School of Electrical Engineering, Southwest Jiaotong University, Chengdu 611756, China

For the capacitive wireless power transfer (CWPT) system, the accurate estimation of the pickup detuning degree is the premise for the system to maintain resonance. However, because the induced voltage at the pickup loop of the system cannot be directly observed, it is difficult to estimate the detuning degree of the pickup loop by measuring the phase difference between the induced voltage and the loop current. A CWPT system for indirectly measuring the phase information of the induced voltage at the pickup loop is presented and the detuning degree of the pickup loop is evaluated. Based on the Z parameters, the mathematical model and equivalent circuit of the three-port CWPT system are established. Based on the model, a secondary-side decoupled capacitive coupler is proposed. The errors in the measurement of induced voltage and the estimation of detuning degree are analyzed, and the correction method for the detuning degree of the pickup loop is proposed. A prototype of the proposed CWPT system with secondary-side decoupled coupler is constructed. Experimental results indicate that the estimation error of the detuning degree shall not exceed 1 Ω when the pickup fully tunes, and the estimation error of the detuning degree under the inductive detuning and capacitive detuning conditions shall be less than 2% and 5%, respectively.