Consequent-pole Permanent Magnet Machines Research Articles

A Novel Flux Concentrated Stator Consequent-Pole Permanent Magnet Machine With Nonuniform Stator Modulation Teeth

A Novel Flux Concentrated Stator Consequent-Pole Permanent Magnet Machine With Nonuniform Stator Modulation Teeth

Design and Evaluation of Reduced-Rare-Earth Interior Consequent-Pole Permanent Magnet Machines for Automotive Applications

This article investigates the feasibility of interior consequent-pole permanent magnet (ICPM) machines with reduced rare-earth magnet consumption for automotive applications. A new ICPM machine with a double-layer V-shaped permanent magnet (PM) arrangement is proposed and compared with a commercial Nissan Leaf interior PM (IPM) machine. Their basic electromagnetic performances and rotor mechanical strength are evaluated by finite-element (FE) simulation. It shows that the proposed ICPM machine exhibits comparable torque capability, similar high-efficiency region, and significantly improved PM utilization ratio compared with traditional Nissan Leaf IPM case. Besides, to verify the universality of ICPM designs with reduced-rare-earth consumption, two typical ICPM machines with different magnet configurations (single- and double-layer V-shaped) and power levels (80 kW and 2 kW) are, respectively, investigated and compared with their corresponding traditional IPM counterparts. Finally, some tested results on an ICPM machine prototype with V-shaped magnets are carried out to validate the FE analysis.

Influence of Armature Reaction on Electromagnetic Performance and Pole Shaping Effect in Consequent Pole Pm Machines

Consequent pole permanent magnet (CPPM) machines can improve the ratio of average torque to PM volume, but suffer from more serious armature reactions. In this paper, the variations of electromagnetic performance of surface-mounted PM (SPM), conventional CPPM machines, and pole-shaped CPPM machines with armature reaction at currents up to 5 times overload are analyzed and compared. The flux densities, flux linkages, back EMFs, inductances, torque characteristics, and demagnetization withstand capabilities are analyzed by the finite element method (FEM) and frozen permeability method. It is validated that the third order harmonics in inductances for CPPM machines tend to be reduced as current rises since the saturation in iron pole is prone to reducing the saliency effect. But the armature reaction tends to result in the increase of torque ripple components for all the machines. It is also found that the overall torque ripple of asymmetric pole-shaped machine tends to increase significantly under overload conditions. On the contrary, the symmetrical pole-shaped machine can maintain a relatively stable torque ripple under overload conditions which is similar to the SPM counterpart. Additionally, due to the large armature reactions, CPPM machines suffer from weaker demagnetization withstand capabilities and weaker overload capabilities than their SPM counterparts. Four CPPM prototypes with and without pole shaping are tested to confirm the FEM analysis.

Vibration Reduction Design of Consequent Pole PM Machine by Symmetrizing Local and Global Magnetic Field

The consequent pole permanent magnet (CPM) machine is well known for its high magnet utilization ratio and poor vibration performance. This article focuses on electromagnetic vibration and its reduction design in CPM machines, and the conventional surface-mounted permanent magnet (SPM) machine is used as a benchmark. First, the asymmetrical magnetic field and unbalanced radial force of the CPM machine are investigated with emphasis. The slot-pole combination and force modulation effect are the two reasons for the unbalanced radial force generation. Afterward, two new designs to reduce the vibration caused by the unbalanced radial force are proposed, and the reduction principles are described in detail. Finally, the prototypes of the 12-slot/10-pole SPM and proposed CPM machines are manufactured. The tests are conducted to validate the theoretical analysis and proposed vibration reduction design.

Suppression of Torque Ripple in a New Consequent-Pole Permanent Magnet Machine by Segmented Structure

A new consequent-pole permanent magnet (CPM) machine with segmented structure/unequal teeth (CPM-SU machine) is proposed in this article. The segmented structure is adopted to decrease the torque ripple. To improve the torque density, the structure of unequal teeth is used in this proposed machine. The five-phase winding located in the stator is composed of three fractional-slot concentrated windings (FSCWs), which are helpful to improve the fault-tolerant capability. Permanent magnets (PMs) are placed in the rotor. To decrease the PM cost, V-type PMs and iron cores are arranged with the sequence of S-iron-S-N-iron-N. The magnetic field generated by PMs is investigated, which is helpful to demonstrate the working mechanism of this proposed CPM-SU machine. To verify the superiority of the proposed CPM-SU machine, a conventional CPM machine with unsegmented structure/equal teeth (CPM-UE machine) is proposed. The electromagnetic properties of these two machines, including the electromagnetic torque, the cogging torque, and the back electromotive force (back EMF), are analyzed by the finite element (FE) method. The simulating results show that the CPM-SU machine can exhibit excellent performances, such as low torque ripple and high torque density.

Nonlinear Varying-Network Magnetic Circuit Analysis of Consequent-Pole Permanent-Magnet Motor for Electric Vehicles

To conserve rare earth resources, consequent-pole permanent-magnet (CPPM) machine has been studied, which employs iron-pole to replace half PM poles. Meanwhile, to increase flux-weakening ability, hybrid excitation CPPM machine with three-dimensional (3-D) flux flow has been proposed. Considering finite element method (FEM) is time-consuming, for the analysis of the CPPM machine, this paper presents a nonlinear varying-network magnetic circuit (NVNMC), which can analytically calculate the corresponding electromagnetic performances. The key is to separate the model of CPPM machine into different elements reasonably; thus, the reluctances and magnetomotive force (MMF) sources in each element can be deduced. While taking into account magnetic saturation in the iron region, the proposed NVNMC method can accurately predict the 3-D magnetic field distribution, hence determining the corresponding back-electromotive force and electromagnetic power. Apart from providing fast calculation, this analytical method can provide physical insight on how to optimize the design parameters of this CPPM machine. Finally, the accuracy of the proposed model is verified by comparing the analytical results with the results obtained by using FEM. As a result, with so many desired attributes, this method can be employed for machine initial optimization to achieve higher power density.

Comparative Study of Torque Production Mechanisms in Stator and Rotor Consequent-Pole Permanent Magnet Machines

This article presents a comparative study of torque production mechanisms in stator and rotor consequent-pole permanent magnet (CPM) machines. Due to the CPM design, a unipolar PM magnetomotive force (MMF) distribution can be observed in both stator CPM (S-CPM) and rotor CPM (R-CPM) machines. As a consequence, more resultant air-gap field harmonics are responsible for torque production due to the double-side slotting effect. The PM MMF-permeance-based model is employed to identify and reveal the difference of sources and patterns of the working air-gap field harmonics in the two investigated CPM machines. The torque contributions of the main-order working harmonics of the two studied machines are analytically quantified by a unified torque equation and compared with the corresponding finite-element (FE) results. Finally, some experimental measurements are carried out on a 12-slot/14-pole R-CPM machine prototype to validate the theoretical and FE analyses.

Reduction of Saturation and Unipolar Leakage Flux in Consequent-Pole PMV Machine

This article proposes some effective approaches to address the inherent issues of consequent-pole (CP) permanent magnet (PM) machines, such as saturation of the salient rotor core and unipolar PM leakage flux of the end region caused by asymmetric field. The effect of CP-Halbach PM array with different magnetization directions and parameters that affect the saturation has been investigated for the CP PM machine with short pole pitch. By employing the CP-Halbach array, the saturation issue can be solved and superior performance can be obtained without reducing the PM pole arc. In addition, unequal and multistep staggered rotors with magnetic barriers have been proposed to reduce the unipolar leakage flux in the end region. Compared with regular staggered rotors, not only better electromagnetic performance can be achieved, but also the end unipolar leakage flux can be reduced. Finally, a prototype is manufactured and the predictions have been validated by measurements.

Investigation of Double-Side Field Modulation Mechanism in Consequent-Pole PM Machines With Concentrated Windings

In this article, the field modulation effect (FME) of consequent-pole permanent magnet (CPM) machine is revealed and investigated from the perspective of a double-side slotting effect (DSSE), which can characterize and elaborate its torque production mechanism. Since the CPM machine features that both PM and armature fields are modulated by stator /rotor teeth, which generates more field harmonics contributing to the torque production compared with conventional surface-mounted PM (SPM) machine. A simplified PM magneto-motive force (MMF)-permeance based model is first established to confirm the effective working harmonics of the CPM machine. The contributions of dominant air-gap field harmonics to the torque production are then demonstrated and quantified based on Maxwell stress tensor (MST) method. The impacts of FME on the torque performance of the CPM machines with different stator-slot/rotor pole combinations are subsequently investigated by the finite element (FE) method and compared with those of conventional SPM counterparts. Besides, the influences of rotor PM parameters on the FME of the CPM machine are also evaluated. Finally, the experimental measurements on a 12-slot/14-pole CPM machine prototype are carried out to validate the theoretical and FE analyses.

Comparative analysis of spoke‐type, consequent‐pole and hybrid‐pole permanent magnet machines

In recent years, consequent-pole permanent magnet (CPM) machines draw much attention due to their high utilisation ratio of permanent magnet (PM) material. However, they have some disadvantages, such as the even-order harmonics of airgap flux density, which may cause asymmetric phase back-EMF and the increase of torque ripple. In this study, a novel hybrid-pole PM (HPM) machine is proposed, in which the rotor combines consequent-pole and spoke-type PM rotors. The working principle of the proposed HPM machine is analysed based on the equivalent magnetic circuit, and validated by the finite-element method. Then, the electromagnetic performance of the HPM machine is compared with those of the existing CPM and spoke-type PM machines. It is shown that the HPM machine obtains similar average torque, PM utilisation ratio, torque ripple and efficiency to the spoke-type PM machine, whilst it has a higher PM utilisation ratio and much lower torque ripple than the conventional CPM machines. Finally, these analyses are validated by the tested results of a 9-slot/6-pole HPM machine.

Improvement of torque performances in consequent-pole PM machines with optimized six-layer winding and Halbach PMs array

This paper presents a torque performance improvement method for three-phase consequent-pole permanent magnet (PM) (CPM) machines. The key of this method is to consider torque ripple and output torque simultaneously in CPM machines. This method is rea

Design of a Novel Low-Cost Consequent-Pole Permanent Magnet Synchronous Machine

This article proposes a novel low-cost consequent-pole permanent magnet (CPM) synchronous machine structure, considering the reluctance torque utilization. First, a novel CPM machine with doubled salient ferromagnetic iron poles (ICP-PMSM) is proposed, featuring an N pole - iron - S pole - iron sequence to maximize the reluctance torque utilization and reduce cost. Flux barriers are integrated into the rotor structure to maintain the same magnetic rotor pole number as the conventional CPM synchronous machine (CP-PMSM). Second, for a low torque ripple, soft ferrite is used to replace part of the iron pole in the ICP-PMSM (ISCP-PMSM) to improve the air-gap flux density distribution. Furthermore, the CP-PMSM, ICP-SPMSM, and ISCP-PMSM rotors are optimized for a fair comparison. The electromagnetic performances of all the optimized machines are compared with those of a conventional surface permanent magnet synchronous machine (SPMSM). It is demonstrated that the ISCP-PMSM can obtain an almost equivalent torque and torque ripple, but with reduced PM (NdFeB) usage and cost when compared to the SPMSM.

2-D Analytical Model for Outer-Rotor Consequent-Pole Brushless PM Machines

Consequent-pole permanent-magnet machines are of particular interest owing to their special features. They have alternate hard and soft magnet poles. In this paper, a two-dimensional (2-D) analytical model is proposed for outer-rotor slotted-stator consequent-pole brushless PM (CPBLPM) machines. The model is developed from the quasi-magneto-static Maxwell's equations, which are analytically solved. The magnetic flux density expressions are initially derived and then other quantities such as the no-load induced voltage, electromagnetic torque, reluctance torque, cogging torque, self and mutual inductances as well as unbalanced magnetic forces (UMF) are computed. The suggested model is generic and applicable to CPBLPM machines with any number of poles and phases, type of magnetization patterns and current waveforms. A case study is presented to evaluate the performance of the proposed model. The accuracy of the 2-D analytical solutions is verified against those obtained from the finite element method (FEM). The proposed method can replace the FEM in designing and optimization of outer-rotor consequent-pole permanent-magnet motors.

Novel Hybrid-Pole Rotors for Consequent-Pole PM Machines Without Unipolar Leakage Flux

This paper presents two novel consequent-pole permanent magnet (PM) machines featuring N-iron-N-iron-N-S-iron-S-iron-S and iron-S-iron-S-iron-iron-N-iron-N-iron sequences. In order to provide assistant flux and suppress the subharmonics of the air-gap flux density, the tangential PMs are embedded into the proposed rotors of the consequent-pole PM (CPM) machines to form the novel hybrid-pole PM (HPM) machines. The principle of eliminating unipolar leakage flux and the performance improvement by hybrid pole are analyzed based on the simplified PM magnetic circuit. Then, the proposed rotors of CPM and HPM machines, as well as their conventional counterpart with an N-iron sequence, are optimized by finite-element analyses. Furthermore, the electromagnetic performances of the proposed machines, including the open-circuit air-gap flux density, average torque, torque ripple, loss, efficiency, unbalanced magnetic force, demagnetization withstand capability, and unipolar leakage flux, are compared with that of the conventional surface-mounted PM (SPM) and CPM machines. It is demonstrated that both the conventional CPM and proposed HPM machines have >20% higher PM material utilization ratio than the SPM machine. The proposed HPM machine can obtain almost equivalent torque and efficiency compared to the conventional CPM machine. Moreover, unipolar leakage flux does not exist in the end shaft, and thus the magnetization of the mechanical components can be effectively eliminated. Finally, a 9-slot/10-pole HPM machine is prototyped and measured to validate the analyses.

A Subdomain Model for Open-Circuit Field Prediction in Dual-Stator Consequent-Pole Permanent Magnet Machines

This paper proposes a subdomain model for open-circuit field prediction in dual-stator consequent-pole permanent magnet machines. The whole field domain is composed of four types of sub-domains, including magnets, air gaps, slot openings, and slots. The proposed model takes the effect of tooth-tips into account, which can accurately calculate the flux density in slots and cogging torque. The finite-element (FE) model is established, which validates that the proposed subdomain model can quickly and accurately predict the magnetic field distribution and cogging torque in dual-stator consequent-pole permanent magnet machines.

Reduction of Torque Ripple in Consequent-Pole Permanent Magnet Machines Using Staggered Rotor

Consequent-pole permanent magnet (CPM) machines have considerable potential for low-cost applications because they can improve the permanent magnet (PM) utilization ratio. However, the phase back electromotive force (EMF) of CPM machines with Ns /( mt ) = odd ( t is the greatest common divisor of the stator slot number Ns and the rotor pole-pair number p , and m is the phase number) is asymmetric, i.e., the phase back EMF has even-order harmonics, which will increase torque ripples. This paper utilized the staggered rotor to eliminate the even-order harmonics and reduce the cogging torque of CPM machines, thereby potentially decreasing torque ripples considerably. The axial flux barrier in the middle of the rotor was used and optimized using three-dimensional finite element (FE) analysis to reduce the axial leakage flux of the CPM machine with the proposed staggered rotor. Furthermore, the axial magnetized PM was embedded in the flux barrier, which improved the flux density of the airgap above the iron-pole and, consequently, further increased the output torque. The electromagnetic performance of the proposed machine, including the open-circuit airgap flux density, back EMF, average torque, torque ripples, and PM utilization, was compared with that of the conventional CPM machine. Results showed that the proposed machine obtained a similar torque and PM utilization ratio but a much lower torque ripple compared with the conventional one.

Electromagnetic Performance Analysis of Consequent-Pole PM Machine With Asymmetric Magnetic Pole

The permanent magnet (PM) machine with consequent-pole (CP) rotor can improve the PM utilization ratio. However, the replacement of the PMs with the same polarity by the salient iron core deteriorate the electromagnetic performance of the machine, including higher torque ripple and unipolar leakage flux. Therefore, a CP PM machine with asymmetric magnetic pole (AMP) structure is proposed, through which the smaller torque ripple and unipolar leakage flux can be obtained, without deteriorating the torque characteristics compared with the traditional CP PM machine. Furthermore, the electromagnetic performance and the unipolar end leakage flux of the AMP and traditional CP PM machines are investigated by the finite-element method (FEM). It is demonstrated that AMP structure can reduce the cogging torque and torque ripple; furthermore, the unipolar leakage flux can be suppressed effectively. Finally, the prototype with AMP and CP PM rotor are fabricated and tested to verify the theoretical and FE analysis.

Investigation of stator slot/rotor pole combination of flux reversal permanent magnet machine with consequent‐pole PM structure

Here, the influence of stator slot and rotor pole combination on performance of flux reversal permanent magnet (FRPM) machine with consequent-pole permanent magnet (CPM) structure is analysed. First, for 12-slot FRPM machines, the torque capabilities of CPM and conventional surface-mounted PM (SPM) structure having different rotor poles are compared. It shows that the torques of CPM machines are largely affected by the rotor pole number while the torques of SPM machines are similar. This is further explained by the equivalent pole-pair number and corresponding saturation condition. The influence of stator slot number and PM width ratio on torque performance of the CPM-FRPM machine is then investigated. Finally, detailed electromagnetic performance of the 12/14 SPM- and CPMFRPM machine is analysed and compared.

Elimination of Even-Order Harmonics and Unipolar Leakage Flux in Consequent-Pole PM Machines by Employing N-S-Iron–S-N-Iron Rotor

This paper presents a novel consequent-pole permanent magnet (CPM) machine featuring N-S-iron–S-N-iron sequences to eliminate the even-order harmonics of phase back electromotive force (EMF) and the unipolar leakage flux in the end region. The flux barrier is employed to improve the symmetry of the air-gap flux and reduce the saturation of the stator yoke, and hence the output torque can be improved. The proposed CPM machine, as well as its conventional counterpart with N-iron sequences, is optimized by finite-element analyses. Moreover, the electromagnetic performance of the proposed CPM machine, including the open-circuit air-gap flux density, back EMF, average torque, torque ripple, loss, efficiency, and unipolar leakage flux, is compared with the conventional CPM and surface-mounted PM (SPM) machines. Although both the proposed and conventional CPM machines have lower output torque than the SPM machine, the utilization ratio of PM material is increased by >33%. It is demonstrated that the proposed CPM machine has similar output torque and efficiency, but much lower torque ripple compared to the conventional one. Moreover, unipolar leakage flux does not exist in the end shaft of the proposed machine, and thus, the magnetization of the mechanical components can be effectively eliminated. Finally, the 9-slot/6-pole CPM machine is prototyped and measured to validate the analyses.

Influence of Various Magnetic Pole on Electromagnetic Performance of Consequent-Pole Permanent Magnet Machine

Permanent magnet (PM) machine with consequent pole (CP) rotor can improve the PM utilization ratio. However, one group PMs with the same polarity is replaced by iron core which deteriorating the electromagnetic performance of the machine, including even-order back-EMF harmonics, torque ripple, as well as unipolar leakage flux. Therefore, CP PM machine with various magnetic pole, i.e., equal pole-arc magnetic pole (EMP) and asymmetric magnetic pole (AMP) structure is proposed, with smaller torque ripple can be achieved, without deteriorating the torque ability compared with the conventional CP PM machine. Further, the influence of various CP PM magnetic pole on the end leakage flux is analyzed by three-dimensional (3-D) finite element (FE), which includes leakage flux distributions as well as magnetization of shaft. The electromagnetic characteristics of the machine with EMP and AMP rotor are compared with traditional surface-mounted and CP PM machines by FE analysis. It is demonstrated that EMP and AMP rotor structure can reduce even-order harmonics, torque ripple and end leakage flux for the machines. Finally, one prototype with CP AMP rotor is tested to confirm the theoretical and FE analysis, which includes suppression effect of even back-EMF harmonics, torque characteristics as well as leakage flux at the end shaft.