Wind Energy Harvesting System - Energy Harvesting Autonomous Sensor Systems - page 81

Power Curve (Variation of Wind Speed)

160

140

120

6.7 m/s

100

80

60

6.2 m/s

40

4.7 m/s

5.7 m/s

20

5.2 m/s

0 0

100 200

220

300 400 500

Resistance (kΩ)

600 700 800 900 1000

FIGURE 2.41
Piezoelectric wind energy harvester power source curves over a range of wind speeds.

the PPU is used to power the RF transmitter. The main function of the PPU
is to convert and condition the unregulated raw electrical voltage into usable
regulated voltage for the RF transmitter load. In the PPU, the unregulated raw
power needs to undergo three different stages of power conditioning before
the usable regulated power is provided to the RF transmitter load. The first
stage of the power conversion, which is AC-to-DC power conversion, is well
known and straightforward, so it is not elaborated further. The second stage of
the PPU is the energy storage and supply circuit, which has the ability to store
electrical energy from the harvester before supplying it to the load. Energy
harvested from the piezoelectric wind energy harvester is first stored in a
capacitor, and when sufficient energy to power the wireless RF transmitter is
accumulated, a triggering signal would trigger the storage circuit to release
the stored energy to the RF load. The last stage of the PPU is the voltage
regulation stage; the output voltage supplied to the RF transmitter load is
regulated by a voltage regulator to be 3.3 V.
The vibration-based piezoelectric wind energy harvester and its related
PPU were implemented into a hardware prototype to power the wireless RF
transmitter load as shown in Figure 2.42 . The physical dimensions of a piezo-
electric wind energy harvester (half grey and half white) are 76.7 ×

2.2 mm, and it is held tightly at one end by the square clamp (cantilever mount-
ing), and the other end is left to flap freely. When wind blows at the piezoelec-
tric wind energy harvester, AC voltage is generated and converted into DC
voltage by the diode bridge rectifier chip. After this, the DC voltage is stored in

× 12.7