IEEE Power Electronics Magazine - March 2022 - 37

the by-pass diode operates in the reverse bias region,
restricting the string current from flowing through the
by-pass diode and detection circuitry. But, if the entire
healthy panel voltage happens to appear across the
input terminals of the boost converter, the high reverse
voltage breaches the specified threshold of the boost
converter, which is not recommended. At the same
time, we do not want the boost converter to be in operation
when the panel is healthy. Therefore, the designers
of this circuit plan to install a diode 'D' in series
with the boost converter as represented in Figure 3.
This diode prevents any healthy panel voltage from
appearing across the input terminals of the dc-dc converter.
Therefore, there is no power loss because of the
detection circuitry when the panel is operating in a
peak power delivery mode.
(ii) Fault mode operation: As discussed in previous sections,
the by-pass diode specific to the faulty panel,
operates in the forward bias region to prevent the
source panels from hot spotting because of the suboptimal
operation of the panel. The conducting bypass
diode develops a forward voltage which can be
utilized to drive the detection circuitry. The input of
the dc-dc converter is designed in such a way as to
draw as little current as possible from the PV string in
concurrence with the rule to avoid any excess loading
on the array. The dc-dc converter should also be able
to provide the minimum necessary current to drive
the optocoupler. This current value is being determined
by the duty ratio of converter, which has been
calculated based on the minimum required driving
voltage of the optocoupler. For the circuit in consideration,
it uses the TPS61021 boost converter, which
caters to all of the needs specified in the design
requirements. The output voltage for the dc-dc converter,
given input of 0.3 V, is 1.8 V [8]. The duty ratio
of the boost converter can be calculated based on this
information. On completion, the output current of the
converter or the input current of the optocoupler
needs to be specified. The minimum current required
for the operation of the optocoupler, FODM8071, is
2 mA [9]. Taking into consideration only the minimum
required parameters for these devices, the input current
drawn from the array can be calculated. This
current can be drawn into the detection circuitry
with the help of a current limiting resistor installed in
series with the input terminal of the boost converter.
The dc-dc converter parameters and its input parameters
are given in Table-2 and Table-3
respectively.
R =
VV VD
IN
BPDIN
-I
When
all these procedures fall in line, the
optocoupler triggers an inversion in its
output state when the detection circuit identifies a fault
with the panel it is connected to. This inversion is then
communicated to the plant controller via a communication
module. The selection of the communication has been left
to the prerogative of the operator who can opt for a communication
scheme based on the array ratings and array
size for optimal communication. The circuitry in this article
employs a Wi-Fi based communication for range purposes.
Results and Discussions
For the validation of this design, a 500 W, 88 V ()VMPP
5.65A ()IMPP
IMPP
and
SPV panel test setup has been considered (Figure
4). The panel was initially subject to complete irradiance
at 26°C which resulted in the panel operating at its
MPP of 68.9 V ()VMPP
and 4.95A (). The detection circuitry
has been installed as an additional hardware module
(AHM) to the rear pane of the panel. When operating in
healthy conditions, the panel was observed to have been
delivering the desired power. There was extremely negligible
power loss, if not zero, because of the detection circuitry.
The panel setup was then subject to reduction in
photon energy by the introduction of an opaque spatial
entity to simulate a partial shaded condition. The output of
the optocoupler was being continuously monitored for any
change in the stimuli of the system. When there was an
introduction of a fault, the development of a forward voltage
across the by-pass diode triggered an inversion in the
output of the optocoupler signaling the detection of a fault
within the SPV array. The inverted output signal was then
communicated to the panel controller via a communication
module, which in this case, is ESP32 Wi-Fi test module.
This outcome conclusively proves that the proposed detection
circuitry not only consumes extremely low power, but
also is able to identify and isolate the fault location with pin
point accuracy and high speed. This setup has also been
tested for SPV system setups of 1000 W and 3000 W
arrays and has yielded accurate and desired results.
Applications
The intention to introduce a fault detection circuit is to
improve the performance of the system by neutralizing the
Table 2. DC-DC Boost Converter Parameters.
IOUT (Output
Current)
2 mA
Iin (Input
Current)
22 mA
Duty
ratio
0.91
VOUT (Output
Voltage)
3.3 V
Table 3. Input Parameters of DC-DC Converter.
VBPD (Voltage
drop across
by-pass diode)
1 V
R (Resistance
of the current
limiting resistor
(CLR))
18 Ω
VR (Voltage
drop across
CLR)
0.4 V
VD (voltage
drop across
the restricting
diode)
0.3 V
PR (Power
consumed
by the
resistor)
8.88 mW
March 2022 z IEEE POWER ELECTRONICS MAGAZINE 37
VIN (Input
Voltage)
0.3 V
IEEE Power Electronics Magazine - March 2022

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