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, because the principle of superposition does not apply. The complexity of the task is increased by the fact that internally generated harmonic currents can be compensated by externally applied currents of either the same harmonic frequency or of other harmonic frequencies. In other words, a transformation of fundamental power to harmonic power, and vice versa, takes place. In addition the flux-density waveshape varies-and therefore 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 enables the investigation of the variation of the iron-core losses with the amplitude of the fundamental flux density Bˆ₁, the amplitude of the ν^th harmonic Bˆ_ν, the harmonic order ν and the phase shift φ_νof the ν ^th harmonic with respect to the fundamental. Phase-factor functions-which reflect the dependency of the iron-core losses on the harmonic phase shift φ_ν-are directly measured for given Epstein frame iron-core samples. Thereafter, the effect of these newly defined phase-factor functions on the total transformer losses is demonstrated. The attenuation of low-frequency (60 to 3,000 Hz) flux-density harmonics in inductors is determined, if the core is biased with fundamental flux density