page C18
DS-100C Operating Manual
3.0 Theory of Operation
The DS-Tracer obtains an I-V curve by varying the electrical impedance
connected across the PV array output terminals. Varying the impedance from
zero to infinity causes the array operating point to change from I
sc
to V
oc
. The
DS-Tracer accomplishes this impedance change by connecting the array to a
capacitive load. As the capacitor charges, the array moves through its operating
range and presents a set of current and voltage values that form the I-V curve.
When the capacitor load reaches V
oc
data sampling stops.
The DS-Tracer employs two high-speed, analog-to-digital converters to sample
the current and voltage. One converter digitizes the array voltage while the other
digitizes the array current. The DS-Tracer analyzes the digitized values, saves
those that show significant change, and transfers the data set to the control
computer. The data set includes the I-V curve data plus values of open-circuit
voltage, V
oc
, and short-circuit current, I
sc
. Peak-power, voltage at peak-power
V
pk
, current at peak-power I
pk
, and fill factor are calculated and displayed with
the curve.
Irradiance and temperature data, and array identification may be added to each
data set. The irradiance and temperature data are either entered by the operator
using IVPC or sampled by the DS-100C.
The DS-Tracer sweeps an I-V curve by switching the PV system to a bank of
capacitors. As these capacitors charge, the PV system voltage increases until
open circuit voltage is reached. While the voltage is increasing, and the current
to the capacitors is decreasing from its maximum, short-circuit value, the voltage
and current are sampled by high-speed analog-to-digital converters. These data
points define the I-V curve.
Before acquiring data, the DS-Tracer reverse charges its capacitive load to
approximately -25 V. This negative pre-charge is used to offset any voltage
Содержание DS-100c
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