ABSTRACT:
Efficient DC to DC and DC to AC converters play a vital role in
the reliable performance of standalone and grid connected photovoltaic systems.
This paper deals with DC to AC conversion by a seven level cascaded H-bridge
multilevel inverter for a standalone photovoltaic system. The PV fed seven
level cascaded H-bridge multilevel inverter is analyzed in two ways: 1) with
equal voltage sources as input to the H bridges and 2) with unequal voltage
sources as input. A comparative study of the total harmonic distortion
reduction in the PV fed multilevel inverter system with and without equal
voltage sources as input is carried out. It is observed that with unequal
voltage sources, the total harmonic distortion is increased than that with
equal voltage sources as input to the PV fed seven level cascaded H-bridge multilevel
inverter. Further, the study attempts to show that with an LC filter at the
output stage of the multilevel inverter, the total harmonic reduction is
significantly reduced and the power quality of the PV fed multilevel inverter
system is highly improved. Results are verified using simulations done in
MATLAB/Simulink environment.
KEYWORDS:
1.
Photo voltaic Array (PV
Array)
2.
Cascaded Multilevel Inverter
3.
Pulse Width Modulation (PWMJ
4.
Total Harmonic Distortion
(THD)
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Fig.1. Seven level Cascaded
H-bridge multilevel inverter
EXPECTED SIMULATION RESULTS:
Fig.2. (a)Seven level
cascaded MLI output voltage (b) Harmonic spectrum of the output voltage
Fig.3.(a) Seven level
cascaded MLI output current (b) Harmonic
spectrum of the output current
Fig.4. (a) Output voltage of
MLI with LC filter (b) Harmonic spectrum of
the output voltage with LC
filter
Fig.5. (a) Output current of
MLI with LC filter (b) Harmonic spectrum of
the output current with LC
filter
Fig.6. (a) Output voltage of
seven level multilevel inverter with unequal
voltage sources (b) Harmonic
spectrum of the output voltage
Fig.7. (a) Output Current of
seven level MLI with unequal voltage sources
(b) Harmonic spectrum of the
output current
Fig.8. (a) Output voltage of
seven level cascaded MLI with unequal voltage sources and LC filter (b)
Harmonic spectrum of the output voltage with LC filter
Fig.9. (a) Output current of
seven level cascaded MLI with unequal voltage sources and LC filter (b)
Harmonic spectrum of the output current with LC filter
CONCLUSION:
In this paper, an analysis of a seven level cascaded H bridge multilevel
inverter for a standalone photovoltaic system is carried out 1) with equal
voltage sources as input to the H-bridges and 2) with unequal voltage sources
as input. It is found that when equal
voltage values are fed as input to the H-bridges of the multilevel inverter,
there is a reduction in the total harmonic distortion of the MLI output when
compared to that with unequal voltage sources as its input. It is also observed
that with an LC filter at the output stage of the multilevel inverter in both
the scenarios, the total harmonic reduction is significantly reduced and the power
quality of the PV fed multilevel inverter system is highly improved.
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