments indicate that the proposed method can significantly weaken the dead-time effect with no additional hardware. Besides, it is also proved robust to the variable machine parameters.