Design and Analysis of a Height-Adjustable Multirelay Wireless Power Transfer System for Desktop Charging

In recent years, desktop wireless charging has attracted more and more attention. To realize smart home systems and address the safety hazards posed by sockets while also accommodating the diverse usage preferences of different consumers, this article proposes a height-adjustable multirelay wireless power transfer (WPT) system for desktop charging. The transmit (Tx) coil is embedded into the wall, and the desktop is perpendicular to the wall. Two relay coils are used to modify the power transfer pathway and adjust the height of desktop. Then, the circuit model of the proposed magnetic coupler has been built. The cross-coupling issue has been analyzed in detail, and the variable coupling coefficients and load resistance could result in the capacitive-inductive shifts of the impedance angle. To solve the cross-coupling issue, the circuit impedance is designed to operate in the inductive state, combined with the specially designed automatic tuning assist circuit (ATAC) module, the circuit’s impedance angle is fixed at 5° with a slight inductive characteristic, thereby enabling near zero-phase angle (ZPA) and zero-voltage switching (ZVS) operations, irrespective of variations in coupling coefficients and load resistance, and without necessitating dynamic real-time monitoring components. The effects of the distance between coils, the number of relay coils, and the parasitic resistances of each coil have been analyzed in detail. The pickup was placed at four different positions to verify the effectiveness of the proposed method. The experimental prototype has been built, and the ZVS and near ZPA (with a power factor of 0.996) features have also been substantiated through experimental verification. The system achieves a maximum output power of 120 W (79.5%) and a peak efficiency of 91.6% (10.28 W).