A design scheme for intelligent control system of solar street lamp

Since the Copenhagen Climate Summit, environmental protection and energy conservation have become hot topics in the world today. Energy conservation and emission reduction are not only an action goal of the government, but also can bring operating income to enterprises and allow urban residents to have a better living environment. Energy conservation and emission reduction is a necessary path for mankind to solve environmental problems. my country still has great potential for electricity saving. In the industrial field, through the development and application of power electronics technology and the optimization of electric drive systems such as fans and water pumps, significant power saving effects can be achieved; in terms of building electricity consumption, the full implementation of building energy efficiency standards, especially the improvement of air conditioning refrigeration and heating technology and system energy efficiency, will have a huge power saving effect. Efficient lighting and improving the energy efficiency of household and office appliances also have huge potential for power saving. Taking a variety of measures to promote energy conservation and power saving can not only achieve good economic results, but also save power construction investment and reduce power construction risks. If we strengthen guidance in the adjustment of industrial product structure, so that my country's economic structure will shift to a low energy intensity direction as soon as possible, and at the same time strengthen energy conservation and comprehensively improve energy efficiency, my country may achieve the economic growth target of doubling GDP with much lower power consumption growth, while bringing a series of effects such as environmental protection, economic benefits, and energy security. The power system should comprehensively implement demand-side management for the purpose of power saving and load management.

Solar energy not only has a good economic prospect, but also will provide more and more employment opportunities with its industrial development. Therefore, the development prospect of solar photovoltaic power generation market is quite broad and has attracted great attention from developed countries in the world.

Compared with developed countries, China's photovoltaic power generation industry has developed slowly, and the development of various photovoltaic materials is relatively backward. Most of the existing street lamps are powered by municipal electricity, and the application of street lamps powered by solar energy is not widespread. Based on this background, a solar street lamp infrared control automatic sensing lighting intelligent control system is designed. In addition to being powered by solar energy, it also adds infrared control and light control, which are not available in other solar street lamps. As an intelligent solution for applied electronics, it is expected to provide convenience or help for the intelligent management and energy conservation of street lighting equipment in various public places such as universities, government departments, and streets.

1 System Principle and Circuit

The solar street light intelligent control system is mainly composed of power supply, battery overcharge and over-discharge protection circuit, infrared control and light control circuit and lamps.

The power supply is divided into battery power supply and a stable power supply after 220 V mains power passes through the AC-DC conversion circuit. The AC-DC conversion circuit is mainly composed of a transformer and an integrated voltage regulator. The battery overcharge protection circuit is a simple circuit composed of a voltage regulator diode, a triode and a resistor. When the solar panel charges the battery, a diode needs to be connected between the solar panel and the battery to prevent the battery from reversely charging the solar panel. The main components of the battery over-discharge protection circuit are hysteresis comparator and relay. The hysteresis comparator is used to determine whether the battery has reached the over-discharge state, and the relay is used as a selection switch to select whether to use the battery or the backup power supply (when the battery is in the overcharge state and in rainy weather). The main components of the infrared control and light control circuit are infrared probes, digital circuits and photoresistors, and the infrared control part can integrate a chip, namely the BISS001 chip. The lamp has a lighting fixture and an indicator light for demonstration. Since the design is a lawn lamp, the lighting fixture needs to be bright enough, and a ready-made lamp composed of 81 light-emitting diodes can be selected. The indicator light can be a simple light-emitting diode.

According to the above scheme, the overall block diagram is shown in Figure 1.

Figure 1 Overall block diagram

This system has two energy-saving features: first, it uses solar panels to generate electricity as energy, achieving zero loss in street lighting; second, light control and infrared control energy-saving systems are used in subsequent circuits to achieve the effect of lights turning on when people arrive and turning off when people leave. At the same time, in continuous rainy weather, a backup power supply of 220 V is used to ensure the normal operation of the circuit.

During the day, the light-controlled switch circuit is in the open state, the subsequent control circuit does not work, and the street lights are not on; at night, the light-controlled switch circuit is automatically closed. When pedestrians pass by, they are detected by the infrared detector, the infrared control switch is closed, the street lights are on, and the delay circuit is started. After tens of seconds, the street lights automatically go out. When encountering continuous rainy weather, the voltage of the solar battery is too low, reaching the threshold of the low-voltage control switch, the switch automatically closes, the circuit switches to 220 V mains power supply, and the stable DC power is transmitted to the light-controlled switch circuit through the AC-DC conversion circuit to achieve the purpose of replacing the battery power supply, while also achieving energy saving.

1.1 Overcharge protection circuit

In order to prevent the battery from being overcharged and affecting the battery life, a simple battery over-discharge protection circuit is designed.

The principle is shown in Figure 2. Q1, D2, and D1 in the figure form a protection circuit, in which D1 (1N4743) is a voltage regulator diode (+13.5 V), and D1 and D2 together form the bias circuit of the transistor Q1. R1 is the current limiting resistor of the Q1 tube. When the circuit is charged by an external charger, if the maximum threshold voltage of the battery is around 14.4 V, the battery will slowly rise in the normal undervoltage state at the beginning of charging. When the battery voltage reaches the breakdown voltage of the voltage regulator tube D1, the D1 tube begins to conduct, and the Q1 tube is also turned on at this time, causing the voltage at the A and B terminals to drop. Appropriate parameters are set so that the maximum voltage at both ends of the battery will not be greater than 14.4 V. When the battery is fully charged, the protection circuit will put the battery in a trickle charging state, which gives the battery a charging protection function.

Figure 2 Overcharge protection circuit diagram

When the voltage across the battery is higher than the voltage across the solar panel, the battery may reverse charge the solar panel. Once this happens, the solar panel is likely to burn out, causing losses. Therefore, the overcharge protection circuit should also include an anti-reverse charging circuit, that is, a diode is connected between the solar panel and the battery to prevent the battery from reverse charging the solar panel, as shown in Figure 3.

Figure 3 Anti-reverse charging circuit

1.2 Over-discharge protection circuit

The principle of the circuit is shown in Figure 4. In the figure, Q2 makes the comparator have hysteresis, so that the comparison circuit has two threshold voltages: VTHR and VTHL (VTHH>VTHL) and a hysteresis zone. When the battery voltage rises from low to VTHH, the comparator outputs a high level; when the battery voltage drops to VTHL, the comparator outputs a low level. At this time, although the battery terminal voltage will quickly rise to above VTHL, it cannot reach VTHH, so the comparator still outputs a low level until the battery is charged and the voltage rises above VTHH before it can output a high level again. This avoids circuit oscillation and protects the load and battery.

Figure 4 Over-discharge protection circuit diagram

The positive terminal of the comparator reflects the battery sampling voltage U3, and the negative terminal of the comparator reflects the battery reference voltage U2. When U3>U2, the comparator outputs a high level, Q1 is turned on, the C pole of Q1 is at a low level, Q3 is turned off, and the load does not work; when ... 电平，q1截止，q1的c极为高电平，q3导通，负载工作。电池电压接近最小阈值电压时电池不给负载供电，只有当电池电压大于最小阈值电压与滞回电压的和时才会再次给负载供电。当比较器输出高电平时，q2导通，u2= vthl；当比较器输出低电平时，q2则截止，u2="VTHH。图中Q1、Q3起开关作用。

1.3 Backup Power Supply

When the solar panels cannot charge the batteries to a working state on rainy days, a backup power supply is needed to power the circuit. The backup power supply uses AC to DC conversion to convert AC power to the rated DC voltage value to ensure the normal operation of the circuit.

1.4 Infrared light control circuit

The system uses the BISS0001 chip, which is a high-performance sensor signal processing integrated circuit. It is equipped with a pyroelectric infrared sensor and a small number of external components to form a passive pyroelectric infrared switch with an independent high-input impedance operational amplifier. This component is implemented by hardware, and can be designed with the integrated chip BISS0001, transistor 8050, photoresistor and infrared sensor. The infrared sensor processes the infrared signal transmitted by the sensor and feeds it back to the control end, which undergoes internal linear amplification, two-way amplitude detection, signal processing, delay timing, blocking timing and other processing. Its pin 2 outputs a high level to turn on the transistor 8050, drive the relay K to attract, and then the relay contacts control the corresponding controlled object. The relay here can be replaced with a bidirectional thyristor.

Figure 5 Infrared light control circuit

In Figure 5, the operational amplifier OP1 amplifies the output signal of the pyroelectric infrared sensor in the first stage, and then couples it to the operational amplifier OP2 for the second stage amplification by C3. After being processed by the bidirectional amplitude detector composed of voltage comparators COP1 and COP2, the effective trigger signal Vs is detected to start the delay timer, and the output signal Vo is amplified by transistor T1 to drive the relay to connect the load. Among them, R3 is a photoresistor, which is used to detect the ambient illumination. When used as a lighting control, if the environment is bright, the resistance value of R3 will decrease, so that the input of pin 9 remains at a low level, thereby blocking the trigger signal Vs. SW1 is the working mode selection switch. When SW1 is connected to terminal 1, the chip is in a repeatable trigger working mode; when SW1 is connected to terminal 2, the chip is in a non-repeatable trigger working mode. In the figure, R6 can adjust the size of the amplifier gain. The original figure selects 10 k, and 3 k can be used in actual use, which can increase the circuit gain and improve the circuit performance. The output delay time Tx is adjusted by the size of the external R9 and C7, and the trigger blocking time Ti is adjusted by the size of the external R10 and C6. R9/R10 can be 470 Ω, and C6/C7 can be selected as 0.1 V.

2 Innovations

(1) The circuit of the battery over-discharge protection system is simple and flexible to use. It can be applied to circuits of any voltage level by simply selecting a comparator with a higher supply voltage; arbitrary on- and off-thresholds can be set by simply changing the resistance value, thus providing a wider safety range.

(2) In the control system, the lighting power supply is separated from the chip working power supply, and the battery power supply is divided and stabilized separately. When using a micro-power relay, the appropriate voltage is automatically selected. A small voltage is supplied to the chip for operation, and a large voltage is supplied to the lamp for lighting, thus avoiding the power loss caused by using the same large voltage supply. At the same time, in the lighting circuit, avoid using transistors with high power consumption as switches, and use thyristors instead.

(3) The street lamp is designed with a backup power supply. In case of continuous extremely bad weather, if the battery runs out of power and cannot be charged in time, the backup power supply can be automatically turned on to ensure the normal operation of the street lamp.

3 Conclusion

The design of this solar street light intelligent control system has positive significance for urban environmental protection, lighting energy saving, and alleviating the shortage of conventional energy. The entire system is automatically controlled, with a simple working principle, easy installation, and reliable technology. Scope of application: On the one hand, its technology and market have great development prospects in road and landscape lighting, as well as centralized power supply applications in regional solar energy systems that may be promoted in the future. On the other hand, the application advantages in some specific occasions (islands, mountaintops in scenic spots, remote locations, etc.) are obvious, including demonstration applications, which also have positive significance, so the research is very meaningful.