Design & Implementation of a Solar Powered LED Road Traffic Sign
Design & Implementation of a Solar Powered LED Road Traffic Sign Control System Byeong-chan Jeon, Won-ki Park, Hyun-young Lee, Yuu-Hwang Lee, Sung-chul Lee Convergent SoC Research Center Korea Electronics Technology Institute (KETI) Seongnam-si, Korea e-mail : [email protected] Abstract— The control system for Solar powered LED Road traffic sign was designed. This system consists of 4 parts: energy transformation unit, energy charging unit, energy discharging unit and control unit. It has various functions such as day/night transition, light-time control and battery protection. This system is powered by both solar and battery. Test results showed 94% energy charging efficiency and 99.6% discharge efficiency (8.8mW standby power) Solar Controller; Road Traffic Sign; Day/Night transition; Solar Panel;
I.
INTRODUCTION
Road traffic sign recognition rate is very low at night than daytime because of low light intensity. Reaction time and stop distance increases when vehicles are driven at night. Therefore, installation of light emitting road traffic sign is required to prevent traffic accident [1]. Usually light emitting road traffic signs are connected to external commercial electricity. But it takes much time and costs for construction and maintenance. Therefore, Independent and renewable power supply system for road traffic sign is needed. Solar powered independent road traffic sign control system has emerged as the most realistic alternative. Existing controllers for solar powered road traffic signs use PWM method to charge the lead-acid battery. But these days, Li-ion battery is preferable to lead-acid battery in efficiency and life-time. In this paper, we present the implementation of a solar powered LED road traffic sign control system. II.
SYSTEM FUNCTIONS AND DESIGN
A. Design of MPPT Circuit Charging efficiency was increased by adoption of MPPT(Maximum Power Point Tracking) method. Fixed voltage MPPT method was applied and experiment showed that 17V was optimal voltage for high-efficient solar panel output voltage.
Figure 1. System Diagram
saves this to battery and it supplies this saved energy to LED load at night. In this case, the standard for day and night is based on open-circuit voltage of the solar panel. Through the experiments, Night from daytime was set to 5V and Daytime from night was recognized to 6V. Also, Variety of functions for controlling the illumination time was included. Table II shows the control system’s setting functions. To prevent the temporary effect of day and night change, 10 minutes monitoring time circuit was designed. When the battery voltage is below the threshold voltage, this control system disconnects the LED load until battery recovers from over- discharge state to stable state. Fig. 2 shows the control software algorithm. TABLE I.
DC LOAD CONTROL MODE
Mode
Function
1
Always On
2
Dust-to-Dawn, light is on all night
3
5 hours on after sundown
4
Always Off
B. Design of System Control Software During the daytime, the control system converts the solar energy supplied by the solar panel to electrical energy and
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B. Measurement Results of Fabricated control system 1) Efficiency of Energy conversion : Energy conversion efficiency from solar energy to electrical energy was measured when the battery was charged. Power consumption and efficiency of road traffic signs for solar control system was measured at 17V fixed MPPT operation. Measure result showed that charging power was 9.14W when solar panel supplied 9.7W. Therefore, Charging Conversion efficiency was 94% 2) Load discharging efficiency (Standby power Efficiency) : Standby power was measured with Agilent N6782A CC(Constant Current) function while led load power was 2W. The Standby power consumption was 8.8mW. Therefore, the load efficiency was measure at 99.6 % 3) Verification software : Day/Night transition and time setting functions were implemented for energy efficient management of road traffic sign. In case that solar panel output is below 5V, battery was connected with light load and light load was disconnected below 6V. Also It was confirmed that each of the delay time for led load connect and disconnect was 10 minutes. IV.
Figure 2. Day/Night transition Algorithm.
III.
FABRICATION AND MEASUREMENT
A. Fabricated control system Fig. 3 shows a Solar powered LED road traffic sign control system board. It’s possible to select and confirm modes via two buttons and one multi-color LED on the board. Red color indicates mode change and green shows mode confirmation.
CONCLUSION
A Solar powered LED road traffic sign control system was developed. This control system consisted of solar energy transformation unit, energy storage unit, and control unit for day/night transition and time setting. In order to increase the energy conversion efficiency and battery life time, Li-ion battery charging system and MPPT function was adopted. The developed road traffic sign system shows 94% solar energy conversion efficiency and 8.8mW standby power while 2W load power consumption. It is expected to improve the competitiveness of solar road traffic sign systems in case that this control system will be used in the field. TABLE II.
SYSTEM SPECIFICATION
Specification
Our System
Remark
Charging Mathod
MPPT
Usually PWM
Battery Type
Li-ion
Main Power Source Day/Night Distinction Load Time Setting Charging Efficiency Discharging Efficiency
Panel / Battery
Only Battery
Able
Day -> Night : 5V Night -> Day : 6V
Able 93%
Input Panel Voltage : 17V
99.6%
Consume 8.8mW, when use 2W load
REFERENCES Figure 3. System Board
[1] [2]
Research and analysis of illuminated road traffic sign install effect, Korea National Police Agency, June, 2008. Jeff Falin, Using the bq24650 to Charge LiFePO4 Battery, TI, August, 2010.
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ISOCC 2015
I.
INTRODUCTION
Road traffic sign recognition rate is very low at night than daytime because of low light intensity. Reaction time and stop distance increases when vehicles are driven at night. Therefore, installation of light emitting road traffic sign is required to prevent traffic accident [1]. Usually light emitting road traffic signs are connected to external commercial electricity. But it takes much time and costs for construction and maintenance. Therefore, Independent and renewable power supply system for road traffic sign is needed. Solar powered independent road traffic sign control system has emerged as the most realistic alternative. Existing controllers for solar powered road traffic signs use PWM method to charge the lead-acid battery. But these days, Li-ion battery is preferable to lead-acid battery in efficiency and life-time. In this paper, we present the implementation of a solar powered LED road traffic sign control system. II.
SYSTEM FUNCTIONS AND DESIGN
A. Design of MPPT Circuit Charging efficiency was increased by adoption of MPPT(Maximum Power Point Tracking) method. Fixed voltage MPPT method was applied and experiment showed that 17V was optimal voltage for high-efficient solar panel output voltage.
Figure 1. System Diagram
saves this to battery and it supplies this saved energy to LED load at night. In this case, the standard for day and night is based on open-circuit voltage of the solar panel. Through the experiments, Night from daytime was set to 5V and Daytime from night was recognized to 6V. Also, Variety of functions for controlling the illumination time was included. Table II shows the control system’s setting functions. To prevent the temporary effect of day and night change, 10 minutes monitoring time circuit was designed. When the battery voltage is below the threshold voltage, this control system disconnects the LED load until battery recovers from over- discharge state to stable state. Fig. 2 shows the control software algorithm. TABLE I.
DC LOAD CONTROL MODE
Mode
Function
1
Always On
2
Dust-to-Dawn, light is on all night
3
5 hours on after sundown
4
Always Off
B. Design of System Control Software During the daytime, the control system converts the solar energy supplied by the solar panel to electrical energy and
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ISOCC 2015
B. Measurement Results of Fabricated control system 1) Efficiency of Energy conversion : Energy conversion efficiency from solar energy to electrical energy was measured when the battery was charged. Power consumption and efficiency of road traffic signs for solar control system was measured at 17V fixed MPPT operation. Measure result showed that charging power was 9.14W when solar panel supplied 9.7W. Therefore, Charging Conversion efficiency was 94% 2) Load discharging efficiency (Standby power Efficiency) : Standby power was measured with Agilent N6782A CC(Constant Current) function while led load power was 2W. The Standby power consumption was 8.8mW. Therefore, the load efficiency was measure at 99.6 % 3) Verification software : Day/Night transition and time setting functions were implemented for energy efficient management of road traffic sign. In case that solar panel output is below 5V, battery was connected with light load and light load was disconnected below 6V. Also It was confirmed that each of the delay time for led load connect and disconnect was 10 minutes. IV.
Figure 2. Day/Night transition Algorithm.
III.
FABRICATION AND MEASUREMENT
A. Fabricated control system Fig. 3 shows a Solar powered LED road traffic sign control system board. It’s possible to select and confirm modes via two buttons and one multi-color LED on the board. Red color indicates mode change and green shows mode confirmation.
CONCLUSION
A Solar powered LED road traffic sign control system was developed. This control system consisted of solar energy transformation unit, energy storage unit, and control unit for day/night transition and time setting. In order to increase the energy conversion efficiency and battery life time, Li-ion battery charging system and MPPT function was adopted. The developed road traffic sign system shows 94% solar energy conversion efficiency and 8.8mW standby power while 2W load power consumption. It is expected to improve the competitiveness of solar road traffic sign systems in case that this control system will be used in the field. TABLE II.
SYSTEM SPECIFICATION
Specification
Our System
Remark
Charging Mathod
MPPT
Usually PWM
Battery Type
Li-ion
Main Power Source Day/Night Distinction Load Time Setting Charging Efficiency Discharging Efficiency
Panel / Battery
Only Battery
Able
Day -> Night : 5V Night -> Day : 6V
Able 93%
Input Panel Voltage : 17V
99.6%
Consume 8.8mW, when use 2W load
REFERENCES Figure 3. System Board
[1] [2]
Research and analysis of illuminated road traffic sign install effect, Korea National Police Agency, June, 2008. Jeff Falin, Using the bq24650 to Charge LiFePO4 Battery, TI, August, 2010.
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ISOCC 2015
