Ph. K. Sattler

Nature of the equivalent magnetizing current for the force calculation

The physical and the mathematical meaning of the equivalent magnetizing current method is clarified. It is proved that the method is the same as the method of Maxwell stress for the total force, but different for local force computation. Different computational procedures are analyzed. Another procedure is proposed, which makes it possible to compute either the total or the local force with an improved accuracy. >

Procedure for the numerical computation of mechanical vibrations in electrical machines

The authors describe a way to calculate the mechanical vibrations of the stator and case in the two-dimensional modeling of electrical machines. The mechanical vibrations are the result of the magnetic forces acting on the surfaces of the stator. The vibration calculation consists of three steps: (1) finite element method calculation of the magnetic field; (2) local force density calculation and its Fourier decomposition; and (3) calculation of the dynamic displacements of the electrical machines stator and case. >

Force calculation with analytical accuracy in the finite element based computational magnetostatics

A method that can improve the accuracy of force calculations by the Maxwell stress method is presented. The local fields on the stress contour is obtained from the original finite element solution by subtracting the field of the discretization current sheet. Every field point has a contribution in the force calculation. The results show that this method is independent of the contour. The contour can be laid on the surface of the iron, and that allows the surface force density to be calculated. >

Sensitivity analysis of the nodal position in the adaptive refinement of finite element meshes

A sensitivity analysis has been used to determine the energy perturbation of the nodal position in a finite-element mesh. The sensitivity of the nodal position gives the refinement indication and can therefore be used in the adaptive procedure. This method provides an alternative approach to adaptive mesh generation and is illustrated by numerical examples. >

An accelerated Newton-Raphson method associated with the ICCG algorithm

An accelerated Newton-Raphson (NR) method associated with the ICCG (incomplete Cholesky conjugate gradient) algorithm is proposed, which can reduce the global computational time to 50-60% of the standard method. Numerical examples are tested, and precision and convergence are analyzed. The method is suitable for implementation in finite-element software which uses the NR for the nonlinear solution and the ICCG for the linear system. >

Numerical calculation of the dynamic behaviour of electromagnetic actuators

The authors describe a numerical method for calculating the dynamic behavior of electromagnetic actuators supplied by voltage or current pulses of any waveform. Moving parts, eddy currents caused by the time variable, and the relative velocity to the field, as well as strong saturation of the ferromagnetic materials are taken into account. The numerical solution is based on the finite-difference method with acceleration of convergence and the time-stepping method. In order to always obtain a tridiagonal system matrix, even by impressed voltage, a double iterative solution is used. An application example is given for a system used in electromagnetic striking tools with a large displacement of the moving part. >

Optimizing of the Efficiency by the Control of Inverter-Fed Induction Machines Especially Regarding Saturation and Heat Effects 1

Abstract The operation of inverter-fed induction motors at optimal efficiency and low current consumption demands an adaption of the magnetic flux to the several loads. The flux-torque characteristic suited for this purpose cannot generally be predicted for any machine, its derivation rather demands a detailed knowledge of the saturation and the additional losses. The paper presents an improved equivalent circuit taking these effects into account and derives for a given test machine a control characteristic producing the desired performance. If any method of indirect flux control is applied, the load dependant rotor temperature appears as considerable disturbance variable. An observer is presented which estimates the temperature without additional sensors using measured terminal voltage and current.

Lineare Wirbelstrombremse mit ferromagnetischer Reaktionsschiene

ÜbersichtLineare Wirbelstrombremsen mit ferromagnetischer Reaktionsschiene werden bei Hochgeschwindigkeitsbahnen eingesetzt. Da Modellversuche zur Optimierung sehr aufwendig sind, wird hier die Entwicklung eines Rechenprogramms zur dreidimensionalen Berechnung vorgestellt, bei dem auch die Eisensättigung berücksichtigt ist. Die Berechnung erfolgt in einem zum Erregersystem ruhenden Koordinatensystem und wegen der ungünstigen Eigenschaften des Gleichungssystems ergeben sich zunächst keine stabilen physikalisch sinnvollen Lösungen. Erst die Einführung des sogenannten “Upwind”-Operators ermöglicht eine befriedigende Lösung des Problems. Wie der Vergleich mit Prüfstandsmessungen zeigt, gibt das Rechenprogramm hinreichend genau die wirklichen Verhältnisse wieder.ContentsLinear eddy-current brakes with ferromagnetic reaction rails are used for modern high-speed trains. Since optimization by tests on models is very expensive a numerical solution of the three-dimensional field equations has been developed taking the saturation of the iron under consideration. For the calculation a coordinate system fixed to the field coils is used and because of the disadvantageous property of the equations result in the beginning solutions which are instable or wrong from the physical, point o view. The introduction of the socalled upwind-operator renders possible a satisfying solution of the problem. The calculated values are in sufficient accordance with the measured values of a bench test.

Massivrotoren mit Kurzschlußkäfig und gerillter Oberfläche für Asynchronmaschinen an verschiedenen Umrichtersystemen

ÜbersichtDie Rotoren schnellaufender Asynchronmaschinen können im Falle mechanischer Festigkeitsprobleme als Massivrotoren mit Kurzschlußkäfig und tangential gerillter Oberfläche ausgeführt werden. Die Rillungsstruktur dient dabei der Unterdrückung von Wirbelstromverlusten im Eisen, die vorwiegend als Oberflächenverluste auftreten. Im Aufsatz werden Rechenverfahren angegeben, die die Nachbildung mit gerilltem Massivrotor versehener Maschinen bei Netz- und Umrichterspeisung gestatten. Schwerpunkte der Betrachtungen sind die rechnerische Ermittlung der Wirbelstromverluste im Rotoreisen und die Optimierung der Rillungsabmessungen. Der Einfluß verschiedener Umrichtersysteme, und zwar strom- und spannungseinprägender Zwischenkreisumrichter, auf die Maschinenverluste wird gezeigt.ContentsWith regard to mechanical stresses rotors of high speed induction motors can be constructed from solid iron with squirrel cage and tangentially grooved surface. The grooves cause a reduction of the eddy current losses in the rotor surface. In this paper a method is described to calculate the behaviour of solid rotor machines with sinusoidal or inverter supply. Especially the iron losses are calculated and the groove dimensions are designed. The influence of current source and voltage source inverters upon the machine losses is shown.

Experimental and Theoretical Investigations Concerning the Design of Induction Machines, Especially Machines with High Power Density with Respect to the Inverter Supply and Speed Regulation*

Abstract The special reasons concerning inverter fed induction machine design are described. The design may be quite different from the design of a network fed induction machine. Small numbers of slots with regard to high power density are possible. The ripple torque arrising from rectangular current blocks gives high mechanical stresses for certain speeds. Test models with normal laminated and solid rotor fed by inverter were measured, also equation for the steady state and dynamic behaviour were established. Test results and calculation are in good agreement.