A Maximum-Power-Point Tracking Method Based on Constant Conduction Time Control With Constant Voltage Output for Magnetic Field Energy Harvesters in the Saturated Region

To improve the power density of magnetic field energy harvesters (MFEHs) and supply stable voltage output, a maximum-power-point tracking (MPPT) method with constant voltage (CV) output for the MFEH in the saturated region is proposed. The proposed MFEH system consists of a bidirectional buck-boost converter connected with a supercapacitor and an active rectifier. The bidirectional buck-boost converter is employed for CV output control, and MPPT under CV output conditions is realized by controlling the conduction time of the active rectifier. Besides, the calculation formula for the optimal conduction time in the saturated region is derived, which is constant and does not vary with the primary current. Subsequently, the optimal coil turn design method of the MFEH under optimal conduction time control is proposed, which can be used to guide the design of the coil turns. An experimental prototype is constructed to verify the effectiveness of the proposal. Experimental results demonstrate that the output voltage can be maintained at 3.3 V, and CV output can be realized. Besides, compared to conventional methods, the output power of the MFEH with the proposed method at 50 A rms increases from 0.47 to 0.60 W, achieving a 27% improvement.