The principle of LED illumination is solid-state illumination. According to the principle of solid-state illumination physics, the spectrum of LED is almost entirely concentrated in the visible light band, so the luminous efficiency is as high as 90%. Therefore, LED is known as the new light source of the 21st century, and will soon become the incandescent lamp and fluorescent lamp. The fourth generation of light source after high-intensity discharge lamps is recognized as one of the top ten cutting-edge technologies. The new illumination source of LED light source will replace the traditional illumination source and is driving a new industrial revolution. Lighting revolution. In response to the global financial turmoil, the Central Development and Reform Commission has allocated 4 trillion yuan together with local financial support. It is estimated that more than 10 trillion yuan will be invested in national transportation, supporting enterprises, and improving infrastructure. Recently, the Ministry of Science and Technology of the People's Republic of China launched the "Ten Cities and Ten Thousand Miles" LED street lighting semiconductor lighting application project in the country. Under this strong east wind, the semiconductor lighting industry, which has consistently received government support, will be an opportunity for great development.
1 System Introduction
A complete LED solar street light system includes: LED light source, controller, battery, solar cell module and lamp body. During the day, the solar cell module converts the light energy into electrical energy and stores it into the battery through the controller. At night, the battery supplies power to the light source through the controller, converting it into light energy and illuminating the road. The lamp body mainly plays the role of system protection and daytime decoration to ensure the normal operation of this cycle. Among them, LED light source, controller and battery are the key to determine the performance of street lamp system. It must be optimized and properly configured in the design.
1 System matching problems Nowadays, manufacturers of solar lamps often pursue excessive styling design, and ignore the most important system matching design. Without careful consideration, they simply calculate things, and finally cause a lot of problems in the lamps; It is not advisable to create the price advantage of your own products and sacrifice the stability of the system.
Matching design is an important factor related to system reliability and stability. To pay attention to it, the following aspects should be considered:
(1) The ratio of solar cell power generation and load power consumption is reasonable.
(2) The ratio of power consumption and battery capacity should meet the requirements of continuous rainy days and the discharge depth is reasonable.
(3) The solar cell charging current and battery capacity ratio are reasonable.
(4) The ratio of load discharge current to battery capacity is reasonable.
2 LED street light technology features The purpose of road lighting is to provide night vision drivers with a visually safe and reliable condition, high-brightness LED street lights, whose brightness must meet the brightness requirements that must be achieved in traffic safety under existing road conditions. Its luminous efficiency and luminous intensity can meet the brightness requirements required for existing road lighting. Road lighting has been implemented since July 1, 2007. The industry standard CJJ45-2006 "Urban Road Lighting Design Standards" of the Ministry of Construction, the road illumination illumination requirements are shown in Table 1. In order to make the design more perfect, the following points should be carefully considered:
(1) The choice of light source Compared with conventional lighting, LED has obvious advantages. LED is a low-voltage power supply, the insulation requirements are not high, no transformers, ballasts, starters and other accessories are needed, which saves investment. The structure is simple, it is a solid light source, does not need to be inflated, does not require a glass casing, and does not have gas seals. It is also resistant to shock, vibration and breakage; LED is a cold light source with good controllability, fast response time, repeated frequent flashing, no fatigue; ultra-low energy consumption and long life.
The intelligent core of LED street lights lies in the design of switching power supplies. At present, the widely used LED street light switching power supply generally has a rectifying and filtering circuit, an adjusting circuit, a sampling circuit, an overcurrent protection circuit and a DC constant current output circuit.
In high-power LED applications, heat dissipation is another major consideration. At present, about 80% of LED energy consumption is converted into heat, while semiconductor devices are not resistant to high temperatures. If heat dissipation is not good, it will cause very serious light. Decline, some serious half-years may fall to half of the original, high-power LEDs on street lamps are mostly multiple-parallel applications, it is necessary to use aluminum alloy multi-fin wind to make the radiator.
(2) Selection of battery The valve-regulated sealed lead-acid battery has been popularized and applied in China for more than ten years, because of its small size, light weight, small self-discharge, long life, investment saving, easy installation, safe and reliable, and use. Convenient, less maintenance, no acid mist, no corrosion to the environment, no pollution, and other modern management methods for unattended and computer monitoring; therefore, it is widely used in optical circuit lights and photovoltaic engineering. But to correctly understand the meaning of "maintenance free", to ensure that the system is safe and reliable.
In the process of use, the maintenance of the valve-regulated lead-acid battery needs to establish an accurate charging and discharging system and implement it in order to achieve the optimal performance and the longest service life of the battery. The results of a large number of studies at home and abroad show that the charge and discharge mode determines the life of the battery. Some batteries are not so badly used, as the charging method is not properly damaged.
Solar luminaires are comprehensively considered from the perspective of economy and reliability. Generally, the luminaire configuration is designed and calculated according to the annual average sunshine hours. In actual work, the controller time control function is often used to set a working hours, such as 6 hours. 8 hours, 10 hours, etc., this will result in the same working hours every day of the year, that is, the daily electricity consumption is the same, but the solar lamps work by the sun, and the amount of solar radiation varies greatly with different seasons. That is, the average daily power generation of each luminaire (the solar cell module must be) varies greatly from season to season.
The average annual peak sunshine hours in Texas is about 4.44 hours, spring: 4.43 hours, summer: 6.1 7 small days, autumn: 4.47 hours, winter: 2.65 small days. Since the average daily power generation is directly proportional to the average peak daily sunshine number, it is possible to achieve a balance between power generation and power consumption in spring and autumn, and abundant electricity in summer;
This causes a certain waste in the summer, but the winter is seriously insufficient, which can easily cause the battery to be over-discharged and affect the battery life. Factors such as self-discharge, system matching, cost, etc. are extremely uneconomical and impractical. Therefore, controlling the load time is a solution. According to the peak sunshine hours in Texas, the average peak sunshine hours in summer is higher than the average peak sunshine hours in winter. The average peak sunshine hours in winter = 6.1 7:4.44: 2.65=7:5:3, according to the annual peak sunshine hours, design solar lamps that work 10 hours a day. According to the ratio of 7:5:3, it can be said that the maximum allowable work is 14 hours in summer and 6 hours in winter. (Note: The effects of different temperatures in the season are not considered). In view of this, in order to prevent the battery from being over-discharged in winter, the load working time can be adjusted to be less than or equal to 6 hours.
(3) Controller design Because the power generation of solar modules varies with weather conditions and sunshine time, it is very unstable. Therefore, the charge and discharge control of the battery in the solar photovoltaic independent power generation system is more than the charge and discharge of the battery in the common application. Control is more complicated. Whether the controller design is perfect or not directly determines whether the entire solar street light system can operate smoothly.
The most important modules of the controller are the PWM dimming controller and the constant current module. In the past, many investments have been made in solar cells and LEDs. Few people care about these two parts, so that most of the controllers on the market today do not have the ability to PWM dimming, and most of the current constant current modules use chips imported from abroad. In solar street lamps, lead storage batteries are usually used as energy storage units, and the output voltage of lead storage batteries is from full charge to full discharge, and the voltage change is close to 20%. Therefore, the LED current change caused by it may exceed 4 times. Obviously this is totally unacceptable. So be sure to keep the current constant.
In addition, by adding an intelligent controller to the LED street light, the LED street light has light control, time control and temperature control, which can automatically turn on and off the street light according to the ambient brightness to prevent waste caused by daylighting; can make the street light in the middle of the night to dawn time When the road traffic and pedestrian flow are reduced, the power supply current is automatically reduced, and the illumination is controlled within a safe range, thereby increasing the energy saving effect and prolonging the service life of the lamp; when the working temperature of the LED is close to its limit critical temperature, the working current is automatically reduced. It not only protects the light source from damage, but also ensures the safe illumination of the road.
(4) In other respects, because the street lamp is a cantilever structure, in the natural environment, it is subjected to the shearing force of the wind, suspended at high altitude, and the structural safety is the first. Therefore, the structure should be simplified as much as possible, designed to be streamlined, to reduce wind resistance, increase the flow rate of rainwater, and pay attention to reduce weight. One is to save non-ferrous metals, the other is to reduce the stress caused by self-weight and increase the safety of road lighting. At present, the known solar cell module adopts a package structure: a glass-EVA-single solar cell-EVA-TPT film laminated package, a reassembled wire, a junction box, an edge sealing tape and an aluminum frame. The connection of the body battery is directly connected through the interconnection strip. The solar cell module only functions to generate electricity by converting solar energy into electricity, and the decorative effect is extremely small, and it is necessary to pay attention to the weather influence under long-term outdoor conditions such as windproof and dustproof.
2 Conclusion
The total number of street lamps in China exceeds 100 million baht. As long as 60 million gongs are converted into solar street lamps, the annual electricity saved exceeds the power generated by a Three Gorges hydropower station. If the 20 million new street lamps added in the future are all converted to solar street lamps, it will be a Three Gorges hydropower station in three years. The effect of energy conservation is very impressive, and there is no need to mobilize the power of the whole country to build, so that the power of local governments at all levels and the power of all relevant enterprises can be completed.
