الفهرس 
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Abstract
There are currently many thousands of small stand alone photovoltaic systems
operating through out the world for power applications. They range in size from a few watts to
several tens of kilowatts. Due to the increasing importance and spread of photovoltaic systems
and to increase the life time of these systems; a modified equipment is designed, constructed,
and implemented to measure the 1-V characteristics of PV generators in the field. The
equipment can measure the characteristics of PV generators in the range of 30 W (one PV
module) up to 16 kW PV array without any problem. It uses a developed electronic load to get
more accurate data for the PV generator under test.
The electronic load depends on the use of 16 MOSFET power transistors; enhancement
type that have unique characteristics and capabilities not offered by bipolar power transistors.
The MOSFET power transistors are controlled by a gate-source voltage rather than base
current which means that their driving circuits can be simplified. All the transistors are
connected in parallel to decrease the drain to source on state resistance that affects on the short
circuit current measurements, also the current of large PV arrays can be shared among them.
All the transistors are operating together at the same instant to represent the electronic load.
The time of measurements is less than 6 ms that is a very short time and is suitable for the
measurements of PV systems under field conditions. The system is designed to use only one
transistor during the measurements of the characteristics of PV generators less than I kW
while it uses 8 transistors for measuring the characteristics of PV generators of sizes between I
kW and 8 kW. The measuring system is tested by using it in the measurement of I-V
characteristics of different sizes of PY generators. To ensure the good performance of the
developed electronic load, the measured 1-V characteristic of a PY generator is compared
with the calculated (- Y characteristics of that PV generator using the solar cell model. A good
matching is achieved between the measured and calculated 1-Y characteristics.
The developed electronic load is used in detecting the common faults that occur in PY
systems such as short circuit faults and partial shadowing. These types of faults don’ t only
affect the operation and performance of PY generators but they may lead to a large damage in
these PY generators. When only one module is short circuited in a PV array consisting of two
parallel strings each of three modules connected in series, the maximum output power of thPV generator is decreased by 29.3 %. When two modules in the same string are short
circuited, the maximum output power is decreased by 51.2 %. When 30 % of one module in
the same PV generator is shaded, the PV array lost about 34.45 % from its maximum output
power and the same result is obtained when the percentage of shading is increased to 60 %
from the module area. It is noticed during these experiments that these types of faults don’t
affect on the short circuit current or open circuit voltage of PV generators but they have a
large effect on the fill factor and consequently on the maximum output generated power from
PV generators. Also it has been shown that these faults change the voltage at which maximum
power takes place