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

This paper proposes a novel sensorless method for open-winding (OW)-permanent magnet synchronous machine (PMSM) (OW-PMSM) with circulating current suppression. First, a zero-sequence steerable space vector pulse width modulation together with zero-sequence controller (ZSC) is implemented to suppress the circulating current existing in the OW-PMSM drive system with common dc bus. Afterward, the zero-sequence back EMF reconstructed from the output signal of the ZSC is utilized to extract the position information via synchronous phase-locked loop-based position observer. Hence, the voltage transducer and resistance network used in the conventional zero-sequence back-electromotive force-based sensorless methods can be consequently eliminated. Moreover, the proposed method requires no machine parameters, such as winding resistance, d- and q-axis inductances which are indispensable for the conventional fundamental back-EMF-based methods. The voltage disturbance components due to the resistance, inductance, and rotating cross coupling voltage drops can be avoid. Therefore, stronger robustness against the variation of machine parameters due to load or temperature variation can also be obtained. Finally, the proposed method is validated via experiments on a 3-kW OW-PMSM drive system. [ABSTRACT FROM AUTHOR]

Due to asymmetric three-phase system and influence of inverter nonlinearity, large torque, and stator flux harmonics would exist in the space vector modulation-based direct torque controlled (DTC-SVM) three-phase permanent magnet synchronous machines (PMSMs). A general expression for electromagnetic torque is derived for DTC of asymmetric three-phase PMSMs considering the influence of inverter nonlinearity. To mitigate the influence of the undesired harmonics, a compensation method is developed by enhancing the standard proportional-integral (PI)-regulator in the torque and flux loops with appropriate resonant controllers. Since the 2nd- and 6th-order harmonics are the most dominant components, two resonant controllers tuning at the 2nd and 6th of stator angular frequency, respectively, are utilized. The proposed method can achieve good steady-state performance in terms of low torque and flux ripples, while keeping the merits of the conventional DTC-SVM strategy such as good dynamic torque response and machine parameter independence. The experimental results validate the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

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

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

A partitioned stator hybrid excited machine is proposed, in which the permanent magnets and field windings are alternately placed on an inner stator separated from the outer stator having armature windings. This machine inherits the features of brushless machines and benefits from better space utilization. The operating principle and the effects of slot/pole combinations are investigated in detail. Further, based on 2-D finite-element analysis, the electromagnetic performances of the proposed machines, including back-electromotive force, cogging torque, flux regulation range, torque capability, power factor and torque–speed curve, are evaluated. The results reveal that the proposed machines can exhibit wide flux regulation range as well as good torque density. The prototype is manufactured and tested to validate the predictions. [ABSTRACT FROM PUBLISHER]

A dual-stator hybrid-excited switched-flux (DS-HESF) machine, which is based on the conventional SF permanent magnet machine but employs a secondary stator to accommodate the field windings, is proposed in this paper. The DS-HESF machine inherits the robust rotor and benefits from a better space utilization. The topology and operating principle of the proposed machine are introduced in detail. Based on the 2-D finite-element analysis, the comparison between the DS-HESF machines having different rotor pole numbers is carried out, accompanied with a conventional HESF machine as a baseline. The results reveal that the DS-HESF machines exhibit not only higher torque density but also a better flux regulation capability. The prototype is manufactured and tested to validate the predictions. [ABSTRACT FROM PUBLISHER]

This paper presents a partitioned stator switched flux memory machine (PS-SFMM) with triple magnets to enable expedient flux control with reduced converter power rating. Meanwhile, the torque/magnet cost ratio of the machine has been significantly improved without much compromise of the torque capability. Three kinds of permanent magnets (PMs), NdFeB, SmCo, and AlNiCo, are hybridized, and hence the irreversible demagnetization of vulnerable AlNiCo PMs can be well prevented by SmCo magnets. The machine configurations with dual PM (DPM) and triple PM (TPM) are described first. Thereafter, the performance improvement mechanism is unveiled and addressed in the perspective of hysteresis curves as well as simplified magnetic circuits. In addition, the electromagnetic characteristics of the proposed machine with triple-magnet design are investigated and compared with those having DPMs. Finally, two PS-SFMM prototypes with DPM and TPM are manufactured and tested to verify the theoretical analyses. [ABSTRACT FROM PUBLISHER]

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

In this paper, a novel pulsating carrier signal injection strategy utilizing zero-sequence voltage is proposed for sensorless control of permanent-magnet synchronous machine (PMSM) drives. Different from the conventional zero-sequence carrier voltage sensing method using rotating signal injection in the stationary reference frame, the proposed pulsating injection is based on the estimated reference frame, which rotates anticlockwise at twice estimated rotor electrical angular speed. Then, the rotor position estimation is fulfilled via enabling the zero-sequence carrier voltage to zero. Compared with conventional rotating injection using zero-sequence voltage, the proposed strategy is simpler for signal demodulation and more robust to signal processing delays due to the fact that it is amplitude modulated by machine saliency and phase shifts of saliency position due to signal processing delays are intrinsically cancelled, which is the same as the classical pulsating injection in the estimated synchronous reference frame with carrier current sensing. Therefore, the proposed method can combine the synergies of zero-sequence method (i.e., high bandwidth and stability) and pulsating injection (i.e., increased accuracy and fast dynamic response). Furthermore, the cross-coupling magnetic saturation effects on zero-sequence voltage sensing-based sensorless control are discussed in detail. All the theoretical analyses are validated by experiments on a laboratory surface-mounted PM (SPM) machine. [ABSTRACT FROM AUTHOR]

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

The hybrid-excited stator slot permanent magnet (HSSPM) machines have good flux regulation capability due to the dc excitation. This makes them attractive candidates for variable speed applications. In this paper, the choices of stator/rotor pole combinations for an arbitrary number of armature phases are discussed. The three-phase 12-10/11/13/14 stator/rotor poles HSSPM machines with single- and double-layer windings are further investigated. Their open-circuit characteristics, torque, inductances, and unbalanced magnetic forces are comparatively studied using 2-D finite-element analysis (FEA). Finally, the 2-D FEA is experimentally validated. [ABSTRACT FROM AUTHOR]

The partitioned stator (PS) machine adopts two stators to allocate windings and permanent magnets (PMs) separately, increasing the space for PMs as well as armature coils to boost the electromagnetic torque and improving the thermal condition of PMs. In this paper, the PS switched-flux PM (PS-SFPM) machine and the PS flux reversal PM (PS-FRPM) machine are proved to inherently share the same operating principle and similar machine topology but with interior PM (IPM) and surface-mounted PM stators, respectively. Furthermore, four globally optimized PS machines with different inner stator topologies are compared in terms of back EMF, cogging torque, electromagnetic torque, torque per PM volume, and flux-weakening capability. The results reveal that the spoke-shaped IPM (IPM-spoke) inner stator exhibits the highest back EMF and hence the highest average torque, while the I-shaped IPM (IPM-I) stator has the best flux-weakening capability, and the V-shaped IPM (IPM-V) produces the highest torque per PM volume. Furthermore, four machines are redesigned with the same PM usage volume, and the results show that the PS-SFPM machine still exhibits the highest back EMF as well as torque although with sacrificed advantages. The finite-element analyses and experiments are used to confirm the predictions. [ABSTRACT FROM AUTHOR]

A new flux reversal permanent magnet (FRPM) linear machine known as the partitioned stator FRPM (PS-FRPM) linear machine is proposed. The structure and the operation principle of the machine are described, and the major design parameters are optimized for maximum thrust force. A periodic model is also used in the analysis in order to highlight the significant effect of the longitudinal end effect on the machine performance, particularly in terms of unbalanced magnetic circuit and cogging force. Furthermore, the proposed machine is compared with the conventional FRPM linear machine. It is concluded that higher thrust force, less cogging force, and consequently less thrust force ripple can be obtained by the proposed machine. [ABSTRACT FROM PUBLISHER]

Permanent magnet (PM) tubular machines have been applied to many applications, since they offer high force density with no end winding and no net attractive force between the mover and the stator. In this paper, two novel PM tubular machines named partitioned stator interior PM (PS-IPM) and partitioned stator surface-mounted PM (PS-SPM) tubular machines are proposed. Both the proposed machines are optimized for maximum thrust force, and their electromagnetic performance has been compared. It is found that the PS-IPM tubular machine has higher thrust force capability and better magnet utilization compared with the PS-SPM tubular machine. However, due to lower cogging force, the PS-SPM tubular machine has fewer thrust force ripples. Furthermore, the effect of the cross-coupling magnetic saturation on PM flux linkage, and the $d$ -axis and $q$ -axis inductances for both the proposed machines is investigated. It is demonstrated that the PM flux linkage and the $d$ -axis and $q$ -axis inductances are affected by the cross-coupling magnetic saturation. Moreover, the force–velocity characteristics of the proposed machines are calculated and compared. It is observed that both the machines have good constant power operation capability. [ABSTRACT FROM PUBLISHER]

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

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

This paper presents a quantitative comparative study on the two novel memory machines (MMs) with two sets of different magnets on the stator, which are derived from the switched flux (SF) and the variable reluctance (VR) topologies, respectively. The machine topologies, the operating principles, and the design considerations are described. The hybrid magnet sizing is analytically optimized with the aid from a simplified magnetic circuit. Then, the major parametric optimization is conducted on the two machines sharing identical outer diameter and stack length, as well as the copper loss constraint. The electromagnetic performance of the two optimally designed models is analyzed and comprehensively compared, which confirms the advantage of the SF topology for MMs. [ABSTRACT FROM AUTHOR]

Owing to different magnetic saturation conditions in surface-mounted permanent magnet machines operating under different loads, the optimal design to minimize the cogging torque may not be the one to minimize torque ripple as well. This paper investigates the design tradeoff between the open-circuit cogging torque and the on-load torque ripple by taking the design of slot opening as an example. With the aid of the frozen permeability method, first, the torque components under different slot opening widths and load conditions are presented based on a 12-slot/8-pole machine. The result reveals that the on-load cogging increases significantly, especially when a small slot opening width is adopted, which is opposite to the condition for minimizing the open-circuit cogging torque. Then, two machines separately designed for minimum open-circuit cogging torque or minimum on-load torque ripple are compared to illustrate alternative design tradeoffs. Finally, a prototype machine is manufactured and tested to validate the analysis results. [ABSTRACT FROM AUTHOR]

A novel stator hybrid-excited, parallel flux path, synchronous machine of doubly salient topology is proposed. It has the novel features of: 1) hybrid dc field and permanent magnet (PM) excitation in the stator; 2) magnets placed in the slots between adjacent salient stator poles; and 3) the magnetic poles of PMs arranged, such that the flux premagnetizes the stator, but it is in a direction to oppose the dc excitation flux. The electromagnetic characteristics of the machine are analyzed on open-circuit and load. Since the new machine topology is developed from the variable-flux machine (VFM), a comparison of their electromagnetic torque and machine losses is conducted. The average electromagnetic torque of the hybrid-excited machine can be increased by 18% for fixed copper loss in comparison with the VFM due to the reduction of magnetic saturation in the stator. It is also shown that at high temperatures some risk of PM demagnetization exists when excited with dc and armature currents due to fringing flux that exists between the stator and the rotor poles. However, this affects only a very small area of the PMs. The performance of the hybrid-excited machine is predicted by a 2-D finite-element analysis and experimentally validated. [ABSTRACT FROM AUTHOR]

The mechanism and the influence of the on-load terminal phase voltage distortion by the armature reaction in interior permanent magnet (IPM) machines with fractional-slot concentrated windings (FSCWs) are investigated in this paper, by taking a 12-slot/8-pole machine as an example. The phenomenon is presented first, which shows that the peak voltage will be much higher than the fundamental value, especially under the flux-weakening operation. Then, the mechanism is investigated with the aid of the frozen permeability method. Due to the geometric feature of the FSCW IPM rotor, the armature reaction flux will asymmetrically enhance the local magnetic saturation in the tooth-tips and the rotor lamination region near the rotor ribs, which disrupt the smooth variation of phase flux linkage and lead to a voltage distortion. With the increasing of current advancing angle ( $\beta $ ), this effect will become more obvious and result in the higher distortion level. Furthermore, the influences of voltage distortion on the machine torque performance are investigated, which show that it will only contribute to the torque ripple in the constant torque region, but will largely reduce the flux-weakening operation region compared with the ideal one calculated by the fundamental voltages only. Finally, a prototype is manufactured and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

This paper presents a simple analytical model for two types of three-phase surface-mounted permanent magnet machines: modular and unequal tooth (UNET) width machines with different slot/pole number combinations. It is based on the slotless open-circuit air-gap flux density and the slotted air-gap relative permeance calculations. This model allows calculating the opencircuit air-gap flux density, phase flux linkage, back electromotive force, and average torque of both the modular and UNET machines. Its accuracy has been validated by the 2-D finite-element (FE) method. A flux focusing/defocusing factor has also been introduced to analyze the influence of flux gaps in alternate stator teeth of modular machines on the machine electromagnetic performances. It has been found that by properly choosing the slot/pole number combination and flux gap width, the open-circuit air-gap flux density, the winding factor, and the flux focusing effect can all be improved. As a result, the performance of the modular machine can be significantly boosted. The analytical and FE models have been validated by experiments. [ABSTRACT FROM AUTHOR]

The on-load voltage distortion in fractional slot surface-mounted permanent magnet machines refers to the phase terminal voltage distorted by armature reaction. With the aid of frozen permeability method, the mechanism of this phenomenon has been investigated based on a 12-slot/8-pole model as an example, showing that the local magnetic saturation in tooth-tips is the main cause, especially when small or closed slot openings are adopted. Then, its impacts on machine performance under vector control have been investigated. If the dc-link voltage is sufficient to satisfy all distorted voltage, i.e., operating in constant torque region, the phenomenon mainly contributes to torque ripple. However, it becomes more problematic in the flux weakening region if the dc-link voltage is limited. Both base-speed and torque-speed curve will significantly differ from the expected results calculated by fundamental voltages. Meanwhile, if the machine operates beyond the base speed, or considering the limited bandwidth in real systems, the phase currents may be distorted, which consequently increase the current harmonics and reduce the average torque. Finally, a prototype machine is manufactured and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

Aposition offset-based multiparameter estimation for permanent magnet synchronous machines (PMSMs) under variable speed control is proposed in this paper, which does not need the aid from nominal parameter values of the PMSM and could estimate the rotor permanent magnet (PM) flux linkage and winding resistance separately. For the estimation of rotor PM flux linkage, two sets of PMSM data corresponding to two position offsets are measured while the dq-axis reference currents are set to constants so as to ensure that the estimated machine parameters will not vary during the data measurement. Afterwards, the winding resistance will be estimated from measured PMSM data without addition of position offsets, in which the estimation and compensation of distorted voltage due to inverter nonlinearity are also taken into account. The conventional quantum genetic algorithm is used for aiding the calculation of proposed estimation,which is finally tested on an interior PMSM and shows very good performance in the estimation of rotor PM flux linkage and winding resistance. Thus, it could be used for the condition monitoring of stator winding and rotor PMs of PMSMs. [ABSTRACT FROM AUTHOR]

This paper proposes how to use the addition of rotor position offsets as perturbation signals for the parameter estimation of permanent-magnet synchronous machines (PMSMs), which can be used for the condition monitoring of rotor permanent magnet and stator winding. During the proposed estimation, two small position offsets are intentionally added into the drive system, and the resulting voltage variation will be recorded for the estimation of rotor flux linkage. With the aid from estimated rotor flux linkage, the stator winding resistance can be subsequently estimated at steady state. This method is experimentally verified on two prototype PMSMs (150 W and 3 kW, respectively) and shows good performance in monitoring the variation of rotor flux linkage and winding resistance. [ABSTRACT FROM PUBLISHER]

This paper proposes a multiparameter estimation scheme for permanent-magnet (PM) synchronous machines (PMSMs) under variable-speed control, of which the estimation model is full rank and has taken into account the estimation and compensation of voltage-source-inverter nonlinearity. During the proposed estimation, the PMSM will work under variable speed control, and two sets of machine data corresponding to two sets of different rotor speeds will be recorded and used for the calculation of the proposed estimation model. It shows that the proposed estimation model can be solved by using a conventional quantum genetic algorithm and can ensure the identifiability of all needed parameters owing to its inherent full rank feature. The performance test of the proposed estimation is then conducted on an interior PMSM, and it shows that parameters such as rotor PM flux linkage and winding resistance can be accurately estimated without the aid from nominal parameter values of PMSM. Therefore, the proposed method can be used for the condition monitoring of stator winding and rotor PMs. [ABSTRACT FROM PUBLISHER]

This paper systematically presents the development of novel stator electrically field excited synchronous machines having salient pole rotors without any coils or magnets. This kind of new machine does not use slip-rings/brushes required in the conventional rotor wound field machines and combines the synergies of wound field machines, permanent magnet (PM) machines, switched reluctance, and synchronous reluctance machines. This paper describes the machine topologies, winding configurations, electromagnetic performance, and torque/power density, as well as acoustic noise and vibration, together with a comparison with the Toyota Prius interior PM machine in terms of torque/power speed characteristics. [ABSTRACT FROM AUTHOR]

A rotor shaping technique with optimal third harmonic is presented to enhance the average torque of interior permanent-magnet (IPM) machines in this paper. The optimal value of third harmonic injected into the rotor outer surface shape has been derived and further confirmed by both finite-element analyses and experiments. The impact of the optimal third harmonic to the rotor shape on the electromagnetic performance, including harmonics in the back electromotive forces, cogging torque, average torque, and torque ripple, is investigated. It is demonstrated that without any modification of the costly rare earth permanent magnet employed for the inverse-cosine-shaped rotor, the average torque of the machine of an inverse cosine injected with an optimal third-harmonic-shaped rotor can be improved by > 6%. Simultaneously, the torque ripple remains almost unchanged, and the saliency ratio is also improved, further boosting the average torque. Finally, the machines with both conventional and optimal third harmonic rotors are prototyped and tested to validate the analysis. [ABSTRACT FROM PUBLISHER]

This paper presents the simplified analytical optimization and comparison between electrically excited (EE) and permanent-magnet (PM) machines in terms of torque per volume T/V and torque per weight T/G for low-speed applications when their copper loss and overall size are the same. Analytical torque models for both machines are individually developed and optimized to obtain the optimal flux density ratio, split ratio, and maximum torque densities. Furthermore, the variation of optima with the number of poles and machine size is also investigated. The analytical analyses are validated by both finite-element analyses and experiments. It is concluded that torque densities of PM machines can be more than \sqrt2 times higher than those of EE machines. For EE machines, there is an optimal pole number to maximize torque densities, and large volume applications are preferred. In actual applications, EE machines are more likely to compromise the torque density to meet the thermal constraints. It also shows that the optimal T/G designs have significantly higher split ratio and are more cost- and weight-effective than the optimal T/V designs. [ABSTRACT FROM PUBLISHER]

This paper presents a simplified analytical model based on one slot per pole for predicting the open-circuit AC winding loss of surface-mounted permanent-magnet machines accounting for the influence of tooth-tips but neglecting the redistribution effect of eddy currents. The comparison between the analytical models and finite-element results shows that the simplified analytical model has similar accuracy as the analytical model accounting for all slots together. The influence of various design parameters, such as conductor layout, slot width, slot opening width, tooth-tip height, magnet pole-arc to pole-pitch ratio, and gap between tooth-tips and conductors, on the open-circuit AC winding loss is investigated. It shows that the open-circuit AC winding loss gradually decreases with the number of radial conductor layers if the number of circumferential layers is larger than 1, although the radial segmentation is ineffective when there is no circumferential segmentation. The loss decreases greatly when the number of circumferential layers changes from 1 to 2, but reduces slowly when the conductors are further circumferentially segmented. [ABSTRACT FROM PUBLISHER]

This paper presents optimal third harmonics in both permanent magnet (PM) shaping and current waveform to improve the output torque of five-phase surface-mounted PM (SPM) machines. The optimal value of third harmonic injected into the sinusoidal PM shape and current waveform for maximum torque improvement is analytically derived and validated by both finite element (FE) analyses and experiments. It is found that the optimal third harmonic is 1/6 of the fundamental one for both PM shape and current waveform. For the five-phase SPM machines having rotors without shaping, Sine shaping, or Sine shaping with third harmonic injected, the electromagnetic performance including the back EMF waveform, cogging torque, average torque, torque ripple, copper loss, iron loss, impact on power inverter, and demagnetization withstand capability are compared. It is demonstrated that, although the copper loss and iron loss increase due to additional third harmonic in the winding current and magnet shape, the average torque with optimal third harmonics injected in PM shaping and current waveform can be improved by >30% while the torque ripple and remains similar to that of the one with Sine shaping. In addition, this will reduce the dc bus voltage while maintaining the machine torque density. Furthermore, the machine with Sine and Sine+3rd rotors presents much better demagnetization withstand capability performance than conventional rotor. [ABSTRACT FROM PUBLISHER]

In order to simplify manufacture processes and improve fault-tolerant capabilities, modular electrical machines, especially the ones with segmented stators, are increasingly employed. However, flux gaps between segments are often inevitable. In this paper, to take advantage of these flux gaps to enhance the machine performance, novel modular permanent magnet machines with different slot/pole combinations have been proposed. The influence of these flux gaps on the electromagnetic performance of modular PM machines, such as winding factor, open-circuit air-gap flux densities, back-EMFs, cogging torque, on-load torque, inductances, magnetic saturation and copper losses, are comprehensively investigated and general rules have been established. It is found that for modular machines having slot number higher than pole number, the flux gaps between stator segments degrade the electromagnetic performance due to the lower winding factor and the flux defocusing effect. However, for modular machines having slot number lower than pole number, the electromagnetic performances can be significantly improved using proper flux gap width due to the higher winding factor and the flux focusing effect. The finite element results are validated by experiments using two prototype modular machines. [ABSTRACT FROM PUBLISHER]

This work presents a permanent magnet (PM) shaping technique with optimal third harmonic to improve the output torque without deteriorating the torque ripple in surface-mounted PM (SPM) machines. The optimal value of third harmonic injected into the sinusoidal PM shape for maximum torque improvement is analytically derived and confirmed by finite-element analysis. Further, the influence of magnet edge thickness on the airgap field distribution is investigated and utilized to compensate the inter-pole flux leakage and curvature effect. It is found that the optimal third harmonic is 1/6 of the fundamental one. For the SPM machines having rotors without shaping, Sine shaping, Sine shaping with third harmonic injected, the electromagnetic performance, including the back-EMF waveforms, cogging torque, average torque, and torque ripple are compared. It is demonstrated that the average torque in the machine of a Sine shaping with an optimal third harmonic injected can be improved by >9\%, while the torque ripple remains similar to that of the one with Sine shaping. Finally, the machines with both conventional (without shaping) and optimal third harmonic PM rotors are prototyped and measured to validate the analyses. [ABSTRACT FROM PUBLISHER]

Winding resistance and rotor flux linkage are important to controller design and condition monitoring of a surface-mounted permanent-magnet synchronous machine (PMSM) system. In this paper, an online method for simultaneously estimating the winding resistance and rotor flux linkage of a PMSM is proposed, which is suitable for application under constant load torque. It is based on a proposed full-rank reference/variable model. Under constant load torque, a short pulse of id \neq 0 is transiently injected into the d-axis current, and two sets of machine rotor speeds, currents, and voltages corresponding to id = 0 and id \neq 0 are then measured for estimation. Since the torque is kept almost constant during the transient injection, owing to the moment of system inertia and negligible reluctance torque, the variation of rotor flux linkage due to injected id \neq 0 can be taken into account by using the equation of constant torque without measuring the load torque and is then associated with the two sets of machine equations for simultaneously estimating the winding resistance and rotor flux linkage. Furthermore, the proposed method does not need the values of the dq-axis inductances, while the influence from the nonideal voltage measurement, which will cause an ill-conditioned problem in the estimation, has been taken into account and solved by error analysis. This method is finally verified on two prototype PMSMs and shows good performance. [ABSTRACT FROM PUBLISHER]

In sensorless control of permanent-magnet brushless ac machines, it is necessary to identify the initial rotor position prior to start-up of the machine. Although saliency-tracking-based sensorless techniques are proven to be a good candidate to estimate the initial rotor position in sensorless control, magnetic polarity identification is another important issue. Since the machine saliency undergoes two cycles in a single electrical period, the estimated position information based on machine saliency has an angle ambiguity of \pi. With the aid of magnetic saturation effect, this paper proposes a robust initial rotor position estimation scheme, which utilizes both d- and q-axis carrier currents, instead of only the q-axis carrier current, in conventional pulsating-carrier-signal-injection-based sensorless control algorithm. Integrated with conventional carrier-signal-injection-based sensorless algorithm, the proposed technique could obtain the initial rotor position for both standstill and free-running rotors. Finally, the experimental results confirm the effectiveness and robustness of the proposed method. [ABSTRACT FROM PUBLISHER]

The paper investigates the influence of slot/pole number combination and winding configuration on the electromagnetic performance, such as flux density, back-EMF and electromagnetic torque, of permanent magnet machines having static or rotating rotor eccentricities. It shows that the eccentricity does not affect the back-EMF and electromagnetic torque of rotational symmetrical machines whose configuration repeats every certain amount of angle. However, it significantly distorts the back-EMF and torque waveforms of rotational asymmetric machines. Further, the static eccentricity does not change the harmonic contents of back-EMF, but results in unbalanced three phase back-EMF. Hence, the temporal order of the main torque ripple due to the static eccentricity is equal to the pole number. On the other hand, the rotating eccentricity results in more back-EMF harmonics of orders equal to the PM magnetisation order plus/minus one. Therefore, the temporal order of the main torque ripple due to the rotating eccentricity is equal to the triplen number closest to the pole number. The prediction is validated by the experiment. [ABSTRACT FROM PUBLISHER]

Since the claw-pole machines can exhibit a number of attractive features, they have been widely applied to automotive and domestic markets. Nowadays, with the development of rare-earth permanent magnet (PM) and powder metallurgy techniques, high performance and cost-effective design of a multiphase claw-pole stator SPM brushless machine becomes achievable. However, the inherent 3-D structure makes finite-element analysis very time-consuming. Thus, a lumped-parameter magnetic circuit model is developed and validated by 3-D finite element analysis in this paper to design three-phase 10-pole claw-pole stator surface-mounted PM brushless machine having soft magnetic composite made stator core. A prototype machine is built and tested in accordance with analytically optimized overall design parameters. [ABSTRACT FROM AUTHOR]

This paper proposes a permanent magnet machine having mixed high-cost NdFeB and low-cost ferrite magnets with modular unequal magnet height poles, i.e., the modular Hat- and T-type magnet poles, together with optimized Halbach magnetization. The investigation shows that the modular T-type magnet poles with mixed magnet grade and unequal side-magnet height exhibit significant potential to achieve low torque ripple, relatively large electromagnetic torque, and high magnet usage efficiency simultaneously. [ABSTRACT FROM AUTHOR]

In order to improve the electromagnetic performance and ease the manufacture process, particularly stator winding, it is often preferable to employ a modular stator, e.g., individual stator tooth/back-iron segments, or separate stator tooth segments and back-iron segments. However, due to manufacture limits, there always exhibit additional air gaps between the stator teeth and back-iron segments. In practice, such gaps are likely to be nonuniform due to manufacture tolerances. This paper investigates the influence of uniform and nonuniform additional gaps on the cogging torque of permanent-magnet machines having either unskewed or step-skewed rotors. It is found that the presence of these gaps increases the cogging torque magnitude due to increased flux leakage through the tooth tips, while the uneven gaps can cause a significant increase in both the peak and periodicity of cogging torque waveform, which causes the skew method ineffective, as confirmed by both finite-element analyses and experiments. [ABSTRACT FROM PUBLISHER]

This paper presents a comparative study of torque–speed characteristics and cogging torque of the fractional-slot interior permanent magnet brushless ac machines having different slot openings, viz. open slot, closed slot, and hybrid slot (sandwiched open and closed slots), and unskewed and step skewed rotors. The influence of such alternate slot openings on the magnetic cross-coupling and cogging torque is particularly emphasized. Furthermore, the repercussion of the manufacturing limitations and tolerances on the cogging torque of machines having these alternate slot openings is also investigated. The magnetic cross-coupling level and the sensitivity of cogging torque to manufacturing limitations and tolerances strongly depend on the slot opening materials. The finite-element analyses are experimentally validated. [ABSTRACT FROM PUBLISHER]

The paper presents an analytical model for predicting the open-circuit magnet eddy-current loss due to slotting in surface-mounted permanent-magnet machines based on the exact subdomain field model. The spatial and temporal characteristics of field harmonics due to slotting and corresponding eddy-current harmonics in the magnet are analyzed in both stator and rotor reference frames. The contribution of interaction between eddy-current harmonics having the same frequency but different spatial order to magnet loss is revealed for the first time by an analytical model. The magnet loss can be under- or overestimated if the interaction is neglected. The developed model is capable of providing both high accuracy and insights of loss generation. The influence of the slot and pole number combination, slot-opening to slot-pitch ratio, pole-arc to pole-pitch ratio, circumferential segmentation, and rotational symmetry order on the open-circuit magnet is investigated using the developed model. The finite-element results validate high accuracy of the developed analytical model. [ABSTRACT FROM PUBLISHER]

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]

Cogging torque, as a very important design consideration in permanent-magnet (PM) machines, has been widely investigated for decades. In this paper, the study will be focused on the cogging torque behavior in surface-mounted PM (SPM) machines with two types of cost-effective PM designs. The results show that in a SPM machine with either type of cost-effective PM design, low cogging torque performance can be achieved, as confirmed by both finite-element analyses and experiments. [ABSTRACT FROM PUBLISHER]

This paper investigates the effectiveness of sensorless operation in carrier-signal-injection-based sensorless-control methods for permanent-magnet brushless ac motors. The sensorless safety operation area (SSOA) is introduced with due account for the quantization error in the analog to digital conversion. The SSOA defines a working area in the d–q plane in which the motor can operate in sensorless mode with a guaranteed performance in steady state. With the aid of SSOA, a proper injected carrier signal can be selected for the specific prototype machine and current-measurement resolution. Experimental results confirm that the performance of sensorless operation can be guaranteed when the machine operates inside the SSOA with cross-saturation compensation. [ABSTRACT FROM PUBLISHER]

This paper presents direct torque control (DTC) methodology for a four-switch three-phase (FSTP) inverter-fed permanent magnet brushless ac (PM BLAC) machine, with reference to a conventional six-switch three-phase (SSTP) inverter. It has been found that when derived from conventional voltage model flux estimation scheme, the predicted stator flux imbalance may be caused by unbalanced inverter voltage drop in the FSTP inverter, in which one phase winding is directly connected to dc-link midpoint. While this imbalanced problem does not adversely affect the performance of current-model-based DTC, it causes significantly nonsinusoidal current waveforms and considerably unbalanced current magnitudes in voltage-model-based DTC. A new compensation scheme taking into account the different forward voltage-drop values in the switching device and the freewheeling diode is proposed for the voltage-model-based DTC to correct for stator flux imbalance via the addition of corrective voltages to flux equations. The proposed scheme has significantly improved the shape of current waveforms with satisfactory balanced magnitudes, total harmonic distortion, and torque ripple factor, as verified by both simulation and experimental results. It has been shown that it is possible for an FSTP inverter to provide similar performance to an SSTP inverter when driving a PM BLAC machine. [ABSTRACT FROM AUTHOR]

The significant influence of slot opening on the optimal stator and rotor pole combination and on the electromagnetic performance of the switched-flux permanent magnet (SFPM) machine is observed and investigated in this paper. A new SFPM brushless machine with remarkable slot opening relative to the magnet thickness is developed to reduce the magnet usage and to increase the slot area. Its stator slot opening is almost several times of that in the conventional SFPM machine, but its magnet usage is only half. However, the new machine exhibits \sim40% larger back EMF and electromagnetic torque than those of the conventional machine, while its cogging torque and torque ripple are significantly lower. [ABSTRACT FROM AUTHOR]