Stator Permanent Magnet Machine Research Articles

Comparative analysis of dual stator machines

Electromagnetic performance of three different types of double stator permanent magnet machine is analyzed and compared in this study. The analyzed machines in this study are Machine 1, Machine 2 and Machine 3. These machines are designated as: M 1, M 2 and M 3, respectively. The studies are implemented using two-dimensional and three-dimensional finite element analysis (2D-FEA and 3D-FEA) methods. The predicted performance indices are: total harmonic distortion of the voltage, torque ripple, cogging torque, winding inductances, output torque and unbalanced magnetic force (UMF). The studies show that the investigated machine types have negligible reluctance torque and thus, similar axes inductance values. Therefore, the machines’ bulk torque components are contributed mainly by the magnets while the armature excitation sources yield lesser torque components. Amongst the compared machines, M 3 type has an outstanding performance in almost all the performance metrics, compared to M 2 and M 1 types. Nevertheless, M 1 machine type has some good attributes, particularly, with respect to its high output torque per applied magnet volume, in addition to its widest operating speed range ability. Low-speed high-torque applications are most suitable for the investigated machines in practice.

Performance comparison of double stator permanent magnet machines

Performance comparison of double stator permanent magnet machines

Overview of Stator Slot-Opening Permanent Magnet Machines

In the past few decades, the stator permanent magnet (PM) machines have attracted much research attention because of their reliable rotor structure, high power density, wide speed range, and strong fault-tolerant ability. Among the recently proposed stator PM machine topologies, the stator slot-opening PM (SS-PM) machines are becoming increasingly popular because of their higher stator space utilization and robust rotor structure. According to the SS-PM magnetization direction, the SS-PM machines can be classified into three categories, namely, the tangentially magnetized stator slot-opening PM (TMSS-PM) machines, the radially magnetized stator slot-opening PM (RMSS-PM) machines, and the compound magnetized stator slot-opening PM (CMSS-PM) machines. The associated working principle and electromagnetic performance of different SS-PM machines can be diverse. Therefore, this article gives an overview of SS-PM machines in terms of machine design, working principle, and machine performance. A qualitative performance evaluation and comparative study of SS-PM machines are presented, and the future challenges and potential opportunities in the SS-PM machine design are discussed.

A New Dual Stator Permanent Magnet Machine Based on Field Modulation Theory

Increasing industrial development puts forward high requirements for the performances of stator permanent magnet (PM) machines, such as torque density and efficiency. The paper proposes a new dual stator PM machine based on field modulation theory (DSPMM), which employs the intermediate rotor participating in the electromechanical energy conversion of the internal and external machine. The proposed machine has the advantages of high torque density and high efficiency and solves the problem of insufficient space utilization of a single stator machine. The evolution process and working principle of the proposed DSPMM are studied. The flux-switching-type PM (FSPM) and the flux-reversal-type PM (FRPM) are employed in the proposed DSPMM, which forms four representative machines. For a fair comparison, the proposed machines employ identical key parameters, i.e., PM volume, the outer radius of the outer stator, and active airgap length. Based on finite element analysis (FEA), the electromagnetic performances of the four representative DSPMM under no-load and rated load, and different copper consumption conditions are analyzed and compared. The calculated results show that the proposed DSPMM with inner FSPM stator and outer FRPM stator can provide high output torque, low torque ripple, high power factor, and high efficiency.

Analysis of Synergistic Stator Permanent Magnet Machine With the Synergies of Flux-Switching and Flux-Reversal Effects

Dual permanent magnet (PM) machines have attracted numerous interests due to the high torque density and compact volume <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">.</i> This article investigates a synergistic PM machines with the synergies of flux switching and flux reversal effects. The flux-reversal and flux-switching PM (FSPM) flux paths circulate from two sides of the split teeth separately, which avoid the over-saturation with dual PM excitations. The preferred stator and rotor pole number is derived from a simplified analytical model and the influence of leading parameters is analyzed as design guidelines. Furthermore, the synergistic stator PM machine is optimized and compared with FSPM machines. It is revealed that the synergistic stator PM machine exhibits ∼20%, ∼10%, and ∼17% higher torque density than conventional FSPM machine, C-core FSPM machine, and E-core FSPM machine, respectively. Besides, good flux weakening capability is achieved with a larger inductance than conventional FSPM machine, and higher efficiency is obtained at both low-speed and high-speed operations. Finally, an experimental prototype is fabricated to validate the proposed concepts.

Estimation of losses and efficiency of double-stator switched flux permanent magnet machines

Losses such as rotor iron and stator iron losses, magnet eddy current loss, as well as efficiency of a double stator permanent magnet machine having varying rotor pole numbers is estimated and presented in this study. This current investigation would be vital for electrical machine designers in quantifying the amount of losses in the various sections of a given double stator electric machine and as well provide better insight on resulting output efficiency of the machine. Time-stepping finite element analysis (TS-FEA) procedure is adopted in the calculations using ANSYS-MAXWELL simulation software. The compared machines having the same stator teeth/pole number (Ps) and different rotor pole (Pr) numbers are designated as: 6Ps/10Pr, 6Ps/11Pr, 6Ps/13Pr and 6Ps/14Pr. The predicted total loss values at rated current and operating base speed is 13.02 Watts, 13.13 Watts, 13.539 Watts, 13.537 Watts, from the 6Ps/10Pr, 6Ps/11Pr, 6Ps/13Pr and 6Ps/14Pr machine types, respectively. The corresponding efficiency of the machine types at rated working conditions is: 81.76%, 88.17%, 86.95% and 78.61%, respectively. The results show that magnitude of losses in a given machine would largely depend upon factors such as number of rotor poles and hence, the machine’s operating speed, electric loading and angular rotor position of the machine, etc. It is also found that the number of loss waveform cycles (Nc) in an electric revolution of the investigated machine would depend upon its stator and rotor arrangements. The most performing compared machine types are the ones that have 11- and 13-rotor pole numbers, while the least amount of efficiency is obtained from the machine type that has 14-rotor pole number. Above all, the 6Ps/10Pr and 6Ps/14Pr are characterized with high amount of pulsations or ripples and this is detrimental to the overall performance of the machines.

Impact of structural dimensions and poles on the torque performance of dual-stator permanent magnet machines

The impact of structural dimensions and rotor pole numbers on the load and no-load torques of dual stator permanent magnet machine is investigated and presented in this work. Finite element analysis (FEA) is adopted in the prediction, since it exhibits higher computation accuracy compared to other methods such as analytical modelling and techniques, etc. Version 15.0 of MAXWELL/ANSYS-2D software is implemented in the entire computations. The considered structural dimensions include: rotor centrifugal size (Rth), aspect ratio (Sr), permanent magnet width (Mth), outer stator tooth width (Tth), rotor outer pole arc/pitch ratio (ϒ1) and rotor inner pole arc/pitch ratio (ϒ2). Also, model topologies having stator pole (S) and rotor pole (P) numbers i.e. 6S/10P, 6S/11P, 6S/13P and 6S/14P, are compared. The results show that the shaft torque and no-load torque would reasonably depend on the adopted machine’s structural dimensions; in addition to the impact of rotor pole number. More so, it is observed that the optimal output torque of a given machine may not necessarily occur at the same operating structural point with that of the required least no-load torque. Implementation of the optimum structural dimensions would result to largest average output electromagnetic torque from the machine. Moreover, practically all the most optimum results are obtained from the 6S/11P machine type. The useable average shaft torque from the simulated models is approximately: 2.33 Nm, 4.16 Nm, 3.75 Nm and 2.31 Nm, for the 6S/10P, 6S/11P, 6S/13P and 6S/14P categories, respectively. Similarly, least values of the no-load torque in the compared machine types are 1.2 Nm, 0.08 Nm, 0.04 Nm and 0.68 Nm i.e. for the 6S/10P, 6S/11P, 6S/13P and 6S/14P machine topologies.

High-order sliding mode control of a doubly salient permanent magnet machine driving marine current turbine

Due to the harsh and changeable marine environment, one low speed stator-permanent magnet machine named doubly salient permanent magnet machine with toothed pole is applied for marine current energy conversion system. Indeed, this machine has simple structure, intriguing fault tolerance, and higher power density, which could adequately satisfy the different complicated operation conditions. However, its permanent magnet flux-linkage has the same variation period as the inductance which leads to a strong nonlinear coupling system. Moreover, the torque ripple caused by this special characteristics, uncertainty of system parameters and disturbance of load greatly increases the difficulty of control in this strongly coupling system. Consequently, the classical linear PI controller is difficult to meet the system requirement. In this paper, the high-order sliding mode control strategy based on the super-twisting algorithm for this system is creatively utilized for the first time. The stability of the system within a limited time is also proved with a quadratic Lyapunov function. The relative simulation results demonstrate convincingly that, the high-order sliding mode control has little chattering, high control accuracy and strong robustness.

Study and design of dual stator permanent magnet machine with spoke-type configurations using phase-group concentrated-coil windings

In this paper, a novel dual-stator permanent magnet machine (DsPmSynM) with low cost and high torque density is designed. The winding part of the DsPmSynM adopts phase-group concentrated-coil windings, and the permanent magnets are arranged by spoke-type. Firstly, the winding structure reduces the amount of copper at the end of the winding. Secondly, the electromagnetic torque ripple of DsPmSynM is suppressed by reducing the cogging torque. Furthermore, the dynamic performance of DsPmSynM is studied. Finally, the experimental results are compared with the simulation results.

Novel Dual-Stator Machines With Biased Permanent Magnet Excitation

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.

Hybrid Excitation Stator PM Vernier Machines With Novel DC-Biased Sinusoidal Armature Current

Stator permanent magnet (PM) machines are gaining more research interest in recent decades. Since the permanent magnets (PMs) are moved from the rotor side to the stator side and the salient rotor structure is adopted, it is claimed that the stator permanent magnet machines exhibit several promising features, such as simple and robust rotor, and good ability of heat dissipation as the main losses are located in the stator. On the other hand, to improve the shortcomings of the inherent limited magnetic field adjustment ability, and the low efficiency and power factor of stator dc current excited machines, hybrid excitation PM machines with additional field windings are proposed. However, the complexity of the machine structure is increased inevitably. At present, it is found that both the stator PM and the stator dc current excited Vernier machines operate with the flux modulation principle, and generally, the armature windings of the stator PM machines are fed with pure sinusoidal current. In this paper, a novel hybrid excitation stator PM Vernier machine is analyzed. In addition to the features of the salient rotor structure, stator located PMs, and concentrated armature windings, the novelty of this machine is dc-biased sinusoidal phase current, which contains an ac component and a dc component. The fundamental theories of stator PM machines fed with dc-biased current are researched, operation principle and slot/pole combination is concluded, and the optimal current configuration is studied theoretically and by finite element analysis. Finally, a prototype was designed and manufactured; the experimental tests were done to validate the proposed analysis.

Influence of PM- and Armature Winding-Stator Positions on Electromagnetic Performance of Novel Partitioned Stator Permanent Magnet Machines

Since the permanent magnets (PMs) and armature windings of partitioned stator (PS) PM machines are located in two separate inner and outer stators, their positions can be exchanged to optimize the space utilization, especially in radial field rotating machines. Therefore, in this paper, the influence of PM and armature winding stator positions on the electromagnetic performance of PS-PM machines is investigated based on the novel PS-PM machines (PS-PMMs) with surface-mounted PM (SPM) stator. Similar to the single-stator surface-mounted PMMs (SS-PMMs), flexible rotor pole number, bipolar phase flux linkage, and symmetrical phase back electromotive force (EMF) are also obtained in PS-PMMs. Based on the same 12/10 stator/rotor pole number combination, PS-PMM-I (PMs located in the inner stator) and PS-PMM-II (PMs located in the outer stator) exhibit 120% and 160% higher phase back EMFs as well as 120% and 139% larger average torques, respectively, than the SS-PMM together almost without scarifying the PM utilization efficiency under the same machine size and the same rated copper loss. Further, the proposed PS-PMM-IIs have both higher phase back EMFs and larger average torques than PS-PMM-Is among all the main stator/rotor pole number combinations. Meanwhile, for both PS-PMM-Is and PS-PMM-IIs with 12-pole stator, the machines with the 11-pole rotor exhibit the optimal torque capabilities. Moreover, the reluctance torque is also negligible in the proposed PS-PMMs due to very low saliency ratio. The analyses are validated by experiment results of the prototype machine.

Comparative Study of Novel Tubular Partitioned Stator Permanent Magnet Machines

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

Core Loss Analysis and Calculation of Stator Permanent-Magnet Machine Considering DC-Biased Magnetic Induction

In this paper, core loss characteristics of stator permanent-magnet (PM) machines are analyzed and calculated, in which the unique dc-biased magnetic induction is taken into account. The flux density variation patterns in some key points in a doubly salient PM (DSPM) machine are analyzed by the two-dimensional time-stepping finite-element method. To calculate the core loss of stator and other minor hysteresis loops under dc magnetic bias, core loss characteristics of silicon steel sheet under dc-biased induction condition are first tested by a simple test system based on traditional Epstein frame and a functional relationship between the change of dc-biased induction and hysteresis loss is proposed. Two core loss calculation methods considering rotational magnetization based on flux density waveform are improved to take the influence of dc-biased magnetic induction into consideration. The calculation results are verified by experiments on a prototype DSPM machine. The conclusions are also applicable to other kinds of stator PM machines.

Design, Analysis, and Optimization of Ironless Stator Permanent Magnet Machines

This paper presents a methodology for the design, analysis, and graphical optimization of ironless brushless permanent magnet machines primarily for generator applications. Magnetic flux in this class of electromagnetic machine tends to be 3-D due to the lack of conventional iron structures and the absence of a constrained magnetic flux path. The proposed methodology includes comprehensive geometric, magnetic and electrical dimensioning followed by detailed 3-D finite element (FE) modeling of a base machine for which parameters are determined. These parameters are then graphically optimized within sensible volumetric and electromagnetic constraints to arrive at improved design solutions. This paper considers an ironless machine design to validate the 3-D FE model to optimize power conversion for the case of a low-speed, ironless stator generator. The machine configuration investigated in this paper has concentric arrangement of the rotor and the stator, solenoid-shaped coils, and a simple mechanical design considered for ease of manufacture and maintenance. Using performance and material effectiveness as the overriding optimization criteria, this paper suggests optimal designs configurations featuring two different winding arrangements, i.e., radial and circumferentially mounted. Performance and material effectiveness of the studied ironless stator designs are compared to published ironless machine configurations.

Hybrid Excitation Topologies and Control Strategies of Stator Permanent Magnet Machines for DC Power System

The stator permanent magnet (PM) machines have simple and robust rotor structure as well as high torque density. The hybrid excitation topology can realize flux regulation and wide constant power operating capability of the stator PM machines when used in dc power systems. This paper compares and analyzes the electromagnetic performance of different hybrid excitation stator PM machines according to different combination modes of PMs, excitation winding, and iron flux bridge. Then, the control strategies for voltage regulation of dc power systems are discussed based on different critical control variables including the excitation current, the armature current, and the electromagnetic torque. Furthermore, an improved direct torque control (DTC) strategy is investigated to improve system performance. A parallel hybrid excitation flux-switching generator employing the improved DTC which shows excellent dynamic and steady-state performance has been achieved experimentally.

Design and analysis of full pitch winding and concentrated stator pole winding three-phase flux reversal machine for low speed application

The flux reversal machine (FRM) is a doubly-salient stator permanent magnet machine with flux linkage reversal in the stator concentrated winding. The existing machines at low speed, low power (2·4 kW, 300 rpm) range are not economical. FRM topology is best suited for this application. An attempt has been made to improve the power density of machine by introducing full pitch winding. Full pitch winding FRM (FPFRM) has higher power density than the conventional concentrated stator pole winding FRM (CSPFRM).Design and comparative analysis of FPFRM and CSPFRM are made. Both machines are designed for 88·58 Nm and 300 rpm. Design details of both machines are presented. Finite Element Method (FEM) analysis is carried out to evaluate and compare the performance of CSPFRM and FPFRM. Series capacitive compensation is provided for better voltage regulation of both machines.

Static Characteristics of Doubly-salient Brushless Machines Having Magnets in the Stator Considering End-effect

This article investigates the static characteristics of both doubly-salient brushless machines having magnets in stator, namely the flux-switching permanent magnet machine (three-phase topology) and doubly-salient permanent magnet machines (including three-phase and two-phase structures), especially taking the influence of end-effect into account. The structures and operating principles are described first, and then the end-effect in the stator permanent magnet machines is investigated by a 3-D calculation, and a leakage factor reflecting end-effect is defined to modify the 2-D predicted results. The proposed approach is validated experimentally for the prototype machines.

A Study of the Design for the Flux Reversal Machine

The three-phase flux reversal machine (FRM) is a doubly-salient stator-permanent magnet machine with flux linkage reversal in the stator three-phase concentrated windings. It can operate in both motoring and generating modes. In this paper, we identify stator/rotor geometrical design variables that influence the cogging, interaction torques, and winding flux linkage using a two-dimensional finite-element method and the flux-magnetomotive force diagram technique. Also, the novel design to improve the performance of the FRM is studied both theoretically and experimentally.