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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]

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]

The control performance of Hall sensor-based high-speed brushless dc (BLdc) motor drives depends heavily on the accuracy of Hall sensor signals. Due to the existence of Hall signal errors, the system may operate under unbalanced conditions that will lead to asymmetric currents and high-torque ripple. For high-speed BLdc drive, using voltage source inverter (VSI) with the pulsewidth modulation (PWM) technique will also lead to PWM update delay that causes inaccurate commutation. In this article, two Hall signal errors, i.e., misaligned and uneven Hall signal errors, are investigated and a Hall signal balancing strategy is developed to detect Hall signal errors and regenerate balanced Hall signals. A novel PWM generation scheme is then proposed to eliminate the PWM update delay when using traditional VSI. Both simulation and experiment results have verified the effectiveness of the proposed strategy. [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]

Voltage induced in the dc winding by the armature field in wound field switched flux (WFSF) machines will induce voltage perturbation in the voltage supply and cause dc winding current ripple and field excitation fluctuation. This will challenge the dc voltage controller and deteriorate the control performance, especially when the load and/or the rotor speed are high. In this article, the dual three-phase armature winding design with a phase-shift of 30 electrical degrees is employed in the partitioned stator WFSF machines to reduce the on-load dc winding-induced voltage. Analytical deductions and finite element (FE) results demonstrate that the dominant sixth-order-induced voltage harmonic can be suppressed to zero. Hence, the peak-to-peak induced voltage in the 12/11- and 12/13-pole partitioned stator WFSF machines can be reduced by 83.35% and 82.53%, respectively. Due to the improvement of winding factors, the torque densities are 4.85% and 5.60% higher, respectively. Prototypes are built and tested to verify the analytical and FE results. [ABSTRACT FROM AUTHOR]

Surface mounted permanent magnet Vernier (SPM-V) machines, because of their high torque density and multi-pole structure, are promising candidates for low-speed direct-drive applications. To achieve high torque density, the SPM-V machines are generally designed with high gear ratios. Therefore, their operating frequencies can be much higher than those of the conventional SPM machines. This potentially increases the alternating current (AC) winding losses, especially those with form-wound coils proposed for high-power applications. This article investigates the AC losses (including skin effect, proximity effect, rotor PM induced, and circulating current losses) in form-wound stator coils of a 3 MW direct-drive SPM-V machine with different slot/pole number combinations. The study reveals that the SPM-V machines have significantly higher AC winding losses than their conventional SPM counterparts for similar operating conditions. To reduce the AC winding losses in SPM-V machines, a novel flux shunt concept is proposed along with other conventional techniques such as increasing the number of turns/coil (with terminal voltage being kept constant) and parallel strands/turn, providing extra clearance at slot opening. With the loss reduction techniques implemented, the SPM-V machines can achieve comparable efficiency but much higher torque density than their conventional counterparts. Moreover, the proposed flux shunt was also found to be very effective in reducing the potential risk of permanent magnet (PM) irreversible demagnetization, a key issue for SPM-V machines at high power ratings. [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]

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 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]

For dual three-phase machines, vector space decomposition allows the control of fundamental and main harmonic components in αβ and xy subspaces, respectively. However, the modulation of voltage references in the two subspaces using the space vector pulsewidth modulation (SVPWM) is not independent but coupled. In that, voltage references of two subspaces cannot be modulated simultaneously beyond the modulation restraints, thereby distorting the voltage regulation and causing harmonics or even system misbehavior. Meanwhile, the fundamental voltage in αβ subspace responsible for electromagnetic torque generation should be prioritized and secured. Thus, this article proposes a systematic analysis of modulation restraints of three representative SVPWM techniques, i.e., the linear modulation range of xy subspace under an assured modulation index of the fundamental voltage. Voltage references of xy subspace within this range can be modulated successfully without affecting the assured modulation index and the margin left for harmonic control in xy subspace is then acknowledged. This can be used to limit the output of current controllers not to exceed the voltage modulation restraint, thereby avoiding the modulation failure. Finally, the experimental results validate the linear modulation range and demonstrate the modulation behaviors within and out of the linear modulation range. [ABSTRACT FROM AUTHOR]

In this article, three 6-slot/2-pole high-speed permanent magnet motors with 1, 2, and 3 coil-pitch windings are optimized by the finite element method taking into account stator copper loss and iron loss. Their electromagnetic performances are analyzed and compared, including air-gap flux density, back electromagnetic force, electromagnetic torque, winding inductances, and various loss components. For high-speed application, compared with 1 and 3 coil-pitch windings, the proposed 2 coil-pitch windings have a good tradeoff between winding factor and end-winding axial length which are attractive for improved torque density. Finally, the experimental results are given to validate some of the finite element predicted results. [ABSTRACT FROM AUTHOR]

This article investigates the influence of stator slot number on electromagnetic performance of two-pole high speed permanent magnet (HSPM) slotted motors with toroidal (TO) windings. Four two-pole slotted motors with different slot numbers, i.e., 3, 6, 9, and 12, are globally optimised for maximum torque, and their electromagnetic performance are compared, including winding factor, air-gap flux density, back electromotive force, cogging torque, electromagnetic torque, winding inductances, unbalanced magnetic force (UMF), and various loss components. It shows that the six-slot/two-pole HSPM motor with TO windings is eminently suitable for high speed application due to no UMF and easy to realise a modular structure. In addition, TO and tooth-coil windings are compared in the three-slot/two-pole motors, and the results confirm that TO windings are not suitable for use in the three-slot/two-pole HSPM slotted motor due to large airgap field harmonics. Finally, a six-slot/two-pole prototype motor is manufactured and tested to validate the finite element predictions. [ABSTRACT FROM AUTHOR]

In this article, we propose a novel switching-table-based direct torque control (ST-DTC) method to eliminate the current harmonics in dual-three-phase permanent-magnet synchronous machines due to the back electromotive force (back EMF) harmonics and voltage vector selection. By employing a novel space voltage vector selection strategy and the optimal action time for different groups of vectors, a novel ST-DTC method is developed. Furthermore, in order to implement standard pulsewidth modulation (PWM) switching sequence, a centralization PWM method for 36 voltage vectors is introduced. The proposed method can effectively reduce the phase current harmonics caused by both back EMF distortion and voltage vector selection, and still reserve the advantages of the conventional ST-DTC, such as fast torque response and simple structure. Its effectiveness is verified by simulations and experiments. [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]

High-speed brushless dc (BLDC) drives usually operate with low carrier–fundamental frequency ratio, which causes abundant sideband harmonic current components. Some sideband harmonics will be induced in low-frequency range, leading to low-frequency current oscillations and low-frequency torque ripples. To minimize these undesired sideband harmonics, a novel pulsewidth modulation commutation pattern, i.e., carrier-synchronized commutation (CSC), is proposed in this article. For comparison, two conventional commutation patterns, including regular-sampled commutation (RSC), and natural-sampled commutation (NSC), are analyzed. To reveal the characteristics of sideband harmonics caused by RSC and NSC patterns, an extended geometric wall model is introduced, which can be used for the Fourier decomposition of complex vectors. Theoretical, simulation, and experimental results demonstrate the conventional RSC and NSC patterns will produce additional sideband harmonic currents and torque ripples, while the proposed CSC pattern can considerably suppress these adverse influences and meanwhile presents high performance and robustness. [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]

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]

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]

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]

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]

In the high-speed brushless dc drives, long commutation freewheeling duration will increase the difficulty of sensorless operation that is based on the back electromotive force (EMF) zero-crossing detection. In extreme cases when the freewheeling angle exceeds 30°, the zero crossing of back EMF will be undetectable, resulting in the failure of sensorless drives. As a result, the sensorless safety operation area (SOA) is limited by the long freewheeling angle issue. In this article, it is found that the pulsewidth modulation (PWM) patterns have a big influence on the freewheeling angle. Hence, in the first place, through analytical methods, the mechanism that how different PWM techniques affect the freewheeling angle is investigated. The PWM pattern resulting in a minimum freewheeling angle is identified. Furthermore, a method to predict the SOA is developed, which provides a theoretical way to verify whether the predesigned torque and speed area can be achieved with the given motor parameters. Finally, the theoretical analysis is verified by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

An electronic pole-changing winding induction machine with eight and four poles for a 48-V starter-generator application is studied in this article. Starter-generators require high torque capability for short durations at low speed for cranking, a wide flux weakening region for regeneration, as well as high torque density, so that the machine may be integrated into a drive train with minimum change to the existing system. In this article, it is shown that when pole-changing windings are used, the axial length of the machine can be reduced compared to the baseline induction machine design, resulting in a more compact machine. The effects of shorter stack length and pole-changing windings on the performance of the induction machine are studied. Efficiency, loss, and power factor maps are calculated with analytical and finite-element methods and experimentally validated to compare the performance of the pole-changing winding induction machine with a baseline design under various operating conditions. [ABSTRACT FROM AUTHOR]

In this article, a current profiling technique is proposed for the torque density enhancement in switched reluctance machines (SRMs). The novel current profile is initially developed from the harmonic current injection method and is then modified into a unipolar waveform to allow the application of an asymmetric bridge inverter. It is found that, neglecting the magnetic saturation, the optimal current profile for the maximum torque per ampere operation in an SRM is close to a pulse with high-order harmonics. However, an optimized current with relatively low-order harmonics can provide better performance in the practical situation. Based on the analytical and the finite element results, the proposed method is proved to be able to enhance the torque density by 20% at the light load condition and by 15% at the rated condition compared with the conventional SRM excitation. Also, the large torque ripple and core loss in SRMs are suppressed and the efficiency is improved. More importantly, unlike many other current profiling techniques, the proposed current profile has fixed parameters and is easily adaptable to different machine specifications. The effectiveness of the proposed method is verified by both the finite-element analyses and the experiments. [ABSTRACT FROM AUTHOR]

The second harmonic current injection method is recently developed to enhance the torque density of variable flux reluctance machines (VFRMs). This article investigates the feasibility and effectiveness of the second harmonic current injection method in VFRMs with different stator/rotor pole combinations. By using magnetic gearing effect, it is found that the second harmonic injection method can only be applied to the 6j/(6i ± 2)j (i, j = 0, 1, 2…) stator/rotor pole VFRMs for the torque density enhancement. For the other stator/rotor pole combinations, the second harmonic current has no contribution in average torque production but only leads to excessive torque ripple. Further, by using global optimization method and finite element analysis, 6/8 stator/rotor pole combination is proved to be the optimal stator/rotor pole combination for 6-stator-slots VFRMs with the second harmonic current injection method, being able to exceed the maximal torque density of conventional VFRMs by 12% at a fixed copper loss. [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]

A new analytical torque model based on dq0-axis frame has been developed for 3-phase, 12-slot/8-pole single layer doubly salient synchronous reluctance machines. This newly developed torque model, compared to the one often based on abc-axis frame, is necessary to simplify the investigation of dynamic performance such as torque–speed curve and efficiency maps. It has been found that the third-order current harmonic injection not only improves the torque performance (increased average torque and reduced torque ripple) in constant torque region but also maintains a similar torque level as the fundamental current supply in the flux weakening region. Moreover, although the fifth- and seventh-order current harmonic injection can reduce the torque ripple of machine, their dynamic performances are compromised due to low average torque and significant voltage distortion. Finite element simulations and dynamic tests have been carried out to prove the accuracy of the developed torque model and also the efficiency of the proposed current harmonic injection method. [ABSTRACT FROM AUTHOR]

This article investigates the impact of scaling on the electromagnetic performance of surface-mounted permanent-magnet Vernier (SPM-V) machines with a main focus on open-circuit induced Electro Motive Force (EMF). Three different power ratings, i.e., 3 kW, 500 kW, and 3 MW, have been chosen for this article. For each power rating, the SPM-V machines are analyzed for different slot/pole number combinations to compare their optimal performance with a conventional SPM machine. Step-by-step development of an analytical equation is presented for the prediction of induced EMF taking into account the interpole leakage of rotor permanent-magnets. 2-D finite-element analysis (FEA) has been used to validate the analytical equation across different power ratings. The analytical equation is thereafter utilized to study the influence of different geometric parameters on the performance of the SPM-V machines. It reveals that the back EMF and torque of SPM-V machines, for a given normalized pole pitch (rotor pole pitch to magnetic airgap length), are unaffected by the increase in airgap length due to scaling. However, the power factor of SPM-V, unlike the conventional SPM, reduces significantly with the increase in electrical loading due to the scaling effect. The analytical model for induced EMF and the 2-D FEA predicted results are validated by experiments using conventional SPM and SPM-V machine prototypes. [ABSTRACT FROM AUTHOR]

This article investigates the torque characteristics of a switched flux hybrid magnet memory machine (SF-HMMM) by employing a coupled solution combining a quasi-linear hysteresis model (QLHM) of low coercive force (LCF) magnet and frozen-permeability method (FPM). This provides an in-depth understanding of the torque production of SF-HMMM. The QLHM is utilized to characterize the repetitive remagnetizing/demagnetizing behaviors of LCF permanent magnets (PMs), while the FPM is employed to separate and quantify the torque contributions due to two sets of PMs and armature windings. The machine topology and analysis methodology are described, respectively. The torque segregation results accounting for magnetization state variation are analyzed by the proposed coupled solution. The influence of the LCF PM property on the torque segregation result is investigated to facilitate the establishment of general design guidelines. Finally, the prototype is tested to experimentally validate the theoretical analysis. [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]

This paper proposes a novel flux reversal permanent magnet (FRPM) machine with asymmetric-stator-pole (ASP) configuration. Different from the conventional FRPM machine with uniform “NS-NS-NS” PM sequence, the proposed ASP-FRPM machine is characterized by a “NSN-S-NSN” magnet arrangement. Hence, the interpolar flux leakage is significantly reduced with the developed design, which can improve the torque capability. The machine topologies, features, and operating principle are introduced, respectively. A simplified magnetic circuit model is established to reveal the underlying flux leakage reduction mechanism of the ASP design, and the rotor pole number is analytically optimized as well. The design parameters are then globally optimized so as to improve the torque quality. In addition, the electromagnetic characteristics of the ASP- and conventional FRPM machines are compared. Finally, experiments have been carried out to validate the theoretical results. [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]

For hybrid-excited doubly salient synchronous machine, both the field excitation current and the d-axis current can be utilized to adjust the flux-linkage, which provides more flexible control parameters for flux-weakening operation. In this paper, three flux-weakening control methods, i.e., utilizing field excitation current alone (Method I), utilizing armature current alone (Method II), and optimal method (Method III), are proposed and compared. All three methods can achieve similar torque performance in the constant-torque region. In the flux-weakening region, Method I exhibits low torque and limited operating speed range. The operating speed range can be further extended by Methods II and III. In addition, Method III can provide a higher efficiency in flux-weakening region than Method II since the copper loss of field winding can be decreased in proportion to the reduction of field excitation current. Those flux-weakening control methods are verified by experimental results. [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]

In this paper, the partitioned stator (PS) structure is extended to variable-flux memory machines, forming two newly emerged PS switched-flux memory machines (PS-SFMMs) with series and parallel hybrid magnet configurations. From the perspective of geometry, both two PS-SFMMs share identical outer stator and rotor segments, while two different types of permanent magnet (PM) arrangements are employed in the inner stationary part. Thus, the developed machines can inherent the geometric separation of the armature winding and PM excitations from the PS design, thus achieving acceptable torque capability, and excellent air-gap flux control. A comparative study between PS-SFMMs with series and parallel structures is established. First, the topologies and operating principle are introduced, respectively. In addition, the design tradeoffs and PM sizing of the two PS machines are revealed and optimized with a simplified magnetic circuit model. Then, the electromagnetic characteristics of PS-SFMMs with different magnetic circuits are investigated and compared with the finite-element (FE) method. The FE results are validated by the experiments on a parallel prototype. [ABSTRACT FROM AUTHOR]

In this paper, two flux-switching permanent-magnet (FSPM) wind power generators with 9- and 12-phase windings are designed and comparatively analyzed. Both two generators are designed under the rated specifications of 10 kW output power and 220 V phase voltage at 500 r/min. The static characteristics and power generating performances including output voltage, power, and efficiency at rated and variable load/speed conditions are predicted by finite-element analysis and validated by experimental tests based on the two FSPM prototypes. It shows that the 12-phase 24-stator-slot/22-rotor-pole FSPM generator exhibits a higher air-gap flux density, a higher torque/power density, and a lower voltage regulation factor. Besides, it has a better overload capability than its 9-phase 36-stator-slot/34-rotor-pole counterpart when the load and wind speed exceed the rated levels. The comparative study reveals the benefits of the lower leakage flux and permeance from the larger stator-slot opening and longer magnetic circuit. [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]

A memory machine (MM) equipped with hybrid permanent magnets (PMs), i.e., NdFeB and low coercive force PMs, exhibits acceptable torque capability at low speeds and high efficiency at high speeds. Previous literatures have addressed that the constant power speed range (CPSR) of MMs can be further extended by online PM flux control and the requirement of the flux-weakening (FW) inverter current can be reduced as well. Nevertheless, how to coordinate the d-axis vector FW and PM magnetization control over a whole operating range in a reasonable manner remains unreported. Therefore, this paper proposes and implements a stepwise magnetization control strategy on a dc-magnetized MM based on the operating characteristics under various PM magnetization states and speed ranges. The configuration, principle, and mathematical model of the investigated machine are introduced first. Then, the proposed control strategy is established by dividing the operating envelop into several FW regions and an appropriate FW control scheme is utilized at each stage. It demonstrates that the CPSR can be effectively extended by simply applying the demagnetizing current pulses in several steps. This simplifies the control efforts considerably without resorting to continuous PM flux control and frequent actions of the switching devices. The effectiveness of the proposed control strategy is verified by experimental results. [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]

This paper investigates the torque production and the torque ripple reduction of a six-stator/seven-rotor-pole (6/7) variable flux reluctance machine (VFRM). As a main advantage, the 6/7 VFRM produces higher torque density, but less torque ripple compared with the 6/4 VFRM. The instantaneous torque equation of the 6/7 VFRM is derived by considering the spectra of the winding inductance and current. Based on the derived equation, the average torque is found to be mainly produced by the mutual inductance between the field and armature windings. The even-order harmonics of self-inductance and odd-order harmonics in mutual inductance between the field and armature windings are eliminated due to the opposite polarity connection of the armature coils in each phase. This results in the elimination of the third harmonic torque ripple, while a multiple of the sixth harmonic torque ripple exists. In order to mitigate the sixth harmonic torque ripple, the harmonic current injection method is implemented into the field winding. The field harmonic current is calculated from the analytical torque ripple equation. The performance of the proposed methods is verified by both finite element analysis (FEA) and experiment. [ABSTRACT FROM AUTHOR]