Design Of PV-LED Lighting System For Highway Tunnel

With the rapid development of economy, the number and miles of highway tunnel are rising continuously. Along with this, the huge energy consumption of tunnel lighting has been received more and more attention. Photovoltaic lighting is an important energy saving method in the tunnel lighting system. Currently, in order to meet the AC(Alternating Current) load, the inverter is always utilized in the photovoltaic lighting system. However, the inverter may increase the consumption of energy and cost. In recent years, the LED light source has a major breakthrough in technology. The inverter can be abandoned in the photovoltaic lighting system, and then, PV(PhotoVoltaic) module can drive LED directly. This work is supported by Major Scientific and Technological Industrialization Projects of Shaanxi Province. Aiming at the problem of huge energy consumption for highway tunnel lighting, a PV-LED(Photovoltaic-Light Emitting Diode) highway tunnel lighting system is five aspects:(1) The whole design of PV-LED highway tunnel lighting systemAt both ends of the tunnel, the strengthed lighting is designed, in which PV drives LED directly. The brightness of this strengthed lighting will synchronous change along with the outside sunlight intensity. It solves the problems of "the black hole" and "the white hole". Meanwhile, the cost is reduced significantly because of the absence of battery and inverter. In order to meet the basic lighting’s requirement of 24 hours lighting, the basic lighting system stores the excess energy in the daytime and prepares for the cloudy and night. The whole design scheme can achieve full coverage of the tunnel lighting. A large number of tunnels, which lie in remote mountainous areas and have no electricity, can also be lighted.(2) Design of the battery charging controllerTo enable an efficient and safe recharging process, we have designed an intelligent charging method including Maximum Power Point Tracking (MPPT) charging, constant-voltage charging and floating charging. By analyzing the principle, advantages and disadvantages of the existing MPPT algorithm, the tangent type incremental conductance algorithm is proposed. It solves the problem of step selection of voltage variation when PV module tracks maximum power point. The experimental results show that the charging method has a good control effect.(3) Design of LED driverIn order to meet working requirement of constant brightness, the LED constant-current driving circuit is designed based on SMD802. On the basis of this, the paper proposed a method that could prolong life span of LED based on low-load condition. The method has accomplished the goal of extending life span of LED by reducing heat and cooling down junction temperature from heat sources. The result shows that the proposed method can prolong the life of LED by about 1.2 times.(4) Design of solar single axis trackerWhen the tunnel lies in perpendicular cliff, the installation area of PV modules and lighting power is very limited. In this case, the solar single axis tracker is designed. It improves the output power of PV modules by using closed loop control and adjusting azimuth angle.(5) Experimental test and engineering designThe experiment data shows that the PV-LED lighting system has satisfied the following requirements. The enhanced lighting can adiust the luminance automatically, and the basic lighting can work all the time. For a certain tunnel, the parameters of each component in PV-LED lighting system are analyzed and calculated in detail. It provides valuable preferences for practical application.PV-LED lighting system not only realizes full coverage of the tunnel lighting based on the requirement of tunnel lighting, but also improves the utilization rate of solar energy effectively. It lays a solid foundation for solar energy popularization and application in the field of tunnel lighting.