Search

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]

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]

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]

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]

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]

In this article, two novel sinusoidal pulsewidth modulation (SPWM) strategies with simple implementation are proposed for an open-winding machine fed by isolated dc-bus dual two-level three-phase inverters to reduce switching frequency and current harmonics. The proposed strategies utilize zero sequence voltage injection and unbalanced reference voltage distribution to generate discontinuous PWM with low current harmonics and less switching action. Two different zero sequence voltages are introduced in this article corresponding to two proposed PWM strategies with different switching actions in a PWM cycle. The novelty of this article is low current harmonics and less switching actions in a PWM cycle compared with the conventional SPWM strategy. Moreover, compared with the subhexagonal center PWM strategy, the proposed SPWM strategies have advantages of easy implementation and half switching commutations with the same current harmonic characteristics. The superiority of the proposed SPWM strategies is validated by simulation and experiment results. [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]

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]

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]

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]

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]

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

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

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

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]

The commutation errors undermine the control performance of a brushless direct current (BLdc) drive especially at high-speed operation. In this article, a novel commutation error compensation strategy for BLdc drive that eliminates the phase deviation between the current and the back electromotive force is proposed. The d-axis current is introduced and used as the criterion to determine the commutation errors. Since the phase currents of BLdc drive contain large amounts of harmonics, which makes the d-axis current hard to detect, a least-mean-square-algorithm-based adaptive linear neuron filter is proposed. The optimal phase advance angle is adaptively generated by reducing the filtered d-axis current to zero. The proposed method does not need the motor parameter information or additional hardware, and can be implemented in general inverter controllers. The effectiveness of the proposed strategy is verified by both simulation and experimental results. [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]

This article investigates novel fractional slot nonoverlapping winding hybrid excited (HE) machines with consequent-pole permanent magnet (PM) rotors. The proposed machines accommodate the rotor PM and stator field winding separately, which has solved the spatial confliction of double excitations. Different consequent-pole interior PM rotor configurations are extended to retain the PMs and utilize the flux-concentrating effect. Then, the relationship of field and armature current ratio with the PM and wound field fluxes is identified theoretically, which provides design and optimization guidelines for the HE machines. Furthermore, the HE machines are optimized and compared with conventional PM machines. It is revealed that the HE machines exhibit enhanced torque density with flux-enhancing field excitation, and extended operation range with flux-weakening field excitation. Besides, the HE machine utilizing flux-concentrating effect exhibits the highest PM torque but sacrificed flux regulation capability due to magnetic saturation. Finally, the HE prototypes with different rotor configurations are fabricated and tested to validate the analyses. [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]

This article investigates the virtual third harmonic back electromotive force (EMF)-based sensorless drive method for high-speed brushless dc (BLDC) motors. Conventional zero-crossing point (ZCP) detection methods of virtual third harmonic back EMF require hardware low-pass filters and voltage comparators, causing serious phase lag. To avoid the undesired phase lag of hardware, the proposed method employs algorithmic oversampling technique to reconstruct the envelope of virtual third harmonic back EMF. Besides, the number of sampling points is dynamically adjusted according to the pulsewidth modulation duty ratio to guarantee the accuracy of ZCP detection. In addition, the influence of asymmetric motor parameters, i.e., phase resistance and inductance, on sensorless commutation is analyzed in depth. With asymmetric impedances, ZCPs of virtual third harmonic will deviate from their ideal positions. Consequently, the commutation events, which are searched based on ZCPs, will also be triggered at inaccurate positions and then the control performance will be deteriorated. In order to suppress the negative influence, a novel phase compensation method is proposed. All the theoretical analyses are validated by experiments at a 60 000 r/min BLDC drive platform. [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]

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 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]

In this article, an adaptive linear neuron based current harmonics suppression method for permanent magnet synchronous motors with nonsinusoidal back electromotive force (EMF) is presented, with due account for dead-time effect. The current harmonics can be well-suppressed by feedforwarding a self-tuning compensation voltage. The proposed method does not rely on the knowledge of back-EMF harmonic components and dead-time effect. Moreover, the proposed method is easy to implement, since it does not need the process to extract the current harmonics. The effectiveness of the proposed method is verified by both simulation and experimental results without requiring additional hardware. [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]

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]

This article investigates the influence of two nonideal factors on zero-crossing-point-detection-based sensorless control of high-speed brushless dc (BLDC) motor, i.e., asymmetric machine parameters and the resistance tolerance of back electromotive force (EMF) measurement circuit. Influenced by the machine parameter asymmetry, the back EMF envelopes will shift horizontally from its ideal position. Furthermore, the acquisition accuracy of back EMF is limited by the resistance tolerance of measurement circuit. Inaccurate acquisition of back EMF will result in vertical deviation of the envelopes. These two nonideal factors decrease the commutation accuracy and deteriorate the control performance. In order to suppress the commutation errors, an adaptive threshold correction strategy, including horizontal and vertical corrections is proposed for eliminating the influence of these two nonideal factors, respectively. In addition, the proposed correction method does not depend on any parameters of the machine or the measurement circuit. Finally, the theoretical analysis and the proposed correction method are verified by experiment on a 54 000 r/min high-speed BLDC drive platform. [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]

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

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