Flux-switching Machine Research Articles

Subdomain modeling of linear hybrid excited flux switching machine

PurposeThis paper aims to develop an analytical approach to validate the finite element analysis (FEA) results. FEA itself is a powerful tool to evaluate the performance of electrical machines but takes more time and requires more drive storage. To overcome this issue, subdomain modeling (SDM) is used for the proposed machine.Design/methodology/approachSDM is developed to validate the electromagnetic performance of a new linear hybrid excited flux switching machine (LHEFSM) with ferrite magnets. In SDM, the problem is divided into different physical regions called subdomains. Maxwell's governing equation is solved analytically for each region, where the magnetic flux density (MFD) is generated. From the generated MFD, x and y components are calculated, which are then used to find the useful force along the x-axis.FindingsFEA validates the developed SDM via JMAG v. 20.1. The results obtained show excellent agreement with an accuracy of 95.13%.Practical implicationsThe proposed LHEFSM is developed for long stroke applications like electric trains.Originality/valueThe proposed LHEFSM uses low-cost ferrite magnets with DC excitation, which offers better flux regulation capability with improved electromagnetic performance. Moreover, the developed SDM reduces drive storage and computational time by modeling different parts of the machine.

Analysis of Linear Hybrid Excited Flux Switching Machines with Low-Cost Ferrite Magnets

Linear hybrid excited flux switching machines (LHEFSM) combine the features of permanent magnet flux switching machines (PMFSM) and field excited flux switching machines (FEFSM). Because of the widespread usage of rare-earth PM materials, their costs are steadily rising. This study proposes an LHEFSM, a dual stator LHEFSM (DSLHEFSM), and a dual mover LHEFSM (DMLHEFSM) to solve this issue. The employment of ferrite magnets rather than rare-earth PM in these suggested designs is significant. Compared to traditional designs, the proposed designs feature greater thrust force, power density, reduced normal force, and a 25% decrease in PM volume. A yokeless primary structure was used in a DSLHEFSM to minimize the volume of the mover, increasing the thrust force density. In DMLHELFSM, on the other hand, a yokeless secondary structure was used to lower the secondary volume and the machine’s total cost. Single variable optimization was used to optimize all of the proposed designs. By completing a 3D study, the electromagnetic performances acquired from the 2D analysis were confirmed. Compared to conventional designs, the average thrust force in LHEFSM, DSLHEFSM, and DMLHEFSM was enhanced by 15%, 16.8%, and 15.6%, respectively. Overall, the presented machines had a high thrust force density, a high-power density, a high no-load electromotive force, and a low normal force, allowing them to be used in long-stroke applications.

Design and lumped parameter magnetic network model of hybrid excited consequent pole flux switching machine

PurposeThe purpose of this paper is to analyze electromagnetic performance and develop an analytical approach to find the suitable coil combination and no-load flux linkage of the proposed hybrid excited consequent pole flux switching machine (HECPFSM) while minimizing the drive storage and computational time which is the main problem in finite element analysis (FEA) tools.Design/methodology/approachFirst, a new HECPFSM based on conventional consequent pole flux switching permanent machine (FSPM) is proposed, and lumped parameter magnetic network model (LPMNM) is developed for the initial analysis like coil combination and no-load flux linkage. In LPMNM, all the parts of one-third machine are modeled which helps in reduction of drive storage, computational complexity and computational time without affecting the accuracy. Second, self and mutual inductance are calculated in the stator, and dq-axis inductance is calculated using park transformation in the rotor of the proposed machine. Furthermore, on-load performance analysis, like average torque, torque density and efficiency, is done by FEA.FindingsThe developed LPMNM is validated by FEA via JMAG v. 19.1. The results obtained show good agreement with an accuracy of 96.89%.Practical implicationsThe proposed HECPFSM is developed for high-speed brushless AC applications like electric vehicle (EV)/hybrid electric vehicle (HEV).Originality/valueThe proposed HECPFSM offers better flux regulation capability with enhanced electromagnetic performance as compared to conventional consequent pole FSPM. Moreover, the developed LPMNM reduces drive storage and computational time by modeling one-third of the machine.

Understanding Switched-Flux Machines: A MMF-Permeance Model and Magnetic Equivalent Circuit Approach

Due to their particular structure, switched-flux permanent magnet machines have become a very interesting alternative for many applications. This is why some recent studies have been focused in the understanding of the operating mechanism of these machines via the MMF-permeance modelling. However, the models that can be found in the literature make some simplifications that reduce their accuracy when predicting the performance of switched-flux machines. For example, the models that can be found in the literature are commonly not precise enough for machines with a wide slot, because the influence of the modulator of the primary side of the machine is neglected. In this article, a precise analytical model is developed for a 6/13 C-Core switched-flux machine via a combination of a magnetic equivalent circuit and a MMF-permeance model. The model is based on the magnetic field modulation principle. The analytical model is used to explain the flux focusing effect and the force generation mechanism of switched-flux machines. A new concept of PM field harmonic efficiency ratio is used to identify the most efficient PM field harmonics of 2 switched-flux machines. The precision of the model is validated via 2D and 3D Finite Element Method simulations, and experimental measurements that were obtained with a linear machine prototype. The results show that the model can predict the performance of switched-flux machines with a high accuracy level.

Cooling Analysis of High-Speed Stator-Permanent Magnet Flux-Switching Machines for Fuel-Cell Electric Vehicle Compressor

Thermal management of electrical machines is an important issue to improve electromagnetic performance, reduce system size and prolong lifetime. Based on the equivalent thermal circuit (ETC) and computational fluid dynamics (CFD) methods, the temperature rise characteristic of a high-speed stator-permanent magnet-type flux switching (HS-SPMFS) machine for fuel-cell electric vehicle compressor is predicted. Firstly, the structural features, key dimensions, material properties and heat generation rate of the HS-SPMFS machine and its cooling system are introduced. Secondly, the ETC model of the machine with a liquid cooling channel is proposed, and the size of the cooling system is preliminarily designed. The influence mechanism of the number, size and flow rate of the water channel on the convective heat transfer area, convective heat transfer coefficient, water head loss and winding temperature rise is revealed. On this basis, combined with the CFD method, the temperature distribution of the machine is studied, and the detailed temperature distributions of each component of the machine are obtained and verified by the ETC method considering the cooling system. Finally, a HS-SPMFS machine prototype is manufactured and the temperature test platform of the prototype is built. The temperature rise behaviors of the machine under different working conditions are tested, verifying the theoretical analysis and the prediction methods.

Optimization and Performance Evaluation of Non-Overlap Wound-Field Converter-Fed and Direct-Grid Wind Generators

Non-overlap winding technology continues to remain relevant in the design of wound-field machines as an alternative for high torque density permanent magnet machines. In this paper, the finite element analyses-optimisation of two variants of the non-overlap wound-field machines viz., wound-field flux switching machine (WF-FSM) and phase shifting wound rotor synchronous machine (WRSM), are compared, first in terms of their performance for large-scale converter-fed wind generator drives, then experimentally as sub-scaled converter-fed versus direct grid-connected wind generators, respectively. This study is unique because there are no prior attempts to design, optimize and analyse on these machines for medium-speed wind power generation, as well as experiment on sub-scale prototypes for direct-grid and converter-fed operation. All investigations are contemplated in the medium-speed wind generator drivetrain which provides a tradeoff for generator efficiency and size. From the global optimisation of both machines at large-scale power levels, the torque per mass of the WF-FSM is found to be 50 % lesser compared to the WRSM. This is due to approximate volume, with closely matched optimal split and aspect ratios. In terms of the sub-scaled experimentation, both generators can easily vary their generated output power to match with varying wind resource, but direct grid-connected WRSM generator yields better efficiency performance compared to the WF-FSM converter-fed operating mode, given that the generator terminal voltage of the former is highly regulated.

Analytical Modeling and Optimization of Partitioned Permanent Magnet Consequent Pole Switched Flux Machine With Flux Barrier

Switched Flux Permanent Magnet Machine (SFPMM) encompass unique features of conventional direct current machine, permanent magnet (PM) synchronous machine and switch reluctance machine therefore, applicable for high-speed applications. However, conventional SFPMM exhibits demerits of high PM volume ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_PM</i> ), high torque ripples ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_rip</i> ), higher cogging torque ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_cog</i> ), lower torque density ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_den</i> ) and significant stator flux leakage. In this paper, a new topology of consequent pole (CP) SFPMM (CPSFPMM) is proposed having partitioned PM that improved flux modulation phenomena utilizing flux barriers. Moreover, due to non-linear behaviour of PM and complex stator structure alternate analytical sub-domain model is utilizes for initial design. However, initial design offers lower open-circuit phase flux linkage (Φ), average mechanical torque ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_avg</i> ) and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_den</i> . Aforementioned electromagnetic key performance indicator with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_cog</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_rip</i> , total harmonics distortion in Φ (Φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>THD</i></sub> ), average power ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_avg</i> ) and power density ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_den</i> ) are refined utilizing Geometric-Based Deterministic Optimization (GBDO). Analysis reveals that proposed new topology of CPSFPMM with flux barriers reduces <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_cog</i> by 34.90%, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_rip</i> by 20.27%, Φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>THD</i></sub> by 28.08% whereas it enhanced <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_avg</i> by 17.79%, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_den</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_den</i> by 34.38%.

Thrust Ripple Reduction in Linear Switched-Flux Machines via Additional Pole Optimisation

Linear switched-flux machines are a kind of permanent magnet machine with a passive ferromagnetic secondary. Therefore, they can achieve both a good performance and a low cost in long stroke applications. However, due to the end effect, these machines generate high detent force and on load thrust force ripples. There are several solutions in the literature that aim to minimise the thrust ripple. One of those solutions is the placement of additional poles in the ends of the machine. These can be passive, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i. e.</i> simple ferromagnetic teeth, or active, with additional magnets. The former is the most common solution in the literature. In this article, the optimal configuration of the additional poles is discussed via 4 additional pole sizing strategies, and the influence of the design variables and optimisation objectives is analysed. Then, a generic additional pole configuration is proposed, which combines a high effectiveness and a simple design. Finally, an experimental validation is carried out, and the measurements confirm the results from the optimisation.

Design and analysis of dual‐stator hybrid excited linear flux switching machine for long‐stroke applications

In this work, a novel dual-stator hybrid excited linear flux switching machine (DSHELFSM) is proposed. The proposed machine is suitable for long-stroke applications as all the excitation sources are mounted on a short mover and the stator is completely passive. Second, the proposed machine uses ferrite magnets rather than the expensive rare earth permanent magnets (PMs) with the addition of field excitation to achieve flux-regulation capability at various field currents. An iron bridge that provides an additional path for flux linkage to complete its circuit is used. Various design parameters such as split ratio, stator pole width, width and height of PM, the width of the iron bridge, width of mover's tooth, and stator slot depth are optimised using multivariable geometric optimisation (MGO) while keeping the slot area, electric and magnetic loading constant. The optimised design has improved the performance as compared to the initial design. Furthermore, the results obtained by 2D analysis are verified by 3D analysis. Thermal analysis is carried out to set the operating limit of the proposed machine.

Analysis and optimization of a five-phase hybrid excitation flux switching machine based on the consistency and complementarity principle

In this study, the general optimal stator poles/rotor teeth (P/T) combination equation of the E-core hybrid excitation flux switching (HEFS) machines are introduced, and a new HEFS machine is proposed and optimized. Firstly, the influences of three different P/T combinations (10/18, 10/19, and 10/21) on the HEFS machines are investigated with two-dimensional (2D) finite element analyses (2D-FEA). Meanwhile, the consistency and complementarity principle of the armature windings is analyzed in detail to give reasonable explanations to the simulated results. The general optimal P/T combination equation of the E-core HEFS machines is deduced mathematically to provide an effective guidance on the selection of P/T combinations. The optimal P/T combination calculated by the general equation agrees with the simulated results which confirm the correctness of the mathematical inferences. Finally, the optimizations on the proposed HEFS machine are implemented to obtain higher output torque and better flux-regulation ratio characteristics based on which the cogging torque and torque ripple are reduced significantly.

Voltage Pulsation Induced in DC Field Winding of Different Hybrid Excitation Switched Flux Machines

Voltage pulsation induced in dc field winding of hybrid excitation machines can cause current ripple in dc field winding and may even lead to unstable field excitation. Moreover, it may also impair the torque performance and complicate the drive, especially at high speed. In this article, the voltage pulsation induced in the dc field winding of different hybrid excitation switched flux machines (HESFMs) under both open-circuit and on-load conditions are comparatively studied. It shows that the HESFM topologies significantly affect the dc field winding induced voltage pulsations. To further suppress the induced voltage in field winding, three suppression methods, i.e., rotor step skewing, rotor pole notching, and rotor pole shaping are proposed and compared. It reveals that rotor step skewing has the best suppression performance. Finally, a prototype HESFM with both nonskewed and 2-step skewed rotors are fabricated and tested to confirm the finite element analyses.

Influence of rotor iron bridge position on DC-winding-induced voltage in wound field switched flux machine having partitioned stators

In this study, the influence of the position of the rotor iron bridge on the DC-winding-induced voltage pulsation in a partitioned stator wound field switched flux machine is investigated. Analytical and finite element (FE) analyses show that both the open-circuit and on-load DC-winding-induced voltages can be minimized by positioning the rotor iron bridge adjacent to the inner air gap closer to the DC winding. This is due to a smoother inner air-gap magnetic reluctance while maintaining the average electromagnetic torque at 92.59% of the maximum value. The analyzed machine with the rotor iron bridge adjacent to the inner air gap is prototyped, and the experimental results validate the analytical and FE results.

Enhancement of torque density in wound field switched flux machines with partitioned stators using assisted ferrites

In this paper, ferrites are applied in a partitioned stator wound field switched flux (PS-WFSF) machine to increase the air-gap flux density, and hence, the average electromagnetic torque and overload capability. Introducing short-circuited ferrites in the inner stator in the PS-WFSF machine can increase the open-circuit phase fundamental back-EMF and average electromagnetic torque at a 60 W copper loss by 2.33% and 3.77%, respectively. Moreover, the proposed PS-WFSF machine with ferrites can exhibit a better overload capability than conventional PS-WFSF machines without ferrites, e.g., a 7.36% torque increment can be achieved when the copper loss is 120 W. The torque increment mechanism is analyzed and verified using finite element (FE) analysis. Moreover, the demagnetization of the ferrites in the proposed machine under rated on-load and overload conditions is investigated. Both prototypes of the proposed PS-WFSF machine with ferrites and a conventional one without ferrite are built and tested to validate the analytical and FE analyses.

Analytical methodologies for design of segmented permanent magnet consequent pole flux switching machine: a comparative analysis

PurposeThis paper aims to reviewed analytical methodologies, i.e. lumped parameter magnetic equivalent circuit (LPMEC), magnetic co-energy (MCE), Laplace equations (LE), Maxwell stress tensor (MST) method and sub-domain modelling for design of segmented PM(SPM) consequent pole flux switching machine (SPMCPFSM). Electric machines, especially flux switching machines (FSMs), are accurately modeled using numerical-based finite element analysis (FEA) tools; however, despite of expensive hardware setup, repeated iterative process, complex stator design and permanent magnet (PM) non-linear behavior increases computational time and complexity.Design/methodology/approachThis paper reviews various alternate analytical methodologies for electromagnetic performance calculation. In above-mentioned analytical methodologies, no-load phase flux linkage is performed using LPMEC, magnetic co-energy for cogging torque, LE for magnetic flux density (MFD) components, i.e. radial and tangential and MST for instantaneous torque. Sub-domain model solves electromagnetic performance, i.e. MFD and torque behaviour.FindingsThe reviewed analytical methodologies are validated with globally accepted FEA using JMAG Commercial FEA Package v. 18.1 which shows good agreement with accuracy. In comparison of analytical methodologies, analysis reveals that sub-domain model not only get rid of multiples techniques for validation purpose but also provide better results by accounting influence of all machine parts which helps to reduce computational complexity, computational time and drive storage with overall accuracy of ∼99%. Furthermore, authors are confident to recommend sub-domain model for initial design stage of SPMCPFSM when higher accuracy and low computational cost are primal requirements.Practical implicationsThe model is developed for high-speed brushless AC applications.Originality/valueThe SPMCPFSM enhances electromagnetic performance owing to segmented PMs configuration which makes it different than conventional designs. Moreover, developed analytical methodologies for SPMCPFSM reduce computational time compared with that of FEA.

Coupled electromagnetic-thermal analysis of segmented PM consequent pole flux switching machine

Compact stator structure of flux switching machines (FSMs) encompassing both permanent magnets (PMs) and armature winding slots (AWS) attract research interest whenever high power and density are the basic requirements. However, it also results in temperature rises owing to heat generation by electromagnetic power losses degrading the electromagnetic performance and affecting machine performance. In this study, a segmented permanent magnet (SPM) consequent pole FSM (SPM-CPFSM) is developed, which provides a stator cooling channel (duct) for improved heat dissipation to avoid demagnetization of PM as well as overheating. Furthermore, this study investigates detailed electromagnetic performance analysis and prediction of temperature variation in various machine parts owing to the heat generated by iron, copper, and magnet eddy current losses utilizing coupled electromagnetic-thermal analysis accounting for magnetic flux density variation. In comparison with the 2D analysis, the developed 3D coupled-field analysis more accurately predicts electromagnetic performance and temperature distribution. Analysis reveals that a cooling duct at the stator significantly assists in stator heat dissipation in the axial direction ensuring a safe operating condition of the PMs as well as machine parts to avoid overheating.

2-D analytical modelling of novel consequent pole linear permanent magnet flux switching machine

2-D analytical modelling of novel consequent pole linear permanent magnet flux switching machine

On the Electromagnetic Performance Prediction of Turbo Synchronous Condensers Based on Wound-Field Flux Switching Machine Design

The revival of the old synchronous condenser (SC) technology is presently occurring. Hence, this study is proposed on the electromagnetic design and evaluation of turbo wound-field flux switching machines (WF-FSMs) for SC operation, for the first time. Unlike classical wound-field rotating machines, WF-FSMs do not need brushless exciters while possessing a robust topology. A design process based on the frozen permeability technique in static 2-D finite element analysis script-based package, which enhances both iterative and analytic adjudications, is proposed to accurately predict the SC operation. To attain the specific design requirements (~300 MVAR, 16 kV), a global-optimized model (GOM) of the SC machine is obtained through a stochastic optimization process involving multiple objectives. Based on the GOM, simple torque ripple minimization techniques are implemented, from which a final benchmark design is selected. The proposed SC analytical design procedure is then tested and the expected V-curves clearly obtained. The whole design approach is further verified by experimenting on a small-scale prototype, which when synchronized to the grid, confirms the novelty and feasibility of the proposed SC design and operation.

Analysis of DC Winding Induced Voltage in Wound-Field Flux-Switching Machine With Air-Gap Field Modulation Principle

In this article, the direct current (dc) winding induced voltage in wound-field flux-switching machines is qualitatively analyzed with air-gap field modulation principle. Operation principle and effective harmonics of dc winding induced voltage are modelled and deduced. It is found that only air-gap field harmonics with specific spatial orders, which numerically equals to odd times of half stator poles, can contribute to dc winding induced voltage. Harmonic order of dc winding induced voltages under open-circuit only, armature reaction only, and on-load condition, are predicted for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> -phase WFFS machines with any feasible stator/rotor pole number combinations. Different armature winding configurations, including concentrated winding and distributed winding, are also analyzed and compared using the winding factor. Finite element analysis is employed to verify the prediction results. Finally, a prototype is built and tested for validation.

Comparison of Flux-Switching and Interior Permanent Magnet Synchronous Generators for Direct-Driven Wind Applications Based on Nelder–Mead Optimal Designing

The permanent magnet flux-switching machine (PMFSM) is one of the most promising machines with magnets inserted into the stator. To determine in which applications the use of PMFSM is promising, it is essential to compare the PMFSM with machines of other types. This study provides a theoretical comparison of the PMFSM with a conventional interior permanent magnet synchronous machine (IPMSM) in the gearless generator of a low-power wind turbine (332 rpm, 51.4 Nm). To provide a fair comparison, both machines are optimized using the Nelder–Mead algorithm. The minimized optimization objectives are the required power of frequency converter, cost of active materials, torque ripple and losses of a generator averaged over the working profile of the wind turbine. In order to reduce the computational time, the substituting profile method is applied. Based on the results of the calculations, the advantages and disadvantages of the considered machines were revealed: the IPMSM has significantly lower losses and higher efficiency than the PMFSM, and the PMFSM requires much less rare-earth magnets and copper and is, therefore, cheaper in mass production.

Comparative study of a new structure of HTS-bulk axial flux-switching machine

A high-temperature superconducting (HTS) axial flux permanent magnet (AFPM) machine was designed, using superconducting bulks over the rotor surface and rare-earth magnets in the middle of the stator teeth. Because of diamagnetic behavior of the HTS bulks and zero field cooling, leakage flux significantly reduces in the proposed machine compared to the existing machine with mounting rare-earth magnets. Three-dimensional finite element (FE) modelling was used to validate the design performance. The magnetic flux distribution, induced electromotive force (EMF), inductance, PM flux, losses, total harmonic distribution and cogging torque are computed and compared in two structures. The results show that the proposed machine structure is more efficient than the existing one.