This article presents a pioneering brushless dual-electric-port machine (BLDEPM) distinguished by its unique ac flux-control features. Utilizing a dual-stator, stator dual-electric-port design, the BLDEPM incorporates armature windings and ac field control windings, allowing for brushless operation without the requirement for rotor windings. Unlike traditional dc hybrid-excited machines, the control winding is powered by ac currents, enhancing current control flexibility. In overload conditions, the control winding serves as power winding, injecting q-axis current to enhance torque, and optimizing space utilization and torque density. Conversely, during high-speed flux weakening, the control winding transforms into the flux-control winding by injecting a d-axis current, capitalizing on coupling effects between the d-axis of the two winding sets. This article initially presents the machine's topology and operating principles, followed by an evaluation of electromagnetic performance using a finite element method (FEM) and an analysis of ac flux-adjusting principles. Finally, a novel fault-tolerant strategy, injecting only field current, is proposed, leveraging high redundancy. The machine demonstrates superior performance in torque density, flux weakening, and fault tolerance, making it promising for electric vehicle (EV)/hybrid electric vehicle (HEV) applications. Experimental verification of a prototype confirms the feasibility of the proposed machine.

The fractional-slot concentrated-winding (FSCW) machine with spoke-array permanent magnets (SAPM) achieves enhanced torque density due to the flux-focusing effect. Nevertheless, the SAPM impairs torque pulsation performance since the open-slot rotor structure results in the armature field modulation phenomenon. The influence of this phenomenon on torque pulsation has not been elaborated in existing research. Therefore, this article investigates the torque pulsation mechanism of the SAPM-FSCW by considering the armature field modulation. Firstly, both the PM field and armature field modulation behaviors of the SAPM-FSCW are investigated, which guides the identification and classification of key air-gap flux density harmonics. Based on the harmonic analysis, the cogging torque and reluctance torque pulsation models are established to illustrate the corresponding pulsation generation mechanism. Then, the overall torque pulsation model is built accounting for the interaction of the PM and armature fields. The influence of armature field modulation on torque pulsation is elaborated. Finally, a prototype of the SAPM-FSCW is fabricated and tested to verify the analysis.

This article proposes two kinds of asymmetric flux reversal permanent magnet linear machine (AFR-PMLM) for long excursion application. By utilizing asymmetric permanent magnet excitation, the AFR-PMLM can effectively generate and fully exploit the second-order harmonic magnetomotive force (MMF), leading to a significant enhancement in thrust force density. First, the machine topology and operation principle are introduced. Then, the thrust force generation mechanism under multi MMFs is analytically calculated based on an improved MMF-permeance model, and further verified by finite element analysis. Various electromagnetic performances, including open-circuit characteristics, thrust force performances, and power factor, are comparatively studied. It shows that the proposed AFR-PMLM with consequent pole structure can provide 40.1% higher average force than conventional FR-PMLM under rated condition. In addition, it consumes only about 39.5% of the PMs volume while providing approximately 90.4% of the thrust force compared with switched flux PMLM. More importantly, the AFR-PMLM consumes only 1/80 PMs volume while achieving 75.0% of the thrust force density compared with conventional PMLM for a long excursion with 10 m. Finally, two prototypes of AFR-PMLM are manufactured for experimental validation.

In this article, we propose a double-sided flux concentrated permanent magnet linear machine (DS-FCPMLM) with a saturation relieving effect. With the adoption of slot permanent magnets (PMs), DS-FCPMLM can effectively relieve the primary saturation and greatly improve the thrust force density. First, the machine topology and operation principle are introduced. Then, the flux generation mechanism under dual PMs and complementary structure is analytically calculated based on the magnetomotive-force-permeance model and further verified by finite-element analysis. In addition, some electromagnetic performances, including open-circuit characteristic, thrust force performances, demagnetization risk, and power factor, are comparatively studied. With the help of slot PMs, DS-FCPMLM can significantly improve the thrust force density by 63.4% compared with that only has yoke PMs, and the overload capability can be extended to nearly four times the rated value. More importantly, DS-FCPMLM only consumes 1/30 PM volumes while can achieve 72.2% thrust force density compared with the conventional permanent magnet linear machines for a long stroke with 10 m. Finally, a prototype of the DS-FCPMLM is carried out for experimental validation.

Two brushless doubly-fed dual-stator machines (BDFDSMs) with different inner-stator field windings, namely ac and dc field windings, are proposed and investigated. It is shown that the proposed machine with ac field windings exhibits the advantages of higher torque density and wider flux-regulation range compared with its dc field winding counterpart. Unlike conventional doubly-fed hybrid-excited machines, the proposed machine consists of ac field windings and hence resulting in more flexible field current control. Its armature and field windings are separately placed in two stators, which can alleviate the space competition between the field and armature slots, as well as significantly enhance space utilization. Consequently, both flux-regulation capability and torque density can be effectively improved. The topology, operating principle, and mathematical model of the proposed machines are introduced. Then, a sectored flux-weakening control method is proposed and elaborated. Based on the finite element method (FEM), the main electromagnetic performances of the proposed machines are comprehensively evaluated. The FEM results manifest that the proposed machine with ac field windings shows greatly improved flux-regulation range, higher torque, and output power under the proposed sectored flux-weakening method over the whole speed range. Finally, the prototype machine of the proposed machine is fabricated, and experimental verifications are performed to validate the feasibility of the proposed machines.

This paper introduces and conducts a comparative analysis of three types of hybrid-excited flux-modulated linear machines (HEFMLMs) equipped with slot permanent magnets. It establishes a comprehensive analytical model to facilitate a deeper understanding of the operational principles of these machines featuring different hybrid excitation patterns. The paper commences by elucidating the machine’s topology and operational principles. Subsequently, it presents a unified analytical model based on the magnetomotive force-permeance model for calculation purposes. Furthermore, the paper examines the electromagnetic performance of these three HEFMLMs, encompassing open-circuit characteristics and thrust force characteristics. The investigation highlights the potential of hybrid excitation as an effective means to enhance thrust force density through the optimization of the distribution of optimal direct current and alternating current. In summary, the three proposed HEFMLMs offer unique advantages and demonstrate suitability for cost-effective, long-stroke direct-drive applications.

A new partitioned-primary flux-reversal hybrid-excited linear motor is proposed and investigated in this article, which features an asymmetrical double-sided primary structure. The novelty of this motor lies in the adoption of a partitioned-primary structure by moving the field excitation winding to an additional primary, thus it benefits from improved space utilization ratio since both armature and field windings can be separately mounted. First, the topology, feasible slot/pole combinations, and operating principles of the proposed machine are introduced. The magnetic flux density distributions in two air-gap regions are comparatively studied from the perspective of magnetic gearing effect. Then, global optimization of the proposed motor with different slot/pole combinations is performed to maximize both the output thrust force and flux-adjusting range based on 2-D finite-element analysis (FEA). In addition, the electromagnetic performance of the motors including flux-adjusting capability, thrust force, detent force, and force ripple with different slot/pole combinations are comparatively investigated. Finally, a 6-slot/7-pole prototype is manufactured and tested to verify the FEA and calculations. It is shown that the proposed motor, benefiting from a partitioned-primary topology, exhibits very good flux-adjusting capability and overloading capacity. Thus, it has good prospect in applications that require flexible speed control.

By developing a simple permeance-magnetomotive force (MMF) model of switched-flux permanent magnet (SFPM) machines, the air-gap flux density produced by both PMs and armature current can be derived, in which harmonics with the same order and rotational speed are called an effective harmonic pair (EHP). By investigating the influences of armature current angle δ on both the phase and amplitude of each EHP, it is found that the amplitudes of both PM and armature reaction flux-density harmonics maintain fixed, whereas the space phase shift between them changes accordingly with armature current angle. Specifically, the PM and armature reaction flux-density harmonics are orthogonal in space if zero d-axis current is fed. Therefore, the maximal torque is realized for each EHP. As the total torque of SFPM machines is the superposition of the contributions by each EHP, the zero d-axis current control method turns out to be the optimum for maximal torque per ampere, thus verifying analytically that the d- and q-axes inductances are equal according to the general torque equation for the investigated machine topology. In addition, the torque adjustment mechanism of each EHP in SFPM machines has also been analytically demonstrated to be resemble that of the surface-mounted PM synchronous machine (PMSM). Finally, the finite-element analysis (FEA) has been performed to validate the previous analytical predictions.

The novel doubly salient slot permanent magnet linear machines (DSSPMLMs) are proposed in this paper. First, the topology and geometric parameters of the DSSPMLMs with 12 slots are introduced, and the corresponding basic operating principle is investigated. Then, feasible slot/pole combinations and winding configurations are further analyzed. To the DSSPMLMs with 12 slots, all structures with 10/11/13/14 poles and double layer (DL)/single layer (SL) winding are optimized. Finally, the electromagnetic performance including open-circuit and static force-current characteristics are comparatively studied using 2-D finite-element analysis (FEA). The results show that the optimal slot/pole combination is 12-slots/13-poles (12s/13p) and the DL winding exhibits lower force ripple while relatively lower thrust force capability than SL winding at low electrical loadings.

This article proposes a novel hybrid-excitation switched-flux linear machine with partitioned-excitations (PE-HESFLM), which places the armature windings and field winding into different primaries. It can be geometrically taken as the combination of a conventional flux-switching linear machine and an additional primary for accommodating the field winding. Therefore, the proposed machine can exhibit increased armature and field slot areas so that the competition for space between these two winding types is effectively mitigated, which in return translates to improved thrust density and flux-adjusting capability. First, the configurations of the proposed PE-HESFLM are introduced, following which different slot/pole combinations are globally optimized based on genetic algorithm (GA). Finally, the electromagnetic performances are comparatively investigated. It is shown that the proposed machine can effectively improve the thrust density and flux-adjusting capability, so that the proposed machine configuration is a particularly good candidate for applications which require wide-speed capability.

A modular linear doubly salient machine with dual-PM in the primary yoke and slot openings is proposed in this paper. First, the machine topology is introduced, where the PMs are employed in both the primary yoke and slot openings. The magnetic fluxes excited by the PMs in the slot openings pass through the air gap and link the secondary, not short-circuited by the primary teeth. Hence, the magnetic fluxes excited by both PMs can be concentrated and enhanced in the air gap. Then, the operation principle is investigated based on the permeance model, which shows that it obeys the flux modulation principle. The electromagnetic performances are analyzed in detail using FEM, which shows that the force density and overload capability can be significantly improved with the slot PMs. Finally, the 2-D finite-element (FE) predicted results are validated by the 3-D FE results that considering the transverse end effect.

In this paper, two novel double-sided hybrid-excitation flux-reversal linear motors (DSHEFRLM) with the surface (S-) and interior (I-) permanent-magnet(PM) arrangements are proposed and comparatively investigated. The proposed motors feature an asymmetrical double-sided primary configuration which enables the armature and field excitations to be placed separately. Through 2-D finite-element method (FEM), two motor structures with different slot/pole combinations are optimized, and then, the magnetic fields and electromagnetic performances are calculated, including inductances, no-load flux linkage, thrust characteristics, and PM demagnetization capability. By comparison, it is found that S-DSHEFRLMs show larger thrust density while I-DSHEFRLMs exhibit superior flux-adjusting capability. Finally, these predicted results are validated by 3-D FEM.

The novel partitioned-primary hybrid-excited flux-switching linear machines (PP-HEFSLMs) with unaligned and aligned structures are proposed, which exhibit advantages of direct-driven, wide speed operation, robust secondary, etc. Unlike conventional hybrid-excited topologies, the proposed PP-HEFSLMs accommodate armature and excitation windings on two separated parts of the partitioned primary, which solves the problem of crowded primary; hence, both flux-adjusting ratio and thrust force density are effectively improved. The topology and operation principle of the two PP-HEFSLMs are introduced in detail first. Based on finite-element method (FEM) analysis, major geometric parameters are investigated and optimized then. For the optimized structures, the electromagnetic performances, i.e., thrust force characteristics, demagnetization, flux-regulation capability, and inductances are calculated and further compared. The results manifest both structures show a satisfactory flux-adjusting ratio particularly for an aligned structure and good fault-tolerant capability due to tiny mutual inductances between phases. Although the thrust density of the aligned structure is relatively low compared with its unaligned counterpart, it can be taken as a mechanical flux-weakening method by aligning permanent magnets with armature teeth. Finally, three-dimensional FEM analysis is performed to validate the two-dimensional FEM predicted results.

The E-core hybrid-excitation linear switched-flux permanent magnet machine (LSFPMM) is low cost, which not only accommodates armature and permanent magnets (PMs) in short primary, but also cuts half of PM volumes compared with its C-core counterpart. It also can easily adjust the air gap magnetic f ield flexibly through the injection of different DC currents. This paper introduces E-HELSFM with different end shapes firstly, while a shape with the best symmetry of flux and minimal detent force is developed and further investigated. Based on finite element model, the flux-adjusting principle of the proposed hybrid-excitation motor is presented, and certain geometric parameters are optimized for better flux-regulating capability and larger thrust force density. Then, the field ratio, which means the ratio of field area to a single slot area, is optimized to reach a tradeoff between force density and flux-adjusting capability. For the optimized model, the flux-adjusting as well as thrust force performances under different excitation conditions are investigated. Then, the flux-weakening control under different excitation levels is discussed. The simulated results show that the optimized machine exhibits good constant power operation capability through flux-weakening control and enhanced overload ability by flux-enhancing control.

Hybrid-excited flux-switching linear machine (HEFSLM) adjusts the air gap flux density by DC excitation current, which may have great influence on its performances and parameters, such as thrust force, thrust ripple, inductances and etc. This paper mainly investigates its thrust ripple and inductances characteristics under different DC excitation currents with the frozen permeability (FP) method based on finite element analysis (FEA). By the thrust ripple separation, the on-load thrust ripple is divided into three components, which stem from different causes respectively. Although the longitudinal end effect is the biggest cause, the DC current is another great factor because of the aggravated magnetic saturation level particularly under flux-weakening condition, which is totally different from traditional hybrid-excited machine. To on-load d-axis and q-axis (d-q) inductances, they also vary along with the increase of DC excitation current. Moreover, their difference is not zero and excitation level dependent, which indicating the on-load reluctance force cannot be neglected. The results are beneficial to optimization design and parameter identification of HEFSLMs.

This paper proposes a fault-tolerant control strategy for three phase linear switched-flux permanent magnet machine (LSFPMM) with modular structure, which has one-phase open-circuit fault. Under this condition, this three-phase LSFPMM has a novel perspective of the operating principle similar to two-phase machine. Based on finite element analysis (FEA), the performance of proposed fault-tolerant control strategy has been simulated. The predicted results show the fault-tolerant control strategy can effectively keep average thrust force and thrust ripple virtually unchanged after fault occurance. In addition, the influence of module gap on fault-tolerant performance has also been investigated. The larger module gap tends to improve fault-tolerant performance due to lower mutual inductances between phases, but decrease average force simultaneously. The proposed fault-tolerant control strategy can also be extended to other three-phase machines.