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In this paper, the results of a European efficiency measurement for a 250-kW high-efficiency grid-connected solar inverter are presented. The efficiency measurements are performed both by electrical input–output and calorimetric methods. Two measurement series with input voltage levels of 500 and 750 VDC are carried out. An open- and balance-type calorimeter system that can measure power losses up to 30 kW is introduced and verified by resistor tests. The measurement results and their uncertainty are analyzed and discussed. [ABSTRACT FROM AUTHOR]

Simulated junction temperatures of the semiconductor switches of a three-level Neutral Point Clamped (NPC) inverter applying Direct Torque Control (DTC) are addressed in this paper. The temperatures are defined by using simple power loss calculation methods, and the thermal network of the component is considered as a one-dimensional partial fraction RC network. The emphasis of this paper is on unequal thermal stressing between the different components of the NPC DTC inverter. Verification of the model is based on the use of well-known calculation and estimation methods. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

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 time consuming in industrial use. In order to evaluate the performance of the axial flux machine rapidly, an analytical design pro- gram 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 to the results, it is possible to evaluate the performance of the surface-mounts axial flux PM machine with reasonable accuracy via an analytical model using quasi-3-D computation. [ABSTRACT FROM AUTHOR]

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 when 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. [ABSTRACT FROM AUTHOR]

The basic direct torque control (DTC) principle is to rotate the flux linkage forward, if the torque must be increased, and reverse, if the torque must be decreased. The torque is, however, in- creased only upto a maximum torque of the machine, which corresponds to a load angle of about 900 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]