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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. [ABSTRACT FROM AUTHOR]

In this article, a targeted step skewing of rotor segments scheme is proposed to reveal the modulated vibration reduction mechanism in integral-slot interior permanent magnet synchronous machines (IPMSMs). First, the vibration characteristics of a 72-slot/12-pole integral-slot IPMSM are investigated. The dominant vibration at specific frequency band is introduced. Then, in order to analyze the main source of vibration, the magnetic field modulation effect and radial force modulation effect are investigated in detail. The results show that the high-order radial force can excite large vibration by radial force modulation effect. This kind of vibration is defined as modulated vibration. Afterwards, the optimal shift angle and number of rotor segments are determined by comparison. Finally, the conventional and proposed 72-slot/12-pole integral-slot IPMSMs are manufactured to validate the theoretical analysis. The experimental results verify that the proposed method can effectively reduce the modulated vibration of the 72-slot/12-pole integral-slot IPMSM. [ABSTRACT FROM AUTHOR]

This article proposes a modified flux observer for sensorless direct torque control (DTC) of the dual three-phase permanent-magnet synchronous motor. The proposed method can improve torque performance without a position sensor. The flux observer is proposed to obtain the stator fluxes and rotor fluxes. The stator fluxes can be utilized to calculate the amplitude of torque and flux for DTC system. Meanwhile, the position information can be detected from the rotor fluxes by using a normalized phase-locked loop. This new flux observer can overcome the disadvantages due to the dc bias, initial value, and harmonic components. The stability of the proposed observer is also analyzed in this article. In addition, a fault-tolerant DTC scheme for open-circuit fault is introduced. The performances of torque control and position estimation are evaluated under healthy, open-circuit fault, and fault-tolerant conditions. Simulation and experimental evaluation are carried out to confirm the effectiveness of the proposed sensorless DTC scheme. [ABSTRACT FROM AUTHOR]

In this paper, an interior permanent magnet (IPM) machine is presented and optimized for heavy-duty vehicle direct-drive applications. Since efficiency decrease and serious heating come along with excessive core loss under flux weakening control, a rotor topology with the combination of the eccentricity structure and magnetic barriers is proposed. The key is to achieve the comprehensive optimization of the proposed rotor topology to satisfy the different requirements under diverse operating points. Then, a multi-objective automatic parallel optimization method is applied, which simultaneously analyzes multi-condition operation without weight coefficients defined artificially. The 3D Pareto solution set is generated by using nature inspired evolutionary algorithm based on the high-precision metal-modals of optimal prognosis, which reduce the needed computation cost significantly. Moreover, the back electromotive force total harmonic distortion, torque and core loss of the optimal machine are analyzed at corresponding operating points. Finally, the finite-element results are validated by experiments based on a prototype machine. [ABSTRACT FROM AUTHOR]

This article proposes a new duty-ratio-based direct torque control (DR-DTC) with enhanced harmonic current suppression for a dual-three-phase permanent magnet (DTP-PM) motor. First, a new virtual voltage vector construction method based on the carrier-based modulation technique is proposed. Twelve virtual voltage vectors with null average voltage values in two harmonic subspaces are constructed. The sequences of the constructed virtual voltages can be calculated directly in the natural coordinate system. In addition, the whole sequences are standard symmetrical, which can be easily generated by a digital controller. After that, an online harmonic current compensation method is investigated. Additional controllers compensate for the harmonic currents induced by the back electromotive force and nonlinear factors. Since the virtual voltage vectors have null average voltage values in two harmonic subspaces and the online harmonic current compensation method is designed, the proposed DR-DTC can be introduced to the DTP-PM motor with a single neutral point and two neural points. With the proposed strategy, the capability of harmonic current suppression can be significantly improved, and the processes of virtual voltage construction can be simplified. In addition, the advantages of the conventional DR-DTC can be inherited. Finally, experiments are carried out to validate the feasibility of the proposed strategy. [ABSTRACT FROM AUTHOR]

This article proposes a novel remedial direct torque control (RDTC) for the postfault operation of the dual three-phase permanent-magnet (DTP-PM) motor. The DTP-PM motor is configured as a two-neutral points model and fed by an eight-leg voltage source inverter. Also, the harmonic torque induced by the third harmonic back electromotive force and zero-sequence currents is considered at the postfault operation. First, the switching tables for different fault conditions are pre-established. The proposed strategy can be applied to different postfault operations with one phase open by replacing the switching table simply. At the normal operation, the redundant auxiliary legs are disabled. So, the proposed eight-leg voltage inverter is the same as the conventional six-leg one. At the postfault operation, the auxiliary leg in the faulty three-phase windings provides an additional control degree of freedom. Hence, the fault-tolerant capability of the DTP-PM motor with two neutral points can be enhanced. Also, the proposed strategy compensates for the harmonic torque by modifying the reference torque. Based on the proposed RDTC, the postfault operational performance can be significantly improved. Finally, the simulations and experiments are conducted to validate the feasibility of the proposed strategy. [ABSTRACT FROM AUTHOR]

A new partitioned stator hybrid excitation (HE) with an internal magnetic ring machine was proposed in this article. The key of the design is to adopt an inner magnetic ring to reduce the inside stator magnetic reluctance. As a result, the working magnetic field harmonics can be improved, which in turn improve the torque and flux regulation abilities. Besides, by following the design of partition stator, the space competition of permanent magnet, armature winding, and field winding can be effectively alleviated as compared with a single stator HE machine. The structure and operation principle of the conventional and proposed machines are described. Moreover, electromagnetic performances of both machines are compared by using finite element method. Theoretical and simulation analysis results show that the proposed machine can exhibit higher torque and enhanced flux regulation ability than the conventional one. [ABSTRACT FROM AUTHOR]

This article focuses on the electromagnetic vibration source and its reduction design in fractional-slot concentrated-windings (FSCWs) permanent magnet (PM) machines. First, the electromagnetic force and vibration characteristics of a 12-slot/10-pole FSCW PM machine are investigated. Then, four electromagnetic vibration sources are investigated and compared, in which the machine operating state is considered. The result shows that the electromagnetic force modulation and stator magnetomotive force (MMF) harmonics are the two sources that contribute most to the vibration underrated and heavy load condition, respectively. Afterward, two new designs to reduce the vibration caused by the electromagnetic force modulation and stator MMF harmonics are proposed, and the reduction principles are described in detail. Finally, the prototypes of the existing and proposed 12-slot/10-pole FSCW PM machines are manufactured. The tests are conducted to validate the theoretical analysis and proposed vibration reduction design. [ABSTRACT FROM AUTHOR]

In this article, a novel parallel hybrid excitation field modulated machine with efficient utilization of multiworking harmonics is proposed. The key of the proposed machine is to efficiently integrate the parallel hybrid excitation and multiworking harmonics to enhance average output torque and flux regulation capability. First, operation principle and air-gap magnetic field harmonics of the machine are investigated by using field modulated principle, which reveals the contribution of each working harmonic to flux linkage and torque. Then, performances of the machine are analyzed, such as open-circuit back-EMF, flux regulation capability, torque-speed characteristics, etc. Also, the proposed machine is compared to conventional ones for evaluation. Finally, a prototype is manufactured and tested to validate the theoretical and simulated results. [ABSTRACT FROM AUTHOR]

In this article, the efficiency function of the permanent-magnet (PM) machines is reconstructed by the quantitative loss expressions. Then, the efficiency function is used to quantitatively analyze the maximum efficiency point and the specific high-efficiency region. General principles of improving the maximum efficiency and the regulation of the specific high-efficiency region for PM machines are investigated. First, the loss expressions of PM machines, which vary with the speed and the current, are presented. Moreover, an accurate efficiency function is established to calculate the efficiency map of PM machines quickly. Furthermore, the maximum efficiency point and the specific high-efficiency region of PM machines are derived, as well as their variation principles with loss distributions are studied. Furthermore, a 12-slots 10-poles PM machine and a 48-slots 22-poles PM machine are designed to verify the analytical results. Subsequently, their electromagnetic performances and the efficiency maps are calculated and compared by the finite-element method. Finally, both PM machines are prototyped and experimental results are given for validations. [ABSTRACT FROM AUTHOR]

This article investigates the effects of phase shift on the inductance and short-circuit current (SCC) in permanent-magnet (PM) machines with dual three-phase winding configurations. First, the relationship between the phase shifts and slot/pole combinations, for the dual three-phase winding configurations, is discussed. Second, analytical expressions of the inductance are derived for the 48-slot/22-pole PM machines with different phase shifts based on the winding function theory. Afterwards, the SCC amplitude of different phase shifts is comparatively analyzed. The investigation reveals that the 7.5° and 30° configurations have great significance to improve the self-inductance value. Thereby, the 30° configuration has comparable SCC amplitude compared to the 7.5° counterpart, while being lower than the 15° configuration one. Moreover, the 30° configuration exhibits lower eddy-current loss and preferable torque performance than its counterparts. Furthermore, the finite-element method is used to calculate electromagnetic performances for evaluation. Finally, some experiments on the prototype machine are carried out for validation. [ABSTRACT FROM AUTHOR]

This article proposes a torque improvement method for dual m-phase synchronous reluctance machines by phase shift technique. The emphasis is put on the relationship of d–q axis inductance harmonics and phase shifts. First, all feasible phase shifts for various slot/pole combinations are discussed in general. Second, the influences of phase shift on reluctance torque performance are investigated based on inductance analysis. It is founded that the first main torque harmonic can be eliminated when phase shift equals to π/2m (m is odd) and π/m (m is even), respectively. This is the optimal phase shift covering all the m cases. Third, the optimal phase shift with torque improvement and ripple reduction is verified by the theoretical analysis and finite element method. Finally, the dual 3-phase 24-slot/10-pole synchronous reluctance machines with 30° and 60° phase shifts are fabricated. The experiments on the prototype machine are carried out for validation. [ABSTRACT FROM AUTHOR]

In this article, we analyze the vibration of the spoke-type permanent-magnet (PM) machine with an asymmetric rotor considering the modulation effect of the stator teeth. First, the semianalytical expression of the radial pressure is derived to quickly estimate the radial pressure characteristic. The equivalent spatial order of the radial pressure is determined by considering the modulation effect. Second, a structural finite-element (FE) model is set up. The modal test validates the accurateness of the structural FE model and modal analysis. Third, the vibration is predicted by an FE method and verified by the experimental results. The results show that the radial pressure harmonics become richer, and the fundamental frequency and lowest nonzero order of the radial pressure are both reduced due to the asymmetric magnetic barrier. Furthermore, the zero-order radial pressure is no longer the dominant vibration source in this integer-slot PM machine with an asymmetric rotor. Some high-order radial pressures that can be modulated as equivalent low-order harmonics excite the low-order and large vibration. In terms of vibration and noise, the equivalent lowest nonzero-order harmonic should be fully considered in the performance optimization for the asymmetric rotor design. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of eccentric magnet design on sideband electromagnetic force (SEMF) and hence high-frequency vibroacoustic performance of integral-slot surface-mounted permanent magnet (SPM) machines. Also, the tangential SEMF components are considered to investigate their contribution for high-frequency vibration and acoustic noise. Firstly, the mechanism of sideband current harmonics introduced by space vector pulse-width modulation technique of open-winding drive system is derived. Moreover, the critical components of sideband synthetic magnet field in air-gap are derived to obtain the radial and tangential SEMF density components, and the effects of concentric magnet design of that is discussed. Then, the vibration synthesis model and acoustic radiation model are used to predict the vibroacoustic performance of machines. The results shows the eccentric magnet design can reduce the high-frequency vibration and noise of integral-slot SPM machines. Finally, two integral-slot SPM machines with concentric and eccentric magnets are manufactured and tested to validate the theoretical investigations. [ABSTRACT FROM AUTHOR]

This article proposes a new asymmetric modular permanent magnet assisted synchronous reluctance motor (PMaSynRM) to offer low torque ripple and high reliability. First, the stator is segmented into three modules without magnetic coupling. The influence of flux gaps between modules is investigated on torque performance. For the torque improvements, the multilevel optimization strategy is conducted, which simultaneously enhances the fault-tolerant capability. Besides, the torque ripple reduction methods are proposed with the asymmetric rotor and shifted end-slots. The analytical formulae of asymmetric flux barrier angle are derived. Then, the asymmetric flux barrier is designed to reduce the 12th harmonic, and the end-slots are shifted to minimize the additional 2nd harmonic component caused by flux gaps. Finally, the enhanced fault-tolerant capability of the proposed modular PMaSynRM is also evaluated. The effectiveness of the proposed approach is verified by both simulation and experiment. [ABSTRACT FROM AUTHOR]

This paper proposes a design technique for electric ship traction machines to achieve high torque density and low torque ripple by adopting dual m-phase windings with an appropriate phase shift. Firstly, the general relationship between the slot number and the phase number for dual m-phase windings is investigated. Secondly, the uniform analytical expressions of torque with different phase shifts are derived. Also, the optimal phase shift angle is summarized from the perspective of improving torque performance. Then, the 48-slot and 22-pole permanent-magnet machines for electric ship with different windings configurations are designed. The finite-element method is used to calculate their electromagnetic performances, such as back electromotive force, torque capability, stator magnetic motive force and radial force. Finally, some experiments on the prototype machine for electric ship are carried out for validation. [ABSTRACT FROM AUTHOR]

In this article, the permanent-magnet (PM) eddy current loss in a four-phase fault-tolerant flux-switching PM (FT-FSPM) machine is investigated from the perspective of air-gap magnetic field modulation. It can be found that the PM eddy current loss in FT-FSPM machines results from the relative motion between air-gap field space harmonics and PMs. Some effective working harmonics produce the major PM eddy current loss. The proportion of PM eddy current loss generated by each working harmonic is studied in detail, revealing that the low-order (third) harmonic is the main factor. Then, two new structures are proposed to reduce PM eddy current loss, in which magnetic flux barriers are designed by reducing low-order harmonics from the aspect of magnetic field modulation theory. Electromagnetic performance is investigated by finite element analysis. The results show that the proposed structure is effective to suppress PM eddy current loss. Finally, an experimental test platform is established to verify the theoretical analysis results. [ABSTRACT FROM AUTHOR]

Owing to bidirectional field modulation effect, dual-permanent-magnet-excited (DPME) machine could offer improved torque capability, which has attracted increasing attention in recent years. However, conventional DPME machine only utilizes a small amount of abundant field harmonics to yield torque, which leads to limited torque enhancement. To solve this issue, a novel DPME machine with enriched working harmonics is proposed in this paper. The key of the proposed DPME machine is to design some non-uniformly distributed permanent-magnets and flux modulation poles on the stator. Thus, increased field harmonics are produced to produce effective torque, offering the potential to enhance torque. Firstly, the topology and feature of the machine are introduced. Moreover, operating principle is analyzed by using air gap field modulation theory. Then, the operating principle and torque enhancement are verified and evaluated by using finite-element method. At last, a corresponding principle machine is fabricated, and some experiments are performed for validation. [ABSTRACT FROM AUTHOR]

Fractional-slot concentrated-winding (FSCW) permanent magnet (PM) machines have been widely studied in recent years. This is mainly due to the several advantages, including high power density, high efficiency, short end turns, high fill factor, low cogging torque, good flux-weakening and fault-tolerant performance. However, the key challenges of utilizing FSCW-PM machines are the abundant stator magnetomotive force (MMF) harmonics. In this paper, the multiphase star–delta hybrid connection (SDHC) windings configuration that can eliminate some stator MMF harmonics is systematically studied. First, the general relationship between the number of slots and phases which are appropriate for the SDHC windings configuration is derived. In addition, the particular principle of the MMF harmonics elimination by the SDHC windings configuration is researched. In order to verify the analysis results, four three-phase SDHC FSCW-PM machines with different slot–pole combinations are built and calculated by the finite-element method. Finally, experiments on a prototype three-phase 12-slot ten-pole FSCW-PM machine are carried out for validation. [ABSTRACT FROM AUTHOR]

This paper proposes a new design method for surface-mounted permanent magnet machines. The key to the proposed method is that all rank harmonics are introduced to the permanent magnet for torque improvement. The proposed method can offer a variety of magnet topologies by injecting various harmonics into magnets, and these magnet topologies are subsequently analyzed to select the best one. To find the optimal torque output requires investigating the effect of all rank harmonics on the average torque and the torque ripple, and then determining the optimal harmonic combination. The results show that the fundamental, third and fifth harmonics, make great contributions to improving torque quality, while the seventh harmonic and those with higher orders are insignificant for torque improvement. Finally, a prototype, which employs the proposed method, is measured for validation. [ABSTRACT FROM PUBLISHER]

This paper investigates magnet eddy-current (EC) loss of a five-phase flux-switching permanent-magnet (FSPM) machine. Using magnetic flux barriers in the two proposed rotor topologies, it is possible to reduce some space harmonics in the air-gap flux density, thus reducing magnet EC loss. A 1-D magnetic permeability model is adopted to account for the reduction of the main sub-harmonics as well. Then, the magnet EC loss of both the existing machine and two proposed machines is compared by using time-stepped finite-element analysis. It is shown that the 55.2% and 49.6% EC loss reduction can be achieved by adopting proposed I and proposed II topologies, respectively. The temperature of proposed machine is lower than that of the existing one, and the temperature of both winding and magnet in the new topologies was reduced by 24°. Therefore, the proposed machine model can provide a direct guidance for dependable design and performance optimization of FSPM machines. [ABSTRACT FROM AUTHOR]

This paper investigates the rotor losses of coaxial magnetic gears (CMGs) with surface-mounted permanent magnets. The iron losses and PM eddy current losses that occurred in the two rotors of an existing gear are calculated and analyzed by the finite-element method. Using magnetic flux barriers in the outer rotor, a novel rotor structure for CMGs is proposed to reduce the rotor losses, in which subharmonics are considered. A 1-D magnetic permeability model is also introduced to understand the principle of reducing the main subharmonics. Then the outer rotor losses of the existing gear and proposed gear are compared. The proposed model and the results presented in this paper will give useful guidelines for a reliable design and design optimization of the CMGs. [ABSTRACT FROM AUTHOR]

In this paper, a linear permanent-magnet vernier machine is proposed, in which both magnets and armature windings are placed in the short mover, while the long stator consists of an iron core only. Hence, it is suitable for long-stroke applications such as urban rail transit. The proposed machine integrates two magnetization directions of magnets together, which can reduce leakage flux and enhance flux density. Meanwhile, since different topologies and different slot/pole number combinations have an effect on the winding factor, several general rules are established. It is revealed that the thrust force ripple of the proposed machine is lower than its cogging force ripple, which is explained by a built analytical model. Both the analytical model and the finite-element results are validated by experiments based on a prototype machine. [ABSTRACT FROM AUTHOR]

Redundant flux-switching permanent-magnet (R-FSPM) motors are a new class of brushless machines having magnets in the stator, offering high power density, simple and robust rotor structure, and good thermal dissipation conditions. This paper proposes a new control strategy for fault-tolerant operation of the R-FSPM motor drive considering the capability limitation of the power converter. The key is to operate the R-FSPM motor in the remedial mode by injecting harmonic currents, the so-called remedial injected-harmonic-current (RIHC) operation mode. Moreover, the motor losses at the existing and the proposed remedial operations are compared for evaluation. Both cosimulation and experimental results are presented, confirming that the proposed RIHC operation can offer good steady-state and dynamic performances while reducing the motor losses and the capability requirements of the power converter during fault. [ABSTRACT FROM PUBLISHER]