Radial Flux Permanent Magnet Generator Research Articles

A Stiffness Approach for Coupling Structural and Magnetic Models for the Sustainable Design, Optimisation and Real-Time Structural Integrity Assessment of Radial Flux Permanent Magnet Generators for Direct-Drive Wind Turbines

The mass of a direct-drive generator is often defined by the requirements for structural stiffness to meet the magnetic stiffness between the rotor and stator surfaces. This paper analyses this magnetic stiffness and estimates the structural stiffness of direct-drive generators for different modes of deflection. The magnetic stiffness modelling is based on an analytical model of the airgap closing forces. The final models are verified using finite element analysis and developed for both permanent magnet and wound rotor generators. It shows that wound rotor machines have higher stiffness requirements than permanent magnet machines. The structural stiffness of the generator rotor and stator is evaluated for different modes by applying spatially varying forces and finding the associated deflections. Structural stiffnesses for the rotor, stator and bearing are then combined. Finally, the magnetic and structural stiffnesses are combined and a stiffness margin can be found. This method is applied to a relatively stiff and a relatively compliant set of generator structures in a case study. The analytical model presented in this paper is useful for structural optimisation purposes or as part of an online structural health monitoring system as it could assess the integrity of the machines in real time.

A Review: Various Designs of Radial Flux Permanent Magnet Generator Technologies

In a renewable energy system, the amount of power generated by a renewable energy source constantly evolves. Furthermore, with the smart energy approach, small distributed renewable energy can be included into an industrialized network, enabling real-time optimization, and enabling communication with other facilities. A magnetic generator is one of the renewable energies that use the permanent magnet. As a result, this generator generated magnetic flux power by using the permanent magnetic field. An overview of the radial flux permanent magnet generator for small industry is provided in this study. First, a categorization and in-depth description of radial permanent magnet generators are reviewed. The important features of the permanent magnets are presented, along with their advantages and disadvantages. Additionally, an overview of the most recent machine developments is also presented. Lastly, an overview of the conventional radial flux permanent magnet generator designs that have been used in the development of small-scale generators is as follows.

Cogging torque reduction for permanent magnet structure of radial flux permanent magnet generator

Recently, Permanent Magnet Generator has been widely used due to its ability of having simple structure yet high efficiency. A radial flux permanent magnet generator’s (RFPM) cogging torque leads to the decrease in output power. Generally, cogging torque is affected from the size of permanent magnet. This paper presents the techniques for cogging torque reduction and low torque ripple of RFPM design. This research used two methods to reduce the cogging torque which is the permanent magnet pole-arc ratio and also the permanent magnet structure. The cogging torque has been successfully reduced by increasing the permanent magnet pole-arc ratio and reducing the permanent magnet structure The best design configuration that can reduced the cogging torque by using pole-arc ratio is 0.49 pole-arc ratio which can reduce the cogging torque to 0.6986Nm. Moreover, for PM structure method 0.25 PM structure has been chosen as the best configuration since it can reduce the cogging torque to 0.2366Nm. This method able to reduce the cogging torque by 69.88%. Hence, both of these techniques are successfully reduced the cogging torque.

Slot-pole structure investigation for radial flux permanent magnet generator

Recently, Radial Flux Permanent Magnet Generator (RF-PMG) has been applied in various applications of generator. The configuration of the radial flux permanent magnet is the magnetic rotor arranged in a circle rotation while the inner core attached to the rotor’s center. However, various sizes and structure of RF-PMG can produce different output power levels, cogging torque and generator’s flux regulation capability. By investigating the output voltage and cogging torque value, this paper showed the suitable slot-pole combinations that can influence the output performance of the generator by using 2D-Finite Element Analysis. This investigation shows the comparison of the slot-pole that resulting the least cogging torque value and high output voltage, 0.1739Nm and 180.81V respectively. Hence, 36slots-30poles indicates as the best slot-pole combinations.

Design Optimization and Analysis of Radial Flux Permanent Magnet Generator Using Local Optimization Method

Recently, Permanent Magnet Generator has been widely used due to its ability of having simple structure yet high efficiency. To maximise the output performance of the generator, advances and trends in mathematical modelling and computer simulation with using optimization techniques have opened the way to a new approach for electrical machine design. In this paper, a Radial Flux Permanent Magnet Generator configuration was examined and optimised throughout sizes and weight using Local Optimization Method as an iterative process in order to achieves optimal output. By utilizing LOM technique as optimization process, the output voltage of RFPMG increase by 13.64% from the initial results. With a corresponding increase in output voltage performances, the configurations geometry adjustment additionally helps in expanding the generator operational area.

An Analysis of the Design of a Low Rotational Speed Permanent Magnet Generator That Uses Radial Flux

A radial flux permanent magnet generator can be effectively used in generating wind power at low speeds. This generator uses a combination of permanent magnets and a stator to produce electricity from the wind’s kinetic energy. The permanent magnets are arranged in a radial pattern, which reduces the amount of heat lost and therefore increases the generator’s efficiency. This design allows for a low rotational speed, which makes it suitable for applications such as wind turbines. The air gap between the rotor and the stator affects the output voltage and power due to the decrease in magnetic flux. This study aims to increase the generator’s output voltage and output power by fitting stator teeth widths to the stator teeth. The stator teeth width fitting design method adjusts the air gap between the stator and the rotor to a uniform size. This helps to reduce the pulsating torque and ensure that the output voltage and power are maximized. The three variables are the stator slot width, the rotor slot width, and the air gap width. By adjusting these variables, the stator teeth width fitting design method can adjust the air gap between the stator and rotor.

Analytical Performance Estimation of a Fall-Back Inner-Rotor Transverse-Flux Permanent Magnet Generator using Magnetic Equivalent Reluctance Circuit

The potential of wind energy resources is propelled fast and power extraction is increasing considerably due to the development of reliable and cost-effective wind turbine generators. Various permanent magnet (PM) wind generators have been implemented for wind power generation, among which, the conventional transverse-flux permanent magnet generator (TFPMG) is popular due to their higher torque density and simple coil design, but it has some disadvantages in comparison with radial flux PM generator, i.e., higher flux leakages and complex 3D flux pattern. In this article, a fall-back inner rotor transverse-flux PM wind generator FB-TFPMG has been investigated to override the disadvantages of conventional TFPMG. It employs half of the total PMs on the rotor and U-shaped stator cores. An analytical model of the proposed FB-TFPMG has derived using magnetic equivalent reluctance circuit (MERC) to predict the performance of the generator, i.e., flux densities in the air-gap, under aligned and unaligned conditions of rotor PMs with U-shaped stator cores. The results of the MERC model is verified with the results obtained through 3D finite element analysis.

Geometrical and dimensional tolerance analysis for the radial flux type of permanent magnet generator design

Mechanical tolerance is something that should be carefully taken into consideration and cannot be avoided in a product for manufacturing and assembly needs, especially in the design stage, to avoid excessive dimensional and geometric deviations of the components made. This paper discusses how to determine and allocate dimensional and geometric tolerances in the design of a 10 kW, 500 rpm radial flux permanent magnet generator prototype components. The electrical and mechanical design results in the form of the detailed nominal dimensions of the generator components, and the allowable air gap range are used as input parameters for tolerance analysis. The values of tolerance allocation and re-allocation process are carried out by considering the capability of the production machine and the ease level of the manufacturing process. The tolerance stack-up analysis method based on the worst case (WC) scenario is used to determine the cumulative effect on the air gap distance due to the allocated tolerance and to ensure that the cumulative effect is acceptable so as to guarantee the generator's functionality. The calculations and simulations results show that with an air gap of 1 ± 0.2 mm, the maximum air gap value obtained is 1.1785 mm, and the minimum is 0.8 mm. The smallest tolerance value allocation is 1 µm on the shaft precisely on the FSBS/SRBS feature and the rotor on the RPMS feature. In addition, the manufacturing process required to achieve the smallest tolerance allocation value is grinding, lapping, and polishing processes.

Performance analysis of radial flux and axial flux permanent magnet generators for low- speed wind turbine applications

India has enormous wind potential and average wind velocity is about 6 m/s, whereas the conventional wind turbine mechanism is operated at 7 m/s–12.5 m/s. It is necessary to design low speed wind energy conversion to harvest the electrical energy from wind. Mostly, Radial flux permanent magnet generator (RFPMG) is used for low speed wind turbine applications. This Conventional RFPMG has the drawbacks of low flux density and increase in weight due to large number of poles accommodation. In order to overcome the above setbacks, this paper proposes a double sided coreless axial flux permanent magnet generator (AFPMG) for low speed wind energy conversion applications. The performance analysis of the proposed AFPMG is carried out through finite element method using ANSYS Maxwell software. Finally the performance of RFPMG and AFPMG is compared based on the flux linkage, flux density, induced emf, stator current, moving torque, cogging torque, Total Harmonic Distortion (THD), material consumption, losses and efficiency. It is evident from the results that AFPMG gives the better performance than RFPMG in all such aspects.

Design and simulation of a conical rotor axial -radial flux permanent magnet generator of power 1.1kW for micro wind turbines

In this study, design, design calculations and simulation of a permanent magnet generator, which includes two sections of radialand axial flux, are discussed. The output power from the generator is 1.1 kilowatt. In the design of the generator, a cone-shapedstructure with a 90-degree cone angle of 45 degrees from the sides is used for the rotor. In order to compare the various structuresof the synchronous generator, and given that today, permanent magnet generators have been considered with regard to featuressuch as lower weight, higher yields and higher power density than other conventional generators. A finite element analysis of thegenerator developed in Maxwell software. In the radial flux section, the generator includes a conical rotor and a cone stator. Thewindings on the external stator are trapezoidal and are located in stator racks. The finite element analysis of the generator confirmsthat permanent magnet magnets designed on the inner rotor have provided a magnetic flux equal to 1.2 Tesla in the air gap betweenthe generator and the winding of the stator. The rotor magnetic field analysis, rotor magnetic field strength, magnetic field intensity,and magnetic field density at a speed of 500 rpm for cone structure have been performed. In the axial flux section, the generatorconsists of two rotors and a grooved stator, which is obtained by simulating a 1.1 kW power with a sinusoidal three-phase voltage.Two sections of radial flux with a cone-shaped rotor and axial flux side by side make up the generator.

DESIGN OF A SINGLE-PHASE RADIAL FLUX PERMANENT MAGNET GENERATOR WITH VARIATION OF THE STATOR DIAMETER

This study aims to observe the influence of the changing stator dimension on the air gap magnetic flux density (Bg) in the design of a single-phase radial flux permanent magnet generator (RFPMG). The changes in stator dimension were carried out by using three different wire diameters as stator wire, namely, AWG 14 (d = 1.63 mm), AWG 15 (d = 1.45 mm) and AWG 16 (d = 1.29 mm). The dimension of the width of the stator teeth (Wts) was fixed such that a larger stator wire diameter will require a larger stator outside diameter (Dso). By fixing the dimensions of the rotor, permanent magnet, air gap (lg) and stator inner diameter, the magnitude of the magnetic flux density in the air gap (Bg) can be determined. This flux density was used to calculate the phase back electromotive force (Eph). The terminal phase voltage (V∅) was determined after calculating the stator wire impedance (Z) with a constant current of 3.63 A. The study method was conducted by determining the design parameters, calculating the design variables, designing the generator dimensions using AutoCad and determining the magnetic flux density using FEMM simulation. The results show that the magnetic flux density in the air gap and the phase back emf Eph slightly decrease with increasing stator dimension because of increasing reluctance. However, the voltage drop is more dominant when the stator coil wire diameter is smaller. Thus, a larger diameter of the stator wire would allow terminal phase voltage (V∅) to become slightly larger. With a stator wire diameter of 1.29, 1.45 and 1.63 mm, the impedance values of the stator wire (Z) were 9.52746, 9.23581 and 9.06421 Ω and the terminal phase voltages (V∅) were 220.73, 221.57 and 222.80 V, respectively. Increasing the power capacity (S) in the RFPMG design by increasing the diameter (d) of the stator wire will cause a significant increase in the percentage of the stator maximum current carrying capacity wire but the decrease in stator wire impedance is not significant. Thus, it will reduce the phase terminal voltage (V∅) from its nominal value.

Radially-Magnetized Transverse Flux Permanent Magnet Generator

The transverse flux permanent magnet motor attracts wide attention in the field of low-speed direct-drive wind power due to its high torque density, good low-speed performance and other advantages. Aiming at the problem of high leakage coefficient of permanent magnet in the attached transverse flux permanent magnet wind power generator, a radially-magnetized transverse flux permanent magnet generator (RM-TFPMG) is proposed in this paper. Details of the structure and principle of the proposed machine are introduced firstly, and then the main parameters of the RM-TFPMG are calculated by the magnetic circuit method. Finally, the three-dimensional finite element analysis of the radial load flux transverse flux permanent magnet generator is carried out by ANSYS Maxwell software, and the parameters of machine and Back Electromotive Force (EMF) are obtained under the condition of no-load, and the rationality of the designed motor is verified.

Preliminary studies of a new permanent magnet generator (PMG) with the axial and radial flux morphology

In this work, a new axial and radial flux permanent magnet generator (PMG) is introduced. The machine has multiple cores in its stator, which has double sides, coils in these sides. It operates in 3 phases and uses disc type magnets in two rotors at each side. PMG has 24 circular coils and 12 laminated cores. Each rotor has 16 magnets and the stator is stable at the middle of the rotors. The simulations include magnetostatics and magnetodynamics analyzes via finite element method (FEM). After the determination of optimal physical, electrical and magnetic parameters, a prototype machine is constructed for the experiments. The rated values of the machine are measured experimentally for different rotor speeds and different ohmic loads. According to the experimental and theoretical analyzes, the rated power is found as 250 W with the efficiency ratio of 92% for the testing values of airgap 5 mm.

Design and Performance Analysis of Double Stator Axial Flux PM Generator for Rim Driven Marine Current Turbines

This paper presents the design and performance analysis of double stator axial flux permanent magnet generators for rim-driven marine current turbines (MCT). In submarine applications, drive train reliability is a key feature for reducing maintenance requirements. Rim-driven, direct-drive, multistator generators can therefore be an interesting solution to improve reliability. In this context, the work presented here focuses on the design of a double-stator, axial flux, permanent magnet (PM) generator as a rim-driven, direct-drive, multistator generator. The models, specifications and an optimization procedure that facilitate the preliminary design of these kinds of generators for rim-driven marine turbines are presented. Validation with finite element computations and a performance analysis for a particular design of rim driven generators are conducted. The results obtained highlight some designs issues associated with PM generators for rim driven marine turbines. To assess the effectiveness of the double stator axial flux PM generator, a comparison with a surface mounted radial flux PM generator design for rim marine turbines is carried out. The comparison shows that the double stator axial flux generator has a better cooling characteristic and a reduced active parts cost and mass than the radial flux PM generator.

A 5MW direct-drive generator for floating spar-buoy wind turbine: Development and analysis of a fully coupled Mechanical model

This work forms the first of a two-part investigation aimed at identifying the challenges and opportunities of implementing a direct-drive generator for a spar-buoy type floating wind turbine. Preliminary specifications are presented for a fully coupled aero-hydro-servo-elastic model of a floating wind turbine with a 5 MW direct-drive generator. The drive-train model uses a low-speed, high-torque radial flux permanent magnet generator supported by two main-shaft bearings. The mechanical properties of the drive-train, including the main dimensions, mass of major nacelle equipment and details for the hub/nacelle assembly are presented. The rationale behind the adjustments to the tower and platform properties and the motivation to selection of best arrangement that is appropriate for supporting the developed system is explained. A discussion on the development of the variable speed-variable pitch control system suitable for the direct-drive system including modifications to avoid negative damping and blade-pitch instability are presented. Fully coupled simulations for the developed aero-hydro-servo elastic model were carried out in HAWC2 for the normal operating conditions of the wind turbine. The aerodynamic response of the model was verified and compared with that of a geared floating wind turbine system. Some initial results comparing the main shaft loads of the land-based and floating versions of the direct-drive wind turbine suggest satisfactory dynamic behaviour of the drive-train. The results prompt further research using a detailed drive-train model to verify the internal response, loading and durability of the components to assess their compatibility with a floating wind turbine system.

회전자의 영구자석 위치 이동을 이용한 이중 고정자 RFPM 발전기 코깅토크 저감 연구

In this paper, we propose the cogging toque reduction technique of the dual stator radial flux permanent magnet generator. The cogging toque is caused by the torque ripple increase and vibration and noise of the generator. And it is important factor determining cut-in speed of the small wind generator. To reduce cogging torque, permanent magnet displacement was studied. And the theory of the permanent magnet displacement was formulated and the cogging torque reduction according to the permanent magnet displacement was confirmed through the finite element method.

Reduction of cogging torque in dual rotor permanent magnet generator for direct coupled wind energy systems.

In wind energy systems employing permanent magnet generator, there is an imperative need to reduce the cogging torque for smooth and reliable cut in operation. In a permanent magnet generator, cogging torque is produced due to interaction of the rotor magnets with slots and teeth of the stator. This paper is a result of an ongoing research work that deals with various methods to reduce cogging torque in dual rotor radial flux permanent magnet generator (DRFPMG) for direct coupled stand alone wind energy systems (SAWES). Three methods were applied to reduce the cogging torque in DRFPMG. The methods were changing slot opening width, changing magnet pole arc width and shifting of slot openings. A combination of these three methods was applied to reduce the cogging torque to a level suitable for direct coupled SAWES. Both determination and reduction of cogging torque were carried out by finite element analysis (FEA) using MagNet Software. The cogging torque of DRFPMG has been reduced without major change in induced emf. A prototype of 1 kW, 120 rpm DRFPMG was fabricated and tested to validate the simulation results. The test results have good agreement with the simulation predictions.

Structural integrity of a direct-drive generator for a floating wind turbine

In this work, the suitability of a direct-drive radial flux permanent magnet generator is examined as a probable drive-train candidate for a stepped-spar floating wind turbine system that supports a 2 MW downwind turbine. The suitability of the generator is assessed based on the structural integrity of its design (i.e., the stability of the air-gap between the rotor and stator) in response to the nacelle motions and its possible design implications on the overall system. Air gap deflections due to structural deflection and bearing tolerances were examined independently. The nacelle motions are obtained from experimental and numerical investigations on a 1:100 scale model. ANSYS suite is used to estimate the structural deformations of the generator and the changes in the air-gap distribution. Also, a simplified analytical model is used to compute the resulting changes in flux density and force distribution along the rotor periphery. The analytical model is also validated by 2D magneto-static simulations by utilising Finite Element Methods Magnetics software (FEMM).Preliminary results suggest that, if the nacelle accelerations are limited to 0.3 times the acceleration due to gravity (g) and the motion response cycles are below the fatigue limit, the air-gap stability of the generator is more sensitive to magnetic forces. Contributions to air-gap eccentricity from shaft displacements can be limited if the bearing supports can be designed for high stiffness. This also confirmed the adequacy of the platform design. The results also emphasise the need for air-gap management when designing direct-drive generators for floating wind turbines. Two methods are investigated as potential solutions to limit the maximum air-gap deflection to 10% level. The method of increasing structural stiffness led to a structurally unfavourable design that could potentially affect the stability and resonance properties of the system. The method of increasing the design air-gap led to a structurally more favourable design, although this meant an increase in magnetic material and hence the costs. Thus, implementing direct-drive radial flux permanent magnet generators for floating wind turbines is challenged by the difficulty in achieving optimal weight and costs at acceptable performance without compromising the air-gap tolerances. There is a need for an amendment to design standards to recognise the design challenges of Floating wind turbines.

A Design on Reduction Cogging Torque of Dual Generator Radial Flux Permanent Magnet Generator for Small Wind Turbine

In this paper, the design for an electromagnetic structure and reduction cogging torque of a dual generator structured RFPM generator, which is a combination of the inner- and outer-rotor types, has been proposed. We call this a dual generator radial flux permanent magnet generator. To reduce the cogging torque, firstly, stator tooth pairing was designed; secondly, stator displacement was designed and finally, stator tooth pairing and stator displacement were carried out simultaneously. We found the optimal design condition about stator tooth pairing angle combination and stator displacement angle for cogging torque minimization. As a result, a cogging was reduced by 93.3[%] by this study.

Rotor Eccentricity Effect on Cogging Torque of PM Generators for Small Wind Turbines

This paper discusses the effect of rotor eccentricity on cogging torque of a permanent-magnet (PM) generator applied to small wind turbines. The 1.4 kW radial-flux PM generator was designed to improve the start-up wind speed ( $ 3 m/s) by reducing the cogging torque. Finite element analysis (FEA) is first used to simulate the generator for a range of eccentricities and their corresponding cogging torques. In experiment, the cogging torque of a prototype generator with a particular eccentricity of 0.25 mm (33% of the air-gap length) is measured and the result matched that of the FEA. This gives confidence in terms of using FEA for further studies. The relationship between the starting torque provided by turbine blades and the cogging torque is also discussed. From the simulation, it is found that the dynamic eccentricity can be detected by measuring the cogging torque waveform.