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This study presents a new coupled inductor magnetic structure with variable coupling coefficient. The new symmetrical magnetic structure is composed of stacked ferrite cores, where control legs are placed in the centre of the core structure, on equal distances from the outer legs. In that way, the coupling coefficient is controlled by the means of a DC current. The DC control flux is confined only to the control legs and it is equally balanced in both of the outer legs. Distribution of the control DC flux in the proposed structure is verified applying finite element analysis simulation of the three-dimensional model. Electrical properties of the new variable coupled inductor are derived applying analytical modelling and verified by experiments. Maximal variations of the controlled coupling coefficient value in respect to the different value of the leakage flux are obtained and presented. Design and experimental results are presented for application in an interleaved boost converter with a variable coupled inductor, achieving boundary conduction mode over a wide load variation.

Summary In this paper, a design of the compensation network with a variable inductor is proposed, considering a wide variation of the coupling coefficient in the inductive power transfer (IPT). The characteristics of the proposed compensation network are analyzed with respect to the variable antenna coupling conditions. The realization of the zero voltage switching (ZVS) and the reactive power demand are discussed through the theoretical deduction and numerical simulation. Influence of the variable inductor on the compensation network characteristics is examined in detail, and the control algorithm for achieving the coupling independent constant output voltage is proposed. Detailed steps to design a prototype fulfilling all performance requirements are given. Verification of the proposed method was carried out on the experimental model. Recorded output voltage variation is within 5% over the wide coupling range, implying a quite well characteristic of the coupling independent voltage output. Experimental results match well with the calculations, validating the rightness of the proposed variable inductor tuning method.

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