A Multi-Input Bridgeless Resonant AC-DC Converter for Electromagnetic Energy Harvesting
Flapping electromagnetic-reed generators are investigated to harvest wind energy, even at low cut-off wind speeds. Power electronic interfaces are intended to address ac-dc conversion and power conditioning for single- or multiple-channel systems. However, the generated voltage of each generator reed at low wind speed is usually below the threshold voltage of power electronic semiconductor devices, increasing the difficulty and inefficiency of rectification, particularly at relatively low output powers. This manuscript proposes a multi-input bridgeless resonant ac-dc converter to achieve ac-dc conversion, step up voltage and match optimal impedance for a multi-channel electromagnetic energy harvesting system. Alternating voltage of each generator is stepped up through the switching LC network and then rectified by a freewheeling diode. Its resonant operation enhances efficiency and enables miniaturization through high frequency switching. The optimal electrical impedance can be adjusted through resonance impedance matching and pulse-frequency-modulation (PFM) control.
The majority of efforts toward efficient rectification of low-voltage irregular outputs of EMR generators has focused on replacing the conventional p-n junction diodes with modified MOSFET connection, including diode-connected MOSFETs, gate cross-coupled MOSFETs, and active diodes. These technologies reduce the forward voltage-drop of diodes through different connections of MOSFET terminals. However, such rectifiers suffer from losses caused either by gate threshold voltage or turn-on resistance of MOSFET. Moreover, these passive rectifiers require a second stage to regulate electrical impedance, inherently reducing the efficiency.
This Project introduces a multi-input bridgeless resonant ac-dc converter suitable for efficient, low-voltage, low-power, ac-dc power conversion of multiple electromagnetic generators. The multi-input single-stage topology is capable of directly converting independent, low-amplitude, alternative voltages of EMR inductive generators to a stepped-up dc output voltage with relatively high efficiency. Low-frequency alternating voltages of EMR generators are first converted into a high-frequency alternating voltage through an LC network and then rectified into a dc output voltage through a soft-switched diode. Optimal electrical impedance matching is achieved through proper LC network design and PFM control to scavenge maximum power of EMR generators. In addition, high-frequency soft-switching increases the potential of size miniaturization without suffering from switching losses.
TOOLS AND SOFTWARE USED:
Yichao Tang, Student Member, IEEE, and Alireza Khaligh, Senior Member, IEEE, “A Multi-Input Bridgeless Resonant AC-DC Converter for Electromagnetic Energy Harvesting”, IEEE Transactions on Power Electronics, 2015