The document discusses a proposed DC-DC converter for integrating the charging and discharging circuits of a solar LED street lighting system into a single converter. In charging mode during the day, the converter uses pulse-width modulation to step down the voltage from the solar panel to charge the battery. In discharging mode at night, it steps up the battery voltage to power the LED street lights. Simulation results show the converter can successfully charge the battery during the day and power the lights at night with only one integrated converter rather than two separate converters.

1. Study of a DC-DC Converter
for Solar LED
Street Lighting

2. Abstract
 The conventional structure of the solar LED street lighting
utilizes two converters. One is used for battery charging in
day. The other is used to supply the LED street lighting
from the battery in night. For cost saving, the two
converters should be integrated. In this project, a DC-DC
converter is presented for the solar LED street lighting. In
the day, the proposed converter is used for a charging
circuit. In the night, the proposed converter is used for a
discharging circuit. The operating principle and boundary
condition are discussed. Finally, the simulation results are
shown to verify the performance of the proposed converter.

3. INTRODUCTION
 Since the fossil fuels are shortage gradually and the
usage of the fossil fuels results in the greenhouse
effect and environmental pollution, the energy
saving and the development of renewable energy
becomes more important. The renewable energies
include solar power, wind power, ocean power,
hydrogen power.
 In the energy saving, the high performance
lightings, including high intensity discharge (HID)
and high brightness light emitting diode (LED)
lamps, are developed rapidly.

4. DESCRIPTION OF SOLAR LED STREET LIGHTING FIGURE 1
 The conventional solar LED street lighting is
shown in Fig. 1(a). The battery is charged
from the solar module through the
converter 1 in the day. Also, the energy
stored in the battery is discharged to the
LEDs through the converter 2. Therefore,
two converters are required in this
structure.

5. Structures of the solar LED street lighting.

6. DESCRIPTION OF SOLAR LED STREET LIGHTING
FIGURE 2
 Fig. 1(b) shows another structure for
the solar LED street lighting. Only one
converter is used in this structure. The
DC-DC converter is shown in Fig. 2.
The charging circuit is a DC-DC step-
down converter and the discharging is a
DC-DC step-up converter. The analysis
is described in the following sections.

7. Structures of the solar LED street lighting.

8. CIRCUIT DIAGRAM OF THE PROPOSED CONCEPT

9. MODES OF OPERATIONS
TWO MODES OF
OPERATIONS
1.CHARGING MODE
2.DISCHARGING MODE

10. CHARGING MODE
 The equivalent circuit of the proposed converter in charging
mode is shown in below Fig, The PWM technique is used to
control the switch S1. below Fig shows some typical
waveforms.
 The operating principle in continuous conduction mode
(CCM) is described as follows:
 (1) Mode 1, [t0, t1]: The switch S1is turned on and switches,
S2and S3, are turned off. The current flow path is shown in
Fig.(a). The energy of the solar voltage source Vpvis
transferred to the inductor L1, the capacitor CB, and the
battery.
 (2) Mode 2, [t1, t2]: The switches S1-S3are turned off. The
current flow path is shown in Fig.(b). The energy stored in the
inductor L1is released to the capacitor CB and the battery.

11. Current flow path of the proposed converter in
charging mode

12. Equivalent circuit and waveforms

13. DISCHARGING MODE
 The equivalent circuit of the proposed converter in
discharging mode is shown in below Fig. The PWM technique
is used to control the switches S2and S3. below Fig shows
some typical waveforms.
 The operating principle in CCM is described as follows:
 (1) Mode 1, [t0, t1]: The switch S2is turned on and switches,
S1and S3, are turned off. The current flow path is shown in
Fig. 9(a). The energy of the battery Vbatis transferred to the
inductor L1. Also, the energy stored in the capacitor Co,is
discharged to the LED.
 (2) Mode 2, [t1, t2]: The switch S3is turned on and switches,
S1and S2, are turned off. The current flow path is shown in
Fig. 9(b). The energies of the battery and the inductor L1are
released to the capacitor Co and the LED.

14. Equivalent circuit and waveforms of discharging
mode

15. Current flow path of the proposed converter in discharging
mode.

16. CONCLUSIONS
 This paper presents a DC-DC converter for the
solar LED street lighting. In the day, the proposed
converter is use to charge the battery from the
solar module.
 In the night, the energy stored in the battery is
transferred to the street lighting LEDs through the
proposed converter.
 From the simulation results, one can see that the
performance of the proposed converter can be
achieved.

17. REFERENCES
 [1] M. J. Riezenman, “Fuel cells for the long haul,
batteries for the spurts,” IEEE Transactions Power
Electronics, vol. 38, pp. 95-97, Jan. 2001.
 [2] Y. K. Lo, T. P. Lee, and K. H. Wu, “Grid-connected
photovoltaic system with power factor correction,” IEEE
Transactions on Industrial Electronics, vol. 55, no. 5, pp.
2224-2227, May 2008.
 [3] J. M. Carrasco, J. T. Bialasiewicz, R. C. P. Guisado, J.
I. Leon, “Power-electronic systems for the grid
integration of renewable energy sources: a survey,” IEEE
Transactions on Industrial Electronics, vol. 53, no. 4, pp.
1002-1016, Aug. 2006.