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Comparison of basic stator winding configurations. (a) Distributed with SPP = 1. b) Concentrated winding with SPP = 0:5.
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A design approach is presented for achieving optimal flux-weakening operation in surface permanent-magnet (SPM) synchronous machines by properly designing the machine's stator windings using concentrated, fractional-slot stator windings. This technique makes it possible to significantly increase the machine inductance in order to achieve the critic...
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... is to present a design approach for achieving optimal flux-weakening operation in SPM ma- chines by properly designing the machine's stator windings using concentrated, fractional-slot stator windings. Con- centrated windings refer to windings that encircle a single stator tooth, eliminating any end-winding overlap with other phase windings. Fig. 1 shows a comparison between con- ventional distributed and concentrated windings. The term "fractional slot" in this paper refers to stator windings with slot-per-phase-per-pole (SPP) values less than ...
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... ) distributed integral-slot windings, among which the one- slot/pole/phase configuration shown in Fig. 1(a) is very popular, especially in the case of brushless dc machines; 2 ) concentrated fractional-slot windings, among which the 0.5-slot/pole/phase shown in Fig. 1(b) is the most popular. Concentrated windings offer some significant advantages over distributed windings. These include: 1) significant reduc- tion in the copper volume and ...
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... ) distributed integral-slot windings, among which the one- slot/pole/phase configuration shown in Fig. 1(a) is very popular, especially in the case of brushless dc machines; 2 ) concentrated fractional-slot windings, among which the 0.5-slot/pole/phase shown in Fig. 1(b) is the most popular. Concentrated windings offer some significant advantages over distributed windings. These include: 1) significant reduc- tion in the copper volume and copper losses in the end region; 2) significant reduction in the machine total length [3], [4]; 3) reduction in machine manufacturing cost; and 4) compati- bility ...
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... closed-form analytical tools have been used to predict the SPM machine performance over the full required speed range. The calculated motoring output power vs. speed envelope is pro- vided in Fig. 9, and the output torque vs. speed envelope is pre- sented in Fig. 10. It can be seen that a very wide constant-power speed range is achieved, meeting the design requirements of at least 10 : 1. More specifically, the machine can deliver 4 kW at 600 r/min and 6 kW at 6000 r/min. (The design requirements are shown as a straight line in Fig. ...
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... predicted air-gap magnetic flux density distribution produced by the uniformly-magnetized rotor magnets (162 electrical degrees) and the corresponding phase and line-to-line back-EMF waveform at 600 r/min are shown in Fig. 11. It can be observed that the phase-to-neutral back-EMF waveform has higher harmonic content than the line-to-line back EMF. It will be shown below that this difference is caused by a third har- monic voltage component that appears in the phase-to-neutral voltage but disappears automatically in the line-to-line back EMF for ...
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... magnet flux axis and the phase winding axis (mechanical rad), ( ) is the rotor angular velocity [electrical rad/s), is the th har- monic winding factor, and is the magnitude of the th har- monic component of the air-gap magnet flux density distribution (T). The harmonic spectrum of the air-gap flux density produced by the magnets is shown in Fig. 12. It can be seen that other than the fundamental component, the only spatial components that have significant values are the third, fifth, and seventh harmonics. The corresponding winding factors for these three harmonics derived for the concentrated fractional-slot stator winding (SPP ) are: , , ...
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... period of the predicted cogging torque of the SPM ma- chine is shown in Fig. 13. The spatial period of the cogging torque waveform is 1.43 mechanical degrees. This result is con- sistent with the fact that the least common multiple of 36 and 42 is 252, determining the cogging torque spatial ...
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... has been used to confirm the electromagnetic parame- ters and performance characteristics of the 36-slot/42-pole SPM machine calculated using the closed-form analytical model. The FEA packages used for this analysis were MagNet 2D by In- folytica and Maxwell 2D by Ansoft. Fig. 14 shows a comparison of the phase-to-neutral back-EMF waveforms predicted by FEA and closed-form analysis as a function of rotor position at 600 rpm. The dif- ference between the predicted peak fundamental values of derived from the closed-form analysis and FEA is 0.47%, indicating excellent agreement. The corresponding difference in the ...
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... between the predicted peak fundamental values of derived from the closed-form analysis and FEA is 0.47%, indicating excellent agreement. The corresponding difference in the two predictions of is approximately 7.5%. This error is considered reasonable for this machine because the leakage inductance is very high and difficult to accurately predict. Fig. 15 shows a plot of the FEA-predicted torque waveform at the machine's corner point speed (600 r/min) with sinusoidal current excitation (no current harmonics). It shows that the ma- chine is capable of producing the required rated torque (64 N m) during motoring operation at the corner point speed. The torque ripple in the FEA-calculated ...
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... torque predictions from the FEA and closed-form analysis also agree within a few percent. Corresponding FEA torque predictions at maximum speed (6000 r/min) confirm the desired 10 : 1 constant-power speed range. Fig. 16 shows the FEA-predicted cogging torque over one period of 1.43 mechanical degrees, confirming the expected periodicity. In addition, the amplitudes of the predicted cogging torque using FEA and closed-form analysis agree quite ...
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Citations
... This is because the structural saliency is filtered out by the field modulation effect. The fractional-slot concentrated winding has been employed in non-salient surface PM machines to improve field-weakening performance by introducing extra slot leakage harmonics and inductances [20]. However, these additional leakage harmonics and inductances are particularly detrimental to PMVMs, I leading to deteriorated power factor and increased core losses. ...
... For PMVMs with negligible saliency, the voltage limits turn to be the dashed circles that shrink as speed increases, as shown in Fig. 8. It is well known that optimal field-weakening control can be achieved when the characteristic current I ch equals the current limit [20]. I ch indicates the center of voltage limit circles and can be calculated as ...
This article investigates a permanent magnet vernier machine (PMVM) equipped with positive-mutual-coupling (PMC) winding. The conventional winding layout typically presents negative-mutual-coupling (NMC) among the three-phase windings due to the 120 spatial phase shift. It is illustrated that in the NMC winding, the q-axis self- and mutual phase flux linkages are superimposed on each other. In contrast, the proposed PMC winding exhibits counteracted q-axis self- and mutual phase flux linkages, which contributes to reducing the terminal voltage. The generic methodology to design PMC winding is presented and exemplified on a 24-slot, 5-armature pole pair, and 19- rotor pole pair PMVM. Finite element analysis shows that the proposed PMC PMVM could improve the rated power factor and widen the constant torque region. With reduced terminal voltage and more voltage margins, the PMC PMVM can employ a higher q-axis current to generate torque, thus significantly enhancing the output torque and power factor during field-weakening operations. As a result, the output power capability and constant power speed range (CPSR) are improved dramatically. Finally, a PMC PMVM prototype is manufactured to validate the efficacy of PMC winding in improving field-weakening and power factor.
... 2. High least common multiple (LCM) of the number of high pole number slots: It is proportional to the cogging torque frequency, so the higher it is the smaller the cogging torque is. 3. High and even great common divisor (GCD) of number of poles and number of slots: The higher the number, the more symmetrically the rotating magnetic field occurs, reducing noise and vibration. 6,7 The design of a relatively efficient motor can begin by considering three possible considerations. However, motor design does not necessarily follow these considerations. ...
Electric devices called motors, which have a history of 100 years, are the devices that use the most electricity in the world. Therefore, the development of high-efficiency motors leads to efficient power use and carbon neutrality. In motor design, the combination of poles and slots is very important. It affects many characteristics including back electromotive force waveform and magnitude, torque and torque ripple, cogging torque, noise and vibration, and efficiency. The most widely used combination of poles and slots is 8 poles and 12 slots. And recently, 8-pole 9-slots are also attracting attention for their various advantages. This paper compares the characteristics of 8-pole 12 slots and 8-pole 9 slots through computer simulation. And to overcome the weaknesses of 8 poles and 9 slots, a multiple of the pole-slot combination is applied. Finally, the comparative values are verified through an experiment.
... Moreover, such high negative d-axis current may lead to irreversible demagnetization of the PMs and high torque ripple. For the nonsalient motors where the difference between the d-and q-axis inductances (L d -L q ) is negligible, e.g., surfacemounted PMSMs [20], flux-switching PM motors [21], [22], vernier PM motors [23], the electromagnetic torque T e in (2) becomes as follows: ...
... The air-gap flux density produced by the outer rotor PMs with the modulation effects from the open-slot teeth along the stator inner diameter, B vernier , can be expressed as follows: Based on the winding function theory [26], [27], the winding function of one stator phase winding, e.g., phase-A of winding II, can be expressed as follows: (19) where N ph_WII is the number of turns in series per phase of winding II and k WII is the winding factor of winding II. Hence, the back EMF of winding II E WII can be expressed as follows: 20) where e I is the back EMF of winding II and k e_WII is the back EMF coefficient. Equation (20) can be rewritten in vector form as follows: ...
... Hence, the back EMF of winding II E WII can be expressed as follows: 20) where e I is the back EMF of winding II and k e_WII is the back EMF coefficient. Equation (20) can be rewritten in vector form as follows: ...
In order to achieve wide speed-range operation in traction applications, an investigation of a permanent magnet (PM) flux-modulated motor with a mechanical flux-weakening solution is presented in this article. This PM flux-modulated motor consists of two sets of windings, i.e., windings I and II, and two rotors, i.e., the outer rotor and the inner rotor. The two sets of windings are connected in series. By adjusting the inner rotor position, the phase angle between the two voltage vectors of windings I and II is accordingly changed. Hence, with the speed increasing, even though the magnitudes of the two voltage vectors of windings I and II are increased, the voltage magnitude of the total series-connected windings can be maintained (instead of increased) within the voltage limit. As a result, a mechanical flux-weakening solution for wide speed-range operation is achieved. Differing from conventional electrical flux-weakening solutions, this mechanical solution shows the advantage that the flux-weakening capability is not heavily dependent on the power rating of the motor. A comparative study is conducted between the presented PM flux-modulated motor with the mechanical solution and a conventional interior PM synchronous motor (IPMSM) as well as a surface-mounted PM synchronous motor (SPMSM) with the electrical solution. The results indicate that compared to the IPMSM and SPMSM, the presented PM flux-modulated motor exhibits the advantages of high torque/power density, high torque per PM volume, and high flux-weakening capability. Finally, a prototype of the presented PM flux-modulated motor is fabricated, and experimental validation of the mechanical flux-weakening solution is provided.
... It is shown that the poor flux-weakening capabilities of the three machines are obvious. For the slotless surface mounted AFPM machines, the inductance values are low due to the large effective air gaps in the machines' magnetic circuit, which is limited to lower the magnet flux linkage [25]. Therefore, it causes limits on the DRSAFPM machines' constant-power region during flux-weakening operation. ...
Axial-flux permanent magnet (AFPM) machines are gaining popularity in low speed and high torque applications due to their high torque density, high efficiency and compact structure. In this paper, a dual-rotor slotless (DRS) AFPM machine equipped with equidirectional toroidal winding (EDTW) is proposed and compared with that equipped with conventional single layer and double layer concentrated windings (SL and DLCWs). Firstly, the differences between the DRSAFPM machine with EDTW and that with conventional CWs in coil layout, electromotive force (EMF) and winding magnetomotive force (MMF) are revealed. Considering the special coil layout of the EDTW, the coil factor and size equations of the DRSAFPM machines with EDTW and conventional CWs are presented. Secondly, the electromagnetic performance including air-gap field, back-EMF, torque and efficiency of the DRSAFPM machines with EDTW and conventional CWs are analyzed based on the three-dimensional finite element method (3D-FEM). The simulation results validate the correctness of the coil factor and size equations and indicate the EDTW-DRSAFPM machine has superiority in back-EMF amplitude and torque density. Finally, a prototype of the EDTW-DRSAFPM machine is manufactured and tested, which validates the feasibility of the EDTW-DRSAFPM machine and the correctness of the analysis.
... The basic purpose of PMVM was to achieve low-speed high torque performance but on the other hand, this feature limits its use in many applications such as EVs and many other high-speed applications. Owing to the higher inductance of the windings due to the yokeless structure of the rotor as mentioned in [24], it is highly desirable to achieve higher speeds because of increased chances of flux weakening as mentioned in [25]. Experimental studies at no-load and load conditions have been performed to evaluate the performance capabilities including torque profile and back EMF. ...
Permanent magnet vernier machines (PMVM) are recently proven to be a good candidate for extended-speed operation in the constant power region. In this paper, a dual-airgap PMVM having a yokeless rotor has been presented for extended-speed operation. The PMVM model is designed with two stators and a sandwiched rotor without an iron yoke. To achieve the extended speed operation, the yokeless structure of dual airgap PMVM benefits from the increased inductance which makes it possible to operate at higher speeds. For this purpose, the prototype of this machine is built, and experimental testing is performed to verify its performance in a constant power region. Electromagnetic performance such as back EMF and output torque at high speeds are analyzed. The experimental results are compared with those obtained using finite element analysis which confirms the ability of dual airgap PMVM having a yokeless rotor to perform well at higher speeds in a constant power region.
... For example, two independent research groups presented possible combinations of machine parameters for the Ich = 1 pu condition but provided little insight into how to design the machines to achieve the performance goals with regard to the electromagnetic aspects [6,7]. Other studies led to the development of a design method to satisfy the optimal FW condition of Ich = 1 pu together with analytical expressions for calculating the machine inductances for surface-mounted permanent magnet (SPM) machines equipped with fractional-slot concentrated windings (FSCW) [10,11]. However, the impact of various IPM machine parameters on achieving the ideal FW conditions has not been fully addressed. ...
... Various combinations of machine parameters can be used to ensure that the Ich = 1 pu condition is satisfied [6,7]. Large machine inductances are often considered to be of key importance to comply with this condition, and details regarding the inductance calculations for FSCW-SPM machines have been reported [10,24]. This section presents an investigation of the impact of machine geometries that were not fully covered in past work with the aim of designing a machine that satisfies the desired condition while minimizing the degradation resulting from the other important performance characteristics of traction PM machines. ...
This paper presents a detailed process for the design of interior permanent magnet synchronous machines (IPMSMs) for electric vehicle (EV) applications. First, a comprehensive design process featuring two objectives and three constraints is proposed to realize an optimal IPMSM design that can satisfy the key performance requirements for an EV application. The objectives and constraints were carefully selected and designed to obtain a balance between performance, efficiency, and cost. Because the inductances and magnet flux linkage of the machine are key design parameters for attaining optimal flux-weakening capability, the impact of the machine dimensions on these two parameters is thoroughly investigated and explained using both analytical and numerical techniques. Additional analyses including normalized key performance metrics and the impact of short-circuit faults in PM machines with three different characteristic current values (1, 1.3, and 2.6 pu) are also provided, highlighting the advantages and limitations of the three baseline designs.
... Also, in some methods, the optimized distribution of the turns in slots does not consider the requirement of the uniform tooth width in the core which may cause magnetic field saturation of the tooth and leads to the excessive heat and losses in the machine. Also, reduces the flux weakening capability [25][26]. Therefore, in the proposed design method, the tooth width is kept constant for avoiding these issues. ...
... Hence, σ is slot span of a quarter of stator periphery. The Fourier series expansion of a general optimized FSCW with P pole can be expressed as [26] ...
This paper presents a new optimized fractional slot concentrated winding (FSCW) design for torque ripple minimization
in permanent magnet motors through space harmonic reduction. The proposed design offers the minimum total harmonics
distortion in the magnetomotive force (MMF) produced by the winding whereas winding factor of the working harmonic
component is set to the maximum value. A detailed mathematical derivation of the winding function is presented for
general symmetrical FSCW using Fourier series expansion. The optimization methodology presented for the new optimized
FSCW design results in optimal number of conductors at optimal slot positions while keeping slot pitch equal in the
core design. The harmonic analysis of various examples of FSCW is presented which shows a significant reduction in
the non-working harmonics in the proposed optimized design. A 24-slot 22-pole permanent magnet synchronous motor is
designed and analyzed using the two-dimensional finite element method. The magnetic analysis of motors shows that
the non-working harmonics in the air-gap flux distribution are minimized in the case of proposed design as obtained
from the analysis of winding functions. The dynamic analysis shows a substantial improvement in the performance of
proposed FSCW machine over the conventional machine.
... Low-speed and high-torque permanent magnet motor can realize the direct contact between power and load, cancel the mechanical transmission equipment such as reducer, shorten the transmission link to the greatest extent, maximize the energy transfer efficiency, and then be widely used in industrial production, wind power generation, mining machinery and other fields [1][2][3]. The fractional slot concentrated winding (FSCW) has many advantages, such as simple structure, short winding ends, reducing copper loss and end copper volume, improved motor efficiency, and small cogging torque [4][5][6][7][8]. More importantly, it effectively solves the difficulty of the low-speed and high-torque permanent magnet motor with many poles and limited slots. ...
The fractional slot concentrated winding structure effectively solves the difficulty of low‐speed and high‐torque permanent magnet (PM) machines with a large number of poles and slots, but it also brings a wealth of magnetomotive force (MMF) harmonic. The winding function method is used to compare and analyze the stator MMF distribution and harmonic content of the fractional slot PM machines with different pole and slot combinations, and the cogging torque waveform and torque ripple are calculated by the finite element method. The influence of pole and slot combination on radial force and vibration modes of fractional slot PM machines is studied. The main vibration mode can be determined from the lowest order of radial force harmonics. The results show that in a fractional slot PM motor, the radial force is the main cause of noise and vibration, rather than the cogging torque and torque ripple. The dominant radial force is mainly produced by the interaction of rotor field harmonics and armature reaction field harmonics, and the vibration and noise will significantly increase with the decrease of the dominant vibration mode order, which largely depends on the pole and slot combination. This paper provides a certain reference for the selection of pole and slot combination in the electromagnetic design process of low speed high torque fractional slot PM motors. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.
... Part of the specification listed in Table 8 and shown in Figure 11 is to deliver a continuous output power of 30 kW from the base speed (2800 rpm) up to the maximum speed (14,000 rpm). In order to accomplish this condition, the machine should be optimized to have an optimal FW operation by fulfilling the condition in Equation (4), as explained in [65]. All the designs have been optimized to satisfy that condition and have a characteristic current near 200 Arms. ...
This paper covers a new emerging class of electrical machines, namely, Magnetic Gears (MGs) and Magnetically Geared Machines (MGMs). This particular kind of gears/machines is capable of either scaling up or down the revolutions-per-minute to meet various load profiles as in the case of mechanical gearboxes, but with physical isolation between the rotating components. This physical isolation between the rotational components leads to several advantages in favor of MGs and MGMs over mechanical gearboxes. Although MGs and MGMs can potentially provide a solution for some of the practical issues of mechanical gears, MGs and MGMs have two major challenges that researchers have been trying to address. Those challenges are the high usage of rare-earth Permanent Magnet (PM) materials and the relatively complex mechanical structure of MGs and MGMs, both of which are a consequence of the multi-airgap design. This paper presents designs that reduce the PM rare-earth content for Electric Vehicles (EVs). Additionally, the paper will ensure having practical designs that do not run the risk of permanent demagnetization. The paper will also discuss some new designs to simplify the mechanical structure.
... Of particular interest are fractional-slot PMSMs (FSPMSMs), which are reputed by their intrinsic high fault-tolerance capability. Basically, these machines are characterized by a very weak magnetic coupling between the armature phases [1]. Consequently, a faulty phase does not affect the operation of the healthy ones. ...
... These are arranged according to the following sequence: two slots of N H + N L conductors followed by a slot of 2N L conductors. The winding arrangement is achieved following repetition of the previous sequence 1 3 N s times. Figure 7 shows the variation in the number of turns per coil ratios N H N and N L N with respect to the number of phases. ...
This paper deals with the winding arrangement of multi-phase fractional-slot permanent magnet (PM) synchronous machines (FSPMSMs), with emphasis on the enhancement of their open-circuit fault-tolerance capability. FSPMSMs are reputed by their attractive intrinsic fault-tolerance capability, which increases with the number of phases. Of particular interest is the open-circuit fault-tolerance capability, which could be significantly enhanced through the parallel connection of the coils or suitable combinations of the coils of each phase. Nevertheless, such an arrangement of the armature winding is applicable to a limited set of slot-pole combinations. The present work proposes a design approach that extends the slot-pole combinations to candidates that are characterized by a star of slots including three phasors per phase and per winding period. It has the merit of improving the tolerance against open-circuit faults along with an increase in the winding factor of multi-phase machines. Special attention is paid to characterization of the coil asymmetry required for the phase parallel arrangement. A case study, aimed at a finite element analysis (FEA)-based investigation of the open-circuit fault-tolerance of a five-phase FSPMSM, is treated in order to validate the analytical prediction.
