Research on Solar Power Complementary LED Street Light Controller

Abstract : The article introduces a kind of photoelectric complementary LED street light controller. The controller controls the solar battery panel to charge and discharge the battery pack, detect the battery capacity in real time, and uses an optoelectronic complementary method to supply power to the load. At the same time, the solar LED street lamp adopts the photoelectric complementary technology, which can not only improve the reliability but also reduce the cost. It is the best choice to solve the solar LED street lighting, and the battery capacity and the solar battery capacity are calculated according to the LED street lamp load. relationship.

introduction

As an ideal clean energy, solar energy is rapidly gaining widespread use. As a solid-state light source, the LED has a long life and consumes little energy, and is a green light source. With the successful research of high-power LED drivers, LED has been promoted in the lighting field. Since the solar cell converts light energy into DC voltage, the actual voltage required by the LED lamp is obtained by a reasonable combination of the solar battery components, the two are easily matched, high utilization rate can be obtained, safety is high, and energy saving can be achieved. And environmental protection requirements. Applying solar LED to the street lighting field can save the cost of a large number of cables, facilitate the intelligent control of street lights, and save a lot of energy. Therefore, solar LED is easy to popularize in street lighting applications.

Since solar energy is constrained by weather conditions, the solar radiation distribution density is small, and the received light time and intensity are random and intermittent. To ensure the stability of the output voltage of the solar battery, the battery must be used to charge the battery when there is sunlight during the daytime. At night, the battery discharges the load LED. If continuous rainy weather is encountered, the battery capacity requirement is large, and the larger the solar battery capacity, the higher the cost. Solar LED street lighting system adopts photoelectric complementary method to better resolve this contradiction, and has practical and economical significance for popularizing solar LED street lamp control.

Photoelectric complementary LED street lighting system is based on solar battery power generation, supplemented by ordinary 220V AC supplemented street lighting system, using this system, photovoltaic battery packs and battery capacity can be designed to be smaller, basically the day during the day sunshine On the same day, the solar battery was used to charge the battery at the same time. When the battery was dark, the load LED was turned on. In most parts of China, there are basically two-thirds or more of sunny weather throughout the year, so that the system uses solar energy to illuminate the streetlights for more than two-thirds of the year, and uses the city's electricity for the rest of the year. The one-time investment of solar photovoltaic lighting system has been reduced, and it has significant energy-saving and emission-reduction effects. It is an effective method for the promotion and popularization of solar LED street lighting at this stage.

1 Optoelectronic complementary LED lighting system design

1.1LED lighting load

Assume that the photoelectric complementary LED street lamp pole height is 10m, the luminous flux is about 25lm, and 1W, 3.3V and 350mA LED lamps are used to form two street lamps, each with 14 series 2 and a total of 28W, and the two are 56W. The street lamp is set to illuminate for an average of 10 hours a day. The LED street light is fully on for the first 5 hours, and the brightness is halved for the next 5 hours, ie, the battery consumption is reduced by half.

Actual driving current required is 350mA×2×2=1.4A

Calculated every day for 10 hours, the required ampere-hours for the load is 1.4A×5h+1.4A×0.5×5h=10.5Ah

The voltage is 3.3V×14=46.2V

1.2 Battery capacity design

1.2.1 Selection of Storage Battery

Since the solar street lamp battery is frequently in the charging and discharging cycle, and often overcharge or deep discharge occurs, the battery performance and cycle life become the most concern. The valve-regulated sealed lead-acid battery is widely used due to its advantages such as no maintenance, no discharge of hydrogen and acid mist into the air, good safety, and low price. Battery over-charging, over-discharging, and ambient temperature of the battery are all important factors that affect the life of the battery. Therefore, protective measures must be taken in the controller.

1.2.2 Calculation of battery capacity

In the photoelectric complementary street light system, it is powered by solar energy and electricity. As the sunlight varies greatly with the weather, the solar panel charges the battery during the day and the battery powers the load at night. On cloudy days, the load is taken from the battery, and when the battery discharge voltage falls to the minimum allowable limit, it is automatically converted to the mains supply. The capacity of the battery is very important to ensure reliable power supply. Excessive battery capacity leads to higher cost and lower capacity, and can not fully utilize solar energy for energy saving purposes.

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

In formula (1), A is a 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 working current multiplied by the daily working hours, QL=10.5Ah;

NL is the longest continuous rainy days, due to the use of photoelectric complementary, it can take NL = 1 days;

T0 is the temperature correction coefficient, generally is above 0°C is 1.1, below -10°C takes 1.2, this formula takes T0=1.1;

CC is the discharge depth of the battery. Generally, the lead-acid battery takes 0.75, and the alkaline nickel-cadmium battery takes 0.8. CC=0.75 in this formula.

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

1.2.3 Solar Cell Square Array Design

The solar cell modules are connected in series by a certain number to obtain the required operating voltage. However, the series connection of solar cells must be appropriate, the number of series is too small, and the series voltage is lower than the float voltage of the battery. The solar array square array cannot charge the battery; if the serial number is too large, the output voltage is much higher than the float voltage. There is no significant increase in charging current. Therefore, the best state can only be achieved when the series voltage of the solar cell modules is equal to the proper charging voltage.

The output voltage of a solar battery generally takes 1.2 to 1.5 times the battery voltage. When 1.35 times is taken, the battery voltage is 48V*1.35=64.8V, and 65V is taken here.

If there is no sunlight on the day, the discharge capacity of the battery at night is Bcb=A×QL×NL=1.2×10.5×1=12.6 Ah

5 hours of sunlight charging the battery in Zhengzhou area, the current is I=12.6Ah/5h=2.52A

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

Can actually use 4 36V48W solar panels, a total of 192W, divided into two groups, each with two series, the voltage is 72V.

2 controller and working principle

2.1 Optoelectronic Complementary LED Street Light Controller System Structure

Photoelectric complementary LED street light control system block diagram shown in Figure 1, the key components of this system is the controller, the controller's functions are:

(1) During the day, the voltage and current of the solar panel are detected, and the MPPT algorithm is used to track the maximum output power point of the solar panel, so that the solar panel charges the accumulator with the maximum output power, and controls the way the solar battery charges the accumulator;

(2) Control photoelectric complementary automatic conversion, control battery discharge at night, drive LED load lighting; when the sun is insufficient or rainy weather, the battery discharge voltage reaches the minimum voltage, can automatically switch to the city for the LED street light;

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

(4) Control the switch of the LED light, through the external environmental monitoring, you can control the LED light on and off time.

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 stably charge the battery. Due to the different solar radiation energy converted by the solar panels at various times of day, the output current and voltage of the solar cells are different from each other, which needs to be controlled by the necessary charging circuit. This circuit is a voltage type pulse width modulation (PWM) control circuit implemented with TL494, and the circuit diagram is shown in FIG. 2 .

When R12 is connected to the microcontroller to a high level 4 feet, TL494 deadline time increased to 100%, TL494 does not work, so that you can use the 4-pin input level to determine whether to charge the battery. TL494 12-pin power supply, 14-pin output 5V reference voltage for microcontroller use, while R5, R6 divider as TL494 error amplifier 1 in phase (2 feet) constant voltage charging reference voltage signal, battery positive voltage The R2 and R3 voltage dividers are used as the inverting terminal (pin 1) of the error amplifier 1 to input the constant voltage charging set voltage signal. The deviation between the two is used as a constant voltage regulator.

The RC element is introduced between 2 and 3 feet to correct the frequency response of the error amplifier. When the system is working, real-time detection of the output voltage of the solar panel, the voltage of the battery, and according to the different status of each voltage value, control whether the solar battery is charged to the battery, and control the LED according to the set street light time control or light control mode. Whether the street light is on or not, and the power supply mode is switched between the battery and the commercial power when lighting. TL494 is mainly under the control of the microcontroller to complete the battery, solar panel detection and charge and discharge control.

The lighting time of street lamps can be set according to the direct-dial switches on H1~H4. The corresponding time for each file is 1 hour, 2 hours, 4 hours, and 8 hours. This can be adjusted in different combinations within 1 to 15 hours. System software control flow chart shown in Figure 3.

In the course of work, the one-chip computer will detect the voltage of the solar battery and the battery all the time, when the output voltage of the solar battery is higher than 2V of the battery, at the same time the battery's power is not full, 11 feet of the one-chip computer export the low level, the chip TL494 starts to work, pass MOS tube Q1 charges the battery. When it is full, it is transferred to the float-filled state and the battery is self-discharged to compensate the battery.

The charging of the battery starts with a large current and constant current charging state, and the charging current is Imax. When the battery voltage reaches 52.8V, the charger is in a constant voltage charging state, and the charging current continues to drop. When the current drops to 250mA and the battery voltage rises to about 56.4V, the battery's power has reached 100% of the rated capacity. The circuit enters the float charge phase and the float voltage provided to the battery counteracts the self-discharge of the battery. When the battery voltage reaches 57.6±0.2V, the battery reaches the overcharge voltage point, the 11-pin output of the microcontroller is high, the chip TL494 finishes working, and the battery charging ends.

3 conclusions

Through the design and actual test observation of the photoelectric complementary LED street lamp system, the results basically meet the design requirements, but must go through the actual long-term operation, and constantly improve the design in order to achieve effective use of solar energy, battery capacity matching is most reasonable, the cost is reduced to a minimum, the performance price Better than the best. 

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