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We propose a fast and accurate online front-end monitoring method for mutual inductance and load movement in series-series compensated wireless power transfer (WPT) systems. Most of traditional front-end monitoring methods for mutual inductance require the knowledge of the equivalent load resistance, the frequency shifting, or special switching actions. Also, existing methods cannot estimate the mutual inductance at the resonant frequency. To overcome these limitations, this article uses the primary-side harmonics information to monitor the real-time mutual inductance value and load movement. No additional device or special switching action is needed in the main circuit. Harmonic Kalman filter-based extractors are designed to sense the voltage and current harmonic information to minimize the noise effects. Practical experiments have been conducted to verify the proposed method even at the resonant frequency. Our results demonstrate that the proposed approach performs accurate estimation within a coupling coefficient range from 0.2 to 0.6 and is suitable for Qi-compatible WPT systems.
Zeng et al. (Fri,) studied this question.