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In this article, a new dual-permanent magnet spoke-type flux-reversal machine (dual-PM SFRM) for direct-drive applications is proposed. Tangentially magnetized permanent magnets (PMs) sandwiched with iron poles are set in stator slots. To increase the torque density within the geometric restrictions, PMs are introduced in the rotor as well and magnetized radially to form a consequent-pole rotor. Global optimizations are conducted and comparisons are made on torque, torque ripple, and torque/PM volume with the existing single-PM SFRM. It is found that the proposed dual-PM SFRM can produce 22.6% larger torque with an optimal PM volume and a 17.5% larger torque with the same PM volume compared with the single-PM counterpart. Moreover, major magnetic field space harmonics are derived analytically and verified by finite-element analysis (FEA) and the torque components produced by the working harmonics are calculated and compared in terms of different stator/rotor pole number combinations. Comparisons are made on back electromotive force, cogging torque, torque performance, and efficiency between dual-PM SFRM and conventional flux-reversal machine. The influence of different stator configurations, i.e., the slot opening, the iron bridge, and the unequal tooth, on torque performance in the proposed dual-PM SFRM has been studied and highlighted. A prototype has been built and tested to validate the FEA calculations. [ABSTRACT FROM AUTHOR]

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]

In this article, a simplified three-dimensional (3-D) hybrid analytical thermal model for surface-mounted permanent magnet (PM) synchronous machines is proposed and applied to investigate the influence of PM segmenting strategies on the spatial PM temperature distributions and hotspots. The developed 3-D hybrid thermal model synergies the lumped-parameter thermal model and analytical method and is able to estimate 3-D spatial temperature distributions and hotspots for both unsegmented and segmented surface-mounted PMs accounting for the uneven PM eddy current loss distributions. Meanwhile, by utilizing the proposed matrix-based post-processing methods, the developed hybrid analytical thermal model has a simple mathematical expression but persists in high estimation accuracy. Finally, the proposed hybrid analytical modelling method is validated by 3-D electromagnetic-thermal coupled FEA and experiments. [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]

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/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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This article proposes an improved sensorless control method for permanent magnet synchronous machines under phase resistance asymmetry. The proposed method acquires positive sequence current and voltage signals by applying a sequence component extractor and a double synchronous reference frame current control strategy. These signals can, then, be applied to improve the extended electromotive force based sensorless observer to eliminate the undesired second-order fluctuation in position and speed estimation due to asymmetric phase resistances. In addition, the resistance deviations, which may be due to asymmetric resistances and temperature variation, could introduce dc offset error in rotor position estimation. Therefore, a model reference adaptive system based resistance estimation is employed to compensate for inaccuracy of resistances. Moreover, from the information contained in the negative sequence voltages, the specific values of all asymmetric phase resistances can be estimated as well. Experimental and simulation results are provided to validate the proposed method. [ABSTRACT FROM AUTHOR]

In this article, an online rotor position error correction method is proposed to eliminate the impact of parameter mismatch in sensorless control for dual three-phase (DTP) permanent magnet synchronous machines drives. The rotor position error production mechanism is first derived and shows that the error changes with the trend of current variation when there is a parameter mismatch. Based on this mechanism, by injecting sinusoidal current signals with low frequency and small amplitude into both sets of three-phase windings, the presence of parameter mismatch and its level can be revealed from the corresponding sinusoidal responses of the estimated speed of sensorless observers, which do not depend on the inertia of the machine. Since the amplitudes of these responses decrease as the parameter mismatch level reduces, with the help of the least mean square algorithm, the parameters can be adaptively adjusted to the actual values, and the position error can be thus corrected. Moreover, with the extra freedom of DTP machines, the detrimental effects on torque production due to current signal injections can be eliminated through adjusting the phase between the two injected signals. The effectiveness of the proposed method has been validated through simulation and experimental results. [ABSTRACT FROM AUTHOR]

This article proposes and investigates two asymmetric consequent-pole hybrid excited flux reversal machine (AS-CP-HEFRM) topologies, which have same numbers of iron poles and permanent magnets (PMs) with concentrated ac and dc windings on each stator pole and a salient pole rotor. If PM number on one stator pole is larger than 1, PMs are magnetized radially in the same direction on one stator pole, while opposite on adjacent stator poles. The phenomenon of the phase shift between the flux linkages of dc and PM excitations in the AS-CP-HEFRMs is revealed for the first time, which will weaken the regulation of dc excitation field to PM produced field. The elimination condition of the phase shift is derived and verified by finite-element analysis in this article, which can be considered as design guidelines in AS-CP-HEFRMs. Airgap magnetic field space harmonics of AS-CP-HEFRM are also investigated and verified by finite-element analyses. Meanwhile, the relationship between the rotor pole number and the stator pole arc (PM ratio) is derived and verified by global optimization based on genetic algorithm for maximum average torque. The influence of stator/rotor pole number combinations is also studied and compared in terms of torque, torque ripple, and flux regulation capability. The torque components produced by airgap magnetic field space harmonics are calculated and compared. A prototype has been built and tested to validate the finite element calculations. [ABSTRACT FROM AUTHOR]

This article proposes a novel asymmetric interior permanent magnet (AIPM) rotor topology that has a mixed V-shape and spoke-type PM configuration, designated as a 1.5-layer PM structure, and asymmetric arrangement of V-shape PMs and asymmetric flux barriers. The AIPM rotor topology is employed for IPM synchronous machines to utilize the magnetic-field-shifting (MFS) effect for increasing average torque by reducing the current angle difference between peak PM and reluctance torque components. Three machines, i.e., the proposed 1.5-layer AIPM, a symmetrical 1.5-layer IPM-I, and a conventional V-shape benchmark IPM-II are designed and optimized using the same stator, rotor diameter, and total PM usage by global parametric optimization considering the mechanical stress. The effect of asymmetric features of the 1.5-layer AIPM rotor design, i.e., asymmetry of V-shape cavity as well as position and dimensions of flux barrier, on maximum torque and open-circuit air-gap field are investigated. The electromagnetic performances of three machines are compared. It confirms that the proposed AIPM machine has the highest maximum torque and the smallest cogging torque simultaneously. It is also revealed that the torque enhancement is achieved by both the 1.5-layer structure and MFS effect. Finally, a prototype of an AIPM machine is manufactured and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

This article proposes a novel asymmetric interior permanent magnet (AIPM) rotor topology for torque enhancement and torque ripple reduction in IPM synchronous machines. The AIPM rotor structure is featured by a hybrid-layer permanent magnet configuration, i.e., for each pole, a part of PM configuration has one-layer while the other part has two layers. It allows the magnetic-field-shifting (MFS) effect to be utilized by reducing the current angle difference between maximum PM and reluctance torque components, thereby effectively increasing the maximum resultant torque. The proposed AIPM machine and a conventional V-shape IPM machine are designed and globally parametric optimized with the same 24-slot/4-pole stator, rotor diameter, and PM usage. The influence of key rotor geometric parameters of the AIPM machine on torque and open-circuit air-gap magnetic field characteristics are investigated. The comparison of electromagnetic performance confirms that significant torque enhancement and torque ripple reduction in the AIPM machine compared with the conventional V-shape IPM machine and reveals the MFS effect is essential for torque increase. Finally, an AIPM machine is manufactured and tested for validation. [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]

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]

Current harmonics are ubiquitous in dual three phase (DTP) permanent magnet synchronous machine (PMSM) drives. Due to back electromotive force (EMF) distortion, significant current harmonics are generated in the DTP-PMSM system. The influence of back EMF harmonics is investigated in this paper and a novel switching-table-based direct torque control method to compensate the selected current harmonics caused by the back EMF harmonics is proposed. It shows that by employing different optimal action time durations for voltage vectors in the z1z2 subspace and setting the synthetic voltage vectors to non-zero, the stator flux harmonics caused by the back EMF harmonics can be selectively compensated, as verified by experiments. [ABSTRACT FROM AUTHOR]

In this article, a new type of consequent pole flux reversal permanent magnet (CFRPM) machine, which features more iron poles than PM poles under one stator tooth, is proposed to improve the torque density. The proposed CFRPM machine with 6 slots and 16 poles (6S16P) is compared with a 12S16P FRPM machine and its consequent pole type, as well as a conventional 6S4P surface-mounted PM (SPM) machine. The proposed 6S16P CFRPM shows the highest torque among the four machines, together with the highest torque per PM volume. For a fair comparison with the 12S16P FRPM machine and its consequent pole type, the torque ripple of the proposed 6S16P CFRPM is suppressed by using two-step skewed rotor. After employing 4° two-step skewed rotor, while exhibits comparable torque ripple, the proposed 6S16P CFRPM still has 43% and 22% higher torque compared with the 12S16P FRPM machine and its consequent pole type. [ABSTRACT FROM AUTHOR]

The lumped-parameter thermal network (LPTN) has been widely used in the thermal analysis for electrical machines. Nevertheless, since the thermal resistances are defined based on the one-dimensional (1-D) heat transfer equation, it will cause the misestimation of the average temperatures when the thermal model extends to two dimensions or three dimensions. In this article, a hybrid thermal model utilizing the synergies of LPTN and 2-D analytical thermal models is developed to address this issue and to predict accurate critical temperatures, especially the average and maximum temperatures of the active and end windings. The 2-D analytical thermal models are obtained by solving the Poisson's equations with the Dirichlet boundary conditions extracted from the LPTN. The derived analytical solutions are expressed as the Fourier series, which can be further simplified by utilizing the first term only to represent average and maximum temperatures with sufficient accuracy and short computation time. The hybrid thermal model is applied to a totally enclosed forced convection permanent magnet synchronous machine and validated by numerical techniques and experiments. [ABSTRACT FROM AUTHOR]

A new simple rotor initial position detection method for permanent magnet machines is proposed in this article. It is based on the magnetic saturation effect, which is commonly used by existing methods. Different from the conventional methods utilizing phase current or phase voltage sensors, the dc-link voltage sensor is used to estimate the rotor initial position. In the proposed method, a specific excitation approach is used to enhance the performance and a so-called “equivalent injection position” is developed to simplify the estimation process. The proposed method can achieve a 30° estimation resolution. Besides, practical considerations, including the dc-link voltage measurement errors, dc-link resistance, dc-link capacitance, and dc-link voltage ripples, are discussed in this article. A guideline of voltage pulse selection is presented to minimize the impact of these practical issues. Moreover, it is found that as the dc-link resistance increases, the proposed method shows a better estimation performance than the conventional methods. Besides, the proposed method is insensitive to sensor measurement errors. The experimental results are given to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In the past, various fundamental model based sensorless control methods have been proposed. However, most of them are developed under a healthy condition. Hence, in this article, fundamental model based sensorless control of permanent magnet synchronous machines (PMSM) under rotor eccentricity (RE) is investigated which is a common issue in many drive systems. It is known that under RE, three-phase back-EMFs, flux-linkages, inductances, and torque will be influenced. Mathematical derivation reveals that these effects will cause undesired harmonics in the position estimation. Since the frequencies of these low-order harmonics are much smaller than the bandwidth of position observer such as phase-locked loop, it is difficult to effectively eliminate them. Hence, the conventional back-EMF method is modified by adding an adaptive notch filter to suppress these undesired harmonics. Furthermore, the RE effects on PMSM characteristics are examined by measurements. The modified position estimator is implemented on a dSPACE platform and is verified by experiment results. [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]

The dc winding induced voltage in hybrid-excited machines can lead to dc winding current ripple and hence, fluctuating field excitation. It may also challenge the dc power source and increase the difficulty of machine control, especially at high speed. The dc winding induced voltage in a hybrid-excited switched-flux permanent magnet (HESFPM) machine is investigated in this article. The phenomenon and mechanism of the dc winding induced voltages under both open-circuit and on-load conditions are analyzed, with particular emphasis on on-load operation which consists of open-circuit induced voltage and armature current induced voltage, respectively. Two techniques, i.e., rotor step skewing and unequal rotor teeth, are proposed and comparatively investigated by the finite-element (FE) method to suppress the dc winding induced voltage under on-load condition. FE results show that the peak-to-peak value of on-load dc winding induced voltage can be effectively suppressed by 96.15% or 89.05% by rotor step skewing or unequal rotor teeth, respectively, while the average on-load electromagnetic torque can be maintained at 89.4% or 87.8%. A prototype HESFPM machine is built and tested to verify the FE results. [ABSTRACT FROM AUTHOR]

In this article, the flux reversal permanent magnet (FRPM) machine with toroidal windings is presented and analyzed with reference to conventional concentrated windings. First, the influence of rotor pole numbers on FRPM machines with conventional concentrated windings is investigated. It is found that although the 12/13 stator slot/rotor pole FRPM machine has a high back electromotive force, the pitch factor, and magnet flux utilization ratio of concentrated windings are very low. By adopting toroidal windings instead of concentrated windings in the 12/13 FRPM machine, the pitch factor and resulted machine performance can be effectively improved. Finite-element analysis shows that the 12/13 FRPM machine with toroidal windings can produce 79% higher torque than its counterpart with concentrated windings. Then, the critical design parameters and detailed electromagnetic performance of FRPM machines with both winding types are analyzed and compared. It is shown that the machine with toroidal windings has higher torque, efficiency, power factor, and lower torque ripple, making it particularly suitable for low-speed, high-torque, and axial length limited applications. In addition, other feasible stator slot/rotor pole combinations to use toroidal winding are identified, with the aid of equivalent pole-pair number. Finally, two 12/13 FRPM prototypes with toroidal windings and concentrated windings are tested to validate the analyses. [ABSTRACT FROM AUTHOR]

Voltage feedback flux-weakening control has the advantages of simplicity and robustness against parameter variation. However, due to less voltage control margin in the flux-weakening region, the increased feedback voltage ripple could deteriorate the system performance in the flux-weakening region and may even cause oscillation. In this article, based on a nonsalient permanent magnet synchronous machine, the steady-state feedback voltage ripple in the flux-weakening region are analyzed first. It shows that the feedback voltage ripple caused by the current command ripple could dominate in some flux-weakening regions. Consequently, the speed bandwidth based on the conventional speed proportional-integral (PI) controller in the flux-weakening region can be hardly increased, which leads to poor dynamic performance. In order to obtain both fast speed dynamics and less steady-state ripple, especially in the flux-weakening region, an adaptive fuzzy logic (FLC) speed controller is designed and compared with the conventional speed PI controller. With the adaptive FLC, the dc-link voltage utilization can be increased and better flux-weakening capability can be obtained. Finally, the improved performances are verified by the experimental results. [ABSTRACT FROM AUTHOR]

This article investigates the nonlinear behavior of the conventional voltage feedback flux-weakening control, i.e., the voltage magnitude feedback control on the nonsalient permanent magnet synchronous machine, and proposes an adaptive control parameter tuning method for the voltage feedback controller. Due to less voltage margin in the flux-weakening region, the current dynamic performance is degraded. This issue is more serious when the system operates in the overmodulation region and could affect the system's stability. Based on the designed voltage feedback controller, the system performance in the flux-weakening and overmodulation regions is further improved by utilizing the current and voltage reference modifiers. Consequently, the system can operate well in both linear and overmodulation regions with the specified scaling factor, which is beneficial to general-purpose applications. The viability of the proposed method is demonstrated by the experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a consequent-pole flux reversal machine (CP-FRM) with biased flux modulation theory, which employs homopolar permanent magnets (PMs) placed between the adjacent stator poles. The machine topology is introduced from the perspective of FRM with a shifted magnet position and CP arrangement, and the performance comparison between the proposed CP-FRM and its original surface-mounted PM (SPM) counterpart is presented to highlight the torque improvement of the CP structure. Then, a simplified permeance model is applied to the CP-FRM to identify the principal effective air-gap field harmonics engaging in the torque productions. It shows that the CP-FRM works based on a biased flux modulation effect due to its asymmetric air-gap field distribution caused by the CP configuration, which unveils its underlying torque improvement mechanism over its SPM-FRM counterpart. In order to obtain the highest torque capability, the key design parameters are analytically optimized by analyzing the winding configuration, which aids the establishment of a general design guideline for the CP-FRM. The analytical and FE results are validated by experiments. [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 article investigates the duty-ratio-based direct torque control strategies for dual three-phase permanent magnet synchronous machine (PMSM) drives. The classical switching-table-based direct torque control (ST-DTC) for the dual three-phase drives usually suffers from significant harmonic currents and a large torque ripple. To reduce the harmonic currents, 12 combined voltage vectors are generated and employed as active vectors. Then, the duty-ratio-based ST-DTC is introduced to reduce the torque ripple. Considering that the typical duty-ratio-based ST-DTC exhibits the drawbacks of machine parameter dependent and a certain degree of failure rate in the duty ratio regulation, a simple and effective method taking into account the effect of the machine speed is employed to obtain the duty ratio. Afterward, to prevent the issue of the inverter thermal imbalance caused by using only one type of zero vectors, two types of zero vectors are employed in the switching sequences. With the proposed method, not only the harmonic currents have been suppressed, but also the torque ripple can be considerably reduced, while the merits of the classical ST-DTC such as simple structure and excellent dynamic performance are preserved. The experimental results validate the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

This paper aims to identify the optimal number of flux modulation pole (FMP) in Vernier permanent magnet synchronous machines (VPMSMs) with concentrated tooth-coil windings. First, the influence of number of FMP on machine performance is revealed based on the unified permanent magnet magnetomotive force permeance analytical model. It is found that for a fixed stator slot number, there always exists an optimal number of FMP to maximize the torque, thanks to the enhanced contribution by the fundamental permeance harmonic. Then, the influence of critical dimensional parameters, including the machine diameter, the permanent magnet thickness, and the width of FMP, on the electromagnetic performance of VPMSMs with different numbers of FMP are parametrically analyzed by both analytical and finite element analyses. Results show that the VPMSMs with the optimal number of FMP always have advantages of a higher torque density together with a reduced PM volume, particularly for those with a relatively large diameter. Finally, two VPMSM prototypes with different numbers of FMP are manufactured and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

Fractional slot concentrated winding (FSCW) permanent magnet synchronous machines (PMSMs) have been a research hotspot over the past few decades. Recently, the magnetic gearing effect in FSCW PMSMs is revealed along with its gear ratio, which is a function of slot/pole number combination. At the design stage of FSCW PMSMs, one of the key issues is the selection of the slot/pole number combination. This paper shows that the gear ratio can contribute to a proper slot/pole number selection in any multiphase FSCW PMSMs by acting as a unified index for a quick overall performance comparison. In this paper, first, the magnetic gearing effect in FSCW PMSMs is explained and the gear ratio is further discussed. The advantages of adopting gear ratio as the overall performance index over other indices are revealed. The influence of the gear ratio on the winding factor, torque output, cogging torque, inductance, and rotor losses of three- and six-phase FSCW PMSMs is analyzed and validated by experiments, thus proving the analyses. [ABSTRACT FROM AUTHOR]

In order to ease the manufacture process of very large permanent magnet (PM) machines, such as direct drive wind power generators, modularity technique is usually adopted. Although conventional fractional slot PM machines with all teeth wound windings show good performance, the coils located at the end part of each segment could be easily damaged because of being exposed to the air. In addition, the local winding faults could easily proliferate to the whole machine due to the physical touch of adjacent coils. Thus, a novel modular fractional slot PM machine with redundant teeth is proposed in this paper, while three phases within each set of winding are still balanced. The construction of the proposed modular PM machine having 42-slots/32-poles (42S/32P) combination is described in detail as an example, which can be treated as the integration of six 6S/5P segments and a redundant 6S/2P machine. The reason for using 6S/2P machine is to get rid of the undesirable unbalanced magnetic force (UMF), which usually exists in rotating asymmetric machines, such as 3S/2P PM machine. Since the end part of each segment in the proposed modular PM machine can be covered by half redundant tooth during the production, more protection can be provided for coils located in these regions. Furthermore, the separation of six segments can improve the fault-tolerant capability of the machine. The electromagnetic performance predicted by finite-element analysis (FEA) also demonstrates that the proposed modular machine will perform better if dual three-phase winding is adopted. Finally, the experiments on the prototyped machine validate the analysis in the paper. [ABSTRACT FROM AUTHOR]

In the safe-critical applications such as electric/hybrid electric vehicles, the reliability of the machine drive system is vital. Among the various machine fault types, the uncontrolled generator fault (UCGF) at high speed is one of the most serious faults that could damage the machine drive system. In this paper, the fault protection capability of a novel hybrid-excited doubly salient synchronous machine (HEDSSM) is examined to illustrate its great capability to prevent the dangerous overvoltage issue from the UCGF. Permanent magnet flux of the novel HEDSSM is inherently short-circuited when the field excitation current is not fed into the excitation windings. Therefore, when the UCGF is detected in the high-speed region, the dc-link overvoltage issue can be effectively reduced by forcing the field excitation current to zero. Since only the field excitation current is utilized to protect the machine and power inverter from the UCGF, it is easy to implement and the concept of proposed control strategy can also be applied to other hybrid-excited machines. Finally, the proposed control strategy is verified by both simulation and experimental results on the HEDSSM. [ABSTRACT FROM AUTHOR]

This paper presents a novel modular stator hybrid-excited synchronous machine with stator slot permanent magnets (PMs). By regulating the field current, the magnetic field, and consequently the back electromotive force, as well as the average torque can be controlled. The existence of stator slot PMs alleviates the magnetic saturation and improves the flux regulation ratio. The frozen permeability method is employed to investigate the torque contributions by different magnetic sources. Possible stator and rotor pole combinations are illustrated, and the corresponding electromagnetic performances are evaluated with the finite-element method. It is revealed that 12-stator pole machines with 11- and 13-rotor poles exhibit superior average torque and lower torque ripple due to even-order harmonics elimination. Finally, a prototype with modular stator segments is manufactured to validate the analyses and simulations. [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]

Hybrid permanent-magnet (PM) variable-flux memory (VFM) machines employ both high coercive force PM, i.e., the constant PM (CPM), and low coercive force PM, i.e., the variable PM (VPM). The high energy-product CPM guarantees the benefits of high torque density of the conventional PM machines, while the PM magnetization state of the VPM is flexibly regulated to match various operation requirements. In fact, the two kinds of PMs can be magnetically connected in either parallel or series, with which the machine characteristics are quite different. In this paper, based on the two-dimensional and three-dimensional finite-element analyses, a pair of VFM machines with parallel and series connections, respectively, are investigated with specific reference to identify their difference in end effects. The comparison results show that the series hybrid PM VFM machine suffers more serious end leakage flux. The prototype machines are manufactured and tested to validate the analyses and predictions. [ABSTRACT FROM AUTHOR]

A new type of three-phase stator hybrid excited machine with permanent magnets (PMs) located at the slot openings of field winding slots is presented in this paper. It has the advantage of good flux regulation capability due to the field excitation. The machines with different stator/rotor pole combinations, i.e., 6-stator pole and 7-/8-/10-/11-/13-/14-rotor poles, have been comparatively investigated in terms of the open-circuit and on-load characteristics, as well as the influence of dc current and the unbalanced magnetic forces. The 2-D finite element analysis (FEA) has been employed for analysis and optimization of the machines together with experimental validation. [ABSTRACT FROM AUTHOR]

This paper provides a comprehensive analysis of performance difference among various kinds of flux reversal permanent magnet (FRPM) machines having different permanent magnet (PM) arrangements. Four PM arrangement types are, first, identified by the number and relative polarities of PMs on the stator teeth, and their influence on the equivalent pole-pair number of the armature winding and working harmonics of the air-gap field is revealed. Then, the torque variation against the rotor pole number of each PM arrangement is analyzed. The electromagnetic performance of four PM arrangements with a 14-pole rotor is compared in detail. It shows that the FRPM machine, in which four PM pieces are mounted on each stator tooth and two adjacent magnets on different stator teeth are of opposite polarities, offers the highest torque density and the highest efficiency, which make it promising in low-speed high-torque applications. In addition, four prototype machines are manufactured and tested to validate the findings. [ABSTRACT FROM AUTHOR]

Permanent magnet (PM) machine has received much attention recently. However, unbalanced magnetic force (UMF) may occur in PM machines with some slot/pole number combinations even when there is no rotor eccentricity, which can cause high vibration and noise. In order to reduce the rated on-load UMF, three 3-slot/2-pole PM machines with different auxiliary slots are investigated and compared in this paper. In the first two machines, namely, machines 1 and 2, the auxiliary slots are inserted in the middle of the stator teeth, while their sizes are optimized under different working conditions, i.e., no-load and rated on-load conditions. In contrast, both position and size of auxiliary slots are optimized under the rated on-load condition in the third machine viz., machine 3. Compared with the conventional prototype machine, the maximum rated on-load UMFs are reduced by 6.3%, 50.7%, and 96.6%, and the rated output torques are decreased by 0.7%, 11.5%, and 4% in these three machines, respectively. In addition, the other electromagnetic performances, such as flux linkage, back electromagnetic force, cogging torque, rated output torque, and torque ripple, are compared. The influence of working conditions is investigated, and the experiments are also carried out to validate the numerically predicted results. [ABSTRACT FROM AUTHOR]

This paper proposes two novel partitioned stator (PS) memory machines based on flux-reversal and switched-flux topologies, respectively. The proposed machines geometrically feature two separate stators with armature winding and hybrid PM excitations, i.e., NdFeB and low coercive force PMs. The proposed PS machines can offer increased available inner stator space for hybrid PM, which is beneficial to the torque improvement. The machine topologies are introduced first in terms of possible PM types with parallel magnetic circuits. The design considerations for hybrid PM are analytically analyzed. Then, the electromagnetic characteristics of the two proposed machines are comprehensively compared by using finite element (FE) method. The commercially available Toyota Prius 2010 machine is referenced as a benchmark for comparison with the optimal PS machine having identical overall dimension in potential context of traction applications. Finally, The FE analyses are validated by experiments on a small-scaled demonstration machine. [ABSTRACT FROM PUBLISHER]

A series hybrid variable flux memory (VFM) machine employing two kinds of permanent magnets (PMs) on alternate rotor poles is investigated. This VFM machine features controllable PM flux and thus good flux-weakening capability, as well as improved torque density. However, it is found that the unipolar end leakage flux occurs if the two kinds of PMs are not balanced. According to the analyses of series connection between two PMs based on the fundamental magnetic circuit, the mechanism of the unbalanced rotor poles and the unipolar end leakage flux is revealed. Further, the rule of obtaining balanced poles is identified and the effects of operating conditions are presented. A series hybrid VFM machine prototype is fabricated and tested. [ABSTRACT FROM AUTHOR]

This paper proposes a double superposition method to quickly and accurately predict the cogging torque and unbalanced magnetic force (UMF) of permanent magnet machines with axial-varying rotor eccentricities. The original axial-varying eccentric machine is cut into several uniform slices along the axial direction and each slice is considered to be axially uniform, i.e., axial even. For each axial-even eccentric machine slice, the circumferential superposition method can be used to predict the cogging torque and UMF of this slice. Finally, the cogging torque and UMF of the original axial-varying eccentric machine can be obtained by using an axial superposition technique which combines the cogging torque and UMF of each slice with different eccentricity magnitudes together. The 3-D finite-element analysis is adopted to validate the efficacy of the proposed method and the merit of high accuracy and computational efficiency is also identified by comparing the results predicted from these two methods. [ABSTRACT FROM AUTHOR]

This paper proposes a novel variable flux memory (VFM) machine, in which the “constant” permanent magnet (CPM) with high coercive force and the “variable” PM (VPM) with low coercive force are alternatively located in the interior-PM rotor. Thus, the VPMs and CPMs are magnetically connected in series, with which the CPMs can assist the VPMs to withstand the unintentional demagnetization caused by armature reaction. Therefore, a high armature current can be applied to the machine. Meanwhile, the reluctance torque is retrieved. Thus, a high torque density can be obtained. Based on two-dimensional finite element analysis, first, the electromagnetic performance of the proposed VFM machine in two extreme magnetization states is evaluated in detail. Then, the demagnetization and remagnetization characteristics are investigated, in which the working points of VPMs are illustrated. Furthermore, the advantages of improved efficiency of the proposed VFM machine are demonstrated. A prototype machine is manufactured and tested to validate the predictions. [ABSTRACT FROM AUTHOR]

A method for enhancing torque capability of a dual three-phase permanent magnet synchronous machine (PMSM) based on conventional dual three-phase drive system by injecting the fifth and seventh current harmonics without any hardware re-configuration is proposed in this paper. Compared with the third current harmonic injection, which is commonly used to enhance the torque capability of dual three-phase machine, the two isolated neutral points of each set of single three-phase windings do not need to be reconnected to the middle point of dc-link capacitors or an additional power switching bridge to provide flowing path for zero-sequence current. Further, no additional current sensors are required to obtain the feedback of zero-sequence current to regulate it effectively. For a prototype dual three-phase PMSM, the average torque increases approximately by 9% at the cost of 0.56% increase in the 12th harmonic torque ripple. The effectiveness of the torque capability enhancement is confirmed by experiments. [ABSTRACT FROM AUTHOR]

The relationship between the two-individual current control and the vector space decomposition (VSD) control for a dual three-phase permanent magnet synchronous machine (PMSM) is investigated in this paper. It is found that the VSD control is more flexible in controlling the fundamental current in \alpha \beta subplane and the fifth, seventh current harmonics in z_{1}z_{2} subplane with different proportional and integral (PI) gains, while the two-individual current control is comparable with the VSD control in having the same PI gains in the \alpha \beta $ and z_{1}z_{2} subplanes. It is also found that the two-individual current control may have potential instability issues due to the mutual coupling between the two sets of three-phase windings. If the mutual coupling between the two sets is weak to some extent, then the two-individual current control could have the same dynamic performance as the VSD control without the stability issues. Experiments are conducted on a prototype dual three-phase PMSM to validate the theoretical analysis. [ABSTRACT FROM AUTHOR]

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]