ABSTRACT:
This paper proposes a novel 3- stand-alone solar PV system configuration that uses
high gain, high efficiency (96%) dc-dc
converters both in the forward power stage as well as the bidirectional battery
interface. The high voltage gain converters enable the use of low voltage PV
and battery sources. This results in minimization of partial shading and
parasitic capacitance effects on the PV source. Series connection of a large
number of battery modules is obviated, preventing the overcharging and deep
discharging issues that reduce the battery life. Also, the proposed
configuration facilitates "required power tracking (RPT)" of the PV
source as per the load requirements eliminating the use of expensive and
'difficult to manage' dump loads. High performance inverter operation is
achieved through abc to dq reference frame transformation, which
helps in generating precise information about the load's active power component
for RPT, regulation of ac output voltage and minimization of control complexity.
Inverter output voltage is regulated by controlling the modulation index of
sinusoidal pulse width modulation, resulting in a stable and reliable system
operation. The active power demand is controlled by regulating the dc link
voltage. All the analytical, simulation and experimental results of this work
are presented.
KEYWORDS:
1.
Power
conversion
2.
Pulse width
modulation converters
3.
Power
conditioning, Inverters
4.
Three-phase
electric power
5.
Power control
6.
Photovoltaic
cells
7.
Energy
conversion
8.
Solar power
generation
9.
High gain
DC-DC Converter
10. MPPT
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.
1. Simplified block diagram of a two stage stand alone PV system
EXPECTED SIMULATION RESULTS:
Fig.
2. Simulation results of the proposed system during the sequence of events
considered
Fig.3
Dynamic response of the dc link: (a) An effective load (Reff) connected
across the dc link; (b) Response to step change in effective load (200W to
400W); (c) Response to step change in reference dc link voltage, *
Vdc
from
250V to 400V.
CONCLUSION:
This
paper has described and implemented a novel 3- solar
PV inverter system for stand-alone applications. Considering that high PV side
voltage leads to several drawbacks, a low voltage PV source is used in the
system. The limitation of low voltage PV source is overcome by using a special
high voltage gain front end dc-dc converter capable of operating at high efficiency
and MPPT. The proposed scheme is particularly conducive to long battery life by
as it ensures no battery overcharge or deep discharge. For this purpose, the conventional MPPT scheme is replaced by RPT,
which ensures only the required power is tracked from the PV source. This prevents
the drawing of excess power from the PV source and the use and management of
expensive 'dump' loads. Not only the main power stage, but the battery
interfacing bi-directional stage also supports high voltage gain with high
efficiency. Due to the use of special high gain, high efficiency converters in
the power stage, the overall efficiency of the system is 94%. Preliminary
investigations have yielded encouraging results. The capacity of the proposed
control strategy can be enhanced for high power operation by interfacing other renewable
sources (fuel cell stack, wind etc.) to the dc link of the proposed system without
significantly altering the control strategy. In spite of the good performance
of the proposed system, as verified through several simulation and experimental
results, there are some limitations too, as listed below:
1.
The high gain, high efficiency dc-dc converters used in the proposed system may
be difficult to design for high power levels.
2.
In the proposed system, battery is interfaced with the high voltage (400V) dc
link requiring a high voltage gain, high efficiency dc-dc converter. Battery
interfacing to the low voltage (40V) dc bus should be explored.
3.
The proposed system uses a large number of sensors, which may increase the cost
and complexity. All these issues are being currently investigated and the findings
will be reported in a future paper.
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