A NEW COMPUTER-AIDED METHOD FOR THE EFFICIENCY MEASUREMENT OF LOW-LOSS TRANSFORMERS AND INDUCTORS UNDER NONSINUSOIDAL OPERATION

The measurement of voltages, currents and losses of saturated magnetic devices under nonsinusoidal conditions is not well understood, becaus e the principle of superposition does not apply. The complexity of the task is increased by the fact that internally generated harmonic curr ents can be compensated by externally applied currents of either the s ame harmonic frequency or of other harmonic frequencies. In other word s a transformation of fundamental power to harmonic power, and vice ve rsa, takes place. In addition the flux-density waveshape varies -and t herefore also the iron-core losses- as the harmonic phase shift of the externally applied harmonic voltage changes, although the percentage of the harmonic amplitude remains constant. It is the first objective of this paper to assemble a computer-aided testing circuit which enabl es the investigation of the variation of the iron-core losses with the amplitude of the fundamental flux density (B) over cap(1), the amplit ude of the nu(th) harmonic (B) over cap nu, the harmonic order nu and the phase shift phi(nu) of the nu(th) harmonic with respect to the fun damental. Phase-factor functions which reflect the dependency of the i ron-core losses on the harmonic phase shift phi(nu)- are directly meas ured for given Epstein frame iron-core samples. Thereafter, the effect of these newly defined phase-factor functions on the total transforme r losses is demonstrated. The attenuation of low-frequency (60 to 3,00 0 Hz) flux-density harmonics in inductors is determined, if the core i s biased with fundamental flux density.