Such systems with or without battery backup have Inverters that consists of a boost converter for
increasing the voltage produced from PV panels and then using a full bridge
circuit that will result a full conversion to AC power from an inverter in
which results must be fulfilled:
1- Converting the DC power
to AC power, reach grid frequency of 60Hz.
2- Elimination of total
harmonic distortions by L-C filters components.
Principles of Choosing
Grid System Inverter: There are aspects
for a grid connected system inverter to be chosen in the appropriate conditions:
Like UL1741 listing, inverter`s
features an indication of the quality, high efficiency, acceptable frequency
and suitable voltage regulation. This inverter consists of meters, indicator
lights, and integral safety disconnects. Also making the selection of inverter
to match the production of the maximum power point tracking functionality that
increases the power output to harvest enough power to be delivered to Load or
fed to the grid after being converted.
Inverter Power: features of inverters which are used in PV grid
connected systems generate better power than Grid power feature.
Voltage: DC voltage is fed to the
input of the inverter from the PV arrays which is regularly to be approximately
from 240 to 610V after being increased in a system that is not battery based backup,
while in a battery based backup system the input voltage must be approximately
12, 24, or 48V.
Inverter Output: the output of the inverter is AC power in which grid
connected PV systems are managed to be chosen based on the output value from
the inverter and from the PV arrays.
Transformer-less systems: Some
systems uses low frequency transformers in order to meet voltage of the grid
according to grid codes and IEEE, while some are transformer less which needs
more protection devices for such system according to NEC and UL standards.
Inverter`s Efficiency: the productivity of inverters in residential or
commercial systems are usually used for having efficiencies about 90 to 96%,
however systems with battery based backup have less efficiencies compared with
no battery backup.
Battery Based Backup
Inverter: Charger controller is
used with inverters on a battery based backup system.
Load Capability: PV system with
battery based backup setting have inverter that can disable some load which is
not necessary in case of grid power cutoff.
Disconnects are based of
circuit breakers used for any faults occurred and safely protect the equipment’s
of the PV system being discussed from figure (5), which consist of five main
disconnect section for each part of the system:
PV Panels Disconnection: PV arrays DC
disconnector breaker functions as observer for any leakage of current to be
stopped in case of maintenance or replacement, also include fuses and breakers
for safety against electrical flows.
Inverter input Disconnect: this function will
help the PV arrays be safely disconnected from the inverter`s input in case of
faults or electrical surge occurred.
Inverter Output Disconnect: the output of the
inverter will be observed and be protected by disconnecting the link between
connection to the building, PV system and the grid to avoid any damage to the
Outdoor Grid Disconnect: Grid operators
usually use an outdoor disconnector or breaker which is lockable from governor
approval in case of immediate shutdown of the grid for resident or consumer
home to unaffected by any fault may be followed.
Battery DC Cut off: For battery operated backup
settings, the use of battery disconnection process is to safely disconnect the
link to the battery bank upon reaching fully charged state and in case of no
use in the meantime.