Asko Parviainen

Modeling of axial flux permanent-magnet machines

In modeling axial field machines, three-dimensional (3-D) finite-element method (FEM) models are required in accurate computations. However, 3-D FEM analysis is generally too time consuming in industrial use. In order to evaluate the performance of the axial flux machine rapidly, an analytical design program that uses quasi-3-D computation is developed. In this paper the main features of the developed program are illustrated. Results given by the program are verified with two-dimensional and 3-D finite element computations and measurements. According to the results, it is possible to evaluate the performance of the surface-mounted axial flux PM machine with reasonable accuracy via an analytical model using quasi-3-D computation.

Performance comparison between low-speed axial-flux and radial-flux permanent-magnet machines including mechanical constraints

Performance comparison between different machine topologies is not a straightforward task since many variables exist if electromagnetic, thermal and mechanical aspects are taken into account. In this paper some methods to take into account relevant mechanical constraints in the performance comparison are proposed. A comparison study between low-speed axial-flux permanent-magnet machines and radial-flux permanent-magnet machines is provided with introduced mechanical constraints, respectively

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.

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.

Axial Flux Permanent Magnet Generator with Concentrated Winding for Small Wind Power Applications

An axial flux permanent magnet machine, designed to operate as a generator in a small-scale wind-power applications, is described in this paper. The machine is realized by using consecrated stator winding with open slots and surface mounted permanent magnets on rotor disk. Such a novel generator structure is simple to construct and its performance is good; it offers sinusoidal back-emf waveform, low torque ripple and high efficiency. A 1.6 kW prototype machine is constructed and is installed to a pilot power plant. Design results as well as test result for the prototype machine are reported in this paper

Concentrated winding axial flux permanent magnet motor with plastic bonded magnets and sintered segmented magnets

Direct drive axial flux permanent magnet (PM) motors are a cost effective and an energy saving choice for industrial use. Open slots make concentrated winding machines a favourable configuration with respect to manufacturing. However, open slots expose rotor surface magnets to large flux pulsations and the losses of sintered magnets may not be neglected. Plastic bonded magnets have very low eddy current losses but other magnetic properties of such magnet materials are not satisfactory at the moment. Divided sintered neodymium iron boron (NdFeB) may be used instead but the magnet configuration must be carefully analyzed to attain an acceptable eddy current losses level in the magnets. This paper addresses permanent magnet rotor constructions, which eliminate or remarkably reduce eddy-current losses in the magnets of a 2500 min-1 / 3000 min-1, 37 kW permanent magnet synchronous motor with concentrated windings. Different magnet materials, such as plastic-bonded Neo-magnets and sintered segmented NdFeB-magnets are evaluated. Also a prototype motor with plastic bonded magnets has been built. Analytical Matlabtrade- and finite-element-method-based (Flux2D/3Dtrade by Cedrat) programs are used in the calculations. The permanent magnets should be segmented into many small sections in the Machine which the flux pulsations in the magnets are high.

Concentrated winding axial flux permanent magnet motor for industrial use

This paper introduces a new cost-effective, energy-saving, axial flux permanent magnet (PM) motor type for industrial use. The particular features of the machine are based on the study of using concentrated winding open slot constructions of permanent magnet synchronous machines in the normal speed ranges of industrial motors, for instance up to 3000 min−1, without excessive rotor losses. In an axial flux permanent magnet motor with the two-stator-single-rotor construction, where the magnetic flux travels through the permanent magnets from one stator to another, the rotor of the machine can be kept totally ironless. If the open stator slot structure can be used with concentrated windings, prefabricated coils can simply be inserted around the stator teeth, and the winding process becomes very cost-effective compared for example with double-layer short-pitched normal integral slot windings. However, open slots expose rotor surface magnets to large flux pulsations, and the losses of bulky sintered magnets cannot be neglected. Divided sintered neodymium iron boron (NdFeB) magnets may be used instead, but the magnet configuration must be carefully analyzed to attain an acceptable eddy current loss level in the magnets.

Influence of the air-gap length to the performance of an axial-flux induction motor

The influence of the air-gap length on the performance of a 45 kW / 6000 min-1 axial-flux aluminium-cage solid-rotor-core induction motor is studied. The length of the air-gap has a significant influence on the characteristics of an electric machine. In the machines that are designed for speeds above 3000 min-1 (which can be reached with the 50 Hz network), the air-gap length has to be increased considerably from the value obtained for a standard electric motor. Especially, if the motor is equipped with a solid rotor core, the air-gap length has to be designed with special care. It is shown that the efficiency of the studied motor is highly dependent on the rotor eddy current losses. The determination of the losses is done by using numerical 2D FEM calculations and measurements for the prototype machine. In this paper, it is shown that by changing the air-gap length the loss minimum can be found between the rising stator copper losses and the diminishing rotor harmonic eddy current losses.

The Effects of the Number of Rotor Slots on the Performance Characteristics of Axial-Flux Aluminium-Cage Solid-Rotor Core Induction Motor

The influence of the number of rotor slots on the performance - electromagnetic torque production, torque ripple, rotor losses and power factor - of an axial-flux (AF) aluminium-cage solid-rotor core induction motor is studied. The number of stator slots in the study was 36 and the number of the rotor slots was varied between 24 and 32. The width and depth of the rotor slots were kept at initial values. The maximum torque at a certain slip value was achieved at the number of 25 rotor slots. The rotor losses as a function of the number of rotor slots seem to decrease almost linearly when the number of the rotor slots was varied between 24 and 31.

Modeling of axial flux PM machines

In modeling axial field machines, 3D FEM models are required in accurate computations. However, 3D FEM analysis is generally too time consuming in industrial use. In order to evaluate the performance of the axial flux machine rapidly, an analytical design program that uses quasi-3D computation is developed. In this paper the main features of the developed program are illustrated. Results, given by the program are verified with 2D and 3D finite element computations and measurements. According to the results, it is possible to evaluate the performance of the surface mounted axial flux PM machine with reasonable accuracy via an analytical model using quasi-3D computation.