ABSTRACT
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. A 5-cm×3-cm,
six-input standalone prototype is fabricated to address power conditioning for
a six-channel BreezBee wind panel.
KEYWORDS:
AC-DC conversion, electromagnetic energy harvesting,
multi-input converter, resonant converter, wind energy.
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.
1. Multi-channel EMR generators and PEI system: (a) conventional PEI; and (b)
proposed multi-input PEI.
CIRCUIT
DIAGRAM:
Fig. 2. Illustrative scheme of the proposed
multi-input converter (v(i)emf: EMF of #i reed; r(i)EMR: coil
resistance; L(i)EMR: self-inductance; i(i)EMR: reed terminal
current; v(i)EMR: reed terminal voltage; C(i)r1= C(i)r2: resonant
capacitors; Lr: resonant inductor; Q(i)r1, Q(i)r2: MOSFETs; Dr:
output diode; Co: output capacitor).
EXPERIMENTAL
RESULTS:
(a)
(b)
Fig. 3. Experimental waveforms of power amplifiers: fin
= 20 Hz; X-axis: 10 ms/div; Y-axis: (a) vemf = 3 Vrms; Ch1 = output
voltage (Vo), 2.5 V/div; Ch2 = terminal voltage (vEMR) of reed
#1, 10 V/div; Ch3 = input current (iEMR) of six reeds, 50 mA/div; and
(b) vemf = 0.5 Vrms; Ch1 = output voltage (Vo), 0.5 V/div; Ch2 =
terminal voltage (vEMR) of reed #1, 5 V/div; Ch3 = sum of the input
currents (iEMR) of six reeds, 10 mA/div.
(a) (b)
Fig. 4. Experimental waveforms of power amplifiers
with step change: X-axis: 40 ms/div; Y-axis: (a) vemf = from 1 Vrms to 2
Vrms; Ch1 = output voltage (Vo), 1 V/div; Ch2 = terminal voltage (vEMR)
of reed #1, 5 V/div; Ch3 = input current (iEMR) of six reeds, 50 mA/div;
and (b) fin = from 20 Hz to 50 Hz; Ch1 = output voltage (Vo), 0.5
V/div; Ch2 = terminal voltage (vEMR) of reed #1, 5 V/div; Ch3 = input
current (iEMR) of six reeds, 50 mA/div.
Fig. 5. Experimental waveforms of EMR generators:
X-axis: (a) 20 ms/div; (b) 100 ms/div; Y-axis: (a) constant wind speed; (b)
wind speed step change; Ch1 = terminal voltage (vEMR) of reed #2, 5
V/div; Ch2 = output voltage (Vo), 1 V/div; Ch3 = terminal voltage (vEMR)
of reed #1, 10 V/div; Ch4 = input current (iEMR) of reed #1, 10 mA/div.
CONCLUSION
This
manuscript 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. The converter performance is verified
through a 5cm×3cm standalone
prototype, which converts ac voltages of six-channel generators into a dc
output voltage. A maximum PEI conversion efficiency of 86.3% is measured at
27-mW ac-dc power conversion. The topological concept, presented in this
manuscript, can be adapted for rectification of any inductive voltage sources
or electromagnetic energy-harvesting device.
REFERENCES
[1]
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Trans. on Industrial Electronics, vol. 57, no. 3, pp. 850-860, Mar. 2010.
[2]
Altenera Technology Inc., accessible online at http://altenera.com/products/.
[3]
H. Jung, S. Lee, and D. Jang, “Feasibility study on a new energy harvesting
electromagnetic device using aerodynamic instability,” IEEE Trans. on
Magnetics, vol. 45, no. 10, pp. 4376-4379, Oct. 2009.
[4]
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