A Hybrid Inductive Switched-Capacitor ACDC Converter with Asymmetric Frequency Modulation for Low-Voltage Electromagnetic Energy Harvesters

Electromagnetic vibration energy harvesting is a key enabler for autonomous IoT sensors; however, the efficient rectification of low-amplitude AC outputs remains a significant bottleneck due to the voltage drops inherent in conventional diode bridges. This article presents a novel, bridgeless direct AC-to-DC power conditioning interface that efficiently rectifies and boosts low AC input voltages without requiring external magnetic components. The proposed topology operates as a Discontinuous Conduction Mode (DCM) inductive boost converter for the positive half-cycle and an active switched-capacitor voltage multiplier for the negative half-cycle. To minimise size and cost, the design uniquely utilises the harvester's inherent winding inductance as the primary energy storage element, eliminating the need for discrete inductors. Furthermore, a hybrid frequency control strategy is introduced to maximise efficiency: the inductive stage operates at a high switching frequency (20 kHz) to achieve the required voltage gain, while the switched-capacitor stage operates synchronously with the fundamental vibration frequency (100 Hz). This approach drastically reduces switching losses during the negative half-cycle energy transfer. A laboratory prototype is designed to process a 0.4 V peak, 100 Hz AC input. Experimental results demonstrate that the converter delivers a regulated 3.34 V DC output at a rated power of 558.8 µW, achieving a peak efficiency of 71.05%.