As an ideal clean energy source, solar energy is rapidly being widely used. As a solid-state light source, LED has a long life, consumes less energy, and is a green light source. With the successful research on high-power LED drivers, LEDs have been promoted in the lighting field. Since solar cells convert light energy into DC voltage, the actual voltage required by LED lamps can be obtained through a reasonable combination of solar cell components. The two are easy to match, can achieve high utilization, have high safety, and can achieve energy saving. , environmental protection requirements. Applying solar LED to the field of street lighting can not only save a lot of cable costs, easily realize intelligent control of street lights, but also save a lot of energy. Therefore, solar LED is easy to promote in street light applications.

　　Since solar energy is greatly restricted by weather factors, the distribution density of sunlight is small, and the light receiving time and intensity are random and intermittent. To ensure the stability of the output voltage of solar cells, batteries must be used and charged during the day when there is sunlight. , the battery discharges the load LED at night. If you encounter continuous rainy weather, the battery capacity is required to be large, and the larger the capacity of the solar cell array, the higher the cost. The solar LED street light lighting system adopts the photoelectric complementary method to better solve this contradiction, which has practical and economic significance for the promotion of solar LED street light control.

　　The photoelectric complementary LED street lighting system is a street lighting system based on solar cell power generation and supplemented by ordinary 220V AC supplementary power. Using this system, the photovoltaic battery pack and battery capacity can be designed to be smaller, basically when there is sunlight during the day. , use solar power to generate electricity that day and charge the battery at the same time. When it gets dark, the battery discharges and lights up the load LED. In most areas of our country, there are basically more than two-thirds of sunny weather throughout the year. In this way, the system uses solar energy to illuminate street lights for more than two-thirds of the year, and uses mains electricity to replenish energy for the remaining time. It reduces the one-time investment of solar photovoltaic lighting system and has significant energy saving and emission reduction effects. It is an effective method to promote and popularize solar LED street lighting at the current stage.

　　1 Photoelectric complementary LED lighting system design

　　1.1LED lighting load

　　Assume that the height of the photoelectric complementary LED street light pole is 10m and the light flux is about 25lm. 1W, 3.3V, 350mA LED lights are used to form two street lights. Each channel has 14 series and 2 parallel for a total of 28W, and the two channels are 56W. Assume that the street lights are illuminated for an average of 10 hours a day. The LED street lights are fully illuminated for the first 5 hours and the brightness is halved for the next 5 hours, that is, the battery consumption is reduced by half.

　　The actual driving current required is 350mA×2×2=1.4A

　　Calculated based on 10 hours per day, the load required ampere hours is 1.4A×5h+1.4A×0.5×5h=10.5Ah

　　The voltage is 3.3V×14=46.2V

　　1.2 Battery pack capacity design

　　1.2.1 Selection of batteries

　　Since batteries for solar street lights are frequently in charge and discharge cycles, and overcharge or deep discharge often occur, battery performance and cycle life have become the most concerning issues. Valve-regulated sealed lead-acid batteries have the advantages of requiring no maintenance, not emitting hydrogen and acid mist into the air, good safety, and low price, so they are widely used. Battery overcharge, over-discharge and battery ambient temperature are all important factors that affect battery life, so protection measures should be taken in the controller.

　　1.2.2 Calculation of battery pack capacity

　　In the photoelectric complementary street light system, LED street lights are powered by complementary solar energy and mains electricity. Since sunlight changes greatly with the weather, when the sunlight is strong during the day, the solar panel charges the battery; at night, the battery supplies power to the load. On cloudy days, the load power is obtained from the battery. When the battery discharge voltage drops to the minimum allowable limit, it is automatically switched to the mains supply. The capacity of the battery is very important to ensure reliable power supply. If the battery capacity is too large, the cost and price will increase. If the battery capacity is too small, solar energy cannot be fully utilized to achieve energy saving.

　　Battery capacity Bc calculation formula Bc=A×QL×NL×T0/CCAh (1)

　　In formula (1), A is the safety factor, which is between 1.1 and 1.4. This formula is A=1.2;

　　QL is the daily average power consumption of the load, which is the operating current multiplied by the daily operating hours, QL=10.5Ah;

　　NL is the longest number of consecutive rainy days. Since photoelectric complementation is used, NL can be taken as 1 day;

　　T0 is the temperature correction coefficient, which is generally 1.1 above 0℃ and 1.2 below -10℃. This formula takes T0=1.1;

　　CC is the battery discharge depth. Generally, it is 0.75 for lead-acid batteries and 0.8 for alkaline nickel-cadmium batteries. In this formula, CC=0.75.

　　Therefore, Bc=A×QL×NL×T0/CC=1.2×10.5×1×1.1/0.75=18.5Ah. In the actual design, we choose 48V, 40Ah maintenance-free valve-regulated sealed lead-acid batteries.

　　1.2.3 Solar cell array design

　　Solar cell modules are connected in series in a certain number to obtain the required operating voltage. However, the series connection of solar cells must be appropriate. If the number of series connections is too small, the series voltage will be lower than the battery float voltage, and the solar cell array cannot charge the battery; if there are too many series connections, the output voltage will be much higher than the float voltage. The charging current will not increase significantly. Therefore, the optimal state can only be achieved when the series voltage of the solar cell module is equal to the appropriate charging voltage.

　　The output voltage of the solar cell group is generally 1.2 to 1.5 times the battery voltage. When it is 1.35 times, the battery voltage is 48V×1.35=64.8V, here it is 65V.

　　If there is no sunlight that day, the battery’s discharge capacity to the load at night is Bcb=A×QL×NL=1.2×10.5×1=12.6Ah

　　In Zhengzhou area, the battery is charged according to 5 hours of sunlight, and the current is I=12.6Ah/5h=2.52A

　　Therefore, the power of the solar cell array is P=UI=65V×2.52A=163.8W

　　Actually, four 36V48W solar panels can be used, totaling 192W, divided into two groups, with two panels in each group connected in series, with a voltage of 72V.

　　2 Introduction to controller and working principle

　　2.1 Optoelectronic complementary LED street light controller system structure

　　The structural block diagram of the photoelectric complementary LED street light control system is shown in Figure 1. The key component in this system is the controller. The main functions of the controller are:

　　(1) Detect the voltage and current of the solar panel during the day, track the maximum output power point of the solar panel through the MPPT algorithm, so that the solar panel charges the battery with the maximum output power, and control the way the solar battery charges the battery;

　　(2) Control the automatic conversion of photoelectric complementary, control the battery discharge at night, and drive the LED load lighting; when the battery discharge voltage reaches the minimum voltage in insufficient sunlight or rainy weather, it can automatically switch to the mains power supply to light the LED street lights;

　　(3) Implement over-discharge protection, over-charge protection, short-circuit protection, reverse connection protection and polarity protection for the battery;

　　(4) Control the switch of the LED light. By monitoring the external environment, you can control the time when the LED light is turned on and off.

　　2.2 Charging circuit and output control

　　2.2.1 Charging circuit

　　The charging circuit is used to adjust the charging current and voltage so that the solar panel can charge the battery stably. Since the solar radiation energy converted by the solar panels is different at various times every day, the current and voltage output by the solar cells are different, which needs to be controlled by the necessary charging circuit. This circuit is a voltage-type pulse width modulation (PWM) control circuit implemented using TL494. The circuit diagram is shown in Figure 2.

　　When the microcontroller connected to R12 gives pin 4 a high level, the cut-off time of TL494 increases to 100%, and TL494 does not work. In this way, the input level of pin 4 can be used to determine whether to charge the battery. Pin 12 of TL494 is connected to the power supply, and the 5V reference voltage output by pin 14 is used by the microcontroller. At the same time, the divided voltage of R5 and R6 is used as the reference voltage signal during constant voltage charging of the non-inverting terminal (pin 2) of the error amplifier 1 in TL494, and the positive voltage of the battery. The voltage divided by R2 and R3 is used as the inverting terminal (pin 1) of the error amplifier 1 to input the given voltage signal for constant voltage charging, and the deviation between the two is used as a constant voltage regulator.

　　A resistor-capacitor component is introduced between pins 2 and 3 to correct and improve the frequency response of the error amplifier. When the system is working, it detects the output voltage of the solar panel and the voltage of the battery in real time, and controls whether the solar battery charges the battery according to the different conditions of each voltage value, and controls the LED according to the set street light time control or light control mode. Whether the street lights are on, and when the street lights are on, the power supply mode is reasonably switched between the battery and the mains. TL494 mainly completes the detection and charge and discharge control of batteries and solar panels under the control of microcontroller program.

　　The lighting time of the street lamp can be set according to the direct dial switch on H1~H4. The corresponding time of each gear is 1 hour, 2 hours, 4 hours, and 8 hours, so that it can be adjusted within 1 to 15 hours through different combinations. The control flow chart of the system software is shown in Figure 3.

　　During the working process, the microcontroller keeps detecting the voltage of the solar cell and the battery. When the output voltage of the solar cell is more than 2V higher than the battery, and the battery is not full, pin 11 of the microcontroller outputs a low level, and the chip TL494 starts to work. MOS tube Q1 charges the battery. When fully charged, it switches to float charge state to compensate for the self-discharge of the battery.

　　Charging of the battery starts with a high current constant current charging state, and the charging current is Imax. When the battery voltage reaches 52.8V, the charger is in constant voltage charging state and the charging current continues to decrease. When the current drops to 250mA and the battery voltage rises to about 56.4V and remains unchanged, the battery power has reached 100% of the rated capacity. , the circuit enters the float charge stage, and the float charge voltage provided to the battery offsets the self-discharge of the battery. When the battery voltage reaches 57.6±0.2V, the battery reaches the overcharge pressure point, pin 11 of the microcontroller outputs high level, the chip TL494 ends its work, and the battery charging ends.

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