Photovoltaic System
An
individual PV cell is usually small, typically producing 1 or 2 watts of power
which is enough to run low power calculator. Since the PV cell is essentially a
diode, forward bise voltage of diode is typically .7 V. The PV cells are connected
together in parallel and series arrangement to increase the power rating. To
boost the power output of PV cell. They are connected together to form large
unites called modules. If V is the
voltage of cell and m is number cells are connected in series, the voltage of
modules is V mod = mV. Modules in turn can be connected in parallel to form
even larger unit called array. Which can be inter connected to produce more
power. If I is the current capability of a cell and n number of modules are
connected in parallel, the current capability of an array is
iar =
ni
Therefor output
power of cell array becomes Par = mnVI.
That is the
array power becomes mn times of a single cell power PC. PV system can be built
to meet almost any electric power need small and large. Several of these array
from PV system. The tracking devices are tilt on arrays to maximize the
exposure of the cells to the sun arrays. A PV system is normally operated to
maximize the power at Vmp and Imp. The operating point is known as Maximum Power Point (MPP).
An input
capacitor is normally connected at the output of the PC array to provide a low
path for input current of the dc-dc convert. Equating the currents at the inputside
of the boost convertor, we get
ip = icdp + ii = Ci (dvp/dt) + ii
Under steady
state condition ip is
equal current ii. Therefor
operating point move toward MPP by adjusting ii. The algorithm shown in
equation for implementation require measuring PV array voltage and current
which is used to measure the Power and slop.
Therefor based on the sign of the slop (dpp/dvp), the reference current Iref is increased or decreased for
moving the operating point toward the zero slope point.
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