Power losses in synchronous reluctance motors

Abstract

V članku smo najprej predstavili osnovne lastnosti, zgradbo in delovanje sinhronskega reluktančnega motorja, nato pa v okviru dvoosne teorije zapisali vezni model obravnavanega električnega stroja. Reluktančni navor omogoča vrtenje rotorja v sinhronizmu z glavnim vrtilnim poljem. Pri takšnem načinu delovanja (sinhronsko vrtenje) je v rotorju gostota magnetnega pretoka vedno enosmerna, kar narekuje brezizguben rotor. Vendar imamo zaradi statorskih utorov spremembo magnetne upornosti zračne reže, kar pri vrtenju povzroči utorske pulzacije magnetnega polja in s tem površinske izgube na rotorju. Na podlagi temeljnih elektromagnetnih zakonitosti smo izpeljali enačbo in z njo ovrednotili površinske izgube na rotorju motorja. Z obremenilnim preizkusom in preskusom prostega teka smo analizirali obratovalne karakteristike in izgube motorja. Kot posledico izgub smo nastalo temperaturno polje v motorju in na njem prikazali v obliki temperaturne slike.The aim of this paper is to present power losses in synchronous reluctance motors (SRM). Generally speaking, this type of motors is an unexcited synchronous machine with stator windings and a stator similar to any regular induction machine. The rotor is cross-laminated and contains flux barriers placed equidistantly around the air gap (Fig. 1). They serve to diminish the quadrature (q-axis) flux flowing between poles and at the same time they permit the direct axis flux to flow largely unimpeded through the poles. On the basis of the Parkćs theory, an impedance model of SRM for stationary operating modes is presented in a matrix form (Eq. 1). Further, the paper devotes special attention to surface power losses. The main flux of synchronous reluctance motors rotates at the same speed as the rotor. The presence of the stator openings gives rise to permeance variations causing a ripple in the main flux (Fig. 2) through which the rotor is driven and resulting in induced losses on the rotor surface. The same is going on on the stator surface due to the permeance variations in the rotor slot opening range. At normal tooth ripple frequencies, only eddy current components of these losses are of any significance and histeresis losses may be ignored. Eqs. (2-5) describe the magnetic flux density distribution and penetration into the rotor. Fundamental electromagnetic equtions (6-8) are used to calculate the eddy current distribution (Eq. 9) on a thin surface layer of a laminated rotor. Surface losses are calculated with Eq. 10 and presented in Figs. (3-4). The measured torque and current characteristics of SRM for asynchronous run are shown in Fig. 5. and for synchronous run in Fig. 7. The principle of the rotor load angle measurement is given in Fig. 6. No-load characteristics of SRM and power losses separation are presented in Fig. 8. Power losses at no-load operation of the measured prototype are separated and given in Table 1. To establish the surface losses impact on rotor temperature variations the temperature measurements (Fig. 9) were made. They are presentedin Table 2. Temperature variations for the SRM stator winding at a nominal load are given in Fig. 11