Original scientific paperThe paper presents an optimized design of a low mass brushless DC (BLDC) permanent magnet motor for propulsion of an ultra light aircraft. The optimization has been carried out using Differential Evolution algorithm implemented in Matlab combined with SPEED and MotorCAD software packages for electromagnetic and thermal modeling of the BLDC motor using ActiveX technology. The credibility of the models created with SPEED and MotorCAD has been confirmed by comparing the results of simulation and measurement performed on a 12 kW synchronous permanent magnet motor available in the laboratory. The goal of the optimization has been to minimize the weight of the motor under condition that the motor delivers rated power of 15 kW at rated speed of 3000 rpm with hot-spot temperature not exceeding the temperature limits of class F insulation (155 • C). Two optimal BLDC motor designs with slot/pole combinations 12/10 and 18/16 have been obtained. The motor with 18 slots and 16 poles yields the highest torque density with the lowest mass of active parts (copper+laminations+magnets) of only 5.1 kg.Key words: Aircraft, Brushless DC motor, Permanent magnet motor, Optimization, Differential evolution Optimirani projekt elektronički komutiranog motora s trajnim magnetima za pogon ultra lake letjelice. Učlanku je prikazan optimirani projekt elektronički komutiranog motora (EKM) s trajnim magnetima male mase za pogon ultra lake letjelice. Optimizacija je provedena korištenjem algoritma pod nazivom Diferencijalna evolucija koji je primijenjen u Matlabu u kombinaciji s programskim paketima SPEED i MotorCAD za elektromagnetski i termički proračun EKM-a koristeći ActiveX tehnologiju. Vjerodostojnost modela načinjenih u SPEED-u i MotorCAD-u je potvr ena usporedbom rezultata simulacije i mjerenja obavljenih na sinkronom motoru s trajnim magnetima koji je bio na raspolaganju u laboratoriju. Cilj optimizacije je bio minimizirati masu motora pod uvjetom da motor razvija nazivnu snagu 15 kW pri nazivnoj brzini vrtnje 3000 min −1 pričemu temperatura najtoplije točke namota ne smije prijeći granicu odre enu klasom izolacije F (155 • C). Načinjena su dva optimalna projekta EKM-a s kombinacijama broja utora i polova 12/10 i 18/16. Motor s 18 utora i 16 polova postiže najveću gustoću momenta uz najmanju masu aktivnih dijelova (bakar+jezgra+magneti) koja iznosi samo 5,1 kg.

This study describes a method for calculation of transformer short‐circuit voltage using conformal mappings, which map the transformer longitudinal and transverse cross‐section geometry to a unit disk where an analytical solution for magnetic flux density is obtained and then transformed back to the original domain. The short‐circuit voltage is calculated by the integration of the magnetic energy of the leakage field in the windings and the space around windings, excluding the core. This method takes into account windings of different height, the fringing effect at the ends of the windings and any relative position of windings located on the same or different limbs. Also, it is possible to calculate the short‐circuit voltage for multiple windings.

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