An investigation of cross-coupling for magnetically coupled wireless power transfer

The effects of parasitic cross-couplings in 4-coil wireless power transfer (WPT) systems are investigated. In WPT applications, the available space for the receive coil is limited in comparison to that of the transmit coil. This physical limitation, therefore, results in different sizes for transmit and receive coils. However, asymmetry in the dimensions of the coupled coils can result in significant parasitic effects. Coupling between coil₁ and coil₃ (k₁₃), and coupling between coil₂ and coil₄ (k₂₄) cause deviation of optimal frequency and degradation of efficiency. Coupling between coil₁ and coil₄ affects only the efficiency degradation, with independence of k₁₃ and k₂₄. To reduce parasitic effects, a capacitive compensation method is proposed. This method can compensate for the unwanted shift in peak efficiency due to parasitic effects by adding capacitance to coil₁. In our work, the proposed method increased the efficiency from 69.5% to 85.3% at the desired operating frequency.