Flux-switching Machine Research Articles

Design Optimization of a Permanent-Magnet Flux-Switching Generator for Direct-Drive Wind Turbines

Due to the increasing need for direct-drive wind turbines, a large number of papers are dedicated to the optimization of low-speed wind generators. A permanent-magnet flux-switching machine can be a valuable option to use in such applications. This paper describes the optimization procedure of a direct-drive flux-switching wind generator. The average losses, the required converter power, and the cost of permanents magnets were chosen as the optimization objectives. To reduce the calculation efforts during the optimization, a method to construct the substituting load profiles is proposed. Two-mode and three-mode substituting profiles were constructed on the basis of the nine-mode initial profile. The losses calculated under the two-mode, three-mode, and nine-mode profiles accurately coincided, which supported the use of the low-mode substituting profiles instead of the initial one. During the optimization, the average losses decreased by 30%, which corresponded to an increase in the average efficiency by almost 6%. The required converter power was decreased by 10%. The total active material mass, cogging torque, and torque ripple were also slightly decreased.

Analysis and Suppression of Induced Voltage Pulsation in DC Winding of Five-Phase Wound-Field Switched Flux Machines

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

Analysis of PM Eddy Current Loss in Rotor-PM and Stator-PM Flux-switching Machines by Air-gap Field Modulation Theory

This paper investigates and compares the eddy current loss induced in permanent magnet (PM) in both rotor-PM flux-switching (RPM-FS) machines and stator-PM flux-switching (SPM-FS) machines. Based on the field modulation principle, the harmonic components of both the PM field and armature reaction field are deduced, as well as the corresponding frequencies. Then, the PM loss production mechanisms due to eddy current are revealed for the RPM-FS and SPM-FS machines, respectively. Consequently, the similarities and differences between two FS machines are investigated from the perspectives of both electromagnetic torque and PM eddy current loss production mechanisms. The results indicate that the PM eddy current loss in SPM-FS machines influences efficiency dramatically. However, for the RPM-FS machine, the armature reaction field affects the PM loss more sensitively. In addition, a large PM eddy current loss is associated with high-power rating and large current density FS machines for electric vehicle application, and can be reduced by utilizing PM segmentation method.

Comprehensive Comparison of Rotor Permanent Magnet and Stator Permanent Magnet Flux-Switching Machines

This paper compares two flux-switching machines, namely, one stator permanent magnet flux-switching machine and one rotor permanent magnet flux-switching (RPM-FS) machine, with the same overall dimensions, main material properties, and current density. The comparison of characteristics is conducted from two perspectives, i.e., the electromagnetic torque production mechanism and torque (power)-sizing equation. The contribution of harmonics to average electromagnetic torque is analyzed based on the modulation principle and gearing effect, which reflects the similarities and differences between two FS machines in torque production mechanism. Moreover, torque performances are investigated from the viewpoints of magnetic parameters and electrical parameters. Then, electromagnetic performances including overload capability, flux-weakening capacity, and efficiency are analyzed and compared further. The predicted results indicate the RPM-FS machine exhibits a larger torque capability, a lower torque ripple, and improved flux-weakening capacity. The finite-element analysis predicted results are validated by experiments on two prototype machines.

A New Outer-Rotor Hybrid-Excited Flux-Switching Machine Employing the HTS Homopolar Topology

Currently, studies of flux switching machines are actively underway owing to several advantages of these machines, including their sturdy rotor structure and high output capability. This paper deals with an outer-rotor hybrid-excited flux-switching machine (FSM). The proposed machine embraces a homopolar structure and utilizes permanent magnets (PMs) for field excitation and a high-temperature superconducting (HTS) coil for flux regulation. The stator houses the HTS field coil, PMs, and armature windings. The outer rotor consists solely of an iron core. Thus, the machines are cost effective and can serve as a solution to the design and fabrication complexities of field current supplying and cooling systems. In this paper, the machine performance outcomes are analyzed using the 3D finite element method (FEM), and the validity of the proposed machine is verified.

Analysis and Reduction of On-Load DC Winding Induced Voltage in Wound Field Switched Flux Machines

DC winding induced voltage pulsation in wound field switched flux (WFSF) machines causes dc winding current ripple and field excitation fluctuation, challenges the dc power source, and deteriorates the control performance. Hence, reducing this pulsation is important in the design of a WFSF machine. In this paper, based on the analytical models, rotor skewing and rotor iron piece pairing are proposed and comparatively investigated by the finite-element (FE) method to reduce the on-load dc winding induced voltage in WFSF machines having partitioned stators and concentrated ac windings. FE results show that peak-to-peak value of the on-load dc winding induced voltage in the analyzed 12/10-pole partitioned stator WFSF (PS-WFSF) machines can be reduced by 78.42% or 77.16% by using rotor skewing or rotor pairing, respectively, while the torque density can be maintained by >90%. As for the 12/11-, 12/13-, and 12/14-pole PS-WFSF machines, by using rotor iron piece inner arc pairing, the on-load dc winding induced voltage can be reduced by 64.11%, 52.12%, and 76.49%, respectively, while the torque density can be maintained by more than 90%. Prototypes are built and tested to verify the analytical and FE results.

Comparative Study of Wound-Field Flux-Switching Machines and Switched Reluctance Machines

In this paper, comparisons between two permanent-magnet-free machines, namely a wound-field flux-switching machine (WFFSM) and a switched reluctance machine (SRM), are carried out. The topologies and operation principles of the WFFSM are illustrated first. Then, the effects of rotor skewing angle on static characteristics, e.g., open-circuit phase flux-linkage and back electromotive force due to field currents, electromagnetic torque, and torque ripple, have been investigated in depth by finite-element analysis (FEA). Consequently, the optimal rotor skewing angle is determined. After that, comparisons at the rated speed 1500 r/min and at the rated RMS current density of 5 A/mm2 among the 6-armature-slots/5-rotor-poles (6/5) straight- and skewed-WFFSMs, and two representative SRMs, namely conventional 12/8 SRM and the short-flux 12/10 SRM with the same stator outer diameter and stack length are conducted in terms of phase flux-linkage, inductance, and torque performance. The results indicate that for these two PM-free machines, at the rated speed and the rated RMS current density, the skewed-rotor WFFSM exhibits considerably larger torque capacity, much smaller torque ripple, stronger saturation withstand ability. In addition, the experiments of the skewed-WFFSM and the 12/8 SRM prototypes working at the mechanical character curve are conducted. The experimental results present that the power factor of the WFFSM is much higher and the efficiency is slightly lower than that of the 12/8 SRM.

Comparison of different synchronous machines with stator‐side permanent magnets for industrial drive application

Three different synchronous machines with the permanent magnets in the stator (doubly salient permanent magnet, flux reversal permanent magnet, and flux switching permanent magnet machine) are compared for use as an industrial drive for 45 kW, 400 V Y, and 1000 …. 3000 min −1 . For comparison, finite element method simulations are carried out to investigate the torque density of the machines, and the results are explained based on the magnetic co-energy. The simulations show that the flux switching machine generates the highest torque density of the three machines. Therefore, a prototype flux switching machine is built, tested, and compared with a conventional permanent magnet synchronous machine (PMSM) with magnets on the rotor surface, the same size (stator outer diameter d so = 314 mm, axial length l Fe = 180 mm) and rating. The measurements indicate that the conventional PMSM and the flux switching machine have roughly equivalent electrical behaviour.

Analysis of Stator Slots and Rotor Pole Pairs Combinations of Rotor-Permanent Magnet Flux-Switching Machines

This paper investigates the influence of stator slots and rotor pole pairs combinations on torque performances in rotor permanent magnet flux switching (RPM-FS) machines. Based on a magnetomotive force (MMF) permeance model, the candidates of stator slots and rotor pole pairs combinations with higher torque capability can be determined by analyzing the PM-MMF and winding factor. Meanwhile, the candidates with a lower torque ripple can be obtained by referring to the cogging torque, which is related to the greatest common divisor of stator slots and rotor pole pairs. In addition, from the field modulation principle, the RPM-FS machines with the same fundamental magnetic loadings and winding factors exhibit identical fundamental harmonic torque, but different modulation harmonic components. Finally, four candidates with attractive torque performance are chosen, and the characteristics are verified by finite-element analysis and experiments.

Modular Rotor Single Phase Field Excited Flux Switching Machine with Non-Overlapped Windings

This paper aims to propose and compare three new structures of single-phase field excited flux switching machine for pedestal fan application. Conventional six-slot/three-pole salient rotor design has better performance in terms of torque, whilst also having a higher back-EMF and unbalanced electromagnetic forces. Due to the alignment position of the rotor pole with stator teeth, the salient rotor design could not generate torque (called dead zone torque). A new structure having sub-part rotor design has the capability to eliminate dead zone torque. Both the conventional eight-slot/four-pole sub-part rotor design and six-slot/three-pole salient rotor design have an overlapped winding arrangement between armature coil and field excitation coil that depicts high copper losses as well as results in increased size of motor. Additionally, a field excited flux switching machine with a salient structure of the rotor has high flux strength in the stator-core that has considerable impact on high iron losses. Therefore, a novel topology in terms of modular rotor of single-phase field excited flux switching machine with eight-slot/six-pole configuration is proposed, which enable non-overlap arrangement between armature coil and FEC winding that facilitates reduction in the copper losses. The proposed modular rotor design acquires reduced iron losses as well as reduced active rotor mass comparatively to conventional rotor design. It is very persuasive to analyze the range of speed for these rotors to avoid cracks and deformation, the maximum tensile strength (can be measured with principal stress in research) of the rotor analysis is conducted using JMAG. A deterministic optimization technique is implemented to enhance the electromagnetic performance of eight-slot/six-pole modular rotor design. The electromagnetic performance of the conventional sub-part rotor design, doubly salient rotor design, and proposed novel-modular rotor design is analyzed by 3D-finite element analysis (3D-FEA), including flux linkage, flux distribution, flux strength, back-EMF, cogging torque, torque characteristics, iron losses, and efficiency.

Outer rotor wound field flux switching machine for In‐wheel direct drive application

Nowadays the flux switching machines offer pivotal role in high speed applications. The flux sources (field excitation coil and armature winding or permanent magnet) are confined to the stator leaving rotor completely passive, and thus making the flux switching machine (FSM) more suitable for industrial applications. This paper emphasizes salient rotor pole and non-overlapping windings embedded in electrical machine design possess some pertinent features such as reduced copper losses, low-cost, and usage in high speed applications. The proposed design is analyzed for coil test analysis and flux linkage and torque. On the basis of the analysis performed, it is clear that 12-slot/13-pole has low cogging torque, high flux linkage, and maximum torque, compared with other topologies of outer rotor field excitation FSM. A deterministic optimization technique is adopted to enhance the performance of 12-slot/13-pole design. Further, finite element analysis (FEA) results are verified through Global Reluctance Network (GRN) methodology, which show close resemblance with error less than 1.2%. Hence, it validates the proposed design for outer rotor field excitation FSM direct drive application. The proposed design for hybrid electric vehicle torque characteristic is compared with existing interior permanent magnet synchronous machine (IPMSM) and 6-slot/7-pole wound field flux switching machine (WFFSM).

Performance comparison and optimisation of dual mover linear permanent magnet flux switching machine

Short moving primary and rigid low-cost secondary are important requirements of linear machines designed for long stroke applications. In the race, linear permanent magnet flux switching machine (LPMFSM) is a competitive candidate by confining excitation sources to short mover, thus making stator robust and low cost (made of only iron). However, single-sided LPMFSM exhibit a demerit of high normal (attraction) force due to its topology. In order to rectify the problem and enhance thrust force profile, two novel double-sided LPMFSMs are proposed with dual stator and dual mover topologies. After stator pole study, both topologies with same design dimensions are analysed and compared by 2-D finite element method here. Detailed analysis revealed that 12/14 DMLPMFSM exhibit low numerical values of thrust force ripples and detent force while maintaining average thrust force value. Hence, 12/14 DMLPMFSM is selected and optimised by structure-based deterministic optimisation (SBDO) approach to further enhance thrust force profile. Finally, comparison of initial and optimised design of 12/14 DMLPMFSM is presented to validate optimisation procedure.

Design and Analysis of an Outer-Rotor-Permanent-Magnet Flux-Switching Machine for Electric Vehicle Applications

In this paper, an outer-rotor-permanent-magnet flux-switching (ORPM-FS) machine is proposed. It not only inherits the traditional flux-switching permanent-magnets (FSPM's) flux-switching principle and the high torque density, but also overcomes the FSPM's magnetic saturation and adds the slot area, thus producing favorable output torque capability at rated load and overload condition. By means of finite element method, the ORPM-FS machine is optimized through multi-level process for multi-objectives: the basic variables optimization for high output torque and low torque ripple, the pitch coefficient optimization for favorable torque characteristics and efficiency, the optimal selection for high efficiency at flux-weakening operation. At last, the electromagnetic performances of the optimized ORPM-FS machine are analyzed, which shows that the proposed machine can receive high torque density, low torque ripple, high efficiency, and favorable overload capability.

Reduction of Open-Circuit DC-Winding-Induced Voltage in Wound Field Switched Flux Machines by Skewing

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.

Optimal Design and Performance Analysis of Double Stator Multi-Excitation Flux-Switching Machine

Due to its special partitioned stator structure and multi-excitation with two different types of permanent magnet, a new double-stator multi-excitation flux-switching machine (DSME-FSM) has advantages of high torque density, wide speed range, and low cost. For this kind of machine with complex structure, in order to realize the optimization accurately and efficiently, a multi-objective comprehensive optimal design method considering the different weights of the design objectives is presented based on parameters sensitivity analysis and genetic algorithm optimization in this paper. The parametric model of the machine is built up, and a trade-off objective function considering the different weights of the design objectives is defined. The key size parameters with strong sensitive are selected through parameters sensitivity analysis and then optimized by using the genetic algorithm method. The performance comparison between the initial and the optimized machines verifies the proposed optimization method. The anti-demagnetization property and the flux-weakening capability for a wide-speed range operation are also analyzed, which further confirms the DSME-FSM an interesting candidate for EV propulsion.

A Novel Method to Reduce of Cogging Force in a Linear Flux-Switching Permanent Magnet Brushless AC Machine

The primary linear flux-switching permanent magnet (LFSPM) motor has the merits of high speed, high response, and direct drive. However, the presence of the cogging force in LFSPM motors compromises position and speed control accuracy, which can be particularly troublesome at low speeds. A novel approach of suppressing the slot effect cogging force for LFSPM is proposed according to repetitive control of time-varying periodic signals. The time-varying periodic thrust disturbance in t-domain is transformed to the signals defined in the x-domain, and a repetitive controller is designed. Furthermore, a series of specific harmonic currents are added into q-axis reference current, resulting in additional force components to counteract the end effect cogging force. Finally, experimental evaluations of the control strategy are performed on an AD5435-controlled LFSPM drive platform. The simulations and experiments verify that the proposed method can suppress the thrust ripple effectively.

Maximum Ratio of Torque to Copper Loss Control for Hybrid Excited Flux-Switching Machine in Whole Speed Range

This paper proposes an optimized control strategy for hybrid excited flux-switching machine (HEFSM) in the whole speed range. First, the machine topology, operating principle, electromagnetic performance, and dynamic models of HEFSM are briefly introduced. Second, in the constant torque range, the optimized positive excitation is utilized to improve the load capacity, and minimize the copper loss, as well as achieve a faster response than the strategy of random combination of excitation and armature current and the zero excitation current control. In constant power range, there are several constraints like torque, current, voltage and speed. The optimized negative excitation current and d -axis current are not only used to achieve higher speed and produce reluctance torque, but also minimize the copper loss for a certain value of torque in the optimized strategy. Then, the maximum ratio of torque to copper loss is realized. Finally, other losses (such as iron loss, friction, and windage losses) and efficiency of HEFSM are analyzed. The feasibility and effectiveness of the proposed control strategy for the HEFSM drive system are confirmed by simulation and experiment.

Tubular unified magnetic‐field flux‐switching PMLM for free‐piston energy converter

A tubular flux-switching permanent-magnet linear machine (PMLM), which features unified magnetic field between the mover and two stators, is investigated for free-piston energy converter. The topology evolution, topology, operating principle and design considerations of the machine are thoroughly analysed. With the sinusoidal speed characteristic of free-piston Stirling engine considered, a tubular unified magnetic-field flux-switching PMLM is designed by finite-element analysis. Several main structural parameters, which include the outer and inner radius of the mover, the mover tooth width, the magnet thickness, the tooth widths of both the outer and inner stators and the widths of both the outer and inner stator yokes are studied to achieve high-force and mass-power density. Finally, the proposed machine is compared with two typical flux-switching PMLMs. The comparison results show that the unified magnetic-field flux-switching PMLM is suitable for applications which require high-power density, light mover structure and fast dynamic.

Vector Control of Stator-Permanent Magnet Memory Machine Based on Three Magnetization State Manipulations

Owing to the estimated permanent magnet (PM) flux linkage fluctuation, the stator-PM memory machine employing the continuous magnetization state (MS) manipulation may suffer from frequent MS manipulations and the accidental inverter damage in its extended speed range. In order to deal with this issue, in this paper, a novel vector control based on three MS manipulations is proposed and implemented on the existing hybrid PM axial field flux-switching memory machine. After a brief analysis of the researched machine configuration, the principle of the three MS manipulations, the remedial sliding mode speed regulator and the current distribution strategy are discussed. The simulated results show that the proposed scheme reduces the speed and electromagnetic torque overshoot and improves the dynamic performance. Meanwhile, compared with the flux-weakening control, the wide speed range can be obtained. Finally, the experiment is carried out to verify the validity of the theory.

Design and Optimization of Complementary Field Excited Linear Flux Switching Machine With Unequal Primary Tooth Width and Segmented Secondary

Linear flux switching machines (LFSMs) are one of the recently emerging and competitive candidates for long stroke applications due to high thrust force density, low cost and robust secondary, and high reliability. In the past decade, permanent magnet linear flux switching machines (PMLFSMs) with continuous secondary is researched by numerous researchers. However, cost of rare earth permanent magnet and iron material for continuous secondary in case of long stroke application makes PMLFSMs not an economical choice. In order to incorporate advantages of segmented secondary, such as: less use of stator iron, high power factor, and less critical saturation, a novel complementary dual mover field excited linear flux switching machine (FELFSMs) with segmented secondary and parallel magnetic structure is proposed and investigated in this paper. Furthermore, geometry-based deterministic optimization approach based on finite element analysis (FEA) is adopted to uplift overall thrust force profile, reduce secondary iron volume, and balance magnetic circuit of the machine. During optimization process, magnitude difference of flux flow between ac winding tooth and dc winding tooth is observed, that compel designers to go for unequal primary teeth design. Finally, optimal ac and dc current densities of geometrically optimized model and without any cooling arrangements are investigated for maximum average thrust force and minimum thrust force ripple ratio.