Bogdan Funieru

Analytical Calculations of Induced Eddy Currents Losses in the Magnets of Surface Mounted PM Machines With Consideration of Circumferential and Axial Segmentation Effects

This paper presents a method for the calculation of eddy current losses in the permanent magnets, which takes into account the reaction of induced eddy currents. The developed quasi-3-D analytical method considers the effects of axial and circumferential segmentation of magnets. The 2-D time-stepping finite element method and 3-D time harmonic finite element method are used to evaluate the accuracy of the analytical method. A high speed surface-mounted permanent magnet motor with Samarium Cobalt magnets is used for detailed simulations. High-frequency time harmonics of the inverter are considered for analysis of magnet eddy current losses. The novelty of the proposed analytical method is the direct consideration of the reaction of induced eddy currents in the magnets due to travelling and pulsating field waves.

Calculation of eddy current losses in permanent magnets of synchronous machines

Eddy current losses in rotor permanent magnets (PM) of synchronous machines with concentrated windings are calculated for sinusoidal stator currents. Three different calculation methods are compared in the Finite-Element environment: 1) analytical post processing of FE magneto-static data with multi-move and eddy currents calculated from vector potential, 2) direct FE magneto-static method, 3) time stepping with a FE program. From thermal measurements performed on existing prototype motors the losses in magnets are compared based on the temperature rises in the magnets at adiabatic heating.

No-load tests of a 40 kW high-speed bearingless permanent magnet synchronous motor

A 40 kW high-speed bearingless permanent magnet (PM) synchronous motor with surface mounted magnets represents the focus of this paper. The rotor suspension system is composed of a bearingless unit that generates torque and suspends magnetically the non drive end (NDE) and a permanent magnet biased combined axialradial magnetic bearing for the axial and radial active suspension of the drive end (DE). This drive arrangement has been tested with good performances under no-load conditions at its full speed range. Some basic theory of bearingless drives, the motor main parameters and no-load measurements of the drive and levitation system will be presented.

Extended field weakening and overloading of high-torque density permanent magnet motors

The results of an extended field weakening and overloading test for two high-torque density permanent magnet (PM) motors with concentrated stator windings are presented in this paper. The two 45 kW motors were designed for continuous rated power of 45 kW between the rated speed of 1000 min−1 and the maximum speed of 5000 min−1. The concentrated stator winding determines a high harmonics content of the air gap field, thus segmented magnets were used for the rotor in order to reduce the rotor eddy current losses. The water jacket cooling of the stator gives at rated operation a thermal reserve of 30 K at 1000 min-1 to the Thermal Class F limit temperature for the first motor. Thus it is possible to increase the power for the rated speed up to 55.2 kW. The motor has due to the relatively high inductance a good field weakening capability. The measurements confirmed that the field weakening can be extended up to 5 times the rated speed with constant output power of 45 kW. The loss calculation is presented and the calculation results are compared with the measurement results.

Modeling of asymmetrical cables for an accurate calculation of common mode ground currents

The paper deals with modeling methods for asymmetrical cables of speed variable AC motor drives to calculate precisely the common mode ground stator currents. The analytical and numerical calculation of the cable parameters is presented and the results are compared to measurements. An impulse run-time method for the cable parameter evaluation by measurements is proposed.

Analysis of the effect of radial rotor surface grooves on rotor losses of high speed solid rotor induction motor

The effect of the radial rotor surface grooves on rotor losses, in the case of a 3-phase, 4-pole, 24000 rpm, axially slitted solid rotor induction motor has been studied numerically and experimentally. The study shows that through radial grooving of the rotor outer surface and thereby cutting the path for high frequency rotor harmonic currents results in considerable reduction of the rotor eddy current losses. In 2D FEM analysis the grooves are considered by correcting the rotor conductivity in harmonic currents penetration depth area.

Direct Modeling of Motional Eddy Currents in Highly Saturated Solid Conductors by the Magnetic Equivalent Circuit Method

Motional eddy currents are induced in conductors due to a localized vrarrtimesBrarr electric field. Direct modeling of this term by finite-element-based analysis may lead to nonphysical oscillations. In this paper, two modified magnetic equivalent circuit (MEC) methods to calculate motional eddy currents in highly saturated moving solid conductors are presented. The comparison between the results of the proposed methods with the finite-element method (FEM) proves high accuracy of the proposed methods in a wide velocity range for highly saturated solid conductors. The mesh sensitivity analysis shows the higher stability of the calculations of the proposed methods, compared with FEM, as no numerical oscillations occur.

Design of a PM direct drive synchronous generator used in a tidal stream turbine

The design of a direct drive PM synchronous generator for a tidal stream subsea turbine is presented in this paper. The generator design must comply with a set of very narrow restrictions concerning the available volume, the required output, the maximum current of the three-phase marine cable and the inverter maximum voltage. For these reasons the obtained design is not able to completely fulfill the requirements, especially for the case of short time overload. The results show however the feasibility of the concept. With a relatively small correction of the requirements it will be possible to obtain the required results.

Acoustic noise calculation for high-speed permanent-magnet motors

The magnetically excited acoustic noise is calculated for three high-speed permanent-magnet motors with identical stators, but with different rotors. An analytical approach is used for the calculation of the magnetic radial forces. The components of the radial magnetic flux density in the middle of the air gap are determined with the help of finite element method (FEM) static calculations, which allow a decomposition of the air gap field into a Fourier series of flux density waves. The natural bending frequency is calculated using an analytical and alternatively a numerical calculation of a simplified mechanic model. The radial deformation of the stator yoke is calculated and the sound intensity level is calculated for the first 13 tonal frequencies and compared for the three motor configurations.

3D numerical calculation method of electrical machines with time efficient air gap coupling and stabilized torque and force calculation

A calculation method, which allows a time efficient coupling of the machine stator and moving rotor parts and force calculation in electrical machines, dedicated to 3D Finite Element (FE) models, is presented in this paper. The method requires only a single mesh generation at the beginning of the simulation. The applied force calculation method is stabilized, using a whole air gap averaging method, which does not require a special air gap mesh. Standard tetrahedral mesh elements can be used in the air gap, without affecting the torque or force calculation results even for the numerically demanding cogging torque calculation.