Magnetic Field Energy Harvesting and Power Management With Transfer Window Modulation

Magnetic field energy harvesters (MEHs) are widely used to supply wireless monitoring devices in power systems. Shorting the MEH to move the energy transfer window is proven to be efficient in enhancing the harvested power. However, magnetizing current losses in short-circuiting phase were usually ignored, making the maximum power harvesting dependent on approximate calculation and empirical design. Besides, a practical power management system has not yet been developed. This paper proposes a novel power management system for MEHs based on transfer window modulation (TWM). Output characteristic of MEH is analyzed with magnetizing current losses considered. It guides a more accurate estimation of transfer window and allows the optimal transfer window to be designed through numerical calculation. Furthermore, a TWM approach is proposed to achieve voltage regulation by modulating the length of transfer window. Finally, a self-powered MEH system is designed with an active rectifier and bi-directional DC-DC converter. Experiments show the root mean squared error of the calculated window length is 3.6% for the proposed model and 10.3% for the traditional model. By designing the number of coil turns, transfer window is optimized through numerical calculation rather than empirical design. The harvested power reaches 80.9% of the maximum potential of MEH. Voltage regulation is also achieved in the long-term operation test, with voltage ripple less than 0.15 V.