Hanne Jussila

Harmonic Loss Calculation in Rotor Surface Permanent Magnets—New Analytic Approach

The paper introduces an analytic permanent-magnet eddy-current loss calculation method for rotor surface permanent magnets. The problem has been studied widely in the literature, yet many of the suggested methods are difficult to use. A straightforward analytic solution is needed to speed up the motor preliminary design as present day computational capabilities are not fast enough to be used for 3-D time-stepped finite element analysis (FEA) of permanent-magnet eddy-current losses in every day design problems. An analytic approach is suggested to calculate different-harmonics-caused eddy-current losses. The results are compared both with 3-D FEA and measurement results. A comparison between the theoretical and experimental results is reported for an axial-flux two-stator single-rotor machine with no rotor yoke. The method has, however, been used in evaluating permanent-magnet losses also in machines with narrow slot openings where the flux density dips do not penetrate through the whole magnet or in machines having a laminated rotor yoke.

Permanent-Magnet Length Effects in AC Machines

Permanent-magnet synchronous machines (PMSMs) are gaining popularity in the industry and, especially, in distributed generation, for instance in windmill applications. Some of the traditional analytical design principles seem not to be valid for permanent magnets in machine excitation. We report on the effects of the permanent-magnet length in machine design.

Guidelines for Designing Concentrated Winding Fractional Slot Permanent Magnet Machines

The paper discusses the guidelines for designing concentrated winding fractional slot permanent magnet machines. The winding factor and different slot and pole combinations are studied. Various low-speed high-torque permanent magnet synchronous motors with concentrated windings and with different slot and pole combinations are calculated analytically and by applying the finite element method (Flux2D¿ by Cedrat). All the motors calculated in this study have the same frame size, air-gap diameter, air-gap length and the same amount of permanent magnet material.

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.

Comparison between models for eddy-current loss calculations in rotor surface-mounted permanent magnets

Permanent magnet losses are important from the magnet material wellbeing point of view. Ignoring the permanent magnet losses in the machine design may lead to partial or full demagnetization and finally malfunction of the whole machine. Permanent magnet loss calculations are always quite difficult. The primary purpose of the present paper is the comparison of the empirical formulas of the eddy current loss estimation in permanent magnets on PMSM. Then the calculation results are compared with some calculated values resulting from FEM simulations. Comparison of the results will be discussed.

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.

Local Heat Flux Measurement in a Permanent Magnet Motor at No Load

Heat transfer is a limiting factor in the performance of electrical machines. Measuring the heat flux in an electrical machine is traditionally carried out indirectly with temperature measurements as there are only a few sensors for heat flux measurements. This paper describes a new experimental method to measure the local heat flux inside an electrical machine. The measurement was proven successful in the air gap of the permanent magnet machine, 37 kW 2400 min-1, under an influence of the air gap magnetic flux. The heat flux was measured by using sensors based on the transverse Seebeck effect. The test machine was an axial flux permanent magnet machine with two stator stacks and one internal, ironless rotor disc. A gradient heat flux sensor was installed in the air gap on the stator side. Local Nusselt and Reynolds numbers were calculated according to the measured heat flux results and compared with the results given by traditional methods to verify the new measurement method.