Influence of Flux Optimization on the Harmonic Losses in an Induction Machine for Traction Drives

Abstract:
Increasing the overall efficiency of a traction system consisting of voltage source inverter and induction motor requires exact knowledge of loss components in the drive. Especially with induction machines the harmonic losses can have a significant influence on the total losses of the traction motor. Using a field oriented control with flux weakening at partial load enables reduction of fundamental losses but has to be treated differentiating concerning harmonic losses depending on the actual operating point and the used pulse pattern. In this paper the interrelation of flux optimization at partial load, usage of different pulse patterns and motor efficiency will be demonstrated for a tram drive. Initial a fast and accurate method for analytical calculation of the harmonic losses will be outlined which enables determination of joule losses and iron losses in the stator and the rotor of an induction machine. Using this model the harmonic loss components are identified and analyzed depending on the operating point and the modulation strategy of the inverter.