Drago Ban

Analytical calculation of magnetic field distribution in the slotted air gap of a surface permanent-magnet motor using complex relative air-gap permeance

We present an analytical method for calculation of no-load magnetic field distribution in the slotted air gap of a surface permanent-magnet (PM) motor with radial or parallel magnetization. The method introduces the notion of complex relative air-gap permeance, calculated from the conformal transformation of the slot geometry, to take into account the effect of slotting. As a result, an accurate solution of both radial and tangential components of the flux density can be obtained which shows excellent agreement with the results of finite-element simulations. As an example of the effectiveness of the model, we present calculations of the back electromotive force and the cogging torque waveforms in a surface PM motor.

Analytical Solution for Cogging Torque in Surface Permanent-Magnet Motors Using Conformal Mapping

We present an analytical method for the calculation of cogging torque in surface permanent-magnet (PM) motors. The cogging torque is calculated by integrating the Maxwell stress tensor inside the air gap. The principle of complex relative air-gap permeance derived from conformal transformation of the slot geometry is used to take into account the effect of slotting and to calculate the radial and tangential components of the air-gap flux density required for integration of the tangential component of the Maxwell stress tensor. We implemented the proposed analytical solution on a 7-kW four-pole surface PM motor and compared the results with finite-element solutions. We present an example of finding the optimal magnet angular span to yield minimum cogging torque as an example of the effectiveness of the method.

Turbogenerator end-winding leakage inductance calculation using a 3-D analytical approach based on the solution of Neumann Integrals

An analytical technique that can be effectively used for the calculation of the end-winding leakage inductance of a turbogenerator has been presented. It is based on a three-dimensional geometric model of the end-winding region in which each coil is modeled as a set of serially connected straight filaments. The calculation of the mutual inductance of the end coils is based on the multiple solutions of the Neumann integral. The method also accounts for the influence of stator core iron on the end-winding leakage inductance by using the method of images. The results of the calculations have been compared with the measured values of the leakage inductance for 247-MVA turbogenerator manufactured by KONCAR Generators and Motors Inc., Zagreb, Croatia. The principle of the end-winding leakage inductance calculation described herein can be effectively used for other types of machines and windings as well.

Analytical Solution for Electromagnetic Torque in Surface Permanent-Magnet Motors Using Conformal Mapping

We present an analytical method for the calculation of electromagnetic torque in surface permanent-magnet (PM) motors. Our method uses conformal mapping to calculate the electromagnetic torque by integrating the Maxwell stress tensor inside the air gap. It uses the radial and tangential components of the flux density in the slotted air-gap produced by the currents flowing in the three-phase armature winding. We demonstrate our analytical solution on a 7-kW four-pole surface PM motor and compare the results with finite-element solutions. We present the results for various angular spans of permanent magnets and various sizes of the slot opening to confirm the validity of the analytical approach.

Calculation of Unbalanced Magnetic Pull in a Salient-Pole Synchronous Generator Using Finite-Element Method and Measured Shaft Orbit

In this paper, the unbalanced magnetic forces which act upon the rotor of a salient-pole synchronous generator due to eccentric motion of the rotor shaft in the presence of magnetic field in no-load and loaded condition are calculated using the finite-element method. The displacement of the rotor is modeled using the actual shaft orbit measured on a 5-MVA salient-pole generator driven by a gas turbine in a cogeneration plant. The influences of the stator winding parallel paths and the rotor damper winding on attenuation of unbalanced magnetic pull are analyzed using the finite-element method. It is shown that under linear conditions the correlations between separate harmonic components of the shaft orbit, the resulting harmonic components of the unbalanced magnetic pull and the induced stator winding currents can be established in both the no-load and loaded condition.

Design optimization of interior permanent magnet (IPM) motors with maximized torque output in the entire speed range

A multiobjective optimization procedure for the design of interior PM motors based on differential evolution algorithm is presented. A comparative analysis has been carried out for the optimized 5 kW, 50 kW and 200 kW IPM motors with two and three layers of cavities in the rotor to show design trade-offs between goals to minimize the motor volume while maximizing the power output in the field weakening regime with the back emf constraint as the main limiting factor in the design. The finite element method has been used to calculate the motor parameters during the optimization process. The effectiveness of the proposed design methodology has been shown on a 1.65 kW IPM motor with two layers of cavities in the rotor for which a prototype has been built and tested

Turbogenerator end winding leakage inductance calculation using a 3-D analytical approach based on the solution of Neumann integrals

An analytical technique that can be effectively used for the calculation of the end winding leakage inductance of a turbogenerator has been presented. It is based on a 3-D geometric model of the end winding region in which each coil is modeled as a set of serially connected straight filaments. The calculation of the mutual inductance of the end coils is based on the multiple solutions of the Neumann integral. The method also accounts for the influence of stator core iron on the end winding leakage inductance by using the method of images. The results of the calculations have been compared with the measured values of the leakage inductance for 247 MVA turbogenerator manufactured by KONCAR Generators and Motors Inc., Zagreb, Croatia. The principle of the end winding leakage inductance calculation described can be effectively used for other types of machines and windings as well.

THE APPLICATION OF FINITE ELEMENT METHOD FOR MORE ACCURATE CALCULATION AND ANALYSIS OF TURBOGENERATOR PARAMETERS

The paper describes a computation of basic electromagnetic parameters of a turbogenerator using 2D finite element method with completely automated preprocessing. The results obtained by 2D method are compared to the ones obtained by classical (analytical) method and to the measured values from tests carried out on a 194 MVA turbogenerator manufactured by KONCAR-Generatori, Zagreb, Croatia. It appears that finite element method combined with analytical method gives more accurate results than analytical method and that the computation time can be quite acceptable.

The behaviour of the LSPMSM in asynchronous operation

The paper proposes a study of synchronization capability of line-start permanent magnet synchronous motor with small saliency ratio and very high cage resistance. The exemplified method is for a motor with the rated power of 3.5 kW, the synchronous speed of 3000 rpm, and the saliency ratio of 1.08.

Calculation of unbalanced magnetic pull in a salient-pole synchronous generator

The unbalanced magnetic forces which act upon the rotor of a salient-pole synchronous generator due to eccentric motion of the rotor shaft in the presence of magnetic field originating from the field current in no-load operation have been calculated using finite-element method. The displacement of the rotor has been modeled using the actual shaft orbit recorded on a 5 MVA salient-pole generator driven by a gas turbine in a cogeneration plant. The results indicate that a variation of unbalanced forces in no-load operation at rated voltage occurs at the precession frequency of 25 Hz with maximum force of 2.32 kN.