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A hybrid analytical and lumped-parameter thermal model is proposed in this paper to estimate the transient and steady-state two- and three-dimensional (2/3-D) spatial magnet temperature distributions for an interior permanent magnet synchronous machine (IPMSM). On the basis of a lumped-parameter thermal model (LPTM), the magnet analytical thermal models (ATMs) are synergized to establish the hybrid thermal model. By utilizing the transient or steady-state boundary conditions calculated by the LPTM, the ATMs are obtained by solving the heat conduction equations to estimate the spatial magnet temperature distributions in the 2-D horizontal-vertical and axial-vertical planes, which can also be extended to the 3-D temperature distribution by utilizing the multi-slice method. Meanwhile, the non-uniform magnet eddy current loss is also considered. Finally, both electromagnetic-thermal coupled finite element analysis method and experiments are used for verification based on a totally enclosed IPMSM. [ABSTRACT FROM AUTHOR]

Lumped-parameter thermal models (LPTMs) have been widely used to estimate critical temperatures in permanent magnet synchronous machines (PMSMs). However, in some cases, they may be incapable of predicting the hotspots and even cause temperature misestimation. In this paper, the synergized lumped-parameter and sub-domain thermal models are proposed for surface-mounted PMSMs to track the hotspots in the most vulnerable components, i.e., active/end-windings and rotor magnet. Firstly, the “T-type” elementary network based LPTM is developed to predict the average temperatures in main components and the boundary conditions. Secondly, the boundary conditions are applied to three sub-domain thermal models for the active/end-windings and the rotor magnet to predict the respective hotspots and to further correct the misestimated average temperatures. Finally, the proposed synergized thermal model is verified by the experiments on a prototype surface-mounted PMSM under various load conditions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Asymmetric interior permanent magnet (AIPM) rotor topologies can achieve torque enhancement in IPM synchronous machines without the increase of PM usage due to utilizing magnetic-field-shifting (MFS) effect by reducing the current angle difference between maximum PM and reluctance torque components. This paper investigates the influence of armature reaction on MFS effect in AIPM machines. A general model of IPM machines considering MFS effect is analytically developed and the AIPM and IPM machines using the same stator, rotor diameter and total PM amount are comparatively studied. It shows that the armature reaction affects the MFS effect in both AIPM and IPM machines and the influence is more significant in AIPM machine. The relationships between MFS effects in PM flux-linkage and inductance characteristics and current angles for maximum PM and reluctance torque components are revealed. It confirms that the change of current angles of torque components is due to the MFS effect in PM flux-linkage and inductance characteristics in both AIPM and IPM machines. Besides, the developed machine model considering MFS effect is verified by finite element analysis. Finally, a small-scale AIPM machine prototype is fabricated and measured to validate the finite element analysis. [ABSTRACT FROM AUTHOR]

In this paper, a high-speed permanent magnet (HSPM) motor having 6-slot/2-pole (6s/2p) number combination and 2 coil-pitch windings are developed for domestic appliance application. Two HSPM motors with different layouts of 2 coil-pitch windings are optimized and their electromagnetic performances are evaluated. The best winding configuration is then identified for shorter motor axial length and larger torque density. Since 3-slot/2-pole (3s/2p) HSPM motors with non-overlapping windings have the same winding factor, a comparison between 3-slot and 6-slot motors is also conducted, particularly for torque density, losses, and unbalanced magnetic force (UMF). It shows that 6s/2p PM motors with 2 coil-pitch windings are suitable for high-speed application without UMF and less rotor PM loss. Finite element predicted electromagnetic performances are validated by experiments made on two prototype motors. [ABSTRACT FROM AUTHOR]

A novel asymmetric interior permanent magnet (AIPM) machine is proposed in this paper for electric vehicle application. It has a skewed V-shape permanent magnet (PM) cavity, two PMs with different dimensions and an additional flux barrier outside the V-shape cavity in each pole. This asymmetric rotor topology can inherently utilize the magnetic-field-shifting (MFS) effect to reduce the current angle difference between the maximum PM and reluctance torque components, thereby enhancing the maximum synthetic torque with the same PM usage. The influences of cavity positions in the proposed AIPM and an existing AIPM with extra flux barrier inside the V-shape cavity are investigated and compared using finite element analysis. It is found that the proposed structure with outside flux barrier has higher average torque than the one with inside flux barrier. Both AIPM topologies are designed with the same stator, rotor diameter, and PM usage as the conventional V-shape IPM benchmark for Prius 2010. Electromagnetic, mechanical and steady-state thermal performance of three machines are compared. The results confirm that the proposed AIPM machine can achieve significant torque enhancement due to utilizing MFS effect, compared with the existing AIPM and the IPM benchmark. Finally, a small prototype of the proposed AIPM machine is designed, manufactured and tested to validate the FE analysis. [ABSTRACT FROM AUTHOR]

Hybrid excited machines, with synergies of permanent magnet (PM) and wound field (WF) excitations, exhibit high torque density as well as controllable flux and are perceived as promising candidate for variable speed application. A novel doubly salient hybrid excited (DSHE) machine with non-overlapped field winding is presented in this paper. It inherits simple structure of conventional doubly salient PM (DSPM) machine and facilitates the regulation of magnetic field by field winding. The electromagnetic performances of the proposed machine with different stator and rotor pole number combinations are investigated by finite element method (FEM), confirming these advantages. Furthermore, the effect of iron bridge on the hybridization between PM and WF excitations is analyzed to obtain a trade-off between high torque density and wide flux regulation range with the frozen permeability method (FPM). It is revealed that the proposed DSHE machine possesses higher power and fault tolerance at flux weakening region compared with the DSPM machine, albeit with sacrificed torque density and efficiency with introduction of field winding. Finally, a prototype is fabricated and tested to validate the theoretical analyses. [ABSTRACT FROM AUTHOR]

This paper combines the use of multi-phase configurations and current harmonic injection methods to achieve significantly improved performance for doubly salient synchronous reluctance machines (DS-SRMs). In order to understand the torque production mechanism of multi-phase DS-SRMs with current harmonic injection, some general analytical torque models have been developed. The models are based on Fourier Series analysis of self- and mutual-inductances. It has been established that with current harmonic injection, the torque ripple of both 5-phase and 6-phase DS-SRMs can be significantly reduced and the average torque can be enhanced. It contrast, harmonic injection always has a detrimental impact on 4-phase machines. The investigations of losses and dynamic performance with current harmonic injection for multi-phase machine have also been carried out and demonstrated that the proposed method can improve the efficiency in constant torque region and maintain comparable performance to fundamental current supply in the flux weakening region. Experimental validation based on single layer, 6-phase, DS-SRM has been performed. [ABSTRACT FROM AUTHOR]

The induced voltage ripple in DC field windings can cause many problems in hybrid excitation machines (HEMs). It can generate ripple current in field winding, thus causing unsteady magnetic field excitation and hence additional torque ripple and losses. Besides, the torque and power density of hybrid excitation machines may be deteriorated as a result of the influence of the induced voltage ripple on field winding's excitation circuit, particularly under high-speed conditions. Based on a hybrid excitation switched flux machine (HESFM), the influence of stator slot and rotor pole number combination on no-load and on-load field winding induced voltage ripples are studied and compared by the finite element method (FEM). It reveals that the harmonic content and thus the peak-to-peak value of the field winding induced voltage ripple are closely related to the stator slot and rotor pole number combination at both no-load and on-load operating conditions. The FEM calculations are verified by experiments on a prototype HESFM. [ABSTRACT FROM AUTHOR]

Spoke array permanent magnet (PM) flux reversal machines (SAFRPMMs), which are suitable for low speed and high torque applications, are able to enhance torque density due to the flux focusing effect. In this paper, what influence both the number of PM per slot and the PM shape have on their electromagnetic performance are investigated. The results show that both the PM number and the PM shape have significant effects on the performance of SAFRPMMs, and proper selections are critical in designing high performance machines. When the PM number per slot is 2, the SAFRPMM exhibits the best electromagnetic performances, i.e., the highest torque, power, efficiency, and power factor. Meanwhile, by properly designing the PM shape, the torque can be further improved by around 11%. A prototype is made and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

In this article, a simple position error correction method is proposed to minimize the influence of parameter deviation on the model-based rotor position estimation, with the help of two sets of windings in a dual 3-phase permanent magnet synchronous machine (PMSM). In the proposed method, when each set of 3-phase windings is individually used for sensorless rotor position estimation, the nominal parameters that are set in each observer are identical but inaccurate, which leads to errors in the estimated rotor position from both observers. Since the error is varied according to the current level, small current pulses are injected respectively into d- or q-axis of one set (or both set) of 3-phase windings, which causes the difference between the rotor position estimation errors from two sets of 3-phase windings. This difference is subsequently used as the input of an updated controller to minimize the parameter deviation and the corresponding rotor position error. The proposed method is experimentally validated on a dual 3-phase PMSM system. [ABSTRACT FROM AUTHOR]

This article investigates some novel modular consequent pole PM machines (CPMs) with E-core and C-core stators. Different slot-pole number combinations including 12-slot/10-pole (Ns>2p) and 12-slot/14-pole (Ns<2p) have been investigated. Their static and dynamic electromagnetic performances have been investigated, e.g. the phase back-EMF, on-load torque, torque-speed curves, power factor-speed curves and also efficiency maps are compared. It is found that the existence of flux gaps (FGs) can improve the average torque of the 12-slot/14-pole E-core modular CPMs while the C-core structure can be a better candidate where relatively low torque ripple is desirable. Moreover, by selecting proper FG width, the 12-slot/14-pole E-core modular CPMs can achieve better flux-weakening capability and higher efficiency while the 12-slot/10-pole C-core modular CPMs can have higher power factors over the whole speed range. The finite element simulation results have been validated by a series of experiments using 12-slot/14-pole modular CPMs with both C-core and E-core stators. [ABSTRACT FROM AUTHOR]

Automotive starter-generator applications require a high peak torque for cranking and a wide speed flux weakening region for generation. In such applications, the pole-changing winding induction machine offers a wide speed flux weakening region with a low pole number and a high peak torque capability when operated with a higher number of poles. In this article, a 6-phase, electronic pole-changing winding induction machine with improved performance over the existing 3-phase pole-changing is discussed. Compared to the 3-phase 120o phase belt winding, the proposed 6-phase pole-changing winding induction machine shows a 15 % increase in peak torque due to improved winding factor. Finite element analysis is used to predict the torque capability, losses and efficiency of the 6-phase and 3-phase pole-changing winding induction machines. A 1kW induction machine is prototyped and the improved torque capability of the 6-phase pole-changing machines over 3-phase counterparts is experimentally validated under various operating conditions. [ABSTRACT FROM AUTHOR]

Hybrid excited (HE) machines have the synergies of high torque density and high efficiency of permanent magnet (PM) machines and excellent flux controllability of wound-field machines. The PMs and field coils (FCs) coexist in HE machines to provide excitations simultaneously, and can be coupled either in series or parallel. The topologies of HE machines are very diverse, which bring challenges in the selection and design of HE machines. Based on the partitioned stator (PS) platform, a pair of series and parallel HE machines having similar structures and PM usage are evaluated and compared to identify their merits and demerits. With the help of finite element analysis, the flux regulation, energy conversion capability, parasitic effects and irreversible demagnetization of the two kinds of the HE machines are comprehensively investigated and the guidance to the machine design is provided. A pair of prototypes are fabricated and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

In order to provide the general guidance in constructing the novel modular machines with redundant teeth, the available slot and pole number combinations based on the balanced conditions are summarized in this article. After the brief review of the machine structure, the general slot and pole number combinations are listed: Firstly, the conventional modular machines used to construct the proposed modular machines need to possess integer times of 3 repetitive machine units. Each machine unit should construct as a 3-phase type. Then, a redundant machine unit providing the redundant teeth for modularity is necessary. This redundant machine only has one pole pair to make sure the space waste is minimal. The slot number of this redundant machine is determined by the greatest common divisor of the slot and pole pair numbers of the conventional modular machine. Finally, the combination of the conventional modular machine and the redundant one generates the proposed modular machine. In order to clearly illustrate the influence of slot and pole number combinations on machine performance, four combinations are chosen as examples to be compared. A 42-slot/32-pole machine is prototyped and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

In this article, spoke array permanent magnet (PM) flux reversal machines (SAPM FRM), which feature spoke array PMs distributed along the stator inner surface, are proposed to improve the torque density. Compared with the conventional surface mounted PM flux reversal machine (SPM FRM), the proposed SAPM FRM can produce about 100% larger torque with negligible torque ripple, as well as higher efficiency and higher power factor. Two prototypes have been built and tested to validate the theoretical analyses. [ABSTRACT FROM AUTHOR]

In wound-field (WF) switched flux (SF) (WFSF) machines, the DC winding induced voltage pulsation causes current ripple in the DC winding and challenges the DC power source, and deteriorates the control performance. In this paper, the induced voltage pulsation in DC winding of five-phase WFSF machines is analyzed and its reduction methods are proposed. The cycles per electric period of the open-circuit and armature reaction induced voltage pulsation in DC winding are derived analytically. Modifying the airgap permeance by optimizing the rotor pole arc or chamfering the rotor pole surface, and axial pairing of rotor segments having rotor pole with different arcs are used to suppress the induced voltage pulsation in DC winding, with >90% average torque maintained. Finite element results show that, by optimizing the rotor pole arc, the peak-to-peak value of the induced voltage pulsation in DC winding can be effectively suppressed to 59.59%, 30.67%, 29.99% and 43.35% for the 10-stator-pole five-phase WFSF machines with 8-, 9-, 11- and 12-rotor-pole rotors, respectively. By applying rotor pole surface shaping, the induced voltage pulsation in DC winding peak-to-peak value can be effectively suppressed to 61.76%, 45.47% and 40.21% for the 8-, 9- and 12-rotor-pole machines, respectively, while by applying axial pairing, it can be suppressed to 46.89%, 7.16%, 15.64% and 12.04%, respectively. The 10-stator-pole/12-rotor-pole WFSF machines having the original rotor, optimized rotor, chamfered rotor and axial paired rotor are prototyped and the experiments validate the analytical and finite element results. [ABSTRACT FROM AUTHOR]

A novel parallel hybrid excited (HE) machine with wide flux regulation range is proposed in this paper. The flux paths of permanent magnet (PM) and field winding are separated to avoid irreversible demagnetization and achieve improved flux regulation capability. Since the field winding and armature winding are located in the same stator slots, open-winding drive circuit can be employed to feed biased ac excitation in one set of winding and solve the spatial confliction of conventional hybrid excited machine. Finite element (FE) method is utilized to analyze the electromagnetic performances of the proposed HE machine, in comparison with the original HE machine. It is revealed that the proposed HE machine exhibits lower PM excited back-electromotive force (EMF), which is beneficial to high speed fault tolerant operation. Besides, the torque density can be higher with flux enhancing, albeit with reduced PM usage. Finally, a prototype is manufactured and tested to validate the FE predictions. [ABSTRACT FROM AUTHOR]

This paper aims to comprehensively analyze the influence of number of permanent magnet (PM) pieces on electromagnetic performance of flux reversal permanent magnet (FRPM) machines. First, the unified analytical model of FRPM machines having different numbers of PM pieces is established, from which the optimal number of PM pieces and the corresponding rotor pole number can be identified. It shows that by employing the optimal number of PM pieces instead of the conventional two on each stator tooth, additional back-EMF component can be generated which is beneficial to boost the machine performance. Then, the influence of critical design parameters including stator slot opening ratio, split ratio, and stator slot number is investigated, providing a guidance to the design of FRPM machines aiming at maximum output torque. In addition, both finite element analyses and experimental tests are conducted to verify the analytical analyses. For 6-slot-stator FRPM machines, experimental results show that more than 40% higher output torque can be achieved in the machine with optimal number of PM pieces when compared to the conventional one. [ABSTRACT FROM AUTHOR]

Variable flux reluctance machines (VFRMs) are developed as magnetless electrical machines. To extend the application of VFRMs, the enhancement of torque density is a key during machine design. In this paper, a novel second-harmonic current injection method is developed for torque density enhancement for 6-stator-slot/4-rotor-tooth (6/4) VFRM. By using the analytical method, the optimal current profile with injected second-harmonic current is obtained. The average torque of 6/4 VFRM is improved by 20% with the proposed method under all load conditions. Moreover, the proposed current profile has fixed harmonic proportions and is easily applicable to machines with different specifications. All the conclusions are confirmed by both finite-element analyses and experimental results. [ABSTRACT FROM AUTHOR]

A total of three types of doubly salient synchronous reluctance machines have been comparatively studied to improve the torque performance using current harmonic injection methods. These machines are derived from the switched reluctance machines (SRMs) with different winding configurations, such as the double/single-layer mutually coupled SRMs (MCSRMs) and fully pitched SRMs (FPSRMs), by supplying them with sinewave current. Such current supply mode can lead to higher torque/power density and lower vibrations and acoustic noise compared with the conventional rectangular current supply. The proposed torque analytical model can predict the instantaneous torque of the doubly salient SRMs with sinewave current excitation and the current harmonics also can be selected in order to reduce the torque ripple and/or increase the average torque. It has been found that the third current harmonic injection shows the best performance for single-layer MCSRMs and FPSRMs because it improves the average torque and reduces the torque ripple at the same time. However, it has little influence on doubly-layer MCSRMs. To improve the torque performance of such machines, other harmonic currents, e.g., fifth and seventh, need to be used. Both static and dynamic tests have been carried out to validate the predictions. [ABSTRACT FROM AUTHOR]

DC winding induced voltage pulsation in the wound field synchronous machines (WFSMs) will cause dc winding current ripple, challenge the dc power supply, and deteriorate the control performance, especially at high speed. In this paper, the influence of dc winding configuration including the dc coil number and the parallel branch number on its induced voltage pulsation is investigated for WFSMs. Based on the modeling of both open-circuit and on-load dc winding induced voltages, the preferred dc winding configurations for WFSMs having various stator/rotor pole number combinations with double layer or single layer ac windings are obtained and validated by finite element (FE) analysis on four typical partitioned stator WFSMs (PS-WFSMs). A PS-WFSM prototype is built and tested to validate both analytical and FE analyses. [ABSTRACT FROM AUTHOR]

This paper proposes high-torque-density dual-stator permanent magnet machines with biased permanent magnet (PM) excitation in the inner stator. The developed machine can be geometrically considered as an outer-rotor stator PM machine plus a separate outer stator similar to the conventional fractional-slot machines. Consequently, the proposed designs feature two different stator structures. Meanwhile, two sets of armature windings are employed to improve the space utilization ratio and torque density. The machine topologies and operating principles are first described. In addition, the analytical models of the machine are introduced, which are utilized to optimize the stator/rotor pole combination as well as the power splitting ratio between two stators. This design optimization is performed in order to maximize the torque capability with the constraint of copper loss. The electromagnetic characteristics of the proposed machine with different inner stator structures are evaluated and compared by the finite-element (FE) method. Finally, an optimized dual-stator biased PM machines prototype is manufactured and tested to verify the FE analyses. [ABSTRACT FROM AUTHOR]

In this paper, four rotor shaping methods, i.e., eccentric circular, inverse cosine, inverse cosine with third harmonic, and multi-step shaping methods, are developed and compared for torque ripple mitigation in variable flux reluctance machines (VFRMs). By using a 6-stator-pole/7-rotor-pole (6/7) VFRM as an example, the design criterions and capabilities of these four methods are illustrated. It is found that all the rotor shaping methods are capable of torque ripple mitigation and applicable to all the VFRMs except those with 6k/(6i ± 2) k (k, i = 1, 2, 3…) stator/rotor pole combinations. Moreover, the inverse cosine with third harmonic and multi-step shaping methods are found to have the best performance. They are able to reduce the torque ripple by 90% at a cost of only 3% torque density reduction. A 6/7 VFRM with both conventional and shaped rotors is prototyped and tested for verification. [ABSTRACT FROM AUTHOR]

This paper analytically derives the optimal third harmonic current to improve the output torque in five-phase surface-mounted permanent magnet (SPM) machines under the constraints of the same peak/rms value. The relationship between the output torque and the third harmonic current is established and its optimal value for maximizing the output torque is derived. It is found that the optimal third harmonic current is dependent on the ratio of the third harmonic back electromotive force (EMF) to the fundamental one but it is not 1/6 of the fundamental one as pulse width modulation in an inverter. In order to improve the output torque by increasing the fundamental and third harmonic winding factors and the third harmonic airgap flux density, the unequal width tooth and permanent magnet (PM) segmentation are employed in the 10-slot/8-pole five-phase SPM machine. The optimal unequal tooth dimensions and the number of PM segmentations are analyzed for maximizing the output torque. The airgap flux density, back EMF, cogging torque, and output torque of the machine with equal/unequal tooth width and unsegmented/segmented PM are compared. Finally, the experiments on the prototype 10-slot/8-pole PM machine with unequal tooth width and segmented rotor are given to verify the analytical and finite element analyses. [ABSTRACT FROM AUTHOR]

Compared to nonmodular machines, modular topologies become increasingly attractive due to their simplified manufacture process, better fault-tolerant capability, and potentially reduced material consumption. In order to maintain or even enhance the machine performance while achieving high fault-tolerant capability, novel modular, single-layer winding switched reluctance machines (SRMs) with different pole numbers are proposed, which are supplied by rectangular wave current with different conduction angles. The influences of the pole number and flux gap width between E-core segmented stators on the electromagnetic performance have been investigated in terms of self- and mutual inductances, electromagnetic torque, copper loss, iron loss, and radial force. It has been found that the modular structures with higher rotor pole numbers than stator slot numbers (12-slot/14-pole and 12-slot/16-pole SRMs) can maintain and even improve the average torque due to the nature of self and mutual inductances. In addition, the torque ripples for modular machines are significantly reduced (below 50%), so do the iron loss and radial force, leading to higher efficiency albeit with potentially lower vibration and acoustic noise. Two prototypes with 12-slot/8-pole and 12-slot/14-pole combinations have been built with both nonmodular and modular structures to validate the predictions in terms of inductances and static torques. [ABSTRACT FROM AUTHOR]

In this paper, the torque production mechanism of variable flux reluctance machines (VFRMs) is investigated. Initially, based on an analytical instantaneous torque model developed from the Lorentz force law and airgap field harmonic analysis, the magnetic gearing effect is revealed in the torque production of VFRMs. Then, by using a 6-stator-pole/4-rotor pole (6s/4r) VFRM as an example, all its torque components, including synchronous torque, reluctance torque, and cogging torque, are analyzed separately under linear condition. Their average torque and torque ripple characteristics are comprehensively illustrated. Finally, the influence of saturation effect is also accounted for with the help of finite element and frozen permeability methods. The analysis results are verified experimentally. [ABSTRACT FROM AUTHOR]

In this paper, the partitioned stator flux reversal permanent magnet (PM) (PS-FRPM) machine and the conventional magnetically geared (MG) machine operating in both stator-PM (SPM) and rotor-PM (RPM) modes are comparatively analyzed in terms of electromagnetic performance to provide design guides for an MG machine regarding an SPM- or RPM-type machine and a higher or lower gear ratio machine. It is found that an SPM-type machine is recommended since both PS-FRPM and MG machines operating in SPM modes have a higher phase back-EMF and hence torque than their RPM counterparts, respectively, as a result of a similar phase flux linkage but a higher electric frequency since the iron piece number is larger than the PM pole-pair number. Moreover, a smaller gear ratio machine is preferred from the perspective of a higher power factor and hence a lower inverter power rating, as the conventional MG machines with higher gear ratios suffer from larger flux-leakage, higher synchronous reactance and hence lower power factors, as well as higher iron losses, than the PS-FRPM machines. However, higher gear ratio machines feature lower cogging torques and torque ripples due to the smaller difference between the PM pole-pair number and iron piece number. Both prototypes of PS-FRPM machine operating in SPM mode and MG machine operating in RPM mode are built and tested to verify the finite element predicted results. [ABSTRACT FROM PUBLISHER]

The sensorless control performance of pulsating carrier signal injection employing zero-sequence voltage for dual three-phase (DTP) permanent magnet synchronous machine (PMSM) drives is investigated in this paper. This method has the synergy of high bandwidth of zero-sequence voltage method and high position estimation accuracy of pulsating injection strategy. However, such a method for single three-phase PMSM exhibits large oscillation in position estimation error due to undesirable harmonic components in the zero-sequence carrier voltage, and the existing compensation methods usually require complex structures or intensive offline measurements. As for DTP-PMSM, the undesirable harmonic components for the pulsating injection can be suppressed with an optimum phase shift between the two injected high-frequency signals. Besides, a new simple measurement method of zero-sequence carrier voltage is proposed with only one voltage sensor placed between the two isolated neutral points. As a result, the rotor position estimation accuracy can be significantly improved. The experimental results verify the effectiveness of the proposed method for DTP-PMSM. [ABSTRACT FROM PUBLISHER]

A novel partitioned stator (PS) hybrid excited (HE) switched flux (SF) (PS-HESF) machine is proposed in this paper. In the PS-HESF machine, the permanent magnets (PMs) and field windings are allocated on one stator while the armature windings are placed on the other. The iron-piece-rotor is sandwiched between the two stators. Consequently, compared with the conventional HESF machine having PMs, field windings as well as armature windings all on one stator, the available space of the novel machine is greatly boosted and therefore the performance is enhanced. Based on 2-D finite-element analysis, the electromagnetic performance of the PS-HESF machine is evaluated and the results reveal that it can exhibit not only better flux regulation capability but also higher torque than the conventional HESF machine. Moreover, the influences of the key design parameters on the hybridization ratio in the PS-HESF machines are investigated. A prototype machine is manufactured and tested to validate the predictions. [ABSTRACT FROM PUBLISHER]

An integrated field and armature current control strategy is proposed for dual three-phase variable flux reluctance machines (VFRMs). The proposed method utilizes a sinusoidal current biased by dc offset rather than separated field and armature currents in an external field current control. In order to generate the dc and ac components together, a dual three-phase inverter is adopted, in which one side of each stator winding is connected to a neutral point. The dq-axis currents are controlled by the dual three-phase inverter, whereas zero sequence current is generated as a field current by the zero vector redistribution between two inverters. Since the integrated current control allows an integrated winding, which reduces the winding resistance to half, the copper loss can be also reduced to half. To apply the vector control scheme, the voltage and torque equations are derived for dual three-phase VFRMs in a synchronous dq-axis frame. These equations are also utilized for the dynamic simulation with the aid of MATLAB/Simulink. The experimental results validate that the proposed strategy can effectively increase the efficiency and extend the operating speed range. [ABSTRACT FROM PUBLISHER]

This paper develops a design methodology for switched flux (SF) hybrid permanent magnet memory machines (HPMMMs). The memorable flux is achieved due to the variable magnetization level of low coercive force (LCF) permanent magnets (PMs) Thus, the associated excitation loss is negligible, resulting in high efficiency operation over a wide speed range. A general hybrid PM magnetic circuit is modeled, which is characterized by spoke-array NdFeB PMs and LCF PMs sandwiched between an outer stator ring and an inner stator pole. Based on the magnetic circuit, the design conflicts within the stationary side are unveiled. Thereafter, the machine configuration is introduced, followed by a description of the design procedure. First, the optimal stator pole number is determined based on one-phase machine models. In addition, a simplified permeance function is utilized to analytically optimize the rotor number, accounting for different ratios of the slot opening to NdFeB PM thickness. The electromagnetic performance of the machines with alternate stator/rotor pole combinations are compared. The design guidelines for LCF PMs are presented. Finally, the theoretical analysis is verified experimentally on the prototype machine. [ABSTRACT FROM AUTHOR]

This paper proposes optimal step-skew methods for cogging torque reduction in interior permanent magnet (IPM) machines. First, a vector diagram method is employed to analyze the principle of a conventional three-step-skewed rotor, followed by two-dimensional (2-D) finite element (FE) validation. However, a considerable component of the cogging torque still exists according to 3-D FE analysis. End leakage flux and interaction between adjacent rotor steps are then investigated. To further reduce the residual cogging torque component, two improved step-skew methods are proposed—first, a rotor with optimal step-skew angles and, second, a rotor with optimal step lengths. Furthermore, the influence of manufacturing tolerance with axial placement of the rotor steps is investigated and leads to further corrections of the proposed methods, followed by analyses on other IPM machines having different stator slot/rotor pole combinations. Finally, prototypes are fabricated and tested to verify the foregoing analyses. [ABSTRACT FROM AUTHOR]

In this paper, in order to enlarge its torque density, an overlapping winding (OW) is applied to the 24/16-stator/rotor-pole flux-switching permanent magnet (FSPM) machine. By adopting an OW-configuration with full-pitch coils, the pitch factor and coil-flux cross-sectional area in the 24/16-pole FSPM machine with nonoverlapping winding (NOW) can be doubled. Thus, the fundamental open-circuit phase flux-linkage and back-EMF can be effectively enhanced by 115.28%, making it comparable to the conventional 12/10-pole NOW-FSPM machine. Therefore, by injecting the same current density, the proposed OW-FSPM machine can produce 65.2% higher torque density than its NOW counterpart, and 17.6% higher torque density than the conventional 12/10-pole NOW machine despite 21.5% lower ampere turns due to a smaller slot area. However, the proposed machine suffers from high torque ripple due to high cogging torque and back-EMF harmonics. Torque ripple reduction by harmonics current injection and rotor skewing in the proposed machine are investigated. Results show that both methods can effectively reduce the torque ripple in the proposed 24/16-pole NOW-FSPM machine, albeit with the level of torque density being compromised. Experiments are performed in order to validate the analysis. [ABSTRACT FROM AUTHOR]

The partitioned stator switched-flux permanent magnet (PM) (SFPM) (PS-SFPM) machine is a novel stator-PM machine in which PMs and armature windings are separately placed in two different stators. Compared with the conventional SFPM machine with a single stator in which both PMs and armature windings are located, the PS-SFPM machine can generate higher torque density due to the utilization of the machine's inner space. In this paper, the magnetic gearing effect in the PS-SFPM machine is investigated in terms of air-gap field harmonics based on a simple magnetomotive force (MMF)-permeance model. It is found that the PS-SFPM machine is one type of magnetically-geared machine, in which the modulations of rotor iron pieces to the open-circuit PM and armature reaction fields are similar to those found in the magnetic gear and the conventional magnetically geared machine. The pole-pair numbers and rotating speeds of the air-gap field harmonics obtained by the MMF-permeance model are verified by finite element (FE) analysis. More than 93% of the average electromagnetic torque is contributed by the main air-gap field harmonics having pole-pair numbers (2i - 1)\boldsymbol p PM and \rm| N\rm{r} \,\pm \, (2i-1)pPM| ( i = 1,2,3) in a PS-SFPM machine with pPM-pole-pair PMs and Nr-rotor-pole. A prototype machine is fabricated and tested to verify the FE analysis. [ABSTRACT FROM PUBLISHER]

Terminal voltage distortion in surface-mounted permanent magnet machines caused by local magnetic saturation significantly influences the machine performance. Thus, this paper focuses on the minimization methods for such phenomenon. The traditional harmonics minimization methods, such as rotor skewing and nonuniform airgap (rotor and stator shaping), are investigated. However, neither of them can effectively reduce the terminal voltage distortion since the local magnetic saturation in tooth-tips always exists, especially for designs with small or closed slot openings. This paper proposes that the terminal voltage distortion could be essentially reduced when larger slot opening width is adopted, since the local magnetic saturation by tooth-tip leakage flux decreases as a consequence. A design trade-off on slot opening is recommended to balance the terminal voltage distortion and other performance, e.g., the torque quality and flux weakening capability. The results show that the optimal trade-off should be made according to the machines most frequent operation conditions. Two prototypes with different design tradeoffs have been manufactured and tested as examples to validate the analyses. [ABSTRACT FROM PUBLISHER]

This paper investigates the terminal voltage distortion in the interior permanent magnet machines with fractional slot concentrated windings, with particular emphasis on the influence of stator slot Ns and rotor pole 2p combinations. The 12-slot/10-pole machine is first employed to show the voltage distortion phenomenon. Using the frozen permeability method, the mechanism is then investigated, which reveals that the variation of armature flux paths due to rotor saliency is the origin of such phenomenon, especially when the current advancing angle \beta approaches 90°. Further, the terminal voltage distortion of the six machines are compared, i.e., {N_s} \pm 1 = 2p (9-slot/8-pole, 9-slot/10-pole), {N_s} \pm 2 = 2p (12-slot/10-pole, 12-slot/14-pole), N_s/2p = 3/2 (12-slot/8-pole), 3/4 (12-slot/16-pole), which shows that the machines with N_s < 2p suffer more severe voltage distortion than their counterparts with N_s > 2p. In addition, considering the inevitable machine saturation, a design trade-off is proposed by selecting proper N_s/2p combinations to minimize the influence. Finally, prototypes are fabricated and tested to validate the analyses. [ABSTRACT FROM PUBLISHER]

Hybrid excited (HE) machines combine the advantages of both high torque density and excellent flux regulation capability, while also having extensive applications. A novel partitioned stator HE machine employing two stators to allocate armature windings and excitations separately, is proposed in this paper. The permanent magnet (PM) pole-pair and wound field pole-pair are alternately placed on one stator to exhibit parallel magnetic paths, while the armature windings are located on the other stator. The iron-piece-rotor is sandwiched between the two stators. This machine inherits the advantages of stator-PM machine and further benefits from attractive flux regulation capability due to parallel topology. The operating principle and the slot/pole combination rule that are different from the conventional PM machine are illustrated. The two-dimensional finite element technique is used to evaluate the electromagnetic performance, confirming the mentioned advantages. A prototype is manufactured and tested to validate the predictions. [ABSTRACT FROM PUBLISHER]

On-load terminal voltage distortion can significantly reduce the flux weakening operation region of electrical machines. This paper investigates the effectiveness of several harmonics reduction methods, e.g., rotor skewing, rotor pole shaping, and stator tooth-tip shaping, on the terminal voltage distortion reduction in fractional slot interior permanent magnet machines. It is found that skewing can only reduce the peak terminal voltages, but not total harmonic distortion, while the average torque is also notably lower. However, on-load terminal voltage distortions can be greatly reduced by rotor pole or stator tooth-tip shaping with only a slight average torque drop. It is found that the local magnetic saturation is largely alleviated based on the magnetic permeance and flux path modification. Finally, these analyses are experimentally validated based on the measured torque speed curves of two prototype machines having the same stator, but different rotors with or without rotor pole shaping. [ABSTRACT FROM PUBLISHER]

This paper proposes a new partitioned stator flux reversal permanent magnet (PM) (PS-FRPM) machine having integer-slot overlapping windings, i.e., the slot number per pole per phase q is an integer, based on the magnetic gearing effect in stator-PM machines. Compared with the existing PS-FRPM machine with fractional-slot nonoverlapping windings, a more sinusoidal armature reaction magnetomotive force can be achieved in the proposed PS-FRPM machine with integer-slot overlapping windings, resulting in lower iron loss and PM loss. Electromagnetic performance of the PS-FRPM machine, which has q = 1 overlapping windings is analyzed and compared with PS-FRPM machine, which has q = 0.5 nonoverlapping windings by finite element (FE) analysis. FE results show that the proposed 24/10/12-outer-stator/rotor/inner-stator-pole PS-FRPM machine with q = 1 overlapping winding exhibits higher fundamental phase back-electromotive force, higher average electromagnetic torque and lower torque ripple, lower loss and higher efficiency, higher self-inductance but lower mutual inductance, higher d-axis inductance, and potential infinite flux-weakening capability compared with the 12/10/12-outer-stator/rotor/inner-stator-pole PS-FRPM machine with q = 0.5 nonoverlapping windings. Both prototype machines with q = 1 overlapping winding and q = 0.5 nonoverlapping windings are built and tested to verify the FE analyzes. [ABSTRACT FROM PUBLISHER]

This paper presents a resonant feedback regulator-based control strategy to compensate the point of common coupling (PCC) voltage imbalance for doubly fed induction generator (DFIG). The proposed control strategy utilizes a resonant compensator to directly generate the rotor voltage reference, rather than conventionally generating the negative sequence rotor current references. Thus, the sequence decomposition and DFIG parameter dependency can be avoided. Impacts of the resonant parameters and the network resistance/reactance (R/X) ratio on the control system performances, including the system stability, the rejection capability of the PCC voltage imbalance and the dynamic response of the control system, are theoretically analyzed. The experimental results validate the effectiveness of the proposed control strategy. The proposed voltage imbalance compensation strategy can be applied under any network R/X ratio condition. [ABSTRACT FROM PUBLISHER]

A novel brushless ac, doubly salient, permanent magnet (PM) machine is proposed. It has the novel features of: 1) PMs placed in the stator slots (SSPM) to premagnetize only the stator on open circuit; 2) fail-safe capability during uncontrolled generator operation or winding short circuits; and 3) negligible cogging torque. The basic operating principle, electromagnetic performance, PM demagnetization, and the influence of leading design parameters on the machine losses and efficiency are investigated for the 12/10 stator/rotor pole machine. Finally, the performance of the proposed SSPM machine is predicted by 2-D finite-element analysis and is experimentally validated. [ABSTRACT FROM PUBLISHER]

This paper proposes a partitioned stator variable flux reluctance machine (PS-VFRM) in which field and armature windings are placed on two separate stators. The influence of different stator/rotor-pole combinations on the electromagnetic performance is examined using finite-element analysis. Candidate designs maximize the average electromagnetic torque. Compared against the conventional single stator VFRM, the proposed PS-VFRM is shown to provide 24.6% and 12.7% increases in torque density and efficiency, respectively. The static electromagnetic performance is validated using experimental prototypes. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel rotor contour design for variable reluctance (VR) resolvers by injecting auxiliary air-gap permeance harmonics. Based on the resolver model with nonoverlapping tooth-coil windings, the influence of air-gap length function is first investigated by finite element (FE) method, and the detection accuracy of designs with higher values of fundamental wave factor may deteriorate due to the increasing third order of output voltage harmonics. Further, the origins of the third harmonics are investigated by analytical derivation and FE analyses of output voltages. Furthermore, it is proved that the voltage harmonics and the detection accuracy are significantly improved by injecting auxiliary air-gap permeance harmonics in the design of rotor contour. In addition, the proposed design can also be employed to eliminate voltage tooth harmonics in a conventional VR resolver topology. Finally, VR resolver prototypes with the conventional and the proposed rotors are fabricated and tested respectively to verify the analyses. [ABSTRACT FROM PUBLISHER]

The local magnetic saturation in tooth-tips of surface-mounted permanent magnet (SPM) machines generates on-load terminal voltage distortion, especially when small or closed slot openings are adopted. This paper focuses on investigating the influence of slot and pole number (Ns/2p) combinations on this phenomenon in both fractional slot and integer slot SPM machines. The mechanism of this phenomenon and how it is influenced by current advance angle and tooth-tip geometric parameters are introduced first. Then, voltage distortion pattern is proposed to analyze the occurring time or rotor positions of voltage ripples and their relative amplitudes according to the winding arrangements of different Ns/2 p combinations, with the influence of PM leakage flux considered. By 2-D finite-element analysis, the voltage distortion of various machines is calculated and compared, such as Ns \pm 1 = 2p, Ns \pm 2 = 2p, N s/2p = 3/2 (3/4), and integer slot machines with slot number per pole per phase q = 1 or 2. The analysis results reveal that under the same comparison conditions, the integer slot machines have less voltage distortion than the fractional slot machines, especially when q \geq 2. Meanwhile, for the same slot number, the fractional slot machines with Ns > 2p suffer from on-load voltage distortion less than their counterparts with Ns < 2p. Finally, three prototype machines with 12/10, 12/14, and 12/8 slot/pole numbers are manufactured and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

In this paper, partitioned stator flux reversal permanent magnet (PS-FRPM) machines having different stator/rotor pole combinations with consequent-pole PM (CPM) stator are proposed and analyzed. Compared with the conventional 12-stator-pole PS-FRPM machines having 10-, 11-, 13-, and 14-rotor-pole rotors and surface-mounted PM (SPM) stator, the PM volume in the proposed PS-FRPM machines with CPM stator can be saved by 28.33%, 30%, 30%, and 33.33%, respectively, while the torque density are similar, i.e., 98.59%, 96.69%, 95.50%, and 97.15%, respectively. Besides, the proposed PS-FRPM machines with CPM stator can exhibit only <1% smaller efficiency compared with the existing PS-FRPM machines with SPM inner stator. [ABSTRACT FROM AUTHOR]

Three-phase nonoverlapping stator wound-field synchronous (NSWFS) machines having salient pole rotors are investigated systematically in this paper. The influence of the rotor pole number on the NSWFS machines is investigated via optimized designs. Using two-dimensional (2-D) finite-element analysis (FEA), the NSWFS machines are found to exhibit higher torque than the nonoverlapping segmented rotor NSWFS (SNSWFS) machines. The FEA-predicted back-electromotive force (EMF), cogging torque, and static torque of the NSWFS machines are validated by experiments on prototype machines. [ABSTRACT FROM AUTHOR]

Several switched flux permanent magnet (SFPM) machines with mechanically movable flux adjusting technique are proposed, analyzed, and compared for applications which demand high speed and efficiency. By using ferromagnetic pieces-–one per every stator pole or every alternative stator pole, which are named as flux adjusters (FAs) and located on the outside surface of the stator—the airgap flux density can be weakened and therefore the operation speed range and flux weakening capability can be improved. The influence of using all or alternative FAs on the open circuit results, electromagnetic performance, and torque–speed characteristics of the SFPM machine is investigated through three SFPM machines with different stator/rotor pole combinations, i.e., 12/10, 12/13, and 12/14. Moreover, although using FAs in all stator poles can significantly improve the flux weakening capability, alternative FAs can also achieve remarkable improvement although higher torque ripple is observed. Additionally, it has been found that the 12/13 combination is considered to be the most suitable candidate for alternative FAs technique. In addition to 2-D finite-element analysis (FEA) and analytical methods, 3-D FEA results accounting for the end-effect are presented. Furthermore, experiments are performed to validate the results. [ABSTRACT FROM AUTHOR]

A novel variable reluctance (VR) resolver with nonoverlapping tooth–coil windings is proposed in this paper. It significantly simplifies the manufacturing process of multilayer windings in conventional products. Finite element (FE) analysis is used to illustrate the basic operating principle, followed by analytical derivation of main parameters and optimization of major dimensions, including air-gap length and slot opening width. Based on winding distributions and FE results, it is shown that identical stator and winding can be employed for a resolver with three different numbers of rotor poles. Further, other stator slot/rotor pole combinations based on the nonoverlapping tooth–coil windings are generalized. In addition, the influence of eccentricity and end-winding leakage on the proposed topology is investigated. Finally, a prototype is fabricated and tested to verify the analysis, including main parameters and electrical angle error. [ABSTRACT FROM AUTHOR]

In this paper, a double stator (DS) wound field (WF) switched flux (SF) (DS-WFSF) machine is proposed. In the DS-WFSF machine, field and armature windings are separately placed in two different stators. Compared with the conventional WFSF machine with single stator, in which both field and armature windings are located, nonoverlapping concentrated windings and large slot areas can be obtained in the DS-WFSF machine. The proposed DS-WFSF machine exhibits >19% higher torque than the conventional WFSF machine, with both machines having the same space envelope and being globally optimized. The influence of leading design parameters, such as copper loss ratio between the field and armature windings, air-gap diameter, and rotor iron piece thickness and widths, on the average output torque is investigated for the DS-WFSF machines having 12/10, 12/11, 12/13, and 12/14 stator slots/rotor iron pieces. All the analyses are confirmed by both finite element and experimental results. [ABSTRACT FROM AUTHOR]