Flux-switching Permanent Magnet Generator Research Articles

Magnetic Coupling Effect and Performance Analysis of Dual Rotor Permanent Magnet Flux Switching Generator for Counter Rotating Wind Power Generation

To eliminate slip rings, brushes, and terminate gear-box mechanism, ferrite permanent magnet (PM) based counter rotating dual rotor PM flux switching generator (CRDRPMFSG) for direct drive counter rotating wind turbine (D <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> CRWT) application is proposed in this paper. Initially, the mechanism of gearless and brushless counter rotating wind power generation is discussed, and a simplified formulation opted for the slot/pole combinations. The proposed CRDRPMFSG encapsulate inner and outer machines with circumferentially magnetized PM enclosed by non-overlapped armature windings; thus, offering reduced overhang with compact design. However, co-axially linking the inner and outer machines through a shared stator yoke results in serious issues of magnetic coupling due to dual air-gap fields. To this end, eight topologies with various slot/pole combinations are comprehensively investigated using finite element analysis (FEA) for magnetic coupling effects and its influence on electromagnetic performance. From the analysis, it is shown that magnetic coupling level influence electromagnetic performance i.e., average torque, ripple rate, power factor, efficiency, losses, and output power. Moreover, it is noted that coupling level can be reduced by adopting same stator teeth in inner and outer machines or same stator teeth with different rotor poles. Finally, the predicted FEA calculations are verified experimentally with four benchmarked CRDRPMFSG prototypes.

Electromagnetic-Thermal Analysis of a Hybrid-Excited Flux Switching Permanent Magnet Generator for Wind Turbine Application

An accurate thermal analysis needs to be performed on the machines with new structures to ensure that their electromagnetic performance is not negatively affected. In this regard, this paper details an investigation into the electromagnetic-thermal analysis of an outer rotor hybrid-excited flux switching permanent magnet generator that gains from ferrite PMs in stator yoke and neodymium PMs in rotor segments. Incorporating ferrite PMs and barriers in the stator core enhances the power density of the proposed generator compared to the basic topology. Also, the temperature of the stator and windings of the HEFSG decreases due to the presence of barriers. As a result, the HEFSG can be a potential candidate for DDWT applications. In this study, the thermal modeling started with a 3-D FEM electromagnetic analysis to calculate the losses as heat sources. Afterward, an accurate thermal network was plotted to elucidate the thermal behaviors between various parts of the generator, where the heat sources, heat transfer coefficients, thermal resistances, and heat capacitances form the thermal characteristics of the network, which was then followed by the 3-D FEM thermal analysis. Finally, the experimental test results from the prototyped generator confirmed the accuracy of the simulation results.

Performance Improvement of Flux Switching Permanent Magnet Wind Generator Using Magnetic Flux Barrier Design

Flux-switching permanent magnet (FSPM) machines have attracted significant research attention in the field of wind power generation. In this study, the utilization of a magnetic flux barrier to improve the performance of the nine-phase FSPM generator designed for low-speed wind power applications is conducted. The proposed approach involves introducing magnetic flux barriers of different topologies to the conventional FSPM generator and analyzing their performance using 2D finite element simulations. Results suggested that |-shaped magnetic flux barriers exhibited the highest performance among other topologies, making them the appropriate choice for this generator. The geometry of the |-shaped flux barriers was further optimized using response surface methodology to maximize the generator’s performance. The proposed generator exhibits a significant decrease in cogging torque, achieving a remarkable reduction of up to 23.7%, while maintaining electromotive force. Moreover, it shows a significant decrease in permanent magnet eddy-current loss, with a noteworthy reduction of up to 51%. Additionally, significant improvements were demonstrated in terms of electromagnetic torque, torque ripple, output power, and efficiency. Details on the physical reasoning behind these improvements have been provided. Overall, the proposed FSPM generator with inserted flux barriers has the potential to meet the demands of low-speed wind power generation effectively.

A Novel Six-Phase V-Shaped Flux-Switching Permanent Magnet Generator for Wind Power Generation

Flux-switching permanent magnet (FSPM) machines have attracted wide attention in many rotating applications that require high-power density. In this research, we propose for the first time a novel six-phase FSPM generator with a stator featuring a V-shaped flux-focusing magnet arrangement. The design is targeted for low-speed wind power generation. To achieve the design objectives as a wind generator, the highly comprehensive structural parameters, including the number of rotor poles, split ratio, and rotor pole width, are designed and optimized using 2D finite-element analysis. From findings, the optimal stator/rotor pole combination is discovered to be 12/19 for the considered power and speed requirements. When compared to the initial structure, the optimized structure of the V-shaped FSPM generator is found to produce a significant improvement in EMF, cogging torque, electromagnetic torque, power, and efficiency. The power-generating performance of the proposed FSPM generator is found to be outstanding when compared to the radial-flux PM generators described in the literature. Therefore, the proposed V-shaped FSPM generator is capable of being used for low-speed wind power generation. The machine configuration adjustment approach presented in this work can also be utilized for the design of permanent magnet wind generators.

A novel axial air‐gap transverse flux switching PM generator: Design, simulation and prototyping

AbstractWind energy as the cleanest source of renewable energy requires a highly efficient lightweight generator that provides maximum power density while having the least vibration noise and maintenance. In this study, an axial air gap transverse flux machine is presented, and all excitation sources are located in the stator. This structure provides lower core loss, weight and cost due to the full utilisation of the permanent magnets, SMC‐free structure and short magnetic flux path. In fact, by combining the features of a flux‐switching machine into a transverse flux generator with an axial air gap, it is possible to improve the performance of a direct‐drive wind turbine generator by overcoming traditional structures' challenges. To analyse the axial transverse flux switching permanent magnet generator performance characteristics, 3D finite element simulations have been performed, which have been validated by comparing them to the practical results of a single‐phase prototype. The results are in agreement with an acceptable error that is caused by manufacturing uncertainties.

A Novel Radial–Axial Flux Switching Permanent Magnet Generator

In this article, a novel radial–axial (RA) flux switching permanent magnet generator (FSPMG) is introduced. In contrast to other RA flux machines, a major advantage of this generator is its implementation only by the use of conventional nonoriented electrical steel sheets, even though the flux linkage of the novel RA-FSPMG has a 3-D path. Besides that, it benefits from the flux concentration strategy and a passive rotor. A concrete foundation of the novel RA-FSPMG is provided, in which, the 3D-Flux path is described, working principles are discussed, and power-sizing equation is derived. No-load characteristics and the full-load performance of an optimized RA-FSPMG are investigated in contrast to an optimized double stator radial FSPMG and an optimized double stator axial FSPMG with similar volume, number of permanent magnets (PMs), and electrical loading. The results show the competitiveness of the novel RA-FSPMG, in particular, in the output power and the required copper mass. Furthermore, the PM demagnetization possibility and the rotor axial pull force of the optimized RA-FSPMG are investigated, in detail. All discussions are supported by the 3-D finite element analysis and experimental results.

Design optimization of a novel linear transverse flux switching permanent magnet generator for direct drive wave energy conversion

Linear transverse flux permanent magnet machines (LTFPMs) are categorized as high force density topologies, which are suitable candidates for direct drive and low-speed applications. This paper introduces a novel LTFPM topology, which also proposes advantages of the flux-switching machines. This proposed linear transverse flux switching PM machine (LTFSPM) has two long passive translators located at the armature's top and bottom sides. The topology offers a high value of force density, and also, it is a cost-effective topology due to its double-sided passive translator. Furthermore, the PMs are fully utilized in the magnetic circuit, the end winding length is negligible, and the iron cores can be laminated easily. In this paper, the operation principle of the topology is explained and its magnetic circuit is discussed. To reduce the computational time of optimization procedure, a double-layer method is adopted, which provides high robustness, low computational time, and high precision. Results of the finite element method indicate that the proposed machine can be considered a potential candidate for linear motion applications especially direct drive wave energy conversion systems, which require high force density values.

Dual mechanical port power distribution in dual rotor permanent magnet flux switching generator for counter‐rotating wind turbine applications

The cover image is based on the Research Article Dual mechanical port power distribution in dual rotor permanent magnet flux switching generator for counter-rotating wind turbine applications by Wasiq Ullah et al., https://doi.org/10.1049/rpg2.12450.

Dual mechanical port power distribution in dual rotor permanent magnet flux switching generator for counter‐rotating wind turbine applications

In this paper, a novel dual mechanical port dual rotor counter-rotating permanent magnet flux switching generator (DMPDRCR-PMFSG) for wind turbine applications is proposed. Power distribution between the inner and outer rotors of the proposed DMPDRCR-PMFSG that contributes to the cumulative output power is investigated. The proposed DMPDRCR-PMFSG shares a stator connected back-to-back through flux bridge. The flux bridge physically isolates the armature winding of the inner and outer ports. Furthermore, the flux bridge provides a flux path to magnetic flux of the inner and outer ports that contributes to cumulative output power. Quantitative comparative analysis of the inner and outer ports illustrates that under static analysis 18.57% more flux, 23.95% highly induced back-EMF, 31.08% of enhanced average torque are obtained in the outer rotor at the cost of 64.01% and 22.7% increase in cogging and torque ripple ratio, respectively. Comparative analysis with a number of turns reveals that the outer port offers 41.17% higher output power and 7.09% improved efficiency at the cost of 42.52% increase in voltage regulation factor. Finally, coupled overload and over-speed analysis shows that despite a stable and low voltage drop ratio, the outer port offers 4.65% higher output voltage. Analysis shows that in the proposed DMPDRCR-PMFSG, the outer port has a dominant contribution to the cumulative power distribution.

Effect of Rotor Topology on the Performance of Counter-Rotating Double-Sided Flux Switching Permanent Magnet Generator

Recently, electric power generation from direct-drive counter-rotating wind turbine has gained considerable attention. Consequently, employing an efficient and a high power density electric generator is important. In this regard, flux switching permanent magnet generator with double-sided structure is one of the potential candidates for this purpose due to its features like inherently magnetic gearing effect, high power density, high reliability, and robust rotor structure. In this regard, rotor structure of double-sided flux switching permanent magnet generator is one of the most important factors which can highly affect the machine's performance due to the fact that, rotor geometry is the main part in the flux switching procedure of double-sided flux switching permanent magnet generator. Consequently, this paper presents a comprehensive analysis of counter-rotating double-sided flux switching permanent magnet generator with segmented rotor and laminated rotor in which a bridge is located between adjacent rotor poles. The finite element simulations and experimental tests results showed that the proposed generator with laminated rotor gained from the higher power density in comparison with the segmented one whereas in the case of segmented rotor, the torque ripple is lower.

A Comparative Study of Dual Stator With Novel Dual Rotor Permanent Magnet Flux Switching Generator for Counter Rotating Wind Turbine Applications

Compared with the single rotor wind turbine, a counter-rotating (CR) wind turbine with two rotor sets leads to twice power density. In this regard, dual stator CR (DSCR) permanent magnet flux switching generator (DSCR-PMFSG) is employed. However, in DSCR-PMFSG both rotor and armature parts are rotating and require slip rings for power transmission. These slip rings associate demerits of constant maintenance, poor speed regulation, increased cost, and additional slip ring losses, whereas DSCR-PMFSG offer lower flux and lesser power density. To overcome the demerits of DSCR-PMFSG as mentioned earlier, this paper proposed a novel dual rotor counter-rotating permanent magnet flux switching generator (DRCR-PMFSG) for wind turbine applications that eliminate the requirements of slip rings and retain brushless operation. The proposed DRCR-PMFSG share one stator connected back-to-back through a flux bridge that provides an alternate flux path between two mechanical ports associated with the inner rotor and outer rotor, contributing to the cumulative output. A detailed comparative analysis of DSCR-PMFSG and DRCR-PMFSG is performed under static characteristics, overload, and wide speed range to generate output power, voltage, current, power density, and efficiency. Quantitative comparative analysis under static analysis evident that proposed DRCR-PMFSG exhibits 33.29% higher flux, suppressed cogging torque and torque ripples up to 53.48% and 67.45%, respectively. Furthermore, a comprehensive quantitative analysis is performed under coupled overload and over-speed capability. Analysis exposes that in comparison with DSCRP-PMFSG, the proposed DRCR-PMFSG improves voltage regulation factor by 55.88%, output current enhanced by 67.9%, raise output voltage to 2.01 times, and power density to 1.72 times while maintaining the efficiency of 90.195% and achieving stable voltage profile with load variation. Finally, a detailed comparative analysis with conventional designs is performed and comprehensive mathematical modelling based on sub-domain model is developed accounting stator slot and rotor pole combinations, magnetic saturation, and winding configuration to validates finite element analysis (FEA) of JMAG Designer v.20.1.

A Novel Dual Rotor Permanent Magnet Flux Switching Generator for Counter Rotating Wind Turbine Applications

In this paper counter rotating (CR) dual rotor permanent magnet flux switching generator (CR-DRPMFSG) is designed and relatively studied with co- rotating DRPMFSG (CoR-DRPMFSG) for wind turbine applications. The developed CR- DRPMFSG and CoR-DRPMFSG share same stator linked with flux bridge which provide flux route. A comprehensive relative assessment of both CR- DRPMFSG and CoR-DRPMFSG are presented with static attributes, over-load, and over-speed capability for generating output voltage, output current, output power, power density, losses, and efficiency. Comparative study with static characteristics illustrates that developed CR- DRPMFSG shows 34.34% elevated phase flux which improve output power, cumulative output torque is improved by 23.86%, and suppressed cogging torque by 66.87% at CoR-DRPMFSG that results lower pulsation in instantaneous torque. Furthermore, a detailed performance analysis is investigated with different number of armature winding turns per phase and combined over-load and over-speed capability. Study discloses that in contrast with CoR-DRPMFSG, counterpart CR- DRPMFSG offer 27.17% higher output power that results 1.25 times power density with a good voltage regulation factor of 18.67%. In additional, despite of 2.27% improvement of efficiency in case of phase winding turns analysis and 4.81% increase in over-load and over-speed capability, contour efficiency map unveils that CR- DRPMFSG offer wide range of higher efficiency operating region during over-load and over-speed condition accompany with stable voltage profile with load variation.

Comparative Study of Stepwise Optimization and Global Optimization on a Nine-Phase Flux-Switching PM Generator

In this paper, the design procedure and optimization process of a multi-phase flux-switching permanent magnet (FSPM) generator for wind power generation system is investigated. Two different optimization methods—stepwise optimization and global optimization—are implemented and applied to the optimization of the proposed nine-phase FSPM generator-based wind power system. Both the advantages and disadvantages of two optimization methods are compared and analyzed. The results indicate that the stepwise optimization can achieve good effects on individual optimization objectives, whereas the global optimization can not only achieve a good optimization effect on a single objective, but also can find design point on the Pareto front, which can effectively optimize different multi-objects. The electromagnetic performance of the nine-phase FSPM generator is verified by experiments on a prototyped machine and the measured results show that the proposed generator exhibits the favorable characteristics of high torque, low torque ripple, and high efficiency.

Investigation of Inner/Outer Rotor Permanent Magnet Flux Switching Generator for Wind Turbine Applications

In this paper two permanent magnet flux switching generator (PMFSG) are designed for 2 kW output power and 220 V phase voltage at 1500 rpm and comparatively analyzed for wind power application. Both PMFSG share same C-core stator connected back-to-back through flux bridge (β) with different rotor position i.e., inner rotor PMFSG (IR-PMFSG) and outer rotor PMFSG (OR-PMFSG). A detailed comparative analysis with various β for both IR-PMFSG and OR-PMFSG are performed under static characteristics, rated condition, overload capability and over-speed capability for generating output voltage, current, power and efficiency. Comparison of the static characteristics reveal that IR-PMFSG offers 47.93% higher rated power, 2.83% higher efficiency, 22.78% more magnetic flux, 56.91% reduced cogging torque and 83.18% lower torque ripples at the cost of 62.69% higher voltage regulation factor. Furthermore, under rated operating condition and overload capability with same specifications it is found that IR-PMFSG exhibits 1.47 times power than that of OR-PMFSG counterpart. Finally, over-speed capability is investigated in term of the output power which shows that IR-PMFSG significantly generate almost 2.25 time of the specification power whereas OR-PMFSG exhibits nearly 1.25 times power. This analysis shows that IR-PMFSG can be operated at wide-speed rage for higher power specification requirements maintaining efficiency greater than 90%.

Multiobjective Design Optimization of a Double-Sided Flux Switching Permanent Magnet Generator for Counter-Rotating Wind Turbine Applications

A counter-rotating wind turbine in which two sets of rotors rotating in opposite directions leads to the twice power density of the conventional turbines. Moreover, employing a high-power modern electric generator is another contributing factor in improving the performance of wind power generation systems. In this regard, double-sided flux switching permanent magnet generators, with ferrite magnet, are getting firm attention. In this regard, the concept and multiobjective design optimization procedure of this generator, connected with counter-rotating wind turbines, is proposed in this article. In order to achieve the optimum performance of the proposed generator, the design of experiments with Taguchi optimization is employed. In this method, although the effect of each design variable on the objective functions can be considered, selecting the best combination of control factors is not easy in the multiobjective optimization. Thus, a decision-making algorithm with the technique for order of preference by similarity to ideal solution is employed in order to select the best combination. Finally, the performance of the optimized counter-rotating double-sided flux switching permanent magnet generator will be evaluated by finite element modeling and experimental tests.

A Comparative Study on Nine- and Twelve-Phase Flux-Switching Permanent-Magnet Wind Power Generators

In this paper, two flux-switching permanent-magnet (FSPM) wind power generators with 9- and 12-phase windings are designed and comparatively analyzed. Both two generators are designed under the rated specifications of 10 kW output power and 220 V phase voltage at 500 r/min. The static characteristics and power generating performances including output voltage, power, and efficiency at rated and variable load/speed conditions are predicted by finite-element analysis and validated by experimental tests based on the two FSPM prototypes. It shows that the 12-phase 24-stator-slot/22-rotor-pole FSPM generator exhibits a higher air-gap flux density, a higher torque/power density, and a lower voltage regulation factor. Besides, it has a better overload capability than its 9-phase 36-stator-slot/34-rotor-pole counterpart when the load and wind speed exceed the rated levels. The comparative study reveals the benefits of the lower leakage flux and permeance from the larger stator-slot opening and longer magnetic circuit.

Flux switching permanent magnet generator design and optimization using response surface methodology

Flux Switching Permanent Magnet Generators (FRPMGs) have been used increasingly in direct drive variable speed wind turbines due to their merit such as their high torque density, easy flux weakening operation and robust rotor structure. Generally, the quality of output power in direct drive systems is lower than multi stage fixed speed systems, because of removing the gears, so it’s important to design these kinds of generators with low ripple and lowest harmful harmonics and cogging torque. This aim is one of the most important terms in increasing the quality of output power of generator simultaneously with back-EMF improvement. The objective of this paper is introducing a simple design method and optimization of high power FRPMG applied in direct drive wind turbine system by lowest possible amplitude of cogging torque and highest possible power factor, efficiency and power density. For optimization reason an optimum method called combined response surface methodology (RSM) and design of experiment has been applied. Also in order to extract the output values of generator and sensitivity analysis for design, 3D-Finite element model, was used. This method has high accuracy and gives us a better insight of generator performance and presents back EMF, cogging torque, flux density and FFT of the FSPMG. This study can help in design approach of such machines.

Performance Analysis of a Novel Three-phase Axial Flux Switching Permanent Magnet Generator with Overlapping Concentrated Winding

This paper proposes a novel axial flux switching permanent magnet generator for small wind turbine applications. Surface mounted axial flux switching permanent magnet (SMAFSPM) machine is a new type of these machines that is introduced in this paper. One of the most important challenges in optimal designing of this kind of machines, is ease of construction and maintenance. One of the main features of this machine is putting the magnets on the surface, which makes the construction of the machine easier. The overlapped three-phase winding improves the quality of voltages and power of the machine.To reach the optimum dimensions of machine, centeral composite design (CCD) and response surface methodology (RSM) combined with 3D finite element methods have been used.

Electromagnetic Design of a 10-kW-Class Flux-Switching Linear Superconducting Hybrid Excitation Generator for Wave Energy Conversion

Research on linear generators for direct-drive wave energy conversion has mostly focused on inner-secondary sole permanent magnet (PM) linear generators, among which vernier hybrid machine and flux-switching generators are considered as the best selection. In this study, an outer-secondary tubular superconducting hybrid excitation linear generator is presented to increase the power density and reduce the voltage regulation. Double-buoys direct-drive WEC is introduced. The operation under hybrid excitation is analyzed. With consideration to cogging force, the linear generator is optimized. The generator performance is evaluated using the finite element method. Based on the on-load performance, a hybrid excitation method is proposed and is compared with only the PM working. According to the working point of the proposed generator, losses of the superconducting hybrid excitation windings are calculated. A PM flux-switching generator is employed to verify the analysis results. The results show that the proposed generator has the advantages of larger air-gap effective area, higher power density, and more steady output power and voltage.

A new outer-rotor flux switching permanent magnet generator for wind farm applications

In this paper a 1.5 kW flux switching permanent magnet (FSPM) generator is presented for direct drive small scale wind turbine applications. For maximizing induced voltage and the output torque while minimizing cogging torque and unbalanced radial magnetic force (UMF), the proposed machine exhibits a new 6/19 stator pole/rotor teeth number and an outer rotor configuration. At first, in the paper an analytical design has been developed, then a finite element method (FEM) analysis is carried out for validating the analytical procedure and for design improvement. The simulation results extracted by FEM confirm the theoretical analysis procedure and help in the understanding of the performance analysis of the machine against the variations of the design variables. Furthermore, an experimental laboratory prototype of the proposed FSPM is implemented to confirm the analytical design and FEM modelling approaches. A comparison of induced voltage, torque, UMF and cogging torque produced by different FSPM configurations present in literature respect to the proposed generator has been developed. The results show the goodness of the adopted methodology and prove that, because of suitable electromagnetic performance of the proposed FSPM generator, it could be counted as a proper candidate for small scale wind turbine applications. Copyright © 2016 John Wiley & Sons, Ltd.