Environmental Engineering Reference
In-Depth Information
electrical power that can be harvested from the solar panel across various
solar irradiance levels of 80 to 800 W/m
2
is 16 to 141 mW. By keeping the
operating voltage of the solar panel near to
V
mppt
, maximum electrical power
is attainable from the solar panel. Other than the complex and energy-hungry
MPPT techniques [87-89] like the P&O method and IncCond method, there
are several simple and low-power indirect MPPT techniques discussed in
Section 5.1 (i.e., FOCV, use of additional pilot solar cell, and CV) that are
suitable for small-scale SEH. However, there are some problems associated
with the FOCV and pilot solar cell methods as discussed by Dondi et al. [36].
To overcome the problems, the CV method is used in the proposed SEH
subsystem to achieve MPPT. With reference to
Figure 5.5
, the reference MPPT
voltage
V
mppt,ref
of the solar panel is set as 2.58 V. At
V
mppt,ref
, all the harvested
powers of the solar panel are close to its MPPs for a variety of solar irradiance
from 80 to 800 W/m
2
.
5.2.2.2 Boost Converter with Constant-Voltage-Based Maximum
PowerPoint Tracking (MPPT)
To optimize the SEH subsystem, a DC-DC boost converter is designed to
perform MPPT based on the chosen CV scheme. The main functions of the
boost converter in the power management circuit of the SEH subsystem (see
Figure 5.6
) are (1) to step up the low DC voltage output of the solar panel
Boost Converter with
CV Based MPPT
Solar Panel
V
solar
V
in
V
out
2.2 mH
R
s,pv
To D C - D C
Regulating
Converter
and Wireless
Sensor Node
I
L
I
D
220 µF
33 µF
Super
Cap
NMOS
Si1563EDH
PWM
V
cc
V
mppt
+
LMC7215
V
solar,fb
-
V
180 kΩ
V
fb
V
err
LTC6906
OUT
Pulses
100 kΩ
+
V
mppt,
ref
V
-
PI
Controller
+
GND
1 MΩ
6.8 µF
120 pF
DIV
SET
Microcontroller TI
MSP430F2274
(Low Power Mode, 100 Hz)
PWM Generation (10 kHz)
FIGURE 5.6
Schematic diagram of an SEH subsystem.
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