Axial Flux Permanent Magnet Generator Research Articles

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.

Design and Performance Analysis of Coreless Axial-Flux Permanent-Magnet Generator for Small Wind Turbines

This paper presents an innovative design for a low-speed, direct-drive, axial-flux permanent-magnet (AFPM) generator with a coreless stator and rotor that is intended for application to small wind turbine power generation systems. The performance of the generator is evaluated and optimized by means of comprehensive 3D electromagnetic finite element analysis. The main focus of this study is to improve the power output and efficiency of wind power generation by investigating the electromagnetic and structural features of a coreless AFPM generator. The design is validated by comparing the performance achieved with a prototype. The results of our comparison demonstrate that the proposed generator has a number of advantages such as a simpler structure, higher efficiency over a wide range of operating speeds, higher energy yield, lighter weight and better power utilization than conventional machines. It would be possible to manufacture low-cost, axial-flux permanent-magnet generators by further developing the proposed design.

Effects of Manufacturing Imperfections in Concentrated Coil Axial Flux PM Machines: Evaluation and Tests

Due to the high torque capability, axial flux (AF) permanent-magnet (PM) machines are an interesting solution for direct driven wind energy conversion systems and low-speed motors. However, the structure of such machines makes them sensitive to geometrical imperfections due to manufacturing process. This paper analyzes the effects that various types of geometrical imperfections produce in concentrated coil AF PM generators. In particular, a case study is presented, where the mechanical stresses, the resulting axial force, and the bending torques on the shaft, as well as the circulation current in the winding parallel paths, are calculated. The results obtained by means of an analytical approach are compared with those based on finite element method simulations and are validated by some experimental results on a prototype.

A Comparative Study of Modular Axial Flux Podded Generators for Marine Current Turbines

This research note deals with performance comparison of axial flux modular podded generators for marine current turbines (MCTs). Due to the submarine environment, maintenance operations are very hard, very costly, and strongly depending on sea conditions. In this context, the drive train reliability is a key feature for MCTs. For that purpose, a comparative study is proposed, to assess modular axial flux permanent magnet (AFPM) machines potential for reliability improvement. Thereby, designs of direct-drive modular AFPM generator for a given experimental MCT are performed. The proposed study shows that even number sizing of spatially shifted AFPM machine modules leads to the elimination of the electromagnetic torque ripples transmitted to the MCT shaft. Moreover, it is shown that the proposed module-based generator configuration achieves better thermal behavior. As the actives parts masses and costs are expected to be higher, compromises should be carried-out in terms of reliability and fault-tolerance

Use of hybrid solar-wind energy generation for remote area electrification in South-Eastern Nigeria

This paper presents simulated hybridized solar-wind generation as an alternative for rural dwellers that do not have access to a conventional grid connection. Solar and wind were used as the main sources of energy with battery storage. Each power source has a DC-DC converter to control the power flow. An axial flux permanent magnet generator, which is suitable for a location with a low wind speed, was driven by the wind turbine. By using this generator, the efficiency of the system increased since certain losses were removed. The perturbation and observation method of MPPT is used to achieve maximum power extraction from the solar panel. The hybrid system was modelled in Matlab/Simulink software. A squirrel cage induction motor was used as the electrical load to the system load. The results obtained for the proposed hybrid system indicates that it can be used as an isolated power supply. By doing so, it improves the standard of living and hence, increasing total number of citizens using energy in the country.

High-Speed Electric Drive for Exhaust Gas Energy Recovery Applications

High-speed electric drives play an important role in the field of power generating units on board vehicles and aircrafts. This paper deals with the solutions for developing the direct coupled electric drive to be used in combination with a radial turbo-expander for exhaust energy recovery in automotive applications. The descriptions of prototypal realization of both the axial-flux permanent-magnet (PM) generator and the three-level boost-rectifier converter, which results as the preferred topology for the controlled rectifier, are given. The high rotational speed of the direct-driven PM generator results in high electric fundamental frequency also, which is challenging for the electric drive control issues. Results of the electric drive prototype experimental activity are finally presented.

Characteristics analysis of magnetic force distribution in double-sided AFPM machine with unbalanced structure

The axial flux permanent magnet (AFPM) machine is widely used in many applications due to its advantages. But the conventional AFPM machine has the major problem such as the deformation and unbalanced air gap occurred because of the large magnetic attraction force between the rotor and the stator. For these problems, the magnetic attraction force must be accuractly calculated in the process of the design step of the mechanical parts. Thus, this paper proposes the analysis method to compute the magnetic attraction force of AFPM machine considering a unbalanced rotor structure. The quasi 3D model with a different air gap condition is introduced to analyze the magnetic flux density and the magnetic attraction force due to the eccentricity of rotor structure. To validate the proposed analysis process with the quasi 3D model, 3D FEM analysis is performed to compare the results. As results, the proposed analysis results was obtained the similar results to 3D FEM analysis results. The proposed method is applied and estimated to the 130 kW AFPM generator.

Ironless Permanent-Magnet Generators for Offshore Wind Turbines

Because nonmagnetic material is used in the stator, ironless permanent-magnet generators (iPMGs) have negligible normal force between the rotor and the stator, and there is low requirement for the strength of the supporting structures. Therefore, the generator can be light. This feature is attractive in offshore direct-drive energy conversion systems where lightweight design is preferred. The objective of this paper is to investigate systematically different concepts of iPMGs. A design strategy is developed, and codes for finite-element analysis are embedded in this design strategy to ensure the calculation accuracy. A genetic algorithm (GA) is used to find the optimal designs. The influences of machine types and diameter to the machine performances are presented and discussed. Furthermore, the laboratory test of an existing ironless axial-flux permanent-magnet generator confirms the high accuracy of the field and inductance calculations of this design strategy, and the comparison with the parametric study is conducted to demonstrate the excellent performance of the GA used.

Comparing Various PM Synchronous Generators: A Feasible Solution for High-Power, Off-Highway, Series Hybrid, Electric Traction Applications

Different disc-type axial flux permanent magnet (AFPM) generators are designed and compared in this article for a Caterpillar D7E track-type tractor (TTT) electric drive model. The design of several feasible generators with multiple stators and rotors are completed for the given electrical and mechanical specifications and compared with a conventional permanent magnet (PM) generator in terms of power density, torque density, loss distribution, efficiency, heat dissipation, volume, inertia, and weight. Electromagnetic, mechanical, and thermal analyses are also accomplished to finalize the designs. The results reveal the benefits of axial gap PM generators over radial gap generators for a hybrid electric traction application.

Optimisation of Inner Diameter to Outer Diameter Ratio of Axial Flux Permanent Magnet Generator

This paper presents design of axial flux permanent magnet generator using torus construction of stator with plastic material. To maximise the efficiency of the generator, the losses are to be minimized in proposed N-S Arrangement iron loss is absent and only copper losses are present. To minimise the copper loss for a given rating, the per phase stator resistance is to be minimised. The relation between Internal Diameter (ID) to Outer Diameter (OD) Ratio and the per phase resistance has been developed and optimal value is worked out. Also the designs were prepared for various ID to OD ratios to verify the optimal results.

An optimal design of coreless direct-drive axial flux permanent magnet generator for wind turbine

Different types of generators are currently being used in wind power technology. The commonly used are induction generator (IG), doubly-fed induction generator (DFIG), electrically excited synchronous generator (EESG) and permanent magnet synchronous generator (PMSG). However, the use of PMSG is rapidly increasing because of advantages such as higher power density, better controllability and higher reliability. This paper presents an innovative design of a low-speed modular, direct-drive axial flux permanent magnet (AFPM) generator with coreless stator and rotor for a wind turbine power generation system that is developed using mathematical and analytical methods. This innovative design is implemented in MATLAB / Simulink environment using dynamic modelling techniques. The main focus of this research is to improve efficiency of the wind power generation system by investigating electromagnetic and structural features of AFPM generator during its operation in wind turbine. The design is validated by comparing its performance with standard models of existing wind power generators. The comparison results demonstrate that the proposed model for the wind power generator exhibits number of advantages such as improved efficiency with variable speed operation, higher energy yield, lighter weight and better wind power utilization.

Implementation of a Coreless Axial-Flux PM Generator for Vertical-Axial Wind Turbine

In this paper, a rigorous and efficient approach, using the fuzzy-Inference Taguchi method with the multiple performance characteristics index (MPCI), is employed for obtaining the rigorous design of a small-scale direct-drive coreless axial-flux permanent-magnet (AFPM) generator for a vertical-axis wind turbine (VAWT) with both larger induced voltage and higher efficiency. The proposed method first establishes the orthogonal array (OA) recommended by the Taguchi method, then multiple targets are coordinated by the fuzzy inference mechanism to obtain a better combination of geometric parameters for achieving multiple quality targets. The three-dimensional (3-D) electromagnetic finite element method (FEM) is used as the tool for analyzing the performance of the coreless AFPM generator. The results have shown the proposed method can obtain the suitable generators geometric parameters for enhancing the induced voltage of the generator while keeping efficiency as high as possible under the rated speed.

Lumped-Parameter Thermal Model for Axial Flux Permanent Magnet Machines

A lumped-parameter thermal model is presented for axial flux permanent magnet (AFPM) machines. The model provides the steady-state thermal solution to derive the temperatures at different parts of the machine, including the temperatures in the stator windings and the temperature of the magnets. Temperature-dependent thermal properties of the materials used in the machine construction as well as the stator winding resistance and consequently copper losses require temperature update in accurate design of the machine. Therefore, an iterative coupled electromagnetic and thermal design program is proposed in this study. A 5-kW AFPM generator is designed using the proposed program with regarding the thermal behavior of the machine. Tests performed on the designed machine verify that the defined thermal resistance network has a high ability to predict the nodal temperatures accurately.

PERFORMANCE ANALYSIS OF AFPM GENERATOR DIRECT DRIVEN WIND TURBINE WITH STORAGE SYSTEM

Direct-drive type with no acceleration rare and the windmill blades attached to the disc surface of Axial Flux Permanent Magnet generator (AFPM) realizes simple structure and omission of central dynamic transformation achieves very high energy conversion efficiency of the generator. The generator itself consists of two magnets rotors that return together directly coupled to the blades. In this research study, one magnet rotor is on each side of the stator and each magnet rotor contains 16 Neodymim-Iron-Boron (NdFeB). The stator contains 12 coils wound with copper wire and cast into plastic resin, in line with and between the paths of each magnet. The AFPM generator direct drive wind turbine converts the mechanical energy by the rotating shaft as the wind pushing 3 wooden blades into 3-phase alternating current (AC) electricity that varies in frequency. In order to get this generated power into a battery bank, three-phase bridge rectifier is connected to the three terminals of the machine. The alternator will start 48 volt charging batteries system at about 140 rpm in 4m/s wind speed and reach rated output of 1.8 kW at 375 rpm in 10m/s wind speed. This machine is specially designed for battery charging and it’s probably quite useful and cost effective for remote locations that are not connected to the national grids where conventional methods of energy supply are expensive or impractical.

The Development of a New Type Rooftop Ventilator Turbine

This paper presents a small power generation system motivated by a coreless stator AFPM (Axial Flux Permanent Magnet) generator which is driven by the rooftop ventilator. The generator consists of discs for the rotor and the stator geometry. The stator disc is sandwiched between two rotor discs and the magnets in the two opposite rotor discs may be placed N-S arrangements. Since there is no silicon steel inside the coils, we should eliminate the magnetic pulling force between the rotors and the stators. When the ventilator rotates, the flux of the permanent magnet rotors part move across the air gap and induces the emf in the coreless coils. After that, the ac voltage is rectified to dc voltage and finally charged to the 12 V 5 Ahr battery for household appliances. To analyze the magnetic circuit, the finite element analysis was used to simulate the magnetic flux density in the AFPM generator. The test is operated in electrical machines laboratory and essentially to determine the characteristics of prototype generator. Based on the experiments, the results of the output voltage can achieve 103 V with no-load, and 20 V on 100 Ω resistive loads at the speed of 200 rpm. For the results after installing the generator on the roof of a building to charge the 12 V battery, the minimum wind speed for enough charging to battery is at 10 rpm. Furthermore, the prototyped of the generator is relatively small and cheap. After the fabrication and testing of the prototype, this system has been proved feasible for practical application.

Nonlinear Modeling and Simulation of a Four-phase Switched Reluctance Generator for Wind Energy Applications

Abstrac t—Thesubject of this paper is a modeling method of switched reluctance generator (SRG) based on the nonlinear inductance model and electromagnetic field finite element analysis (FEA) to be used in wind energy applications. SRG and its behavior, modeling and Simulations results are presented. It was analyzed the characteristics of the SRG under different conditions. The nonlinear inductance model allows us to develop a control strategy that gives high performance controller with a closed loop was designed on PI controller. I. INTRODUCT ION The rapid depletion of fossil fuels has necessitated the need for the utilization of non-conventional energy sources. Among these renewable energies widely used around the world in the last years, wind energy conversion system seems to be very interesting, it is clean energy source suitable for rural areas and the stand alone wind energy conversion system in rural areas must be characterized by economic and maintenance free operation. Doubly fed induction generator (DFIG) suffers from limited rotor converter rating and has problems with over currents during voltage dips and the multistage gearbox that the DFIG must incorporate is unreliable and expensive. The direct coupled variable speed generators for these systems obviate the need for gear box which is the most unreliable and maintenance intensive component in the system. Permanent Magnet Synchronous Generator or Field Wound Synchronous Generator in standalone wind energy conversion systems eliminate the unreliability associated with gear box drive trains through direct coupled variable speed operation and even though permanent magnet machines will have a better torque density than the field wound version, the presence of permanent magnets will make assembly more difficult (1). In the Field Wound Synchronous Generator, the brushes required to excite the field winding demand maintenance at regular intervals. The variable speed direct drive synchronous generator shortfalls fr om cost, size, weight, energy yield and requirement of a converter. Although Permanent magnet generators exhibit low losses, lower weight, better torque density and perhaps low cost with the disadvantage that the excitation cannot be controlled while axial flux permanent magnet generators are heavier and more expensive than radial flux counterparts. To overcome the beyond mentioned obstacles Switched Reluctance Generator (SRG) is being considered as the generator of choice in standalone wind energy conversion

Design of an Axial Flux Permanent Magnet Generator for a Portable Hand Crank Generating System

This paper deals with a design of an axial flux permanent magnet (AFPM) generator which is a key element of a compact size portable and manual generator system composed of a gear system, a generator, a rectifier, and a battery charger. The design objects of the AFPM generator are its compact size, light weight, and high efficiency, and the three design objects are the main criteria to select the value of design variables. A soft magnetic composite core is used instead of a silicon steel core in the AFPM generator to achieve a compact size. In this paper, the overall design process to meet the design goals and the design results are presented with experiment results.

Axial Flux Permanent Magnet Generator Design for Low Cost Manufacturing of Small Wind Turbines

In this paper the design and manufacturing processes for coreless axial flux permanent magnet generators are described for low cost rural electrification applications, where local production of small wind turbines is considered. The process is based on already existing open source design and construction manuals, while a systematic approach to designing generators of varying nominal power and for grid connection or direct battery charging schemes is described. The manufacturing process of a 3 kW small wind turbine generator for grid connection is used as a case study. Emphasis is given to the use of simple tools and techniques to achieve a lower cost, while intricate steps in the manufacturing process are described in more detail. The generator design is simulated and the constructed machine is tested in the laboratory.

High-Speed Generator and Multilevel Converter for Energy Recovery in Automotive Systems

This paper deals with the design solution adopted for a high-speed axial-flux permanent-magnet generator devoted to supplementing power in automotive 42 V electrical systems through a low-voltage multilevel neutral-point-clamped converter. The axial-flux permanent-magnet generator is suitably designed to be directly coupled with a radial turbo-expander which provides recovery of kinetic energy available from the exhaust gases of an internal-combustion engine. The multilevel converter is properly sized for systems having low voltage and high first-order harmonic frequency. The paper describes the proposed 4-kW power rating generating system and discusses various issues resulting from electromagnetic, thermal, and mechanical design of the high-speed axial-flux permanent-magnet generator. As well, investigations on modulation strategy, total harmonic distortion, and power losses are presented for the low-voltage neutral-point-clamped power electronic converter.

이중 고정자 구조의 소형풍력터빈용 AFPM 발전기의 코깅토크 저감에 관한 연구

The cogging torque is important to the cut-in wind speed. And, it causes the acoustic noise and the vibration on the machine. This paper presents a 3D FEA(Finite Element Analysis) to evaluate the effect of magnet skew and stator displacement on cogging torque reduction, for double core AFPM(Axial Flux Permanent Magnet) generator. As a result, the magnet skew and the stator side displacement are proved excellent techniques to reduce the cogging torque.