0 Preface
With the increasing tension of global energy, solar photovoltaic lighting has developed rapidly. In the development of solar lighting systems, people continue to analyze the commonly used control modes of the lighting system, design various practical and feasible working modes, and at the same time, the light source technology is also constantly updated, and the charging mode of the battery is also continuously researched. During exploration, the effective utilization rate is getting higher and higher. In the development and coordination of various components of solar energy, solar lighting systems are constantly developing and improving.
1 Principle and composition of solar light
The solar lighting system is a DC-type independent photovoltaic system. The solar cell module converts solar energy into electrical energy, which is controlled and protected by the controller, and the electrical energy is converted into chemical energy and stored in the storage battery. When electricity is used, the battery then converts the chemical energy into electrical energy for use by the DC load, or inverts the AC power for the AC load through the inverter. This device stops working only when there is no light for a long time so that the power in the battery is used up.
Solar street lights are composed of the following parts: solar panels, solar controllers, battery packs, light sources, light poles and lamp housings, and some are also equipped with inverters.
1) Solar panel
The solar panel is the core part of the solar street lamp and the most valuable part of the solar street lamp. Its role is to convert the sun's radiant energy into electrical energy or send it to a storage battery for storage. Solar cells mainly use monocrystalline silicon and polycrystalline silicon as materials. The photoelectric conversion efficiency of monocrystalline silicon is 13% to 15%, and polycrystalline silicon is 11% to 13%. The latest technology also includes photovoltaic thin-film batteries.
2) Solar controller
The most important part of the solar lighting system is the controller, whose performance directly affects the life of the system, especially the life of the battery. The controller uses an industrial-grade MCU as the main controller. Through the measurement of the ambient temperature and the detection and judgment of the voltage and current of the battery and solar cell components, the MOSFET device is turned on and off to achieve various control and protection functions.
3) Battery
Since the input energy of the solar photovoltaic power generation system is extremely unstable, it is generally necessary to configure a battery system to work. Generally, there are lead-acid batteries, Ni-Cd batteries and Ni-H batteries. The selection of battery capacity generally follows the following principles: first of all, under the premise of satisfying night lighting, the energy of solar cell modules during the day should be stored as much as possible, and at the same time, it should be able to store the electrical energy that meets the needs of continuous rainy night lighting at night. The battery capacity is too small to meet the needs of night lighting. The capacity is too large. On the one hand, the battery is always in a state of power loss, affecting the battery life and causing waste. The accumulator should be matched with the solar cell and electricity load (street light). A simple method can be used to determine the relationship between them. The solar cell power must be more than 4 times higher than the load power for the system to work properly. The voltage of the solar cell must exceed the working voltage of the battery by 20% to 30% to ensure that the battery is normally negatively charged. The battery capacity must be more than 6 times higher than the daily load consumption.
4) Light source
What kind of light source is used for solar street lamps is an important indicator of whether solar lamps can be used normally. Generally, solar lamps use low-voltage energy-saving lamps, low-pressure sodium lamps, electrodeless lamps, and LED light sources.
The LED light source has a long service life, up to 1000000 hours, low operating voltage, no inverter is required, and high light efficiency. Domestically produced 50lm / W, imported 80lm / W. As technology advances, the performance of LEDs will be further improved.
5) The height of the light pole and the light pole of the lamp housing should be determined according to the width of the road, the spacing of the lamps, and the illuminance standard of the road. According to our collection of many foreign solar lamp materials, the lamp housing is energy-saving. Most of them choose to save energy. The appearance of the lamp is not high, and it is relatively practical.
2 Solar street lighting control system
1) System structure
The solar street lamp microcomputer monitoring system is composed of a microcomputer main control circuit, a solar panel, a battery charger and discharger, a battery pack, an LED light source driver, and an LED lamp. The system composition structure is shown in Figure 1:
Figure 1 Composition of the solar street lamp microcomputer monitoring system
2) Function control
(1) Basic requirements of solar street light controller
Solar street lights are made up of multiple LED lights connected in series. The street lighting system not only consumes a lot of electrical energy, but also needs to invest huge daily maintenance costs, bringing double pressure on the city's power supply and financial expenditure. The development of "on-demand lighting" power supply strategy can alleviate this contradiction. Through programming, you can achieve flexible and flexible control of the street lights distributed in the bustling sections of the city. You can achieve the switch control through the PWM method at any time period to achieve the purpose of saving electricity and accentuating the atmosphere of the city lights. The basic requirements for control are as follows:
â‘ Control the brightness of the first half of the night and the second half of the night, the control ratio depends on the situation; â‘¡Turn on the unilateral street light strategy, that is, the existing battery power is only used to illuminate one street lamp, and the other street lamp is turned off; Turn on the lights, turn off the lights in the middle of the night, and the existing battery power is only used for the first half of the night.
Solar street lights are used to control the switch of lighting fixtures with the strength of natural light. The optimal design of these light-controlled solar lighting systems is the prerequisite for long-term reliable operation of the system. The system capacity can be optimized based on local geographic location, weather conditions and load conditions. However, due to seasonal factors, the solar radiation in winter is less than in summer, and the solar cell array generates less electricity in winter than in summer. However, the amount of electricity required for lighting in winter is more than that in summer, so that the power generation of the lighting system and the power demand are in contrast, which is still difficult. Balance the monthly power generation surplus and power consumption loss. In order to improve the utilization rate of the power generation of the lighting system and overcome the shortcomings caused by the lack of power in the system, in the development of solar lighting systems, people constantly analyze the common control modes of the lighting system, design various practical and feasible working modes, and The light source technology is also constantly being upgraded and replaced, and the charging mode of the storage battery is also constantly being researched and explored. The effective utilization rate is getting higher and higher. Therefore, in the development and coordination of various solar components, the solar lighting system is constantly improving .
According to the characteristics of the solar street lamp system, the operation of the street lamp should take into account the influence of the remaining capacity of the battery. When the street lamp is turned on normally, the current battery capacity is obtained according to the battery remaining capacity detection method, and the power supply time to be maintained by the battery is obtained after the inquiry, and the average current of the battery is used, and the street lamp lighting mode is flexibly controlled according to the available battery power of the night. Reasonably use the existing power of the battery.
(2) Battery charge and discharge control function
Battery charge and discharge control is an important function of the entire system, which affects the operating efficiency of the entire solar street light system, and can also prevent the overcharge and overdischarge of the battery pack. The overcharge or overdischarge of the battery has a serious impact on its performance and life. The charge and discharge control function can be divided into switch control (including single and multi-channel switch control) type and pulse width modulation (PWM) control (including maximum power tracking control) type according to the control method. This system adopts pulse width modulation controller and selects MOS transistor as the switching device. When the weather is sunny during the day, according to the remaining capacity of the battery, select the corresponding duty cycle method to charge the battery, and strive for efficient charging; at night, according to the remaining capacity of the battery and the future weather conditions, adjust the duty cycle method to adjust the LED light Brightness to ensure balanced and reasonable use of batteries.
In addition, the system also has the function of protecting the battery from overcharging, that is, when the charging voltage is higher than the protection voltage (15V), the charging voltage of the battery is automatically reduced; after that, when the voltage drops to the maintenance voltage (13.2V), the battery enters the floating charging state When the float charge is lower than 13.2V, the float charge is closed and enters the even charge state.
When the battery voltage is lower than the protection voltage (11V), the controller automatically turns off the load switch to protect the battery from damage. Charging by PWM can not only maximize the efficiency of the solar panel, but also improve the charging efficiency of the system. This design has corresponding protection measures for reverse connection, overcharge and over discharge of the battery.
(3) Control function of solar street lamp operation mode
High-brightness and high-current LED lamps have been widely used because they save about 90% of electricity compared to incandescent lamps under the same brightness. Now, there is a trend to gradually replace conventional lighting lamps.
Solar street lights are made up of multiple LED lights connected in series. The brightness can be adjusted by PWM. That is, the current flowing through the LED can be changed through the EN terminal to adjust the brightness of the LED lights. The current intensity can be from a few milliamps to 1 amp. Reach the expected brightness.
The PWM signal can be generated by the microcontroller or other pulse signals. The PWM signal can change the current through the LED lamp from 0 to the rated current, which can change the LED lamp from dark to normal brightness. The smaller the PWM duty cycle (longer high level time), the higher the brightness. Using PWM to control the brightness of LEDs is very convenient and flexible. It is the most commonly used dimming method. The frequency of PWM can be from tens of Hz to thousands of Hz.
PWM dimming is achieved by controlling MOSFET transistors.
Since the voltage used by the street lamp unit of this system is generated by several batteries in series, the MOSFET withstand voltage must first be considered when selecting MOSFET transistors. This system requires the MOSFET withstand voltage to be higher than 40V; The size of the IDS is chosen to maximize the current of the MOSFET IDS. In the case of DC power supply, the first consideration is the IDS maximum current value and RDS value. In general, the IDS maximum current of the MOSFET should be more than 5 times the LED lamp drive current; in addition, the internal resistance of the MOSFET should be selected; the larger the LED drive current, the smaller the RDS, the smaller the RDS, the more efficient the conversion high.
Urban solar street lights are public facilities closely related to people's lives. It reflects the city's prosperity and development level to a certain extent. For a long time in the past, the update of street lights was mostly limited to the lighting part. With the development of cities and electronic technologies, urban street light systems have experienced the development process of manual control, automatic timing / photoelectric control, and computer program control. Using computers to realize the automatic control of the urban solar street light system has good economic and social benefits for improving the modern management level of the city and saving manpower and material resources. By effectively adjusting the light switch time, it can greatly improve the working quality and efficiency of the street light system, and provide comprehensive solutions and strong technical support for the operation, maintenance, expansion of the urban lighting system, and improve the urban lighting operation. Management level.
(1) Microcomputer main control circuit.
The microcomputer main control circuit is the control core of the entire system, which controls the normal operation of the entire solar street light system. The main control circuit of the microcomputer has a measurement function. By detecting and judging the parameters of the solar panel voltage and the battery voltage, the on or off of the corresponding circuit is controlled to realize various control and protection functions.
(2) Charging drive circuit
The charging drive circuit is composed of MOSFET drive module and MOSFET. MOSFET drive module adopts high-speed optocoupler isolation, emitter output, short circuit protection and fast shutdown function. The selected MOSFET is an isolated, energy-saving single-chip switching power supply dedicated IC. The full-voltage input range for driving the LED is 150 to 200V, and the output current is 8 to 9A. The input voltage range is wide, with good voltage regulation rate and load regulation rate, strong anti-interference ability, and low power consumption.
The system completes the charging of the solar battery pack to the storage battery through the charging drive circuit, and corresponding protection measures are also provided in the circuit.
(3) LED drive circuit
It is composed of IGBT drive module and MOSFET to realize the adjustment of street lamp brightness and the switch of street lamp.
(4) Solar battery pack
The solar battery pack is composed of solar battery cells (operating voltage is about 0.5V, working current is about 20-25mA / cm2, area is 10cm & TImes; 10cm) connected in series and parallel to form a module. A solar cell module can generate a voltage of about 17V, and become a battery pack with a rated voltage of 12V. When the application system requires higher voltage and current components, multiple components can be formed into a square array of solar cells to obtain the required voltage and current.
(5) Battery pack
Since the energy obtained from the photovoltaic array does not always match the demand of the electronic load, when the photovoltaic array itself cannot provide enough power, the battery can still make the load work. If the electronic load needs to work at night or on a cloudy or cloudy day, energy storage is required. The storage energy of the battery is designed to meet the average daily electronic load during autonomous operation. Generally speaking, it should be able to reserve 5-7 days of night lighting power consumption. In an independent photovoltaic system, the electrical energy generated by the photovoltaic array is not always used at the same time as the electrical energy is generated, so batteries are required in most independent photovoltaic systems.
(6) Communication device
Consists of wireless data transmission module. The wireless data transmission module supports GPRS, with RS-232 interface, the communication distance is up to 100 meters, strong anti-interference, is not interfered by broadcast TV, mobile communication, and realizes communication between adjacent street lamp terminals.
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