A Harmonic Suppression-Based System Identification Method for Estimating Output Voltage From the Primary-Side of Wireless Power Transfer

This article presents a primary-side system identification method for estimating the output voltage of wireless power transfer (WPT) systems based on harmonic suppression with dual frequency tuning. The proposed method does not require any changes to the series-compensated power receiver, such as detuning or adding extra components. The transmitter (Tx) side is tuned to have an open-circuit characteristic at the third-order harmonic frequency to block the harmonic current for estimating the coupling coefficient, and it is tuned to be series-compensated at the fundamental frequency to maintain normal power transfer. The third-order harmonic component of the Tx coil voltage and the fundamental component of the coil current are detected online to estimate the output voltage. A practical 20 W prototype is built, and experimental results show that the maximum estimation error is 3.7% for air-core coils and 9.38% for ferrite coils when the coupling coefficient and load are varied from 0.3 to 0.6 and 10–80 Ω, respectively. The estimation delay is less than 2 ms, which is effective for steady-state monitoring of the dc output voltage of a WPT system.