Environmental Engineering Reference
In-Depth Information
sensor node, and able to harvest sufficient energy from weak and uncertain
wind energy sources to sustain the operation of the sensor node for a long
period of time.
2.1 Direct Wind Energy Harvesting (WEH) Approach
Using a Wind Turbine Generator
To better understand the functionality and performance of the direct WEH
system, the circuit architecture of a wind-powered wireless sensor node is
presented in Figure 2.1 . The wind-powered sensor node in Figure 2.1 con-
sists of three main building blocks: (1) an energy harvester incorporating the
wind turbine coupled to the electrical generator; (2) a power management
unit, which consists of a power conditioning circuit and energy storage, and
(3) the wireless sensor node itself.
For a space-efficient WEH system operating at low wind speeds, the AC (al-
ternating current) voltage V p (peak), generated by the wind turbine generator
is in the range of 1 to 3 V, which is relatively smaller than that of the large wind
turbine with a megawatt power rating and an output voltage of hundreds of
volts [55]. It is thus challenging for the AC-DC (direct current) rectifier using
conventional silicon-based diodes, which has a high on-state voltage drop V on
of 0.7 to 1 V, to rectify and convert the low-amplitude AC voltage into a form
usable by the electronic circuits. Based on the instantaneous output DC volt-
age given by V dc = V p
V on ,itcan be seen that the efficiency of the AC-DC
rectifier using diodes is especially low for the small-scale WEH system. To
overcome this challenge, metal-oxide-semiconductor field-effect transistors
(MOSFETs) are used in place of the conventional diodes because the voltage
drop across a MOSFET is smaller than that with a diode. A MOSFET-based
active rectifier using comparators to sense the zero crossings of the input AC
voltage has been proposed in the literature [63-65] to achieve high AC-DC
power conversion efficiency in very-low-voltage applications. The problem
2
Voltage and Current Sensing Circuit
+3 V
External
Sensors (i.e.,
temperature)
2.4 GHz
Wireless
Transceiver
ADC
Z s
ν
AC-DC
Active
MOSFET
Rectifier
MPP
Tracking
Boost
Converter
Energy
Storage
(Batteries/
Supercap)
DC-DC
Regulating
Buck
Converter
s
Microcontroller
and Its Peripherals
gnd Wireless Sensor Node
Conventional Battery-Operated
Wireless Sensor Node
Power Management Unit
Wind
Turbine
Generator
PWM Generation
Circuit
FIGURE 2.1
Functional block diagram of a wind energy harvesting (WEH) wireless sensor node.
 
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