ABSTRACT
A new, hybrid
integrated topology, fed by photovoltaic (PV) and fuel cell (FC) sources and
suitable for distributed generation applications, is proposed. It works as an
uninterruptible power source that is able to feed a certain minimum amount of power
into the grid under all conditions. PV is used as the primary source of power
operating near maximum power point (MPP), with the FC section (block), acting
as a current source, feeding only the deficit power. The unique “integrated”
approach obviates the need for dedicated communication between the two sources
for coordination and eliminates the use of a separate, conventional dc/dc boost
converter stage required for PV power processing, resulting in a reduction of
the number of devices, components, and sensors. Presence of the FC source in
parallel (with the PV source) improves the quality of power fed into the grid
by minimizing the voltage dips in the PV output. Another desirable feature is
that even a small amount of PV power (e.g., during low insolation), can be fed
into the grid. On the other hand, excess power is diverted for auxiliary functions
like electrolysis, resulting in an optimal use of the energy sources. The other
advantages of the proposed system include low cost, compact structure, and high
reliability, which render the system suitable for modular assemblies and
“plug-n-play” type applications. All the analytical, simulation results of this
research are presented.
INDEX
TERMS: Buck-boost, distributed generation, fuel cell, grid-connected, hybrid,
maximum power point tracking (MPPT), photovoltaic.
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM
Fig.
1. Various HDGS configurations. (a) Conventional, multistage topology using two
H-bridge inverters [4], [6]. (b) Modified topology with only one H-bridge
inverter [4]. (c) Proposed topology. λ denotes solar insolation (Suns).
SIMULATION RESULTS
Fig.
2. Simulation results of the integrated hybrid configuration showing transition
from mode III to mode II and then to mode I. T1 and T2 denote the transition
between mode III to mode II and mode II to mode I respectively.
Fig.
3. Simulation results of the integrated hybrid configuration operating in electrolysis
mode (mode I to mode III and then to mode I). T1 and T2 denote the transition
between mode I to mode III and mode III to mode I respectively.
Fig.4.
Performance comparison of the proposed HDGS system with and without an FC
source in parallel with the PV source.
CONCLUSION
A compact topology, suitable for
grid-connected applications has been proposed. Its working principle, analysis,
and design procedure have been presented. The topology is fed by a hybrid combination
of PV and FC sources. PV is the main source, while FC serves as an auxiliary
source to compensate for the uncertainties of the PV source. The presence of FC
source improves the quality of power (grid current THD, grid voltage profile,
etc.) fed into the grid and decreases the time taken to reach theMPP. Table IV
compares the system performance with and without the FC block in the system. A
good feature of the proposed configuration is that the PV source is directly
coupled with the inverter (and not through a dedicated dc–dc converter) and the
FC block acts as a current source. Considering that the FC is not a stiff dc
source, this facilitates PV operation at MPP over a wide range of solar
insolation, leading to an optimal utilization of the energy sources. The
efficiency of the proposed system in mode-1 is higher (around 85% to 90%) than
mode 2 and 3 (around 80% to 85%).
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