Axial Flux Permanent Magnet Synchronous Generator Research Articles

The Neutral Voltage Difference Signal as a Means of Investigating Eccentricity and Demagnetization Faults in an AFPM Synchronous Generator

This article investigates the neutral voltage difference signal, VNO signal, for fault diagnosis. The aforementioned signal is the signal of the voltage between the common star point of the stator and the common star point of the load. The under-study faults are demagnetization and static eccentricity faults, while the machine in which the faults are investigated is an axial flux permanent magnet (AFPM) synchronous generator, suitable for wind power applications. This study was conducted using a 3D finite element method (3D-FEM), and the machine’s FEM model was validated through experiments. This method is one of the most accurate methods for electrical machine computation, allowing for a detailed study of electromagnetic behavior. The components that constitute the VNO signal were determined using a 3D-FEM software program (Opera 18R2). Subsequently, further analysis was performed using MATLAB R2022b software, and a fast Fourier transform (FFT) was applied to this signal. In all the investigated faulty cases, new harmonics appeared, and the healthy amplitudes of most of the already existing harmonics increased. These findings can be used for fault identification. The analysis revealed that the harmonic frequency of 1.5fs was the most dominant in the case of demagnetization, while in the case of static eccentricity, the most dominant harmonic was a frequency equal to the machine’s operating frequency, fs. The novelty of this study is that this signal has not previously been used for fault identification, especially in AFPM synchronous machines. This signal depends on EMF voltage and stator phase currents but is less sinusoidal. Consequently, it can detect faults in cases where the aforementioned signals cannot be used for detection.

Investigation on Connected System of Axial-Flux Permanent Magnet Synchronous Generator and Linear Induction Motor

This article investigates the influence of power converters and linear induction motor (LIM) without energy storage system on an axial-flux permanent magnet synchronous generator (PMSG) based on electromagnetic field characteristic analysis. First, the axial-flux PMSG and the LIM are introduced with characteristic analysis results, and their verification is addressed by a finite element method (FEM) and experiment. The axial-flux PMSG is double-side rotor type with slotless structure for cogging torque reduction, and rare-Earth permanent magnets are employed for high power density. On the other hand, since the LIM has an overhang structure in the secondary plate, the transverse edge effect is considered in the analysis to determine the overhang length of the secondary structure, and the optimized length is verified by the results of thrust force and equivalent circuit parameters. In this study, manufactured machines are connected with power converters, and relevant experiments are performed to measure the current according to various operating conditions of LIM as a load. By analyzing the power losses, the influence of the LIM operation on the axial-flux PMSG is discussed in this study.

Study of a Combined Demagnetization and Eccentricity Fault in an AFPM Synchronous Generator

This article investigates the combined partial demagnetization and static eccentricity fault in an Axial Flux Permanent Magnet (AFPM) Synchronous Generator. The machine is simulated using 3D FEM, while the EMF spectrum is analyzed in order to export the fault related harmonics using the FFT analysis. Firstly, the partial demagnetization fault, without the coexistence of eccentricity, and both the static angular and axis eccentricity faults, without the coexistence of partial demagnetization, are studied. In the case of eccentricity fault, the phase EMF sum spectrum has also been used as a diagnostic mean, because, when only eccentricity fault exists in the generator (either angular or axis) new harmonics do not appear in the EMF spectrum. Secondly the combination of partial demagnetization fault with static axis and static angular eccentricity is investigated and different comparisons are made when the demagnetization and the eccentricity level changes. The investigation revealed that the combination of eccentricity and demagnetization creates new harmonics in the EMF spectrum. The novelty of the article is that these combined faults are studied for the first time in the international literature, and the phase EMF sum spectrum has not been previously used for eccentricity diagnosis in this machine type.

Voltage regulation Rate and THD optimization analysis of coreless axial flux PM synchronous generator for wind power generation

The basic design and characteristic analysis of the coreless axial flux permanent magnet synchronous generator (AFPMSG) for small wind power generation are carried out. The prototype is manufactured and tested to verify the designed generator. In addition, to reduce the voltage regulation rate and harmonic content of the generator, the optimal design is carried out on the basis of the original generator. The voltage regulation rate and THD of a coreless AFPMSG using the Halbach permanent magnet array are studied. The effects of different generator parameters such as pole arc coefficient, air gap length, permanent magnet thickness, and number of turns in series per phase on the voltage regulation rate and THD are analyzed when the generator is loaded with pure resistance. Because the various parameters of the generator are affected each other, the Taguchi algorithm was adopted for multi‐objective optimization. The influence proportion of different generator parameters on the voltage regulation rate and THD was analyzed. According to the results, the parameters are reasonably selected to design the generator and improve the performance of the generator. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Sensitivity Analysis and Optimal Design of a Stator Coreless Axial Flux Permanent Magnet Synchronous Generator

In this paper, the modified initial design procedure and economic optimization design of a stator coreless axial flux permanent magnet synchronous generator (AFPMSG) are presented to improve the design accuracy, efficiency, and economy. Static magnetic field finite-element analysis (FEA) is applied to the magnetic equivalent circuit (MEC) method to increase the accuracy of electromagnetic parameters and reduce the iteration times. The accuracy and efficiency of the initial design is improved by the combination of MEC method and static magnetic field FEA in the design procedure. For the economic optimization, the permanent magnetic (PM) material volume model, which affects the cost of the AFPMSG the most, is derived, and the influence degree of the main structure parameters, to the performance, is distinguished and sorted by sensitivity analysis. The hybrid genetic algorithm that combines the simulated annealing and father-offspring selection method is studied and adopted to search for the best optimization solution from the different influence degree and nonlinear interaction parameters. A 1 kW AFPMSG is designed and optimized via the proposed design procedure and optimization design. Finally, 3D finite-element models of the generator are simulated and compared to confirm the validity of the proposed improved design and the generator performance.

Axial‐flux permanent‐magnet synchronous generator with coreless armature and non‐integral coil–pole ratio

This article presents a study on an axial-flux permanent-magnet synchronous generator (AFPMSG) with a double-sided rotor, coreless armature. The armature winding consists of non-overlapping concentrated coils and has a non-integral coil-pole ratio. It is shown that, with an appropriate choice of armature coil number to pole number, the fundamental winding factor of the AFPMSG can be made close to that of a full-pitched integral slot winding. The field distribution and load performance are computed for a prototype machine based on a two-dimensional, time-stepping finite element method. A study of the armature reaction effect of the coreless armature winding and the origin of torque ripple is also carried out. The computed voltage and current waveforms, as well as the load characteristics, are verified by practical experiments.

Study and Optimal Design of a Direct-Driven Stator Coreless Axial Flux Permanent Magnet Synchronous Generator with Improved Dynamic Performance

In this paper, the study and optimization design of stator coreless axial flux permanent magnet synchronous generators is presented for direct driven variable speed renewable energy generation system applications while considering the requirement of reliability and dynamic performance with unstable input conditions. The dynamic analytical model is developed based on the investigation of the axial flux permanent magnet synchronous generator (AFPMSG) structure and basic electromagnetic equations to find out the relationship between generator parameters and dynamic performance. Simulation via the MATLAB/Simulink platform is carried out to obtain the sensitivity of dynamic performance to generator parameters. An integrated optimization model that takes the key parameters as variables is proposed, aiming to improve the mechanical dynamic performance of AFPMSG. For accurate design, the design procedure is modified by combining the nonlinear iterative genetic algorithm (GA) to perform the calculation. A 3_kW AFPMSG is optimally designed to minimize the output voltage overshooting—the index of dynamic performance for direct driven variable speed generation application. Finally, a three-dimensional (3D) finite element model of the generator is established by Maxwell ANSOFT, and the simulation results confirm the validity of the dynamic performance analysis and optimal design procedure.

Analysis and Optimization of the Axial Flux Permanent Magnet Synchronous Generator using an Analytical Method

This paper presents a 2-D analytical method to calculate the back EMF of the axial flux permanent magnet synchronous generator (AFPMSG) with coreless stator and dual rotor having magnets mounted on both sides of rotor yoke. Furthermore, in order to reduce the no load voltage total harmonics distortion (VTHD), the initial model of the coreless AFPMSG is optimized by using a developed analytical method. Optimization using the 2-D analytical method reduces the optimization time to less than a minute. The back EMF obtained by using the 2-D analytical method is verified by a time stepped 3-D finite element analysis (FEA) for both the initial and optimized model. Finally, the VTHD, output torque and torque ripples of both the initial and optimized models are compared with 3D-FEA. The result shows that the optimized model reduces the VTHD and torque ripples as compared to the initial model. Furthermore, the result also shows that output torque increases as the result of the optimization.

Application of artificial neural network to estimate power generation and efficiency of a new axial flux permanent magnet synchronous generator

An estimation study on the output power and the efficiency of a new-designed axial flux permanent magnet synchronous generator (AFPMSG) is performed. For the estimation algorithm, a multi-layer feedforward artificial neural network (ANN) is developed. Various experimental results from the generator have been used for the training purpose in the cases of different electrical loads and rotational speeds. Some experimental data is kept out of the training process for testing the network and the errors have been evaluated after the formation of the network. According to the findings, a network with three layers has been adequate to achieve very good error percentage between the ANN and laboratory studies. The maximal testing error percentages are found to be nearly 3% and 4% for the output power and efficiency estimations, respectively. According to that finding, the developed ANN has a good property that it can be used in place of the designed generator, especially when the generator mathematical model is required. In addition, since power and efficiency are important for present applications, the present tool can be used to estimate the data for those characteristics of the machines and even it can be beneficial for the applications, where a nonlinear relationship among the power generation, generator efficiency, speed and load is required.

Reduction of Torque Ripple in an Axial Flux Generator Using Arc Shaped Trapezoidal Magnets in an Asymmetric Overhang Configuration

In this paper, model of the axial-flux permanent magnet synchronous generator (AFPMSG) having arc-shaped trapezoidal permanent magnets (PM) is presented. The proposed model reduces the cogging torque and torque ripple, at the expense of lowering the average output torque. Optimization of the proposed model is performed by considering the asymmetric overhang configuration of the PMs, as to make the output torque of the proposed model competitive with the conventional model. The time stepped 3D finite element analysis (FEA) is performed for the comparative analysis. It is demonstrated that the torque ripple of the optimized model is highly reduced as well as average output torque is increased.

Design Optimization of Direct-Coupled Ironless Axial Flux Permanent Magnet Synchronous Wind Generator With Low Cost and High Annual Energy Yield

In this paper, an improved design of an ironless axial flux permanent magnet synchronous generator (AFPMSG) is presented for direct-coupled wind turbine application considering wind speed characteristics. The partial swarm optimization method is used to perform a multi-objective design optimization of the ironless AFPMSG in order to decrease the active material cost and increase the annual energy yield of the generator over the entire range of operating wind speed. General practical and mechanical limitations in the design of the generator are considered as optimization constraints. For accurate analytical design of the generator, distribution of the flux in all parts of the machine is obtained through a modified magnetic equivalent circuit model of AFPMSG. In this model, the magnetic saturation of the rotor back iron cores is considered using a nonlinear iterative algorithm. Various combinations of pole and coil numbers are studied in the design of a 30 kW AFPMSG via the optimization procedure. Finally, 3-D finite-element model of the generator was prepared to confirm the validity of the proposed design procedure and the generator performance for various wind speeds.

Considering Wind Speed Characteristics in the Design of a Coreless AFPM Synchronous Generator

This paper presents an improved design procedure of a coreless Axial Flux Permanent Magnet Synchronous Generator (AFPMSG) for wind turbine application. An analytical design approach is proposed based on sizing equations and a nonlinear Magnetic Equivalent Circuit (MEC) model of AFPMSG. The reluctance of rotor back iron core is separated into two parts, which are calculated through the nonlinear iterative algorithm. An optimal design of the coreless AFPMSG is performed using Partial Swarm Optimization (PSO) method in order to increase the Annual Energy Yield (AEY) of the generator. The statistical model of wind speed distribution and wind turbine characteristic are used for considering the generator performance over the whole operating wind speed range. In order to obtain the optimal values of design variables, the optimization procedure is provided for various number of pole pairs and coil numbers. The proposed procedure is used to design a double rotor-one coreless stator AFPMSG. Finally, 3-D Finite Element Analysis (FEA) is used to validate the design algorithm. Also, the generator performance is evaluated for different values of wind speed and load currents.

Thermal effects of stator potting in an axial-flux permanent magnet synchronous generator

Axial-flux machines often have certain problems with heat transfer as shrink fitting of the stator core in the housing is not an option, unlike in the case of radial-flux machines. In this paper, we study how potting of the stator affects the thermal behavior of a 100 kV A axial-flux generator. The axial-flux permanent magnet (PM) generator is of a one-rotor-two-stator type construction. A liquid cooling system is applied on the stator frame, and the potting material in the end-winding region thermally connects the end winding to the housing heat sink. The design principle of the cooling system is presented in detail. Simplified thermal models based on Computational Fluid Dynamics (CFD) are used to analyze the temperature distribution through the machine. The theoretical results are verified by measurements. For comparison, one stator of the prototype generator is potted with Ceramacast 675-N material while the other stator is not potted. In each stator there are 14 Pt-100 temperature sensors. As the temperature values between the potted and unpotted stator are compared, it is found that the temperatures differ from each other by approx. 10% at the end windings under load condition. The application of the potting material also provides the rotor cooling.

Genetic Algorithm Approach for Improved Design of a Variable Speed Axial-Flux Permanent-Magnet Synchronous Generator

Optimal design for an axial-flux permanent magnet synchronous generator (AFPMSG) using genetic algorithm (GA) is presented, and the condition for minimum active material cost is deduced. A computer-aided design procedure based on the results of the GA is proposed. In the design procedure the practical and performance characteristics are taken into account as some restrictions for the object function used in the optimization algorithm. A 30-kW AFPMSG with two parallel connected stators and rotor-surface PMs is designed using the developed program, and then 3-D finite-element analyses are carried out to validate the design procedure.

Design and comparative analysis of single and multi-stack axial flux permanent magnet synchronous generator

This paper attempts to design a direct driven axial flux permanent magnet synchronous generator (AFPMSG) with better accuracy considering magnetic flux leakages and fringing effect, using D 2 L method. Design results of conventional and improved design processes are analyzed and compared using 3D finite element method (FEM). Single and multi-stack AFPMSG topologies are designed by using an improved design process. FEM structural analysis is utilized to improve power to weight ratio of three-stack AFPMSG. Finally characteristics of both single and three-stack AFPMSG topologies are analyzed and compared using 3D FEM analysis.

Magnetic Field in a Transverse- and Axial-Flux Permanent Magnet Synchronous Generator From 3-D FEA

The magnet field in a new form of transverse- and axial-flux permanent-magnet synchronous generator is studied. In this novel machine configuration, the main flux flows in the transverse direction as the rotation. The flux density distribution is analyzed using a 3-D finite-element method (3-D FEM). Details of field computation, including the convergence criterion, are explained. Experimental flux density measurements are in good agreement with the computed results. Using a time-stepping technique, the output voltage and current waveforms of the generator are also computed and the accuracy is confirmed by load tests.

Optimal Design of a Distributed Winding Type Axial Flux Permanent Magnet Synchronous Generator

This paper presents a distributed winding type axial flux permanent magnet synchronous generator (AFPMSG) with reduced the total harmonic distortion (THD), suitable for wind turbine generation systems. Although the THD of the proposed distributed winding type is more reduced than the concentrated winding type, the unbalance of the phase back EMF occurs. To improve the unbalance of the phase back EMF and the output power of the distributed winding type AFPMSG, the Kriging based on the latin hypercube sampling (LHS) is utilized. Finally, these optimization results are confirmed by experimental results. As a result, the unbalance of the phase back EMF and the output power of the distributed winding type AFPMSG were improved while maintaining the total harmonic distortion (THD) and the average phase back EMF.

A Novel Approach to the Analysis of the Axial-Flux Permanent-Magnet Generator With Coreless Stator Supplying a Rectifier Load

This paper presents a single-sided axial-flux permanent-magnet synchronous generator (AFPMSG). The performance of an AFPMSG feeding an isolated load is studied using a coupled-circuit, time-stepping, 2-D finite-element analysis. The short-circuit performance is also investigated. The second-order serendipity quadrilateral elements are used in the analysis to obtain the accurate analysis result. Nonlinearities in the field and electric circuit are taken into consideration. With the strong nonlinear diode parts existing in the external circuit, the special interpolating algorithm is used for the motion interface between the stator and rotor to overcome the nonconvergence problem in the computation. The algorithm is validated by comparison with conventional algorithm for an AFPMSG feeding with a rectifier resistive load. The steady state and transient performance of an AFPMSG feeding with bridge rectifier RL load condition are analyzed. The computed result has been verified by experiment on the prototype generator.

Optimized Design Considering the Mass Influence of an Axial Flux Permanent-Magnet Synchronous Generator With Concentrated Pole Windings

In this paper, the efficiency optimization of an axial flux permanent-magnet synchronous generator with concentrated pole windings is examined for a 3.6 kW/2000 rpm combined heat and power application. Because the efficiency of the machine is important, specific measures are taken in order to reduce losses in the machine: thin laminated grain oriented material in the teeth, concentrated pole windings, and segmented magnets. A study of the influence of a limited set of geometry parameters on the efficiency of this type of machine is done, using both analytical and finite-element methods. In the analytical as well as in the finite-element model, the inherent 3-D geometry of the axial flux machine is approximated by multiple 2-D models at different radii in circumferential direction. Afterwards, the influence of mass on the optimal values of the geometry parameters and the efficiency is considered, and it is found that mass can be seriously decreased with only a small reduction in efficiency. Finally, the results of both methods are compared with measurements on a prototype to evaluate their validity.

Performance of an Axial-Flux Permanent Magnet Synchronous Generator From 3-D Finite-Element Analysis

For the first time, this paper presents field computation results and performance of an axial-flux permanent magnet synchronous generator (AFPMSG) based on a time-stepping, 3-D finite-element analysis (3-D FEA). The prototype generator studied has a ferromagnetic outer rotor frame and a totally enclosed design, while a coreless stator armature configuration is used. Based on the machine geometry, a 3-D FEA model is developed in order to determine the principal field components. The flux in the rotor back plate and the transverse flux through the ferromagnetic spacer, which is part of the rotor frame, can both be predicted. A time-stepping, coupled field-circuit approach enables the waveforms and load characteristics of the AFPMSG to be obtained accurately. The computed results are validated by experiments on the prototype generator.