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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.
INTRODUCTION:
THE ever-increasing demand for low-cost energy and growing concern about
W ITH
environmental issues, PV- based systems are being increasingly employed in diverse
applications both at domestic and commercial levels [1]. Photovoltaic systems can be
broadly classified into stand-alone system and grid-connected system [2], [3]. The standalone system is widely used in remote places where access to electricity is not viable. The
stand-alone configuration can provide a well-regulated load voltage, but the reliability of
power supply cannot be guaranteed [3]. Storage batteries are widely used to improve the
reliability of the stand-alone system [4]. The integration of a PV system to the grid is rapidly
increasing due to the improvement in the power electronics technology [5], [6]. Various
topologies and control strategies [1]-[4], [7]-[28] for grid-connected inverters have been
reported in the literature. In grid-connected PV systems (GCPVs) [13]-[24], the generated
PV power is fed to the grid, or it supplies the linear and Manuscript received November 24,
2011; revised March 1, 2012 and April 20, 2012; accepted May 25, 2012. Date of
publication June 8, 2012; date of current version April 11, 2013. This work was supported
by the National Mission on Power Electronics Technology (an initiative by Department of
Information Technology, Government of India) toward laboratory infrastructure
development.
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Architecture Diagram:
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 IIFPGA 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.
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www.frontlinetechnologies.org
[email protected]
+91 7200247247