A Synchronous Current Inversion and Energy Extraction Circuit for Electromagnetic Energy Harvesting Enhancement

Synchronous switch (SS) technique has been extensively studied in piezoelectric energy harvesting (PEH). The SS circuits can significantly enhance the output power under the same vibration excitation. Some SS solutions have also been developed for an inductive electromagnetic (EM) source by referring to its capacitive PEH counterpart and taking a reciprocal design. This paper proposes a synchronized current inversion and energy extraction (SCIEE) circuit for EM energy harvesting (EMEH). SCIEE utilizes two switched capacitive branches to carry out the synchronized current inversion at the electromotive voltage negative-to-positive zero-crossing instants and energy extraction at the voltage positive-to-negative zero-crossing instants. By inverting the transducer current, SCIEE increases the torque/force inside the transducer to extract more energy from the relative movement between magnets and coils. Theoretical analysis shows that the proposed circuit is suitable for use with an EM transducer, whose quality factor is relatively large. Experiments compared the output power of three harvesting schemes: SCIEE, synchronized switch energy extraction (SSEE), and conventional pulse-width modulation (PWM)-based harvesting scheme. When using the same prototyped EM harvester under the same mechanical excitation, SCIEE can harvest 38% more power, compared with the cutting-edge SSEE circuit for EMEH; and 900% more power, compared with the PWM-based harvesting scheme.