Greenhouse environment intelligent monitoring system based on solar power supply

In order to meet the needs of the market, greenhouses are currently widely used at home and abroad, with the United States, Japan, the Netherlands and other countries developing most rapidly, and basically realizing intelligent environmental monitoring and remote monitoring. In China, most greenhouses do not use intelligent control technology, and have disadvantages such as low environmental control ability, backward automation, and high prices, which greatly reduce the yield and quality of greenhouse crops. Therefore, it is necessary to widely realize intelligent monitoring of greenhouses. In addition, sufficient electricity is required to maintain the normal operation of greenhouses. Generally, large greenhouses are located in open areas far away from residential areas, and the use of electricity is not very convenient. However, solar energy resources are abundant, so how to realize the use of solar energy has become a problem worth thinking about and solving.

1 Design Idea

To realize the use of solar energy, solar cells can be used to achieve photoelectric conversion. In recent years, the conversion efficiency and service life of solar cells have been greatly improved. At present, the conversion efficiency of monocrystalline silicon can reach about 30%. Therefore, it is possible to use solar photovoltaic systems to power greenhouses. In order to improve the utilization rate of solar energy, MPPT and photovoltaic system self-tracking technology can be used. The main factors that affect the growth of crops are: temperature, humidity, CO2 concentration and light. Intelligent control of each growth factor can greatly improve the yield and quality of crops.

The block diagram of the greenhouse environment intelligent monitoring system based on solar power supply is shown in Figure 1.

2 Modular design

2.1 Solar power supply module

This module mainly includes four parts: MPPT implementation, battery charge and discharge monitoring, self-tracking system and voltage conversion. The MPPT implementation and self-tracking system are both for achieving more efficient use of solar energy. Battery charge and discharge monitoring is to protect the battery, solar photovoltaic module array and load. Voltage conversion enables the system to power various AC and DC loads. The block diagram of the solar power supply module is shown in Figure 2.

2.1.1 Implementation of MPPT MPPT

, or maximum power point tracking, means that the controller can detect the power generation voltage of the solar panel in real time and track the highest voltage and current value, so that the solar panel can charge the battery with the highest efficiency. The principle of MPPT control is essentially an automatic dynamic optimization process. The duty cycle and pulse width modulation signal are changed by power comparison, thereby changing the working load of the solar panel and the position of the output power point to achieve the best. To achieve MPPT, a chopper is usually required to complete the DC/DC conversion. The chopper circuit is divided into a BUCK circuit and a BOOST circuit. In this paper, a BUCK converter is used to implement MPPT. By adjusting the PWM duty cycle output of the BUCK converter, the load equivalent impedance follows the output impedance of the solar photovoltaic array, so that the photovoltaic array can obtain the maximum power output under any conditions. The BUCK circuit is actually a current boost circuit, which is mainly used to drive current receiving loads. The DC conversion is completed by inductance. Its circuit diagram is shown in Figure 3.

The output and input of the BUCK circuit satisfy the relationship:

Therefore, the output load can be adjusted by adjusting the duty cycle, so that the solar photovoltaic module array can work at the maximum power point. The duty cycle is adjusted by controlling the Q base voltage, which can be controlled by microcontroller programming.

2.1.2 Battery charge and

discharge monitoring circuit The battery charge and discharge monitoring circuit is to prevent the battery pack from overcharging and overdischarging. The battery pack plays the role of storing and providing energy in the whole system. It can be realized in hardware with the help of a microcontroller. The software program flow chart is shown in Figure 4.

2.1.3 Self-tracking system

In order to achieve the maximum utilization of solar energy, it is necessary to ensure that the sunlight is irradiated vertically on the solar panel at all times, that is, the solar panel must move with the movement of the sun. At present, the commonly used self-tracking methods are uniform speed control method, light intensity control method, and time and space control method. In order to facilitate the realization and achieve a better tracking effect, the uniform speed control method can be combined with the light intensity control method. And by comparing the actual light intensity with the set value, tight tracking, sparse tracking and non-tracking measures are taken respectively. In terms of hardware, it can be realized through single-chip microcomputers, sunlight tracking sensors, light intensity meters, etc.

2.1.4 Prospects of solar energy application in greenhouses

At present, the use of solar photovoltaic arrays for power supply requires a certain amount of land resources to place solar panels. However, semi-transparent solar modules have been produced, and transparent solar cell modules are also under further research, which makes it possible to install solar cells on the top of the greenhouse. Moreover, the conversion efficiency of solar cells is constantly improving, so the widespread use of solar photovoltaic systems will become an inevitable trend.

2.2 Intelligent monitoring module

The main parts of the intelligent monitoring module are sensor modules, A/D conversion modules, microprocessors and control devices for various factors.

2.2.1 Selection of Sensors

The temperature measurement equipment uses the SLST series digital sensor, which uses the DS18B20 digital temperature sensor from Dallas Semiconductor, USA. It is encapsulated in a stainless steel shell, waterproof and moisture-proof, and has high sensitivity and extremely small temperature delay. The field temperature is transmitted in a digital way of "one-line bus", which greatly improves the anti-interference performance of the system. Its temperature measurement range is -55~+125℃, and the temperature accuracy is ±0.5℃. It can directly convert the temperature into a serial digital signal for processing by the single-chip microcomputer. The humidity in the greenhouse is measured using the JCJ100MH humidity transmitter, which uses high-precision humidity-sensitive capacitors for measurement. It has the characteristics of high sensitivity, good stability, high accuracy and long service life. Its working environment is -40~80℃, the output voltage range is 0~5 V, and the humidity measurement range is 0~100%, all of which meet the needs of greenhouse measurement. The soil moisture is measured by a high-precision soil moisture sensor. It uses the world's advanced soil moisture sensor, which is precise, reliable and durable. It can be directly connected to the data acquisition device and can be buried at any depth underground for a long time for continuous measurement. Its measurement range is 0-100%, the working voltage is 7-15 V, and the output voltage signal is 0-1.1 V, which can be properly amplified for A/D conversion. The illuminance can be measured by the KITOZER system illuminance transmitter. This transmitter uses a silicon blue photovoltaic detector that is also highly sensitive to weak light as a sensor. It has the characteristics of wide measurement range, good linearity, good waterproof performance, and long transmission distance. Its working voltage is 12-30 V, the measurement range is 0-200 000 LUX, and it supports two-wire 4-20 mA current output, three-wire 0-5 V voltage output, LCD display output, and RS 232, RS 485 network output, which is suitable for use in greenhouse environments. The TGS4160 produced by FIGARO can be used to measure CO2 concentration. It is a solid-state electrochemical CO2 sensor with small size, long life, good selectivity and stability. Because of its long preheating time, it is suitable for long-term continuous operation at room temperature. Its measurement range is 0-5000 ppm, with a service life of 2000 days. It contains a thermistor for compensation. The electrical signal is obtained through each sensor, and after A/D conversion, it is input into the microcontroller and compared with the required set value, and then the corresponding equipment is controlled to adjust each factor.

2.2.2 Control of each growth factor

Crop growth factors mainly refer to temperature, humidity, CO2 concentration and light.

Temperature Heating equipment can use hot water boilers, fuel boilers, solar heaters, etc. In view of the sufficient outdoor solar energy resources, solar heaters can be used for heating during the day to realize the direct conversion of light energy to heat energy. When the sun is insufficient, electric heaters are used, powered by battery packs. The cooling equipment uses wet curtain fans, and the ventilation equipment adopts forced ventilation, that is, the fan generates wind pressure to force air flow and cool down. The wet curtain uses the principle of water evaporation and heat absorption to cool down. The combination of the two has strong action ability and stable effect.

Humidity When the actual humidity is lower than the required humidity, it can be achieved by controlling the nozzle installed on the top of the greenhouse, and the humidity can be increased by spraying without making the humidity too high. When the humidity is too high, it can be reduced by ventilation, which is achieved by using the humidity difference to exchange indoor and outdoor air.

CO2 concentration The concentration of CO2 directly affects the yield and quality of crops. The appropriate CO2 concentration may increase the yield by 40% to 200%. The CO2 concentration in the atmosphere is only 350 ppm. If the CO2 concentration needs to be increased in the greenhouse, a CO2 generator can be used to generate CO2 by chemical reaction, coal burning, gas, etc. When the CO2 concentration is too low, it can be increased by controlling the switch of the CO2 generator. When the concentration is too high, it can be turned on by turning on the ventilator.

Lighting The control devices for lighting are sunshade devices and fill-in lights. When the light is too strong, it can be achieved with the help of sunshade devices. When the light is too weak, it can be achieved with fill-in lights. Moreover, the number of fill-in lights turned on is affected by the external light, and finally a more appropriate light intensity is achieved.

2.2.3 A/D conversion The

A/D conversion uses TLC1549 to convert the analog electrical signals collected by each sensor into digital quantities and input them into the microcontroller for processing, and to control each factor. TLC1549 is a 10-bit A/D converter of successive comparison type, which automatically generates conversion time pulses on the chip. The conversion time is less than 21μs. It has an inherent sampling and holding circuit, and the terminal is compatible with TLC549 and TLV549. It uses CMOS technology, has 2 digital inputs and 1 three-state output, and can be directly connected to the microprocessor.

2.2.4 Software implementation

The microcontroller used in this system can select the 51/52 series microcontroller, such as AT89C51. The control of various device switches is achieved through single-chip microcomputer programming, and its control flow chart is shown in Figure 5.

3 Conclusion

The system realizes the effective utilization of solar energy resources, adopts MPPT and self-tracking system to achieve high-efficiency conversion, and can better intelligently control the growth factors of crops, so that crops grow in the most suitable environment, greatly improving the yield and quality of crops. This article only involves the intelligent control of a single greenhouse, but it can communicate with the host computer through the communication interface RS 232 to realize distributed control, which can greatly improve the overall work efficiency.