Herbert Weh

Design concepts and force generation in inverter-fed synchronous machines with permanent magnet excitation

Synchronous machines with permanent magnet excitation can be designed for high power densities and low losses. This paper initially provides an overview of various machine concepts. Constructions with flux concentration and others with air gap oriented magnets are described. A comparison provides dimensioning rules for designs with minimal amounts of permanent magnetic material. On the basis of this, measures are outlined which improve the thrust density and further reduce the losses. These are: 1. design of machine and current inverter with more than three independent phases to achieve a square wave shape for the field and current; 2. employment of appropriately laminated poles to reduce the armature reaction in conjunction with measures which increase flux concentration. The effectiveness of these measures is demonstrated with the use of an example. For a current loading of 100 kA/m, a mean force density of 100 kN/m2is attainable. In conclusion, a machine concept is described which allows control of the exciter field from the armature, thus enabling a more flexible adaptation to the drive requirements.

Design of an integrated propulsion, guidance, and levitation system by magnetically excited transverse flux linear motor (TFM-LM)

A magnetically levitated vehicle dedicated for transportation systems requires propulsion, guidance, and levitation forces. The components used to generate these forces, such as linear motors and magnets, must have less mass especially because the magnetically levitated vehicle has to carry its own linear motor and magnet. In this paper, an integrated propulsion, guidance, and levitation system by magnetically excited transverse flux linear motor (TFM-LM) with high force and high efficiency is introduced. Analytical equations with one-dimensional magnetic equivalent circuit are developed to predict the propulsion force and to guide the design of TFM-LM. A three-dimensional (3-D) finite-element (FE) program calculates the propulsion force, the guidance force, and the levitation force of TFM-LM also, in order to verify the given specification. To verify the results of 3-D FE calculation, the computed propulsion force, guidance force, and levitation force are compared with the experimentally measured forces detected on the experimental setup. The calculated and measured performances of TFM-LM reveal a high potential of mass reduction for magnetic-levitated vehicles.

FIELD ANALYSIS FOR A HIGH-POWER, HIGH-SPEED PERMANENT MAGNET SYNCHRONOUS MACHINE OF THE DISC CONSTRUCTION TYPE

ABSTRACT The disc construction of the synchronous machine is advantageous for applications where low loss and high power density are desired. These requirements are met by permanent magnet machines designed to operate at high speed and frequencies up to 600 Hz. The stator teeth are made with a compacted iron powder-synthetic resin mixture using powder metallurgy and thus have low iron losses at this frequency level. This mixture has a lower magnetic permeability than steel sheets. This paper presents an analytical field calculation method which considers the finite permeability of the stator iron and the non-homogenity of the field along the magnet height caused by the magnet leakage. The analysis is given for a machine configuration with two rotors. This topic is still the object of extensive technological and theoretical studies. The method presented can be modified to apply to other constructional forms of permanent magnet machines. The derived expressions for the field are used to investigate the infl...

A method of modeling permanent magnets for analytical approach to electrical machinery

ContentsA method of simulating permanent magnets in analytical approach for the transfer-matrix-method is given. The method is suited for deriving analytical expressions of the magnetic fields and electromagnetic forces in electrical machines containing permanent magnets. The method was applied to the analysis of a long-stator linear synchronous motor with permanent magnet excitation. Measurements of the forces in the 150-pole Samarium-Cobalt type linear synchronous motor for electric propulsion were used to verify this permanent magnet modeling analysis. Comparison with experimentally obtained results shows a very good agreement.ÜbersichtEine Methode zur Simulation von Permanentmagneten für eine analytische Behandlung mit der Transfer-Matrix-Methode wird dargestellt. Die Methode ist dafür geeignet, analytische Ausdrücke von magnetischen Feldern und elektromagnetischen Kräften in elektrischen Maschinen mit Permanentmagneterregung abzuleiten. Die Methode wurde auf die Analyse eines permanentmagneterregten synchronen Langstator-Linearmotors angewandt. Messungen der Kräfte an einem synchronen Linearmotor mit 150 Seltenerden-Kobalt-Erregermagneten wurden herangezogen, um das in dieser Arbeit dargestellte analytische Berechnungsverfahren zu überprüfen. Beim Vergleich mit den experimentell ermittelten Werten zeigt sich eine gute Übereinstimmung.

Numerische Berechnung magnetischer Felder und Kräfte

ÜbersichtDie Berechnung magnetischer Felder kann heute mit Hilfe der Differenzenrechnung auf großen Digitalrechnern erfolgen. Die hierfür notwendigen Differenzengleichungen werden für kartesische und polare Gitternetzwerke hergeleitet. Zur Konvergenzbeschleunigung werden drei Methoden der Blockrelaxation angegeben. Als Beispiel werden die magnetischen Kräfte auf den Pol einer Gleichstrommaschine berechnet.ContentsMagnetic fields can now-a-days be calculated on large digital computers using difference equations. These equations are derivated for cartesian and polar grid-systems. Three methods of relaxation are specified to achieve an acceleration of convergence. To show the efficiency the magnetic forces at the pole of a d-c-machine are calculated.

Analytische Bestimmung des Nutungseinflusses auf die Feldverteilung und die Wirbelstromverluste in dauermagneterregten Synchronmaschinen

ÜbersichtAusgehend von einem vereinfachten Modell wird ein analytisches Rechenverfahren entwickelt, das den Nutungseinfluß auf die Feldverteilung im Luftspalt und im Magnetbereich einer mit Permanentmagneten erregten Synchronmaschine erfaßt. Das Verfahren liefert die Leerlaufinduktionsverteilung im Luftspalt und im Magnetbereich sowie die Wirbelstromverluste in den Magneten. Die Genauigkeit des Verfahrens wird durch einen Vergleich mit Meßergebnissen und numerischen Feldberechnungen überprüft. Die Abhängigkeit der Wirbelstromverluste in den Magneten von verschiedenen Entwurfsparametern wird angegeben und diskutiert.ContentsThe paper presents an analytical method for calculating the field distribution in the airgap and magnet regions of permanent-magnet synchronous machines. The analysis is based on a symplified model which considers the slotting structure of the stator. The resulting distribution of the no load flux density is utilized to find an expression for the eddy current losses in the magnets due to the tooth harmonic fields. Comparison with test results obtained from experimental model and with numerical field calculation shows close agreement. The influence of some design parameters on the eddy current losses in the magnets is investigated.

Development of Rotating Type Transverse Flux Machine

This paper describes the design and development of rotating type transverse flux motors (TFM) excited by permanent magnets. In-plane phase construction and axial phase arrangement are compared each other and many variants of them are introduced by combining soft magnetic composite (SMC) core and laminated steel core. Magnetic field is analyzed by three-dimensional equivalent magnetic circuit network (EMCN) method with the help of two-dimensional finite element analysis. The experimental results of prototyped motor compared with the analysis ones, and show the possibility of the suggested motor as a direct drive application requiring relatively low speed and high torque.

MACHINE CONSTANTS AND DESIGN CONSIDERATIONS OF A HIGH-POWER, HIGH-SPEED PERMANENT MAGNET DISC TYPE SYNCHRONOUS MACHINE

Abstract Expressions for the element of the equivalent circuit of a disc type synchronous machine excited with permanent magnets are developed in terms of the principal machine dimensions. The calculations are based on a field analysis given by the authors in a previous paper using a linearised model The internal leakage of the magnets and the finite permeability of the stator teeth are taken into consideration. The resulting expressions are useful in predicting the machine performance, in examining the influence of the main design parameters and are suitable for optimization purposes.

Numerische Magnetfeldberechnung durch Diskretisierungsverfahren

ÜbersichtZur Berechnung von Magnetfeldern mit beliebigen Materialverteilungen und beliebigen Anregungen wird die Differentialgleichung für das Vektorpotential angegeben und mit Hilfe der finiten Elemente Methode in ein algebraisches Gleichungssystem umgewandelt. Die Anwendung des Durchflutungsgesetzes führt wesentlich einfacher zu identischen Bestimmungsgleichungen. Eine Berücksichtigung der Nichtlinearitäten geschieht mit dem Newton Raphson Verfahren. Für den Sonderfall von anisotropen Stoffeigenschaften werden die Transformationsmatrizen angegeben. Zum Schluß wird ein Lösungsverfahren für schwach besetzte Gleichungssysteme beschrieben.ContentsTo calculate magnetic fields with arbitrary material distributions and excitations the given vector potential differential equation is transformed into an algebraic system of equations (Finite Element Method). The application of the ampere turns rule leads (considerably more simply) to identical equations. Allowance for non-linearities is provided by the Newton-Raphson method. The transformation matrices are given for anisotropic material properties. Finally, a solver for sparsely populated matrices is deseribed.

ANALYSIS AND CHARACTERISTICS OF THE DISK-ROTOR INDUCTION MOTOR

ABSTRACT The induction motor with an axial air gap and a flat homogeneous disk-rotor shows some performance characteristics that are superior to conventional induction machines. Large rotational speeds and small moments of inertia promise high power densities and small mechanical time constants. This paper presents an analytical model which includes the two-dimensional current distribution in the secondary, thus extending a previous simplified treatment. The model also accounts for fringing phenomena and can handle a secondary with a radius-dependent thickness and conductivity. Numerical results for the local distributions of field, current density, and forces; a typical torque-speed characteristic; a current locus; and an equivalent circuit are presented and serve as a basis for discussion and comparison.