Control Strategy for
Power Flow Management in a PV System Supplying DC Loads
Abstract:
The growing concern for energy saving has increased the
usage of LED-based street lights, electronic chokes, compact fluorescent lamps,
and inverter-fed drives. Hence, the load profile seen by the electrical grid is
undergoing a notable change as these devices have to operate from a dc source. Photovoltaics
(PV) being a major energy source, the aforementioned loads can be connected
directly to the dc bus. A grid-connected PV system involves a power source (PV
array), a power sink (load), and two power sources/sink (utility and battery),
and hence, a power
flow management system is required to balance the
power flow among these sources. One such system is developed for selecting the
operating mode of the bidirectional converter by sensing the battery voltage.
The viability of the scheme has been ascertained by performing experimental
studies on a laboratory prototype. The control strategy is digitally
implemented on an Altera Cyclone II Field Programmable Gate Array (FPGA) board,
and the algorithm is verified for different modes of operation by varying the
load. Experimental results are presented to bring out
the usefulness of the control strategy.
Keywords:
1.
Bidirectional
converter
2.
DC bus
3.
Photovoltaic
4.
Power flow
management system (PMS)
Software: MATLAB/SIMULINK
Fig.1.Grid-connected
PV system with ac and dc loads
Conclusion:
A
versatile control strategy for power flow management in a grid-connected PV
system feeding dc loads has been presented. The importance of the scheme has
been brought out by performing
experimental
studies on a laboratory prototype. The steady-state performance of the
converter for different modes of operation has been observed, and near unity
power factor has been achieved in both the rectifier and inverter modes. The transient
performance of the system for step changes in load and insolation have been also
illustrated. The control strategy has been digitally implemented on an Altera
Cyclone II FPGA board, and the algorithm has been verified for different modes
of operation by varying the load, and a good correlation between the results of
computer simulation and experiments has established the validity of the PMS. The
significance of the proposed scheme has been demonstrated by its effectiveness
in preventing undesirable shuttling of the PV operating point and also in
maintaining the THD of the injected grid current within the allowable limit of
5% by setting a minimum current reference for injection. The proposed
configuration has been proved to be attractive from the perspective of
providing uninterruptible power to dc loads while ensuring the evacuation of
excess PV power of high quality into the grid.
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