Utilization of Virtual Short-Circuit in Wireless Power Transfer System: Mutual Inductance Identification via Second Harmonic

This article discovers the virtual short-circuit characteristic and proposes a novel method to identify the mutual inductance in wireless power transfer systems. When a second harmonic voltage is injected into the inverter's output voltage at the transmitter side, due to the filtering effect of the resonant tank, the input voltage of the uncontrolled rectifier is approximately a square wave with a 50% duty cycle, with only the fundamental component and odd harmonics at the receiver side. The receiver can be considered as a short circuit for the equivalent circuit of the second harmonic. By measuring the second harmonic amplitude of the inverter's output current, the system input impedance of the second harmonic can be obtained. Combined with the coil's self-inductance and resonant capacitor parameters, the mutual inductance can be directly calculated using the impedance formula. The sensitivity analysis verifies that the method is suitable for strong-coupling cases. Compared with traditional methods, the proposed method can identify the mutual inductance online under different operating frequencies within only 150 mu s, and achieve minimal computation, without the physical forced short circuit on the rectifier.