Consequent Pole Research Articles

Design and Optimization of External Rotor Consequent Pole Permanent Magnet Motor with Low Iron Loss and Low Torque Ripple

To reduce the iron loss and torque ripple of an external rotor consequent pole (ERCP) motor used in an electric vehicle air-conditioning compressor, the magnetic pole structure of the motor was improved, and an unequal piecewise consequent pole (CP) structure was designed. The performance of the motor is optimized by reducing the harmonic content in the air gap flux density and reducing the iron saturation degree of the motor. The designed CP structure can significantly reduce the iron loss and torque ripple of the motor. Based on the Taguchi method, the optimal size parameters of the unequal piecewise CP structure are determined, and the final optimization design scheme is obtained. The results of finite element simulation and high-precision iron loss model show the following: compared with the original motor, the iron loss and torque ripple of the motor with the final optimized design scheme are significantly reduced.

Analysis and Comparison of Even-Order Back EMF Harmonics of Fractional-Slot Concentrated-Winding Consequent Pole Permanent Magnet Vernier Machines

Fractional-slot concentrated-winding (FSCW) consequent pole (CP) permanent magnet vernier (PMV) machines have received increasing attention due to their less magnet consumption but larger torque capability. However, the PM magnetomotive force (MMF) distribution is asymmetric in the CP structure. Thus, even-order air-gap flux density and back-electromotive force (back-EMF) harmonics are generated, which increases torque ripples. In this paper, to eliminate the even-order back-EMF harmonics and the resulting torque ripples, a comprehensive investigation on even-order flux density and back-EMF harmonics of five-phase FSCW CP PMV machines was presented, and then the general design rules without even-order back-EMF harmonics were summarized. Firstly, considering single- and double-layer windings, the effects of slot/pole number combination and flux modulator distribution on even-order flux density and back-EMF harmonics were analyzed. Secondly, the optimal slot/pole number combinations were selected, and then the rules for eliminating even-order back-EMF harmonics of CP PMV machines were summarized. As an extension, it was revealed that the harmonic elimination mechanism of CP PMV machines is applicable to CP-Halbach PMV machines. According to the summarized general design rules, the five-phase CP and CP-Halbach PMV machines with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> =20/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_r</i> =21/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z_f</i> =10 were proposed. Their detailed performance has been comparatively analyzed and then the optimal one was selected for prototyping. Both finite element analysis (FEA) and experiments were carried out to validate theoretical analyses.

Design and Analysis of New Dual-Stator Flux Modulated Machines With Dual-PM Excitation

This article proposes new dual-stator flux modulated machines with dual-permanent magnet (PM) excitation (DS-FMDPMMs) for direct-drive applications. The proposed DS-FMDPMMs are characterized by employing consequent-pole (CP) PMs on both the stator and rotor sides. By using dual-layer CP PMs, the DS-FMDPMMs can perform the bidirectional flux modulation effect to enhance the torque capability. In addition, the merits of dual-stator structure, such as high space utilization, high torque density, and power factor are inherited in the proposed machines. The design principle of DS-FMDPMM is provided at first, and the formed three representative DS-FMDPMMs with different stator-PM arrangements are proposed. Then, the design considerations of three DS-FMDPMMs are described in detail, which includes the armature winding design, the selection of stator-slot/rotor-pole combination, and the influence of critical structural parameters on torque. In order to find an optimal direct-drive candidate among the three DS-FMDPMMs, a quantitative electromagnetic performance comparison is developed through finite element analysis (FEA). The results show that among the three machines, DS-FMDPMM-I accommodates the highest torque density, lowest torque ripple, best over-load torque capability, and highest efficiency. Moreover, to further verify its performance advantages, the electromagnetic performances of DS-FMDPMM-I and two typical dual-stator flux modulated PM machines are compared through FEA. Finally, a prototype of the optimal DS-FMDPMM is manufactured and tested to validate the effectiveness of FEA-predicted results.

Influence of slot/pole number combinations and pole shaping on electromagnetic performance of permanent magnet machines with unbalanced north and south poles

AbstractThe influences of slot/pole number combinations on electromagnetic performances, including flux linkage, inductance, and torque ripple harmonic components etc., resulting from unbalanced characteristics between north and south poles in concentrated winding permanent magnet (PM) machines with symmetrical and asymmetric rotor pole shaping methods are theoretically analysed and experimentally validated in this paper. It shows that for the PM machines with odd number of coils per phase per submachine, including consequent pole (CP) and surface‐mounted PM (SPM) machines, the influences of unbalanced pole characteristics can lead to additional torque ripple harmonics due to additive effects in windings, but can be cancelled in other machines. Compared with symmetrical pole shaping method, asymmetric pole shaping method can result in lower torque ripple for CPPM machines with odd number of coils per phase per submachine, while symmetrical and asymmetric pole shapes have similar effects on torque ripple reduction for other CPPM machines and all the SPM machines. The findings have been validated by finite element analyses on 12‐slot/8‐pole, 12‐slot/10‐pole, 9‐slot/6‐pole, and 12‐slot/14‐pole machines, and by experiments with 12‐slot/8‐pole and 12‐slot/10‐pole CPPM prototypes.

Design and analysis of consequent pole permanent magnet synchronous motor with low torque ripple

AbstractPermanent magnet (PM) motor with consequent pole (CP) rotor can improve the PM utilisation ratio. However, one group of PMs with the same polarity is replaced by iron core, which deteriorates the electromagnetic performances of the motor, including asymmetric air‐gap magnetic field and larger torque ripple. To solve this problem, this study analyses the relationship between the torque ripple and the stator‐rotor magnetomotive force (MMF) harmonics, determines the harmonic orders causing the torque ripple of the CP PM (CPPM) motor, and proposes an unequal‐turn four‐layer winding structure which can eliminate the determining harmonics in the stator MMF. Furthermore, the electromagnetic performances of the CPPM motors with the proposed winding structure and traditional CPPM motors are investigated by the finite‐element analysis. It is verified that the CPPM motor with the proposed structure has better motor performances.

Design of a Chamfered Structure on Consequent-Pole Vernier Permanent-Magnet Machine

The consequent-pole (CP) Vernier permanent-magnet (VPM) machine has been developed over the last decade. In VPM machine, the CP structure can produce considerable torque with a half volumn of the PMs compared with the regular structure, so the cost is reduced and the mechanical strength is increased. In this paper, an improvement of chamfering structure on a CPVPM machine is proposed to alleviate the flux leakage and increase the torque density. The chamfered structure is easily machined and will not influence the robustness of the rotor. The comparison results show that under the same volume and copper loss constraint, the proposed structure has smaller cogging torque, smaller torque ripple, larger torque density and larger power factor.

Brushless Wound Rotor Synchronous Machine Based on a Consequent-Pole Rotor Structure with Better Torque Attributes

This paper presents a subharmonic-based brushless wound rotor synchronous machine (BL-WRSM) topology with permanent magnet-assisted (PMA) and consequent-pole (CP) rotor structures to achieve better torque characteristics as compared to the conventional subharmonic-based brushless WRSM. The proposed topologies use the conventional high-efficient subharmonic field excitation technique to achieve a brushless operation and a lower volume of permanent magnet (PM) to achieve better average, starting, maximum, and minimum torques and lower torque ripple. A four-pole, twenty-four-slot (4-pole/24-slot) machine with conventional, PM-assisted (PMA), and consequent-pole (CP) rotor structures are developed in a JMAG-Designer 20.1 environment to carry out two-dimensional finite element analysis (2D-FEA). The developed machines are used to validate the operation and achieve electromagnetic and electromechanical performances of the proposed subharmonic-based BL-WRSM topologies with better torque attributes.

Effect of Pole Shaping on Torque Characteristics of Consequent Pole PM Machines

Consequent pole (CP) permanent magnet (PM) machines offer scope for reducing the quantity of PM material and hence cost compared to more conventional PM machine topologies of the same rating. In this type of machine, the rotor pole arc is usually optimized to realize the largest output torque with pole shaping methods used to reduce torque ripple. However, such approaches tend to be limited by constraints imposed on the pole shapes. It is a common practice to adopt similar PM and iron pole shapes, an approach that does not fully account for the different characteristics of PM and iron poles in CPPM machines, often leading to large even order harmonics in the airgap flux density. This article proposes a shaping method with a variable rotor profile and pole arc span being established by means of optimization by Genetic Algorithm. It is demonstrated that for a fixed quantity of PM material, different PM and iron pole shapes in combination with optimal PM and iron pole arc spans are essential for ensuring both maximum output torque and lower torque ripple when the due account is taken of flux leakage. It also demonstrates that since the flux density in the region under a PM pole is governed by the magnetic potential produced by magnets while it is governed by magnetic reluctance under iron pole, different PM pole and iron pole shapes are necessary to reduce the even-order harmonics in a CPPM machine and consequently to reduce torque ripple. The performances of optimized and more conventional CP machines are compared by finite-element method on 12-slot/8-pole prototype motors.

Suppression of Torque Ripple for Consequent Pole PM Machine by Asymmetric Pole Shaping Method

Consequent-pole (CP) permanent magnet (PM) machines have attracted considerable interest as a means of reducing machine cost through a marked reduction in the volume of PM required to meet a particular torque specification. However, the presence of a large torque ripple that can result from the CPPM structure can hinder their adoption in some applications, especially for the dominant third-order torque ripple. Although several design-specific modifications have been proposed to ameliorate torque ripple, the generalized principles underpinning this behavior have not been fully established. In this article, it will be illustrated that an aggregation of the fluctuations in inductance, back electromotive force, and cogging torque contributes to increased torque ripple. Meanwhile, an asymmetric pole shaping method is proposed to reduce the torque ripple, taking the dominant third-order torque ripple as an example. Both simulated and experimental results of the 12-slot&#x002F;8-pole prototypes show that compared to the symmetrical pole shaping model and the plain pole model, the proposed asymmetric shaping method is effective in reducing torque ripple.

Investigation on Symmetrical Characteristics of Consequent-Pole Flux Reversal Permanent Magnet Machines with Concentrated Windings

Consequent-pole (CP) permanent magnet (PM) configuration suffers asymmetric electromagnetic characteristics although it saves PM usage. The CP-based stator-PM synchronous machines are investigated in this paper, with particular reference to symmetrical issues. The electromagnetic performances of the CP-based stator-PM synchronous machines are firstly evaluated. Afterwards, the rule of even order harmonics cancellation is presented for different slot/pole number combinations and winding layouts, based on which symmetrical phase flux-linkages can be obtained although the unbalanced magnetic flux naturally occurs. Moreover, based on the three-dimensional finite element analysis, the unipolar end leakage-flux caused by the asymmetric magnetic field is identified, and the risk of the shaft magnetization is revealed. Finally, a pair of prototype machines are fabricated and measured to validate the analyses.

Design and Analysis of a New Dual-Stator Consequent-Pole Flux Reversal Machine With Triple-PM Excitation

This article proposes a new dual-stator consequent-pole (CP) flux reversal machine with triple-PM excitation (T-DSCPFRPMM), in which the two stators and rotor are all incorporated with CP permanent magnet (PM) arrangement. The employment of triple-PM excitation is beneficial to enhance the flux densities in the inner and outer air gaps. In addition, the ferromagnetic poles of rotor and stators are, respectively, used to modulate the magnetic field excited by stator-PM and rotor-PM, which introduces the bidirectional flux modulation effect into the proposed machine to enhance the torque production. The topology, operation principle, and design consideration of the proposed T-DSCPFRPMM are analyzed, respectively. The electromagnetic performances of the proposed machine under stator-PM excitation only, rotor-PM excitation only, and triple-PM excitation are evaluated and compared by finite-element analysis. The predicted results show that by using triple-PM excitation, the proposed machine can offer the superior torque production with low torque ripple, excellent overload torque capability, high efficiency and high-power factor, which are desirable for direct-drive applications.

Characteristics Analysis of Consequent-Pole Ferrite Magnet Vernier Machine Using Novel Equivalent Magnetic Circuit

This study deals with a consequent-pole (CP) vernier motor with low-cost ferrite magnets. To investigate the magnetic behavior of the CP permanent magnet vernier machine (CP-PMVM) quantitatively, two magnetic equivalent models are newly proposed which are applied to estimate the main and the modulation flux densities in air gap, respectively. Using the proposed models, it is revealed that the CP structure substantially reduces the effective air-gap length, and thus, a CP-PMVM with half number of magnets has much higher modulation flux density than that of a regular surface PM vernier machine (SPMVM). Consequently, the CP-PMVM is expected to able to keep the vernier effect high even with thick ferrite magnets, producing higher back electromotive force (EMF) than the SPMVM does. Moreover, large variation of air-gap length due to thick magnet thickness leads to a considerable advantage of reluctance torque. For a proto-designed CP-ferrite PMVM, the electromagnetic characteristics, such as main and modulation flux densities, back EMF, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> inductances, and torque, have been investigated by using the proposed method as well as finite-element (FE) method. In addition, through the demagnetization analysis, it is proved that the proposed CP-PMVM has certainly enough antidemagnetization capability, whereas an SPMVM with ferrite magnets loses its magnetism. From the analysis results, it is confirmed that the proposed machine with less magnet volume and low-cost ferrite magnets has higher torque compared with its SPM vernier counterpart. Finally, to validate the analytical and numerical analyses, experimental results are provided.

Multi-objective optimization of high torque density segmented PM consequent pole flux switching machine with flux bridge

Due to double salient structure, Flux Switching Machines (FSMs) are preferred for brushless AC high speed applications. Permanent Magnet (PM) FSMs (PM-FSMs) are suited applicants where high torque density (T den ) and power density (P den ) are the utmost requisite. However conventional PM-FSMs utilizes excessive rare earth PM volume V PM , higher cogging torque T cog , high torque ripples (T rip ) and comparatively lower (T den ) and P den due to flux leakage. To overcome the aforesaid demerits, a new high (T den ) Segmented PM Consequent Pole (CP) FSM (SPMCPFSM) with flux bridge and barrier is proposed which successfully reduces V PM by 46.52% and PM cost by 46.48%. Moreover, Multi-Objective Optimization (MOO) examines electromagnetic performance due to variation in geometric parameters for global optimum parameters with key metric such as flux linkage (Φ pp ), flux harmonics (Φ THD ) average torque (T avg ), T cog , T rip , T den , average power (P avg ) and P den . Analysis reveals that MOO improve Φ pp by 22.68%, boost T avg by 11.41%, enhanced P avg by 4.55% and increased T den and P den by 11.41%. Detailed electromagnetic performance comparison with existing state of the art shows that proposed SPMCPFSM offer T avg maximum up to 88.8%, truncate T rip up to 24.8%, suppress T cog up to 22.74%, and results 2.45 times T den and P den .

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 Torque Improvement Mechanism in Emerging Switched Flux PM Machines

This article aims to investigate and reveal the torque enhancement mechanism in several emerging switched flux permanent magnet (SFPM) machines using a unified torque equation with an improved winding factor function. Based on a hybrid finite-element (FE)–analytical method, the torque contributions of the major air-gap field harmonics in the conventional, C-core and E-core, and consequent-pole (CP) SFPM machines are identified and quantified by taking a conventional 12-stator-slot/13-rotor-tooth (12s13r) SFPM machine as a benchmark, which shows that the dominant torque proportions are contributed by the low-order field harmonics due to the amplification effect of the gear ratio. Besides, a low-order field harmonic impeding effect is observed in the conventional and C-core SFPM structures, resulting in a compromised torque capability. Whereas since the auxiliary teeth and stator iron bridge designs provide relatively lower magnetic reluctances for low-order harmonics, the E-core and CP structures can produce improved low-order harmonics and higher torques than the conventional one. Finally, some experiments on a CP-SFPM machine are conducted to validate the theoretical and FE analyses.

Torque Performance Enhancement in Consequent Pole PMSM Based on Magnet Pole Shape Optimization for Direct-Drive EV

Developing a permanent magnet synchronous machine (PMSM) for direct-drive electric vehicle (EV) has challenges such as obtaining high torque density and low torque ripple. The PMSM should have high pole numbers owing to low-speed operation, thereby increasing the use of rare earth magnets and cost. Therefore, in this article a consequent pole (CP) rotor topology is proposed in which the permanent magnet (PM) volume is reduced when compared with conventional surface PMSM (SPMSM). However, replacing south poles in an SPMSM with induced steel poles can increase torque ripple and reduce torque density. In order to improve torque density in a CP PMSM, structural modifications such as multilayer windings and non-ferromagnetic barriers have been proposed in the literature. These modifications increased the torque density while increasing the torque ripple. Therefore, this article proposes a novel two-level optimization method based on gradient descent algorithm, to address the challenges of improving torque density and reducing torque ripple simultaneously in a CP PMSM. Initially, an expression for the magnet pole arc angle is derived for CP PMSM based on magnetic equivalent circuit. A two-level optimization is performed on a baseline CP PMSM to determine the optimal magnet pole arc. The torque production and torque ripples of the optimized design are validated by simulation and experimental results.

Consequent Pole Permanent Magnet Machine With Modular Stator

Owing to a group of permanent magnets (PMs) with the same magnetization direction are replaced by salient iron core, the consequent-pole (CP) PM machines generally suffer from asymmetry flux density. This will leads to the even-order back-EMF harmonics, which have negative influence on the electromagnetic performance. It is widely known that the even-order back-EMF harmonics cannot be eliminated for the machines with odd back-EMF phasor belongs to one phase in one machine periodicity, i.e., ${\boldsymbol{N}_0}$ is odd ( ${\boldsymbol{N}_0} = {\boldsymbol{N}_{\boldsymbol S}}/\boldsymbol{mt}$ , where ${\boldsymbol{N}_{\boldsymbol S}}$ is the number of slot for one machine, t is the unit sub-machine periodicity, m is the number of phase). Hence, this paper proposes a general modularization method solving this problem. The elimination principle of even-order back-EMF harmonics in the modular stator (MS) is explained by the star of slots. Further, the MS with auxiliary winding (AW) and auxiliary teeth (AT) are proposed to improve the electromagnetic performance of the MS CP (MSCP) PM machine. Then, the electromagnetic characteristics, including open circuit field distribution and back-EMFs, torque characteristics, unbalanced magnetic force (UMF), loss distribution characteristics as well as efficiency contours are comprehensively compared. Finally, the MSCP PM machine with auxiliary winding (MSCP-AW) is fabricated and tested to verify the theoretical analysis as well as the finite element (FE) results.

Effect of angle displacements on electromagnetic performance of dual three‐phase consequent‐pole permanent magnet machine

The machine with consequent pole (CP) rotor can improve the utilisation ratio of permanent magnet (PM). However, all the N poles or S poles are replaced by salient rotor iron, leading to the asymmetric air-gap flux density. It potentially results in even-order back electromotive force (back-EMF) harmonics and unbalanced magnetic force. This study aims to investigate the influence of various angle displacements (i.e. 0°, 15°, 30° and 60°) on the electromagnetic performance of the dual three-phase PM machine with CP rotor. The electromagnetic characteristics, including air-gap flux density, back-EMF, torque performance, short circuit current, braking torque and PM demagnetisation under both healthy and fault conditions are compared comprehensively. Finally, the 24-slot/22-pole prototype machine is manufactured. The back-EMF waveforms and static torque are measured and compared to the finite-element predicted results to validate the theoretical analysis.

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.

Performance comparison between consequent‐pole and inset modular permanent magnet machines

This paper proposes some consequent-pole (CP) modular permanent magnet (PM) machines with different flux gap (FG) widths and slot/pole number combinations. The corresponding inset modular PM machines having the same magnet volume are also presented for comparison. It has been demonstrated that the output torques of the consequent pole modular machines are always higher than those of the inset modular machines regardless of FG widths and slot/pole number combinations. Other electromagnetic performances such as back-EMF, cogging torque, and iron losses etc. are calculated by 2D FEA software and compared as well. The advantages and disadvantages of consequent and inset modular PM machines are summarised here.