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This article proposes a magnetic field modulated screw (MFMS), which exhibits high force low torque transmission ratio. Essentially, the proposed MFMS requires less torque to generate a significant thrust force. The “force per torque” ratio is 1.02 kN/N.m, which is 4 times higher than conventional MFMS. The proposed MFMS is analyzed based on three-dimensional (3-D) magnetic field modulation. Then, the uniform analytical expression of the “force per torque” ratio can be derived. The pole-pairs of the proposed MFMS are reasonably selected, resulting in a significant improvement in the “force per torque” ratio. Besides, a discrete analysis method is employed to analyze the circumferential and axial modulation in the MFMS. Based on this, the modulation process and performances of the proposed MFMS is analyzed and compared. Moreover, the 3-D Maxwell tensor method is first used to analyze the contribution of air-gap flux density harmonics to the torque and thrust force. Finally, the 3-D finite element method and experiments are used to validate the theoretical analysis.

Due to the overloading, vibration, and harsh conditions, switching transistors in open-end winding five-phase permanent magnet synchronous motors (OWFP-PMSMs) drives are more vulnerable to failure. Addressing the increased post-fault current in existing fault-tolerant control (FTC) methods, this article presents an inverter reconstruction approach for the OWFP-PMSM. When transistor failure occurs, the inverter reconstruction approach is achieved by connecting the winding to the midpoint of the bus capacitor. A pattern-based virtual voltage vector synthesis method is introduced to achieve voltage vectors that existing modulation methods cannot synthesize. Then, a hybrid SVPWM strategy is adopted to achieve dual inverter modulation and capacitor voltage compensation in the OWFP-PMSM drive system. The innovation of this article not only enhances the FTC capability of the OWFP-PMSM drive system but also maintains good postfault steady-state performance. Moreover, the amplitude of the postfault phase current resembles that observed during healthy operation, which is a significant reduction compared to the established FTC strategy. Through simulations and experiments, the effectiveness of the proposed method is demonstrated. The results show that the phase current amplitude is reduced by up to 26.5% during steady-state operation compared to the existing method.

This article proposes an auxiliary notch design method for the interior permanent magnet (IPM) machines for suppressing torque ripple. The key principle of this design method is to identify the main source of torque ripple, then guides the modification of reluctance variation along the rotor surface. First, the theoretical analysis of the torque ripple in IPM machines are investigated to guide the auxiliary notches design. Based on this, a spoke-type IPM machine with permanent magnet torque as the main component and a U-type IPM machine dominated by reluctance torque are analyzed, respectively. Additionally, the relationship between the shifted angle of the auxiliary notch and the order of torque ripple is revealed. Furthermore, the electromagnetic performances are investigated by the finite-element method. After using auxiliary notch design, the torque ripple is significantly reduced and the torque amplitude is almost not sacrificed. Finally, a spoke-type IPM machine prototype is manufactured for experiments to evaluate the effectiveness of the theoretical analysis.

Recent literature has confirmed that a high-order radial pressure in airgap can induce significant low-order vibration due to the stator teeth modulation effect on radial pressure. The reported research on this modulation effect only focused on the conventional stator teeth topologies. However, for the permanent magnet (PM) machines, different stator teeth topologies lead to diverse paths for the transfer of pressure in airgap, resulting in varying vibration characteristics caused by the modulated radial pressures. It is plausible that dual or nonuniform modulation on radial pressure may be present. Therefore, to accurately predict and preferably reduce vibration, it is crucial to understand the diverse effects of different stator teeth modulation. In this article, first, the principle behind how the stator teeth modulate the radial pressure is explained. Second, the modulation effects of different stator teeth are detailedly analyzed, including single, dual, uniform, and nonuniform modulations. Lastly, taking a PM vernier machine as an example, its modulated radial pressures and resulting vibration are analyzed considering the nonuniform dual modulation. Results demonstrate that the stator teeth modulation effects on radial pressure are various and should be fully considered in accurate vibration prediction and low-vibration machine design.

This article investigates the effect of winding configuration on the electromagnetic vibration of the 48-slot/8-pole modular dual three-phase (DTP) permanent magnet (PM) machine. First, two winding topologies are discussed based on the phase shift principle, and their phase shift angles are 30° and 60°, respectively. Second, the armature magnetomotive force (MMF) of different winding configurations is derived and compared. The modular DTP-PM machine with 30° phase shift produces the extra 2nd, 18th, 22nd, 26th, and 30th armature MMF harmonic components compared with the 60° phase shift one. Afterward, the electromagnetic force density and radial concentrated force of two modular DTP-PM machines are investigated. The result reveals that the modular DTP-PM machine with 30° phase shift induces the non-negligible 2nd-order vibration under the load condition. This is different from the modular DTP-PM machine with a 60° phase shift which mainly induces 0th-order vibration. Furthermore, the multiphysics field finite-element method is used to calculate the static deformation and vibration acceleration of two modular DTP-PM machines. Finally, the prototype of a 48-slot/8-pole modular DTP-PM machine with a 30° phase shift is manufactured. The experiments are conducted to validate the theoretical analysis.

This article proposes a discrete equivalent magnetic network (EMN) for electromagnetic force and vibration computation of surface-mounted permanent magnet (SPM) machines considering carrier harmonics. First, a new triangle permeance element is proposed and adopted for air-gap meshing of a 12-slot/10-pole SPM machine. Second, the discrete modeling method is applied in the rotor with eccentric magnets of the machine. The proposed method can decouple the relationship between the number of permeances and the transient solution step size in the interface region. Third, this method uses the current dataset involving carrier harmonics as input excitation to calculate the electromagnetic force. Then, the vibration response is synthesized by electromagnetic force and vibration transfer function. Finally, the computation accuracy and efficiency of this method are validated through the finite element method and experimental test.

The dual-permanent-magnet-excited Vernier (DPMEV) machine has attracted increasing interest for its high torque density. However, it is difficult to analyze due to the complex structure. In this article, the torque generation mechanism of DPMEV machines is analyzed from the perspective of magnetic field modulation. First, based on air-gap field modulation theory, the stator and rotor modulation factor models as well as armature and permanent magnet magnetomotive force (MMF) models are established, respectively. Considering the bidirectional field modulation effect of the DPMEV machine, the modulation process of MMF is derived. Then, by analyzing the modulated armature and permanent magnetic field, the torque generation mechanism is investigated. In addition, a machine with stator flux gap structure is proposed and the reasons for its torque increase are explained. Finally, a prototype of DPMEV machine is manufactured and tested to verify the effectiveness of the analytical results.

This article proposes a novel three-redundancy control for the dual three-phase permanent magnet (DTP-PM) motor to enhance the open-phase fault tolerance. Three redundancies can be operated individually or synergistically. Hence, the faulty redundancy can be disconnected from the system to address the open-phase fault. The fault tolerance can be significantly enhanced. Primarily, the structure of the DTP-PM motor is analyzed. Six phases of the DTP-PM motor are separated into three sets of orthogonal phases and considered three two-phase motors. Therefore, three redundancies can be established. Since orthogonal phases provide a balanced structure, the magnetomotive force of each redundancy can be well controlled. Then, a DTP-PM motor control system with three redundancies is established, and a potential topology for the proposed strategy is also illustrated. Furthermore, the basic voltage vectors for each redundancy are investigated. The reference voltage vectors can be modulated expediently. Finally, some simulations and experiments are carried out, validating the feasibility and effectiveness of the proposed strategy.

This article proposes a decoupled fault-tolerant model predictive current control for a dual three-phase permanent magnet synchronous motor with harmonic compensation. The harmonics caused by nonsinusoidal back electromotive force can be well controlled under the open-circuit fault scenario by designing a harmonic closed-loop scheme. First, a decoupled predictive model and fault-tolerant voltage vectors are deduced based on a reduced-dimension matrix, which can eliminate the coupling issues between the harmonic and fundamental subspaces. Afterward, a uniform harmonic-free virtual vector is constructed by rearranging the irregular voltage vectors. More importantly, a virtual null vector is designed in the scheme, where the virtual null vector is effective in the harmonic subspace and has no components in the fundamental subspace. So, the harmonics can be further controlled without affecting torque and flux generation. Extensive experimental results verify the effectiveness of the proposed method.

This article proposes a current deadbeat-based fault-tolerant control scheme for a dual three-phase permanent magnet synchronous generator with a high-resistance connection (HRC) fault. First, the voltage deviation caused by the HRC fault is deduced, and the postfault prediction model is established. Then, the instantaneous active power and reactive power are analyzed considering the negative-sequence voltage and current. To eliminate the fluctuation components and improve the steady-state performance, the fault-tolerant current references are designed under the condition of HRC fault. The deadbeat principle is employed to track the periodic dq current references accurately. The two targets of eliminating output power fluctuations and stabilizing electromagnetic torque are achieved. Finally, the virtual voltage vectors are synthesized to generate the reference voltage and suppress the harmonic current. The proposed method effectively restrains the fluctuations of active power, reactive power, dc-link voltage, and electromagnetic torque. The experimental results verify the effectiveness of the proposed method.

This paper aims to investigate the torque production mechanism and its improvement design in switched reluctance machines (SRMs) based on field modulation principle. Firstly, the analytical expressions of the air-gap magnetic field are derived from the perspective of DC- and AC-components, respectively. Meanwhile, different slot/pole combinations and winding arrangements are considered. Secondly, the torque productions are analyzed and evaluated with emphasis on the interaction between the DC- and AC-components of air-gap fields. Thirdly, the 12-slot/8-pole and 12-slot/10-pole SRMs are established and studied by using the finite-element method. The effects of slot/pole combination and winding arrangement on the average torque production are clarified. Then, two new designs to improve the average torque are proposed. Finally, the prototype of the 12-slot/10-pole SRM is manufactured, and the experiments are carried out for validation.

The conventional duty ratio modulation based direct torque control (DR-DTC) for the dual three-phase permanent magnet (DTP-PM) motor reduces the torque ripple using duty ratio modulation in torque control. However, the flux was controlled by a hysteresis comparator, resulting in deficient steady-state performance. This paper proposes a novel DR-DTC strategy to improve torque and flux simultaneously. Firstly, a switching table with the multiple vector selection is newly established. Two adjacent virtual voltage vectors and a null vector are selected in each control period. Then, the duty ratios of selected adjacent virtual voltage vectors are optimized with the dual objective modulation considering torque performance and flux performance. In addition, the combination of adjacent virtual voltage vectors for the DTP-PM motor generates non-standard symmetrical switching sequences. Two switching sequences generated methods are further investigated to address the issue. So, the switching sequences of the proposed strategy can also be generated easily. Finally, the conventional strategy and the proposed strategy are compared through experiments, and the experimental results verify the effectiveness of the proposed strategy.

This paper investigates the 3-D magnetic field modulation theory of the magnetic screw transmission. A magnetic field modulation screw (MFMS) is proposed to prove this theory. The MFMS consists of three parts, including the inner part and outer part carrying the helically permanent-magnet (PM) with different pole-pairs. The intermediate part has a set of helically ferromagnetic pole-pieces, which modulate the helical PM magnetic field. The innovation of this MFMS is that it can achieve fully helical magnetic coupled, which satisfies the 3-D modulation in the circumferential and axial direction, respectively. Moreover, the intermediate part can move in both rotation and linear motion without PMs. Therefore, it is very suitable for long-stroke, high force, and two-degree of freedom applications. Afterward, the prototype of a magnetic screw is built to verify the magnetic transmission capability. The effectiveness of the proposed approach is verified by both simulation and experiment.

In this paper, two different designs, with dummy slots and bread-loaf magnets techniques, are presented to reduce the electromagnetic vibration in integral-slot surface-mounted permanent-magnet (SPM) machines. Firstly, the stator slotting effect on the magnetic field modulation and radial force modulation is investigated. It reveals the amplitude of the modulated magnetic field and modulated radial force is greatly affected by the slot opening effect, while the spatial order is closely associated with the slot numbers. Subsequently, the dummy slots and bread-loaf magnets design are developed for a 36-slot/12-pole integral-slot SPM machine to reduce the electromagnetic vibration. Finally, two SPM machines, with conventional and bread-loaf magnets, are manufactured. Experimental tests are carried out to validate the theoretical analyses.

A new linear permanent-magnet (PM) vernier machine with high fault-tolerant is proposed and studied in this article. PM array with optimally aligned PM, six-phase winding structure, and modular mover design are adopted in this machine. The PM array with optimally aligned PM is adopted to increase thrust force by adjusting magnetizing direction and thickness of the PMs. The six-phase winding structure and the modular mover are adopted to decrease coupling between phases and detent force. Moreover, the proposed machine can operate under different phase conditions with this winding structure. Hence, the fault-tolerant capability and thrust force performance of the machine can be improved by the adoption of these designs. The topological structure, operating principle, and design optimization of the machine are first studied in this article. And then the fault-tolerant capability and thrust force performance of the machine are analyzed by establishing the finite-element model. Lastly, the effectiveness of these designs is verified by the experiments on a prototype machine.