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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]

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]

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]

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]

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]

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]

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

In this paper, the open-circuit dc-winding-induced voltage in a wound field switched flux (WFSFs) machines is analyzed. The phenomenon of open-circuit dc-winding-induced voltage is illustrated and the mechanism is explained. Rotor skewing is proposed to reduce the open-circuit dc-winding-induced voltage, and the optimal skewing angle is analytically derived based on the analytically deduced harmonic orders of the open-circuit dc-winding-induced voltage. Finite-element (FE) analyses show that the open-circuit dc-winding-induced voltages in the analyzed 12-stator-pole partitioned stator WFSF machines having 10-, 11-, 13-, and 14-rotor-pole rotors can be effectively reduced by >94%, while the ac-winding phase-fundamental back-EMFs can be maintained by >95%. Twelve/ten-stator/rotor-pole prototypes with skewed and nonskewed rotors are built and tested to verify the analytical and FE results. [ABSTRACT FROM AUTHOR]

In this paper, the torque production of fractional-slot concentrated-winding (FSCW) permanent-magnet synchronous machines (PMSMs) is analyzed from the perspective of the air-gap field harmonics modulation accounting for slotting effect. It is found that the average torque of FSCW PMSM is produced by both the principle of conventional PMSM and the magnetic gearing effect. A finite-element analysis (FEA) based equivalent current sheet model and harmonic restoration method is first used in FSCW PM machines with different slot–pole number combinations to quantify the respective contribution of the conventional PMSM and the magnetic gearing effect to the average torque. The influence of slot opening on the magnetic gearing effect, cogging torque, and torque ripple is analyzed. The results show that the magnetic gearing effect makes a nonignorable contribution to the average torque when a large slot opening stator is used. The expression of the gear ratio in FSCW PMSMs is derived. The influence of gear ratio on the contribution of the magnetic gearing effect to the total torque is investigated by FEA. The FEA-predicted torques are validated by experiments on the prototypes. [ABSTRACT FROM PUBLISHER]

Both rotating and anticlockwise pulsating signal injection methods based on zero-sequence voltage sensing have been reported to have large signal-to-noise ratio and bandwidths, and great stability for the sensorless control of permanent-magnet synchronous machines. However, the initial rotor position estimation and magnetic polarity identification using zero-sequence voltage have not been investigated. Therefore, this paper presents two types of magnetic polarity identification methods, based on the amplitude variation of zero-sequence voltage due to saturation changing, and based on the secondary harmonics of zero-sequence voltage, for the two carrier injection methods, respectively. It is found that the amplitude variation based method using zero-sequence voltage has higher detection sensitivity for the real magnetic polarity compared to the conventional method using the carrier current. In contrast, the secondary harmonic based identification method using zero-sequence voltage for rotating signal injection has the advantage of fast response, and moreover has large signal amplitude and less distortion compared to the conventional secondary carrier current harmonics. However, the secondary harmonic method loses the capability for polarity detection for the anticlockwise pulsating injection method. Experiments are carried out on a laboratory permanent-magnet machine to verify the theoretical analyses. [ABSTRACT FROM PUBLISHER]

In this paper, a novel square-wave-type carrier signal injection method using zero-sequence voltage is proposed for sensorless control of permanent-magnet (PM) synchronous machine drives. Different from the conventional square-wave-type injection methods employed in the stationary reference frame and estimated synchronous reference frame, the proposed square-wave injection is performed on the estimated reference frame, which rotates anticlockwise at twice estimated rotor electrical angular speed. Compared to the conventional square-wave methods with carrier current sensing, the proposed strategy using zero-sequence voltage has two main advantages, 1) the amplitude of the resultant carrier response is not related to the injection frequency, and 2) the carrier response does not require differentiation calculation for rotor position estimation. Therefore, the proposed method is more robust and also much simpler for signal demodulation, which can combine the synergies of zero-sequence method and square-wave injection (i.e., increased accuracy, bandwidths, and stability, etc.). Finally, all the theoretical analyses are validated by experiments on a laboratory PM machine. [ABSTRACT FROM AUTHOR]

This paper proposes a zero-sequence model-based sensorless control strategy for open-winding permanent-magnet synchronous machine (OW-PMSM) with common dc bus. The third harmonic back electromotive force (EMF) in zero-sequence is utilized to estimate the rotor position information. The novelty is that the third harmonic back EMF is reconstructed based on the zero-sequence model together with zero-sequence current, instead of using voltage transducer and three phase resistance network which can be eliminated from the control system. Due to the essence of back EMF, the developed method is appropriate for the applications including wind power generation and motor drives operating above certain speed. Meanwhile, the phase shift-based space vector pulse width modulation method for OW-PMSM is also presented for easier implementation to form zero voltage disturbance in zero-sequence from the inverter side and hence the corresponding influence can be consequently minimized. The torque ripple, loss, and parameter sensitivity analysis are also carried out, as confirmed by predictions of two-dimensional finite element analysis. Due to the essence of decouple, the estimation can be more robust than the conventional fundamental model-based sensorless methods. Finally, the effectiveness of the proposed method is validated experimentally on a 3-kW OW-PMSM drive system with 2.5 kg·m2 total inertia. [ABSTRACT FROM AUTHOR]

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]

Permanent-magnet vernier machine (PMVM) is a relatively new type of PM machines. An analytical subdomain model accounting for tooth-tips and flux modulation poles is developed to accurately predict on-load field distributions in PMVMs. Based on two-dimensional (2-D) polar coordinate and magnetic vector potential, this method solves the Maxwell’s equations in slot, air-gap, flux modulation pole slot (FMPS), and PM regions. Consequently, the electromagnetic performance such as cogging torque, back-electromotive force (EMF), electromagnetic torque, power factor, and magnet loss are calculated. In addition, the model can also be used for the evaluation of demagnetization withstand capability. The finite-element analysis (FEA) and experimental results validate the accuracy of the developed analytical model. [ABSTRACT FROM PUBLISHER]

This paper investigates the influence of asymmetric machine parameters on carrier signal injection-based sensorless control of permanent-magnet synchronous machines (PMSMs). With either rotating or pulsating signal injection, the second harmonic position errors arise due to the parameter asymmetry. Furthermore, it is found that for the two carriers, the second harmonic errors are different for resistance asymmetry but the same for inductance asymmetry. In order to suppress the position errors, the carrier signal selection guidelines are discussed for resistance asymmetry, while for inductance asymmetry, novel online compensation strategies with dual-frequency injection are also proposed. Finally, the theoretical analyses and proposed compensation methods are validated by experiments on an interior PM (IPM) machine with added phase resistance/inductance to simulate asymmetric conditions. [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]

In switched-flux permanent-magnet machines, winding coil connections can be rearranged into several types of machine winding configurations (MWCs), such as all poles wound, alternate poles wound, and single and dual three-phase windings. This paper investigates the influence of machine saliency on a sensorless control operation based on different MWCs. First, by injecting an HF carrier signal, the machine saliency level can be evaluated experimentally. The influence of saliency on an HF-signal-injection-based sensorless operation for different MWCs can be then investigated irrespective of any information of machine parameters. However, the secondary saliency caused by magnetic saturation or current harmonics may exist in a machine, due to which the sensorless control performance will deteriorate. Hence, an orthogonal signal-based position tracking observer is proposed to improve the accuracy of rotor position estimation rather than utilizing an existing position observer. Furthermore, experimental results confirm that a prototype machine exhibits different saliency characteristics and apparent saliency, in which the HF-injection-based sensorless control technique can be applied. Moreover, better steady and dynamic state performance can be achieved by the improved position estimator compared with using an existing position observer. [ABSTRACT FROM AUTHOR]

Due to the fixed and limited sampling period in the real-time system, three-phase permanent-magnet synchronous machine (PMSM) drives using switching-table-based direct torque control (ST-DTC) usually suffer from steady-state error and ripple of torque. For the case of the dual three-phase system that has been widely investigated recently, the harmonic currents inevitably occur, which can be regarded as the third issue. This harmonic currents lead to the increase of losses and the decrease of system efficiency. Previous literature has addressed the aforementioned issues but only deals with either the torque ripple issues or harmonic currents. Therefore, this paper first introduces two types of synthetic vectors, which can reduce the harmonic currents effectively, as well as the most suitable switching sequences. Then, a modified five-level torque regulator has been proposed to improve the torque performance. With the proposed method, not only the harmonic currents have been suppressed, but also the steady-state error and ripple of torque can be considerably reduced, whereas the merits of classical ST-DTC, such as simple structure and excellent dynamic performance, are preserved. The experimental results validate the effectiveness of the proposed strategy. [ABSTRACT FROM PUBLISHER]

This paper presents dual three-phase permanent magnet (PM) machines utilizing third-harmonic back electromotive force (EMF) and current to improve the output torque, but the torque ripple remains almost similar. The feasibility and practical issues of dual three-phase machines with third-harmonic EMF and current are first discussed, and the output torque is analytically derived. Furthermore, the optimal value of the third harmonic injected into a current waveform for maximum torque improvement is also analytically derived and validated by finite-element analysis (FEA) with the consideration of the constraints of both the peak and root-mean-square currents. For feasible dual three-phase PM machines, torque characteristics, including the average torque and the torque ripple, are compared without and with third-order harmonic injection. It is found that, for a dual three-phase machine without third-harmonic back EMF, the optimal third harmonic into the current is 1/6 of the fundamental current, and the average torque with the current having the optimal third harmonic injected can be improved by 15%. However, for the dual three-phase PM machines with third-harmonic back EMF, the optimal third harmonic into the current is dependent on the ratio of the third-harmonic back EMF to the fundamental back EMF, and the interaction of the third-harmonic current and the third-harmonic EMF results in the further improvement of the output torque. Finally, the experiments on a prototype are given to verify both the analytical and FEA methods. [ABSTRACT FROM PUBLISHER]

This paper investigates the performance of sensorless control of switched-flux permanent-magnet synchronous machines (SFPM) with different stator winding topologies, such as all poles wound (double-layer winding) and alternate poles wound (single-layer winding), whose back electromotive force (EMF) exhibit different waveform characteristics, i.e., sinusoidal, asymmetric, and non-sinusoidal waves. Most importantly, it is found that the single-layer SFPM machine is with asymmetric back-EMFs, due to which the performance of sensorless control will deteriorate. In order to minimize this influence, a control strategy is developed for the improvement of accuracy of rotor position estimation, which is based on the elimination of back-EMF harmonics and not sensitive to the machine parameters. In addition, it also shows that the developed strategy is easy for implementation and the experimental results confirm that the influence of asymmetric and non-sinusoidal back-EMF can be effectively compensated. Consequently, an improvement in the accuracy of rotor position estimation is achieved at both steady and dynamic states as compared with those conventional methods without compensation. [ABSTRACT FROM PUBLISHER]

This paper investigates the improved switching-table-based direct torque control strategies (ST-DTC) for dual three-phase permanent magnet synchronous machine drives. The classical ST-DTC scheme for dual three-phase drives is usually seriously penalized by significant current harmonics, which cause large losses and reduce the efficiency of the drive system. Hence, a modified switching table consisting of 12 new synthetic voltage vectors is proposed. With this new switching table, not only the variables relating to the torque production are well controlled, but also the variables contributing to the current harmonics are eliminated successfully within one sampling period. Furthermore, a simple modified torque regulator is proposed to reduce the torque ripple and the steady-state error of torque which is usually observed in the real-time system. The switching sequence which is most suitable for the implementation of the real-time system has been proposed to minimize the computation burden. The proposed strategy only changes the switching table and torque regulator without any major modifications, and hence, the merits of the classical direct torque control, i.e., simple structure and good robustness, are still preserved. The experimental results validate the effectiveness of the proposed strategy. [ABSTRACT FROM PUBLISHER]

A novel variable reactor based on magnetic flux control is proposed in this paper. The system configuration of the novel variable reactor is presented, while its operational principle and dynamic performance are analyzed. Based on the developed variable reactor, a novel integrated power quality controller (IPQC) suitable for microgrid is proposed, which can cater for the peculiar requirements of microgrid power quality, such as the harmonic high penetration, frequent voltage fluctuation and overcurrent phenomenon, and bidirectional power flow and small capacity. For the fundamental, the equivalent impedance of the primary winding is a variable reactor or capacitor. For the $n$th-order harmonic, the equivalent impedance is very high impedance and acts as a “harmonic isolator.” The system control strategy is also analyzed in detail. A set of three-phase IPQC has been constructed. The experimental test results verify the validity of the novel variable reactor and the IPQC. [ABSTRACT FROM PUBLISHER]

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]

The conventional switching-table-based direct-torque-controlled (DTC) ac machine drive is usually afflicted by large torque ripple, as well as steady-state error of torque. The existing methods, which optimize the duty ratio of the active vector, are usually complicated and parameter dependent. Based on the analysis of instantaneous variation rates of stator flux and torque of each converter output voltage vector, a simple and effective method considering the effect of machine angular velocity is proposed to obtain the duty ratio. The experimental results carried on a dSPACE platform with a laboratory prototype of the permanent-magnet machine verify that the proposed duty-based DTC method can achieve excellent transient response, less torque ripple, and less steady-state error, without resorting to the complicated control method over a wide range of operating regions. [ABSTRACT FROM PUBLISHER]

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]

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]

This paper investigates the influence of nonideal voltage measurements on the parameter estimation of permanent-magnet synchronous machines (PMSMs). The influence of nonideal voltage measurements, such as the dc bus voltage drop, zero shift in the amplifier, and voltage source inverter nonlinearities, on the estimation of different machine parameters is investigated by theoretical and experimental analysis. For analysis, a model-reference-adaptive-system-based estimator is first described for the parameter estimation of the q-axis inductance, stator winding resistance, and rotor flux linkage. The estimator is then applied to a prototype surface-mounted PMSM to investigate the influence of nonideal voltage measurement on the estimation of various machine parameter values. It shows that, at low speed, the inverter nonlinearity compensation has significant influence on both the rotor flux linkage and winding resistance estimations while, at high speed, it has significant influence only on the winding resistance estimation and has negligible influence on the rotor flux linkage estimation. In addition, the inverter nonlinearity compensation will not influence the q-axis inductance estimation when it is under id = 0 control. However, the dc bus voltage drop due to the load variation and zero shift in the amplifier will significantly influence the q-axis inductance estimation. [ABSTRACT FROM PUBLISHER]

This paper compares four analytical models for predicting the cogging torque in surface-mounted permanent-magnet machines, viz., lateral force (LF), complex permeance (CP), and exact subdomain (SD) models, together with an SD model based on a single slot/pole. The models are evaluated for the air-gap flux density, cogging torque, back electromotive force (EMF), electromagnetic torque, saturation effect, and computational complexity, with particular focus on the influence of design parameters, such as the slot-depth-to-slot-opening ratio and the optimal pole-arc-to-pole-pitch and slot-opening-to-slot-pitch ratios, on the cogging torque. It shows that all studied analytical models have similar high accuracy for the fundamental back EMF and average torque. However, their predictions are quite different for the ripples in the back EMF, cogging torque, and electromagnetic torque waveforms. Overall, the SD models have high accuracy, while the exact SD model is the most accurate among the studied models by accounting for mutual influence between slots, albeit with high computational complexity. The computation of the SD models is slower than that of the LF model but can be quicker than that of the CP model. The comparison is validated by the finite-element and experimental results. [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 proposes a novel flux reversal permanent magnet (FRPM) machine with asymmetric-stator-pole (ASP) configuration. Different from the conventional FRPM machine with uniform “NS-NS-NS” PM sequence, the proposed ASP-FRPM machine is characterized by a “NSN-S-NSN” magnet arrangement. Hence, the interpolar flux leakage is significantly reduced with the developed design, which can improve the torque capability. The machine topologies, features, and operating principle are introduced, respectively. A simplified magnetic circuit model is established to reveal the underlying flux leakage reduction mechanism of the ASP design, and the rotor pole number is analytically optimized as well. The design parameters are then globally optimized so as to improve the torque quality. In addition, the electromagnetic characteristics of the ASP- and conventional FRPM machines are compared. Finally, experiments have been carried out to validate the theoretical results. [ABSTRACT FROM AUTHOR]

Linear permanent magnet Vernier machines (LPMVM) have received more and more attention in recent years due to the advantages of high thrust density and low thrust ripple, which are both required in many direct-drive applications. In this paper, a double-sided toroidal-winding LPMVM (DSTWLPMVM) is proposed, and the thrust ripple sources for this type of machine are analyzed. To emphasize the specificity of LPMVM in aspect of thrust ripple optimization, a traditional fractional-slot linear permanent magnet synchronous machine is selected as a reference. Two indexes [amplitude difference (AD) and phase shifting (PS)] are defined to quantify the thrust ripple caused by the AD and the PS among three-phase electromotive force (EMF), respectively. Additionally, detent force is also considered when optimizing the three-phase EMF. Finally, a prototype of DSTWLPMVM is manufactured and tested. The measured EMF is basically symmetrical sinusoidal waveforms and the peak-to-peak value of the detent force is lower than 10 N. [ABSTRACT FROM AUTHOR]

In this paper, a novel nonconventional angle displacement (i.e., 15°) between two sets of three-phase windings is proposed for dual three-phase permanent-magnet (PM) machines. First, all feasible angle displacements between the two three-phase winding sets for various slot/pole number combinations of dual three-phase machines are discussed in general. Then, an in-depth investigation is carried out on a 24-slot/10-pole dual three-phase PM machine as an example covering various electromagnetic performances. The investigation shows that under healthy and three-phase open-circuit conditions, the proposed 15° configuration has a comparable electromagnetic performance to the 30° configuration, and a better performance than the 0° counterpart. Furthermore, under three-phase short-circuit (SC) condition, the proposed 15° configuration has the lowest SC current, smallest braking torque, and the best PM demagnetization withstand capability. Finally, three prototype 24-slot/10-pole surface-mounted PM machines are built and tested to verify the theoretical analyses. [ABSTRACT FROM PUBLISHER]

A novel variable reactor is presented in this paper. The principle of the novel variable reactor is simply addressed. The equivalent impedance of primary winding of the transformer will vary with the ratio between the primary and the secondary voltages. For the proposed variable reactor, a novel series power quality controller (SPQC) is developed and its principle is analyzed in detail. The SPQC greatly improves the power utility impedance to harmonics instead of the fundamental and plays the role of isolating the harmonics. Because the novel SPQC is with very high impedance to harmonics, the passive power filter can be reduced. Accordingly, three kinds of reduced single-phase passive power filters are presented. The comparison criterion of reducing passive power filter is described. The SPQC is characterized by perfectly isolating the harmonics, simplified passive power filter design, small rating, and being suitable for two kinds of harmonic sources. The validity of the novel SPQC and excellent filtering characteristic are verified by the experimental results. [ABSTRACT FROM PUBLISHER]

The homopolar inductor machine (HIM) has attracted recent interest in the field of flywheel energy storage system due to its merits of robust rotor and low idling losses. In some situations, the analytical methods of a conventional wound-field synchronous machine (WSM) can be used to analyze the HIM, but the clear explanation about why these can be done and the relationship between HIM and WSM were not given in the literature. To address these issues, this paper studies the HIM based on the basic theoretical model and equations. First, the structure and magnetic circuit characteristics of HIM are introduced. Second, the mathematical model of HIM is derived and then decomposed, which indicates that the HIM can be seen as a WSM with large end leakage inductance when rotor tooth width $ {\theta _t} \leq \pi /p$ , or a combination of WSM and synchronous reluctance machine (SynRM) when ${\theta _t} > \pi /p$. Third, the performance indexes of HIM and corresponding equivalent machines, including air gap flux density, back electromotive force, and inductance parameters, are analyzed and fully compared. Finally, an HIM is prototyped and tested on an experimental platform. The simulation and experiment results show that it is reasonable to regard the HIM as a WSM or a combination of WSM and SynRM. The conclusion gives a transparent explanation about the relationship between HIM and WSM, which helps to simplify the analysis of the HIM. [ABSTRACT FROM AUTHOR]

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

This paper comprehensively investigates the electromagnetic performance of 3-phase, 12-slot, and 8-pole switched reluctance machines (SRMs) with different winding configurations, i.e., double/single layer, short pitched (concentrated), and fully pitched (distributed). These SRMs are supplied by sinewave currents so that a conventional three-phase converter can be employed, leading to behavior which is akin to that of synchronous reluctance-type machines. Comparisons in terms of static and dynamic performances such as d- and q-axis inductances, on-load torque, torque–speed curve, and efficiency map have been carried out using two-dimensional finite-element method (2-D FEM). It is demonstrated for the given size of machine considered that for same copper loss and without heavy magnetic saturation, both single- and double-layer mutually coupled SRMs (MCSRMs) can produce higher on-load torque compared to conventional SRMs (CSRMs). Additionally, double-layer MCSRM achieved the highest efficiency compared to other counterparts. When it comes to single-layer SRMs, they are more suitable for middle-speed applications and capable of producing higher average torque while lower torque ripple than their double-layer counterparts at low phase current. Two prototype SRMs, both single layer and double layer, are built to validate the predictions. [ABSTRACT FROM PUBLISHER]

In order to facilitate the selection of machine whether it is suitable for high-frequency (HF)-signal injection-based sensorless control or not, this paper proposes a complete experimental investigation method for the analysis and validation of machine saliency level, including primary saliency, which is essential for HF injection-based sensorless control, and the secondary saliency, which will deteriorate the rotor-position estimation. The experimental results obtained on a new type of switched-flux permanent-magnet (SFPM) machine prove that with identified primary saliency, the accurate rotor-position estimation can be achieved, and with small secondary saliency, the estimation will not be deteriorated much in the SFPM machine. The conclusion is verified by the experiments based on the HF pulsating signal injection-based sensorless control at zero and low speeds. [ABSTRACT FROM PUBLISHER]

Translator eccentricity in permanent-magnet tubular machines is practically inevitable. It results in nonuniform air-gap magnetic-field distribution, which is inherently a 3-D problem. In this paper, the effects of eccentricity on field distribution and on the resulting unbalanced radial force are analyzed. Both no-load and load conditions are presented. The proposed mathematical model only requires the knowledge of the 2-D air-gap flux density distribution when the translator is at the balanced position. The analytical expression of the unbalanced radial force is derived together with the translator deformation analysis. The information of unbalanced radial forces acting on the translator and the translator displacement can be used for machine and bearing sizing. Analytically predicted and 3-D finite-element-calculated results are compared and validated by the experimental results obtained on a specially set-up test rig. [ABSTRACT FROM PUBLISHER]

This paper develops a 2-D field analytical model for predicting the magnetic field distribution and the corresponding electromagnetic performance in air- and iron-cored permanent magnet (PM) brushless machines having radially or parallel magnetized two-segment Halbach array. A simple equation is derived to directly predict the optimal magnet ratio for maximum electromagnetic torque, while the influence of pole-pair number and magnet thickness on the optimal magnet ratio is investigated for both air- and iron-cored machines. The analytical model is validated by finite-element analyses and also measurements on a prototype 12-slot/10-pole PM brushless machine. [ABSTRACT FROM AUTHOR]

The ill-convergence of multiparameter estimation due to the rank-deficient state equations of permanent-magnet synchronous machines (PMSMs) is investigated. It is verified that the PMSM model for multiparameter estimation under id = 0 control is rank deficient for simultaneously estimating winding resistance, rotor flux linkage, and winding inductance and cannot ensure them to converge to the correct parameter values. A new method is proposed based on injecting a short pulse of negative id current and simultaneously solving two sets of simplified PMSM state equations corresponding to id = 0 and id \neq 0 by using an Adaline neural network. The convergence of solutions is ensured, while the minimum \vert id\vert is determined from the error analysis for nonsalient-pole PMSMs. The proposed method does not need the nominal value of any parameter and only needs to sample the winding terminal currents and voltages, and the rotor speed for simultaneously estimating the dq-axis inductances, the winding resistance, and the rotor flux linkage in nonsalient-pole PMSMs. Compared with existing methods, the proposed method can eliminate the estimation error caused by the variation of rotor flux linkage and inductance as a result of state change due to the injected d-axis current in the surface-mounted PMSM. The method is verified by experiments, and the results show that the proposed method has negligible influence on output torque and rotor speed and has good performance in tracking the variation of PMSM parameters due to temperature variation. [ABSTRACT FROM AUTHOR]