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2. PV System Under Nonshading Conditions 143

maximum input voltage acceptable by ADC circuits. The values of BOOS_RDIV3
and BOOST_RDIV4 must be selected to satisfy the following relation:
Boost RDIV4
(4.27)
V PV max V ADC max
Boost RDIV3 þ Boost RDIV4
is the maximum ADC
where V PV max is the maximum PVoutput voltage and V ADC max
acceptable input voltage. The scaled voltage is low-pass filtered and buffered using
the amplifier circuit shown above before passing to the ADC input. The amplifier
device used here is MCP601-XST from Microchip. The MCP601-XST is a low-
cost and simple-to-use Op-Amp; it requires a single voltage supply and provides
rail-to-rail output. The device has a wide bandwidth and is optimized for ADC cir-
cuits driving.
The PV-sensed voltage is the voltage at the PVarray terminals, which is the input
to the boost circuit. To minimize the noise in the power circuits generated by the
high-speed digital circuits (FPGA control board), the PV ground (boost ground) is
isolated from the control ground (FPGA board, sensing and switch driving ground)
by a ferrite bead as shown above.

2.3.2.4 PV Current-Sensing Circuit
The PV current has to be sensed and passed to the FLC. The PV current is first
sensed by a current sensor ACS754XCB-150. This device is a hall effectebased
linear current sensor capable of sensing ac and dc currents with a peak up to
150 A. The sensor output is a positive voltage swing between 0 and þ5 V propor-
tional to the sensed current. The output of the sensor V sens at a given sensed current
I sens can be calculated from the following relation:
2:5
V sens ¼ 2:5 þ I sens (4.28)
150
where, I sens can have any value between þ150 and 150 A. Because of the fact that
the PV array is a dc power supply and the output current cannot have a negative
value, the sensible 0 to 150 A current range is not required and can be ignored.
The sensor has a sensitivity of 14 mV/A.
The second stage of the current-sensing circuit is an amplifier and low-pass filter
circuit. Because the PV array current may not reach the beak of þ150 A, the ampli-
fier amplifies the produced output voltage from the current sensor so it’s measurable
by the ADC circuit.
The amplifier circuit subtracts the þ2.5 Voffset generated by the current sensor
(at 0 A) before amplifying the sensor output and this is why the amplifier is orga-
nized as a difference amplifier. The amplification is controlled by two resistors
R in and R f and these resistors can be selected according to the maximum PV current
to be sensed and the maximum acceptable ADC input voltage. R f and R in selected
values must satisfy the following relation:
14 R f
I sens max
(4.29)
V ADC max
R in