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High-speed permanent magnet motors (HSPMMs) have received attention in direct drive systems from the industry. Modular multilevel converters (MMCs) have become the most practical solution for HSPMMs in industrial applications due to the advantages of their highly modular structure, high-quality output and high reliability. In this article, the symmetrical discrete-time model of the MMC for the HSPMM drive is presented. Based on this symmetrical discrete-time model, the discrete-time current regulator has been designed. Moreover, the submodel (SM) capacitor energy balance models for MMC have been described, and the energy balance control scheme is introduced. Finally, the simulation and experimental results show that the presented discrete-time current regulator has a strong dynamic response at high speed (15 kr/min), and the SM capacitor voltage balance control is also achieved. Compared with the conventional PI current controller, the proposed discrete-time current regulator improves the current loop dynamic performance at high-speed, and the energy balance control scheme can ensure the SM capacitor voltage balance of the MMC. [ABSTRACT FROM AUTHOR]

In this article, an efficient multi-objective optimization strategy for the Halbach array permanent magnet synchronous machine (PMSM) is developed by taking into consideration the nonlinear B-H behavior of soft magnetic materials. Based on the harmonic modeling (HM) technology, the electromagnetic performances (EPs) of the Halbach array PMSM can be computed. To specifically model the local magnetic saturation, the stator teeth are separated into several annular layers, and each tooth is further divided into several regions along the tangential direction. Then, the parameters of the Halbach array PMSM are optimized utilizing combined nonlinear semi-analytical model (SAM) and non-dominated sorting genetic algorithm II (NSGA-II). To validate the effectiveness and accuracy of the developed optimization scheme, a Halbach array prototype is then manufactured in accordance with the optimization results. The multi-objective rapid optimization strategy developed in this article, which includes but is not limited to Halbach array permanent magnet (PM) machines, serves as a reference for the design and optimization of various PM machines. [ABSTRACT FROM AUTHOR]

Nowadays, high-speed permanent magnet synchronous machines (HSPMSMs) are widely used in high-speed direct-drive applications. Moreover, modular multilevel converters (MMCs) have attracted a lot of attention. In this paper, the mathematical model of the MMC for the HSPMSM was built on high- and low-speed regions, respectively, and the control of each model is completely decoupled. Moreover, energy balance control schemes based on the common mode current injection of the MMC with HSPMSM drive applications have been proposed for high- and low-speed cases, respectively. Based on this model, the controller is proposed for high- and low-speed cases, respectively. Simulation and experiment results indicate that the proposed energy balance control method for an MMC in the high-speed PMSM drive application exhibits significant performance, which can ensure the energy balance of the MMC and eliminate the circulating current of the MMC directly. [ABSTRACT FROM AUTHOR]

The increasing complexity of multi-energy coordinated microgrids presents a challenge for traditional demand response providers to adapt to end users' multi-energy interactions. The primary aim of demand response providers is to maximize their total profits via designing a pricing strategy for end users. The main challenge lies in the fact that DRPs have no access to the end users' private preferences. To address this challenge, we propose a deep reinforcement learning-based approach to devise a coordinated scheduling and pricing strategy without requiring any private information. First, we develop an integrated scheduling model that combines power and gas demand response by converting multiple energy sources with different types of residential end users. Then, we formulate the pricing strategy as a Markov Decision Process with an unknown transition. The novel soft actor-critic algorithm is utilized to efficiently train neural networks with the entropy function and to learn the pricing strategies to maximize demand response providers' profits under various sources of uncertainties. Case studies are conducted to demonstrate the effectiveness of the proposed approach in both deterministic and stochastic environment settings. Our proposed approach is also shown to be effective in handling different levels of uncertainties and achieving the near-optimal pricing strategy. [ABSTRACT FROM AUTHOR]

Back–electromotive force estimation-based rotor position estimation methods are usually adopted for high-speed surface-mounted permanent magnet synchronous machines (SPMSM) drive to deal with the limitations of position sensors in high-speed applications. Considering inductance mismatch is the main cause of the position estimation error, this article proposes a novel pulsewidth modulation (PWM) current ripple-based online inductance identification method to improve the position estimation accuracy. The proposed method utilizes the inherent PWM current ripple of the voltage source inverter for inductance identification. In addition, the transient circuit equations on the estimated $\gamma \delta$ frame are adopted as the identification model, and the recursive least squares method is used to obtain the estimated inductance. Compared with the traditional parameter identification methods, the proposed method does not need to inject additional signals or fix parameters. During the sensorless drive of high-speed SPMSM, the proposed method can accurately identify the inductance while not affecting the normal operation of PMSM at all, which is the main contribution of this article. With the proposed method, the estimated inductance can rapidly converge to the accurate value, and then the position estimation error will be eliminated. Finally, the effectiveness of the proposed method is verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

This article proposes a discrete-time dynamic-decoupled current controller for an LCL-equipped high-speed permanent magnet synchronous machine with only the motor currents measured. The controller is designed in the synchronous coordinate based on a complex $\boldsymbol{z}$ -domain transfer function. The main contribution of the proposed current controller is the robust dynamic decoupling performance to achieve better transient behavior. Moreover, an effective coefficient selection method is developed to acquire sufficient phase margin and gain margin, even with the system parameters varying $\boldsymbol{\pm 50\%}$. Additionally, the stable region of the LCL resonance with the proposed method is discussed. Finally, the effectiveness of the proposed method is verified by driving the tested motor to 100 kr/min. [ABSTRACT FROM AUTHOR]

This article proposes an improved position sensorless drive method for interior permanent magnet synchronous machines (IPMSM) in medium- and high-speed regions, which relies on the fully discretized extended back-electromotive force (EEMF) model and online inductance identification. First, the fully discretized EEMF model is developed for constructing position observers, which overcomes the accuracy deterioration of the conventional Euler-discretized model with the speed increasing. And then, an online inductance identification method for IPMSM, which utilizes the inherent pulsewidth modulation (PWM) current ripple of the voltage source inverter (VSI), is proposed to improve the position estimation accuracy. Compared with the traditional parameter identification method, the proposed method does not require the additional signal injection, therefore, the undesirable torque fluctuation and additional voltage occupancy due to signal injection are avoided. Benefiting from the fully discretized EEMF model and the estimated inductances, the improved rotor position estimation of IPMSM can be achieved. Finally, the proposed method is verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

In this article, we propose a novel nonlinear semianalytical model (AM) for the magnetic field calculation of electric machines. The nonlinear properties and local saturation effect of the iron part are taken into consideration in Cartesian coordinates, which is the main contribution of the proposed model. Thus, high accuracy of electromagnetic field results can be obtained with the low computational time cost. The model is developed based on the harmonic modeling technique by solving Maxwell's equations. The detailed theoretical derivations, which use the complex Fourier series and the Cauchy product, are presented. To verify the proposed model, an axial flux permanent-magnet (PM) machine is selected to be investigated. Both finite-element model and experimental results agree well with that of the proposed model. Moreover, the nonlinear AM has potential application for other types of PM electrical motor in Cartesian coordinates, such as flat PM linear machines. [ABSTRACT FROM AUTHOR]

Position sensing is one of the crucial parts of the active magnetic bearing (AMB) system. The printed circuit board (PCB) eddy current position sensor is a new type of position sensor for the AMB system, which makes a compact structure, high sensing quality, and is low cost. In this article, an improved driver circuit is proposed for this new sensor. The driver circuit includes an excitation circuit and signal conditioning circuits. A crystal oscillator circuit with a power stage is used to provide the excitation coil with a stable excitation source of high stability and good precision of frequency. The analog demodulation circuit is designed for signal conditioning circuits to extract the rotor displacement information from the sensing coil outputs. Compared with the state-of-art driver schemes, the proposed method reduces the circuit complexity and cost. Accordingly, the experimental results show that the designed sensor has good linearity and sensitivity, and it can ensure AMB stable operation at the rated speed. [ABSTRACT FROM AUTHOR]

In this article, a novel magnetic field calculation approach that considers the static inclined eccentricity of axial flux permanent magnet (AFPM) machine is presented. The equivalent remanence of permanent magnet (PM) is introduced and calculated, in which the air-gap length can be regarded as uniform. Then, the analytical model based on harmonic subdomain technology can be used directly. The magnetic field distribution (MFD) and electromagnetic performance under eccentric state are calculated and compared. The effectiveness of the proposed method is verified both by the finite element (FE) model and experimental results. The main contribution of this article is to provide a simple and accurate method for the calculation of the eccentric magnetic field of the PM motor, not limited to the AFPM. [ABSTRACT FROM AUTHOR]

To facilitate the active magnetic bearing (AMB) design and analysis, an accurate and fast model that considers both rotor eccentricity and the saturation effect is necessary. In this article, a novel hybrid analytical model (HAM) for effective calculation of the magnetic field of the AMB is proposed. Eccentricity and local saturation are considered in the proposed HAM. In the proposed HAM, the stator and rotor are modeled by elementary subdomains (ESDs) and the air-gap is modeled by magnetic equivalent circuit (MEC). Direct coupling between the solutions in the ESD regions with MEC completes the whole model matrices. Compared to the existing literature, the proposed model considers both the rotor eccentricity and material nonlinearity. The effectiveness and accuracy of the proposed HAM are validated by both the finite element model and experimental results. The results show that the proposed HAM can accurately predict the magnetic quantities of the AMB. [ABSTRACT FROM AUTHOR]

In the design process of a high-speed motor, a reasonable rotor stress analysis is a necessary prerequisite to guarantee its safe and reliable operation. In this paper, the comprehensive design and analysis of the rotor stress of a 200 kW 20,000 r/min high-speed permanent magnet motor (HSPMM) with magnetic bearing are carried out. Firstly, the stress distribution characteristics of rotors with different permanent magnet structures and different thermal expansion coefficients of filling materials are analyzed and compared. Secondly, the rotor design is determined through a comprehensive comparative analysis of different sleeve thicknesses and shrink fit. Furthermore, considering the axial temperature gradient due to the axial ventilation cooling method adopted by the prototype, the rotor stress is checked through the coupling calculation of fluent and static stress. Finally, several long-period running tests are carried out, showing the good agreement between the calculated and measured results, and the safe and reliable operation of the prototype verifies the correctness of the above theoretical analysis. [ABSTRACT FROM AUTHOR]

The slotless permanent magnet motor (SPMM) has low phase inductance due to the larger physical air gap, which will adversely affect motor control and current harmonics. In this paper, the method of forming an extra magnetic circuit by endcap around the outer stator is proposed. The advantage of this method is that a restrained flux path is formed without increasing the motor structure and cost, and the inductance of the motor is effectively improved without causing a significant decrease in torque. The preliminary simulation analysis and corresponding experimental content are carried out. The experimental results and the simulation content showed good consistency, which verified the correctness of the theory and simulation analysis. [ABSTRACT FROM AUTHOR]

In this article, a novel dynamic-decoupled active damping current controller is proposed for an LCL-equipped high-speed permanent magnet synchronous machine. Compared with the conventional stationary current-control method for the LCL-type system, the proposed method is established in the synchronous rotating frame for improving the current transient performance. When taking the controller into the synchronous coordinate, there are two following challenges: first, the synchronous resonance frequency varying in a wide range because of the synchronous coordinate transformation, and second, eliminating the coupling between the ${dq}$ coordinate. To address these issues, an improved synchronous capacitor-current-feedback active damping method is designed based on arbitrary pole assignment and is significantly effective for the LCL resonance within the Nyquist frequency. Moreover, a novel dynamic-decoupled motor-current controller is proposed to eliminate the coupling between the ${dq}$ -axis motor current. The gain selection method is discussed to acquire sufficient phase margin and gain margin. Finally, the effectiveness of the proposed method is verified by driving the tested motor to 72 kr/min. [ABSTRACT FROM AUTHOR]

The impeller design usually expects to achieve high efficiency and a wide working range while they are influenced by tip clearance in different ways. In this study, a blower with a controllable magnetic suspension bearing was studied. The magnetic bearing enables the impeller to adjust the tip clearance during operation to optimize the efficiency of the blower at the design point and significantly expand the surge margin when it deviates from the design point. The clearance ratio (CR) is defined as the ratio of tip clearance over impeller outlet width. The computational fluid dynamics (CFD) method is used to study the performance of a centrifugal impeller under CR = 2.61%∼7.83% and verified by experiments. The results show that the pressure ratio and efficiency of the impeller at the design point decreased linearly with the increase of the gap. For each 1% increment in CR, the pressure ratio reduces by 0.02 and the polytropic compression efficiency declines by 0.5%. Conversely, the surge margin increases with the expansion of CR. For every 1% rise in CR, the surge margin would improve by 7.8%. A control method of changing the reference suspension position according to the optimal efficiency fitting model is proposed. It realizes the real-time control of the axial suspension position of the impeller according to the changes of pressure and flow rate signals to obtain the optimal work efficiency with a broad surge margin. Experimental results show that using an impeller equipped with a controllable magnetic suspension bearing could minimize the gap stably in the nonsurge area to obtain high efficiency, and when necessary, it could enlarge the gap to meet the low flow rate condition. [ABSTRACT FROM AUTHOR]

This article proposes a sliding-mode position estimation method for high-speed surface-mounted permanent magnet synchronous machines with LCL filter. The implementation of the LCL filter aims at smoothing the motor current and reducing the iron loss caused by the harmonic currents. First, the discrete-time model of the LCL-filtered motor drive system is developed. Based on the developed model, the sliding-mode observer is proposed with more robustness against the parameter variation to estimate the back EMF, which contains the information of the rotor speed and position. Because of the elimination of the capacitor voltage sensors, the augmented sliding surface is designed to achieve arbitrary pole placement with only output feedback. Besides, considering the analog-to-digital scaling error and pulsewidth modulation harmonics, a reaching law with enhanced chattering suppression ability is proposed. Compared with the conventional methods, the chattering problem is well alleviated and thus the speed estimation ripple is much reduced. Finally, the effectiveness of the proposed method, even with the mismatched parameters adopted is validated at 100 kr/min with the sampling frequency 20 kHz. [ABSTRACT FROM AUTHOR]

This article proposes a compensation method of position estimation error for high-speed surface-mounted permanent magnet synchronous motors based on robust inductance estimation. The proposed method relies on the variation of the estimated $\delta$ -axis back back-electromotive force when a small current is injected into the $\gamma$ axis. The inductance estimation error is limited within ${\bf \pm \!5\%}$ when the nominal resistance and inductance vary $\bf \pm 30\%$ of their real values. With the estimated inductance, the position estimation error can be well compensated. Compared with the conventional current-injection method, the proposed method has enhanced robustness against the system noises. Benefiting from this, it is effective to estimate the inductance with a small injected current ($ \bf 0.5\%$ of the rated current), where the conventional methods fail. Finally, the effectiveness of the proposed method is validated by simulation and experiment results on a 100 kr/min (1.67 kHz) high-speed permanent magnet synchronous machines accurately with 10-kHz sampling frequency. [ABSTRACT FROM AUTHOR]

This paper proposed an electromagnetic loading process with the high-speed impact. Al-4.2% Cu alloy bars were used to employ electromagnetic impact (EI) experiments. Deformation mechanism and microstructure evolution of EI samples were revealed by theoretical model and microstructure characterizations. The EI process had impact force (peak value 40 kN) and impact velocity (peak value 6.7 m/s) during a short time period (1.25 ms). Adiabatic shearing mechanism dominated the whole deformation process, causing that significant microstructure characteristic was adiabatic shear bands (ASBs). The theoretical analysis implied that the formation of ASBs was accounted for the radial velocity gradient. Most plastic deformations concentrated in ASBs, and approximately pure shear deformations resulted in adiabatic temperature rise of 0.33–0.42 Tm inside ASBs. The width of ASBs was about 135 μm, in which original equiaxial grains were elongated into laminated sub-structures. TEM observations showed multi-slip systems were simultaneously actuated due to severe shear deformations. High dislocation density and dislocation tangles distributed with the ASBs. Adiabatic temperature rise and distorted energies drove sub-grains rotate into recrystallization grains (70–280 nm) with large angle grain boundaries. The needed maximum time (45 μs) for rotational dynamic recrystallization was far less than that of plastic deformation, indicating that rotational dynamic recrystallization mechanism contributed to the formation of recrystallization grains. [ABSTRACT FROM AUTHOR]

In this article, an improved deadbeat predictive current control (DPCC) method with parameters identification for surface-mounted permanent magnet synchronous machines (SPMSMs) is proposed. With the proposed DPCC method, zero steady-state current error and deadbeat dynamic current response could be achieved, even with inaccurate initial motor parameters. On basis of the conventional DPCC method, a novel parameters identification for the stator resistance and inductance is developed, which is the main contribution of this article. The proposed parameters identification method works based on a reconstructed characteristic vector from the disturbance observer with current injection. Compared with traditional recursive-least-square methods, the proposed method can be implemented with greatly reduced computation burden. Additionally, since the design is established based on the fully discretized model, the effectiveness will be guaranteed on both low-frequency and high-frequency motors, which is a significant advantage of the proposed method. [ABSTRACT FROM AUTHOR]

In this article, a position sensorless drive and online parameter estimation method for surface-mounted permanent magnet synchronous machines-based on adaptive full-state feedback current control is proposed. The position sensorless drive is established by the detection of the back-electromotive force in the $\gamma \delta$ synchronous reference frame, which is effective at the medium-speed and high-speed range. Besides, accurate estimation of the winding resistance, the stator inductance, and the flux linkage of the PM is achieved independently. Compared with the traditional recursive-least-square methods, the proposed parameter identification method can be easily implemented because of the significantly reduced execution time. With the help of the parameter identification, the precise position estimation can be achieved by the proposed sensorless control method regardless of the parameter variation during the operation. The stability of the proposed method is proved by the Lyapunov-function method. Finally, the effectiveness of the proposed method is validated by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

This article presents a new rotor design to reduce rotor eddy current loss of a high-speed permanent magnet synchronous machine for flywheel energy storage system. Instead of using common nonmagnetic sleeves, the new rotor incorporates permeable retaining sleeves (PRSs) to fix permanent magnets on the rotor hub. The PRSs are made of permalloy that features high permeability and high electrical conductivity. Thus, skin depths for asynchronous harmonics are extremely small. On the other hand, the PRSs are electrically insulated along the circumferential direction. Owing to these two reasons, rotor eddy current loss at open circuit decreases by 64.2% without sacrificing torque output, compared with an original rotor with nonmagnetic retaining sleeve. In addition, thermal and structural finite element analyses are performed to calculate rotor temperature distribution and evaluate the structural integrity of the new rotor. Rotor eddy current loss reduction benefits lowering rotor temperature rise. Prototype machine with the new rotor is fabricated, and preliminary tests are carried out to confirm the analysis results. [ABSTRACT FROM AUTHOR]

This paper proposes an analytical model for the prediction of air gap magnetic field distribution for axial flux permanent magnet (AFPM) machine with various types of misalignments. The AFPM machine geometry is first transformed to a polar representation. Consequently, the subdomain model based on current sheet technique is developed. Then the stator coordinate system is chosen as reference coordinate to consider both static/dynamic angular and axis misalignments. The back electromagnetic forces and cogging torque are obtained accordingly based on Maxwell's equations. The results show that the proposed approach agrees with the finite-element method. The model is further validated by experiments under healthy, dynamic angular and axis misalignment conditions, which can validate the proposed approach. It turns out that the proposed approach can predict the performance of AFPM machines with types of misalignment quickly and effectively, which is greatly significant for further fault detection. [ABSTRACT FROM AUTHOR]

This paper proposes an analytical model for the prediction of airgap magnetic field distribution for axial flux permanent magnet (AFPM) machine with partial magnet demagnetization. The AFPM machine geometry is first converted to a polar representation. Consequently, the subdomain model based on current sheet technique is developed. Then current sheet representation of PM is derived to consider the partial demagnetization using superposition principle. The back electromagnetic forces and cogging torque are obtained accordingly based on Maxwell's equations. The results show that the results of proposed approach agrees with that of finite-element method. The model is further validated by experiments under both healthy and demagnetized conditions, which can validate the proposed approach. Main contribution of the work is to consider the partial irreversible demagnetization. Moreover, the proposed method is applicable for both AFPM and radial flux permanent magnet machine. [ABSTRACT FROM AUTHOR]

In this paper, a new hybrid model is proposed for the prediction of air gap magnetic field distribution (MFD) in interior permanent magnet machines with any rotor configuration. The slotless magnetic field is first predicted by finite-element method (FEM) with automatic scripting in MATLAB to consider saturation in the rotor iron. Afterward, the conformal mapping viz., Schwarz–Christoffel mapping is introduced to take the slotting effect into account. Consequently, the MFD could be calculated. The back electromagnetic forces, cogging torque, and output torque are obtained accordingly. Then a subdomain model is developed to consider the armature reaction. The results show that the proposed hybrid approach agrees well with the FEM. The model is further verified by experiments. The main contribution of this paper is to reduce the computation time remarkably while maintaining the calculation accuracy. [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 proposes high-torque-density dual-stator permanent magnet machines with biased permanent magnet (PM) excitation in the inner stator. The developed machine can be geometrically considered as an outer-rotor stator PM machine plus a separate outer stator similar to the conventional fractional-slot machines. Consequently, the proposed designs feature two different stator structures. Meanwhile, two sets of armature windings are employed to improve the space utilization ratio and torque density. The machine topologies and operating principles are first described. In addition, the analytical models of the machine are introduced, which are utilized to optimize the stator/rotor pole combination as well as the power splitting ratio between two stators. This design optimization is performed in order to maximize the torque capability with the constraint of copper loss. The electromagnetic characteristics of the proposed machine with different inner stator structures are evaluated and compared by the finite-element (FE) method. Finally, an optimized dual-stator biased PM machines prototype is manufactured and tested to verify the FE analyses. [ABSTRACT FROM AUTHOR]

In this paper, novel dual-stator switched-flux hybrid magnet machines (DS-SF-HMMMs) are proposed. Two sets of armature winding are employed so as to improve the space utilization and torque density. Meanwhile, two kinds of permanent magnets (PMs), i.e., neodymium–iron–boron and low-coercive-force magnets, are placed on either a common stator or separate stators. The proposed machines can provide the merits of high torque density in DS machines, and excellent flux adjusting capability in memory machines. The topologies and operating principle of the DS-SF-HMMMs having different PM arrangements are introduced and highlighted, respectively. In order to overcome the drawbacks of the original “U”-shaped PM type, two alternate designs are presented to increase the copper area in the inner stator and facilitate the manufacturability. In addition, the equivalent magnetic circuits for various machine models are formulated to reveal the field regulation principle. Then, the electromagnetic characteristics of various available DS-SF-HMMMs are evaluated and compared by the finite-element (FE) method. The stator/rotor pole combinations of the selected machine are analytically optimized in order to maximize the torque density. Finally, two prototypes are manufactured and tested to verify the FE analyses. [ABSTRACT FROM PUBLISHER]

This paper presents the simple analytical modeling for switched flux memory machine to provide in-depth insight into its working mechanism. The analytical approach is based on the slotless open-circuit air-gap flux density and the slotted air-gap relative permeance calculations for a doubly salient structure. In addition, due to low coercivity and highly nonlinear hysteresis curve at the second quadrant, the piecewise and virtual-linear hysteresis models of AlNiCo permanent magnet (PM) are presented to determine the PM working point. This combined analytical solution allows rapid calculation of several electromagnetic characteristics, e.g., air-gap flux density and back electromotive force. The effectiveness of the analytical method is validated by both finite-element results and measurements. [ABSTRACT FROM AUTHOR]

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

This paper develops a 3-D analytical model to compute the no-load magnetic-field distribution in a flux reversal linear-rotary permanent-magnet actuator (FR-LRPMA) with two permanent-magnet (PM) poles (PM_pole) and two ferromagnetic poles (Fe_pole) on each stator tooth. Laplace’s and Poisson’s equations are built assuming that the stator and the rotor are slotless and both the permeances of Fe_pole and PM_pole are the same. The tubular mover is transferred into a planar one using a curvature factor. Then a 2-D model and 3-D model for calculating the air-gap relative permeances are proposed considering the effect of slot and the permeance difference of Fe_pole and PM_pole, respectively. The expressions of 3-D magnetic flux density, cogging force, and cogging torque of the FR-LRPMA are subsequently derived and verified using the finite-element method. [ABSTRACT FROM AUTHOR]

The on-load magnetization characteristics of a newly developed partitioned stator switched flux hybrid magnet memory machine are comprehensively analyzed in this paper. First, the open-circuit and on-load permanent magnet magnetization performances are evaluated and compared. The mismatch of the required demagnetizing currents between open-circuit and on-load cases is identified. Then, the on-load demagnetization behavior of low coercive force (LCF) magnet is disclosed by the frozen permeability method. Besides, a numerical solution for the refinement of LCF magnet sizing is presented by a proposed virtual linear hysteresis model so as to effectively prevent the undesired on-load demagnetization. Finally, an optimized prototype is tested to verify the theoretical analyses. [ABSTRACT FROM AUTHOR]

In this paper, a general analytical model is proposed to calculate the back electromotive forces of various manufacturing imperfections in the double-rotor axial flux permanent magnet machine. First, the axial and circumferential flux density in the air gap under healthy condition is developed by Maxwell’s equations and Schwarz–Christoffel mapping. Second, the equations of air gap length and radii are introduced to calculate the flux density with manufacturing imperfections. The back EMFs of each case are calculated. For each case, finite-element (FE) method models are developed to validate the analytical model, and the results show that the analytical model predictions match well with the FE results. Finally, the analytical model is verified by experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a new position sensorless control method for switched reluctance motor drives is proposed. Rotor position is initially calculated based on the flux linkage-position–phase current characteristics by numerical method. Then, a third-order-phase-locked loop considering the acceleration variation is designed to undermine the impact of current sampling noise and numerical residual error on the estimated rotor position. A new start-up sequence is proposed. Simulation and experimental results show that the proposed position sensorless control method has achieved sufficient accuracy in terms of position and speed estimation. [ABSTRACT FROM PUBLISHER]

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]

This study presents a design methodology for a newly emerged switched‐flux memory machine with low‐cost non‐rare‐earth. The adoption of aluminium–nickel–cobalt magnet with low‐coercive force enables the flexible air‐gap flux control without unnecessary excitation loss. Hence, the excellent flux variability and high‐efficiency sustainability within a wide‐speed range can be achieved. Since geometric constraints exist among major parameters, a design trade‐off should be established to facilitate the feasible design. Therefore, a simplified magnetic circuit is modelled to analytically determine the relationships among various parameters, and the generic design considerations including magnet grade selection and stator/rotor‐pole combination are addressed, respectively. The influences of design parameters on back‐electromotive force and torque capability are evaluated to aid the performance optimisation. A machine prototype is then fabricated to experimentally validate the theoretical analyses. [ABSTRACT FROM AUTHOR]

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]

The memory machine concept is recently extended to switched-flux (SF) machines, forming a series of SF hybrid magnet memory machines (SF-HMMMs). They exhibit the merits of good demagnetization withstand capability and effective flux adjustability. Nevertheless, the torque density is inevitably compromised due to the geometric conflict within the stationary part. Meanwhile, the inactivated dc coil, excluding online magnetization transients, results in system redundancy. Hence, in this paper, a new hybrid-excited (HE) concept is developed and implemented in a partitioned-stator SF-HPMM (PS-SF-HMMM). Thereby, the distinct synergies of a dual-magnet memory machine and an HE machine are achieved. With slight compensated field excitation, the torque can be improved at low-speed operation. Meanwhile, the high-speed constant-power region can be further extended without sacrificing high efficiency. The stator/rotor pole numbers are optimized first. The operating mechanism and optimal stepwise HE implementation over a whole operating envelop are then addressed. In addition, a comparison between PS-SF-HMMM with hybrid-excitation and its pure HE counterpart is established. Finally, both the finite-element simulation and experiments are carried out to verify the utility of the proposed HE concept. [ABSTRACT FROM AUTHOR]

In this paper, a novel topology of hybrid-permanent-magnet switched-flux memory machine (HPM-SFMM) is proposed, which is characterized by a conventional SFPM machine with embedded “V”-shaped Al-Ni-Co magnet poles. The proposed machine combines the distinct synergies of torque enhancement in neodymium–iron–boron (NdFeB) PM and flux variability in aluminum–nickel–cobalt (AlNiCo) PM. By changing the magnetization directions of Al–Ni–Co magnets, the wide-speed-range high-efficiency operation can be readily achieved, which is highly favorable for automotive applications. The configuration and operating principle of the machine are first described, and the combination of stator/rotor pole numbers is optimized. In addition, the torque density/flux adjusting capability as the functions of dual-magnet dimensions are analytically derived. The magnet hybridizing proportion is optimized in order to achieve a favorite tradeoff between flux adjusting range and torque density improvement. Then, the electromagnetic performance of the proposed HPM-SFMM is investigated. Finally, a 12/14-stator/rotor pole prototype is fabricated to experimentally verify the analysis. [ABSTRACT FROM AUTHOR]

This paper deals with a sizing optimization approach to reducing the cogging torque and maximizing the flux linkage of a transverse flux permanent magnet generator with double C-hoop stator and flux-concentrated rotor. The previous investigations demonstrated that the cogging torque is significantly influenced by ks and kr , which denote the ratios of circumferential widths of stator hoop and rotor core to pole pitch, respectively. The 3-D finite-element method (FEM) is employed to investigate the relationship between the abovementioned ratios and the cogging torques of both single-phase and three-phase prototypes. The optimal ratios of ks and kr , which comply with the equation, i.e., $(k_{{ r}} >1-k_{{ s}} )\cap (k_{{ r}} >1-0.788~*~k_{{ s}} )=k_{r} >1-0.788~*~ k_{{ s}} $ , are selected, and the procedures are described. The FEM results show that the amplitude of the cogging torque can be reduced significantly due to the reshaped rotor core. Besides, two additional zero-crossing points can be observed with the increase in kr and the decrease in ks . The cogging torque can be decreased by 20% with a skewed rotor core. A three-phase prototype is optimally designed and manufactured to verify the optimization approach. [ABSTRACT FROM AUTHOR]

Transverse flux permanent magnet (TFPM) machine possesses the characteristic feature of decoupled electric load and magnetic load to obtain high power density. A novel TFPM generator (TFPMG) with double C-hoop stator and flux-concentrated rotor is proposed for low-speed applications, such as direct-drive power generation, which has larger torque capability and more poles than traditional double-side TFPMGs. The structure and operation principles of the generator are described in detail. The 3-D finite-element method (3-D FEM) is employed to compute the no-load magnetic field distributions. The analytical results, including flux density waveform, electromotive force (EMF) waveform, and inductance waveform of the armature winding, are obtained to verify the principle and feasibility of the proposed generator. The cogging torque is also analyzed and optimized by the 3-D FEM. A prototype is fabricated, and some experiments are conducted. The experimental results of back EMF and waveforms of current and voltage with different loads verify the FEM analysis previews well. [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]

In this paper, a consequent magnet pole switched flux memory machine (CMP-SFMM) is developed to improve the torque density and simplify the mechanical manufacturing with less magnet usage compared with its hybrid magnet counterparts. Nevertheless, owing to the significant magnetic saturation, the flux-adjustable range appears to be relatively limited, which will deteriorate the flux-weakening performance. Therefore, a novel winding-switching concept is introduced to deal with its limited flux-weakening capability, i.e., the magnetizing coils will alternatively serve as the secondary armature winding after the reversal of magnetization directions of low-coercive force magnets, thus resulting in the flux-linkage cancellation within the same phase. The machine topology, flux-weakening principle, and integrated circuit design are addressed. Then, the electromagnetic characteristics of CMP-SFMM with or without winding-switching are investigated and compared, which confirms the feasibility of the flux-weakening method. [ABSTRACT FROM AUTHOR]