Measurement method of high-frequency winding loss in gapped inductors based on magnetic field equivalence

High-permeability cores, such as ferrite, can increase power transfer efficiency and are often designed to be gapped to mitigate magnetic saturation. The fringing effect caused by the air-gap increases the winding loss of the gapped inductor. The key to accurately evaluating its winding loss is extracting that from the total loss. This paper introduces a method for measuring the winding loss of gapped inductors based on magnetic field equivalence. The gapless inductor with the winding for equivalent air-gap was constructed to characterize the magnetic field within the core window of the gapped inductor, and the auxiliary winding was used to replace the winding of the gapped inductor to generate the equivalent magnetizing magnetomotive force. Based on the transformer winding short-circuit method with the small-signal impedance test, the winding loss was separated from the core loss. After the resistance of auxiliary winding was measured by using an air-core inductor, the winding loss of the gapped inductor was consequently obtained. The proposed scheme was applied to inductors made of different sizes and structures, and the measured errors were within 20% in the range of 100 kHz to 1MHz. The winding loss had a steeper growth tendency in this range than the lower frequency, so the proposed method is effective at high switching frequencies especially.