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This paper addresses the torque production and losses of concentrated winding permanent magnet motors. These synchronous motors having either semi-closed slots or open slots with two different rotor structures are studied. The rotors have either embedded magnets or surface magnets. Embedded magnet rotors are in some cases easier to manufacture than surface magnet rotors, and therefore, it was in the authors' interest to study and compare these two basic constructions. In open slot concentrated winding motors, it is possible to use prefabricated coils, which leads to low-cost and fast stator winding manufacturing. Hence, this stator type is the most interesting one to be studied. Different slot and pole combinations are considered based on the finite element analysis (Flux2D by Cedrat is employed in the computations). Index Terms--Concentrated winding, embedded magnets, open slots, permanent magnet motor, rotor surface magnets, semi-closed slots.

A lumped-parameter-based thermal analysis applicable to radial-flux electrical machines with a high power density is presented. The modeling strategies using T-equivalent lumped-parameter blocks as well as conventionally defined thermal resistances are discussed. Special attention is paid to the modeling of the convective heat transfer in the air gap of radial-flux electrical machines at different rotational speeds. A brief overview of the evaluation of different loss components is given. The performance of the developed thermal model was verified by comparing the calculated temperature values with the measurements in three different applications. Index Terms--Electrical machines, loss modeling, thermal analysis, thermal resistance network.

An algorithm for compensating island network voltage unsymmetricity with a direct torque control modulation-based scalar-controlled power conditioning system is introduced and experimentally verified. The proposed method consists of two separate stages where at first the unsymmetricity is detected and then a compensating negative-sequence system is calculated. Experimental results show that the proposed method fully compensates the voltage unsymmetricity resulting from unbalanced load. Both the magnitude and the phase angle unsymmetricity are compensated. Index Terms--DC-AC power conversion, power converters, unbalanced load.

In modeling axial field machines, three-dimensional (3-D) finite-element method (FEM) models are required in accurate computations. However, 3-D FEM analysis is generally too lime consuming in industrial use. In order to evaluate the performance of the axial flux machine rapidly, an analytical design program that uses quasi-3-D computation is developed. In this paper the main features of the developed program are illustrated. Results given by the program are verified with two-dimensional and 3-D finite element computations and measurements. According In the results, it is possible to evaluate the performance of the surface-mounted axial flux PM machine with reasonable accuracy via an analytical model using quasi-3-D computation. Index Terms--Analytical modeling, axial flux permanent. magnet (PM) synchronous machine. PM machines.

The basic direct torque control (DTC) principle is to rotate the flux linkage forward, if the torque must be increased, and reverse, if the forque must be decreased. The torque is, however, increased only up to a maximum torque of the machine, which corresponds to a load angle of about 90[degrees] in a synchronous machine. This paper presents a method to overcome the possible loss of synchronism when using DTC. This requires either that the rotor angle is measured or estimated. Both of these cases are considered. Simulation and laboratory results are presented to show the effectiveness of the presented method. Index Terms--Estimation, rotating machine stability, synchronous motor drives.

An improved integration method is presented for the estimation of the stator flux linkage for speed- and position-sensorless direct-torque-controlled ac machine drives. The method is based on monitoring the scalar product of the estimated stator flux linkage and the measured stator current. The ac part of the scalar product is extracted using filtering and the correction for the estimated stator flux linkage is formed from that part. Adequate performance is obtained by using simple low-pass filtering. By using adaptive filtering in the extraction, the performance of the drive is excellent. Both simulation and laboratory test results are presented, which show that the presented method works well both in steady state and in transients. Index Terms--AC motor drives, estimation, integrators.

A numerical analysis of rotor losses in a medium speed direct torque controlled permanent-magnet synchronous motor (PMSM) is presented. The calculation of stator currents at no-load and at rated torque was performed by using a DSP-based emulator, which simulates the performance of a real direct torque controlled PMSM. The emulated stator currents were used in the two-dimensional finite-element method analysis where the rotor losses were calculated. It is shown that in the medium speed direct torque controlled PMSM, the rotor losses are considerably higher when operating at no-load compared to rated torque operation at the same rotation speed. Calculated rotor losses are compared to the measured no-load losses of the direct torque controlled PMSM at 7500 rpm. Index Terms--Eddy currents, finite-element method, permanent-magnet motor, rotor losses.