Impedance-Matching-Based Maximum Power Tracking for Magnetic Field Energy Harvesters Using Active Rectifiers

Increasing the power harvested from magnetic field energy harvesters (MFEHs) without expanding their volumes is crucial. Conventional methods for improving power harvest, e.g., flux-shaping capacitor and transfer window alignment techniques, are not applicable under varying primary current and load conditions. To address this vital problem, in this article, we present a control strategy of MFEHs based on impedance-matching theory, which considers the nonlinear characteristic of magnetic energy sources and can track the maximum power under varying current and load conditions based on an active rectifier. A calculation formula is derived to determine the optimal initial operating point of the active rectifier circuit, which aims to adjust the equivalent impedance to achieve maximum power tracking. An experimental prototype is constructed to verify the effectiveness of the proposed method. It is found that the proposed method enhances the harvested power under different current and load conditions, particularly in deep saturation conditions. The experimental results show that the proposed MFEH can harvest an average power of 2.51 W on an 800 Ω load from a 50 Hz 80 A _RMS power line, which is increased by 136.8% compared with the conventional MFEH with a passive rectifier.