As a clean and pollution-free energy, solar energy has a very broad development prospect. Solar power generation has become the fastest growing technology in the world. However, the utilization of solar energy is greatly affected by natural conditions such as topography, topography, location, clouds and rain. There are problems of intermittency and the direction and intensity of light changing with time. This puts forward higher requirements for the collection and utilization of solar energy. . At present, many solar panel arrays are basically fixed, do not fully utilize solar resources, and have low power generation efficiency.

　　According to research, in solar photovoltaic power generation, under the same conditions, the power generation capacity of automatic tracking power generation equipment is 30% higher than that of fixed power generation equipment. The author proposes a new type of automatic solar tracking system that uses self-made sensors to monitor the sun's illumination angle and uses silicon photovoltaic cells to be self-powered. This system not only has a simple structure and low cost, but also does not require manual intervention in the tracking process. In the case of complex weather changes, , the system can also work normally and has broad application prospects. And based on the design idea of the tracking system, application simulation tests were conducted.

　　1. System composition and working principle

　　The automatic tracking system is mainly used to drive 10~20kW solar panels. The solar panel frame automatically follows the direction of the sun's relative motion from the initial position to the west and rotates in an intermittent manner, so that the solar panels of the photovoltaic power generation system maintain in a larger power output state.

　　After sunset, the rotation reset circuit in the rotation control circuit automatically starts, driving the solar panel frame of the photovoltaic power generation system to rotate to the initial position and enter a dormant state. In the morning, when the sun rises, the circuit starts and the control circuit automatically searches for the sun. On the one hand, this device has low energy consumption. On the other hand, it uses silicon photovoltaic cells to provide self-power. Under the same power demand conditions, it can effectively reduce energy consumption and reduce the installation cost of solar cell projects. The basic composition of the tracking system is shown in Figure 1.

　　The solar cell automatic tracking system is mainly divided into the mechanical part and the solar automatic tracking control circuit part. The mechanical part is mainly composed of silicon photovoltaic sensor detection circuit, dual-axis mechanical tracking and positioning system and battery; the solar automatic tracking control circuit is mainly composed of sensing signal processing circuit, microcontroller circuit, drive circuit and other parts. The entire device achieves the following goals: ① Works safely and reliably, ensuring that the panels can face the sun during the designed tracking time; ② Automatically returns to the original working position at night to prepare for the next day's work needs; ③ It has fault diagnosis function. When it fails, the battery panel will stop working to prevent damage to the mechanism; ④ Use silicon photovoltaic cells and batteries to work with self-sufficient power, without the need for external power supplies; ⑤ Adopt intermittent working methods to save energy consumption.

　　The tracking system uses four pieces of 1cm2 silicon photovoltaic cells to form a sensor, 2 pieces in a group, with an included angle of 30° to 60°, forming a wedge-shaped photoelectric sensor, which detects the horizontal and vertical angles of the sun respectively, and controls the mechanical part through the drive circuit.

　　The mechanical part adopts a two-axis mechanical tracking and positioning system, which is mainly composed of a panel bracket, a base, two rotating shafts and a DC horizontal drive motor. The entire solar panel and silicon photovoltaic cell detection device are installed on the upper panel bracket in Figure 1. The tracking device is designed as a dual-axis mechanical tracking and positioning system, which can track in two directions: horizontal azimuth angle and vertical altitude angle at the same time. Under the control of the drive circuit, the battery panel can be freely rotated 270° in the horizontal direction and 0~90° in the vertical direction. The horizontal and vertical control systems have their own sensors, signal amplification circuits, and motor control systems respectively, which drive the solar concentrator to always work at a maximum direct angle of 90° to the sun's rays.

　　The control circuit part is mainly composed of a single-chip microcomputer system, which has the advantages of low cost, low power consumption, high degree of intelligence, and few instructions. With the 8-bit microprocessor AT89C2051 as the core, combined with the internal logic chip and peripheral circuit components, the device intermittently controls the biaxial mechanical mechanism to track the movement of the sun through signal detection and processing. The power of the mechanical mechanism is provided by a DC motor, and can be controlled according to the The mechanical shape and size of the solar cell power adjustment device enable control of solar panels of different areas.

　　The design principle of the control circuit part is shown in Figure 2. In the circuit of Figure 2, silicon photovoltaic cells are used as the orientation detection element. When the sunlight is not direct, the silicon photovoltaic cells in the same group receive different intensity of light. This difference will lead to different voltages of the silicon photovoltaic cells. The voltage generated in the group can be used to judge the intensity of light in different directions through the voltage comparator. The comparison result of the signal comparator (1 high level, 0 low level) is sent to the single-chip microcomputer 89C2051. The single-chip microcomputer control circuit is based on the input signal. The running program controls the steering of two DC motors: one controls the left and right rotation in the horizontal plane; the other controls the up and down rotation in the vertical plane, so that the solar panel can always be perpendicular to the sun.

　　In order to reduce power consumption, intermittent control mode is adopted, and the intermittent time can be adjusted arbitrarily according to requirements. This design adopts an intermittent time of 0.5h and uses timing detection sensor signals to control the rotation of the dual-axis mechanical tracking and positioning system. When not rotating, most of the microcontroller is in a sleep state, and the power consumption at this time is 15% of normal operation.

　　2. Software design

　　The software design of the automatic tracking system adopts a modular structure, and the judgment process of the tracking mode is completely implemented by the software. After the system starts working, the system program starts timing and calls the signal acquisition program regularly. The circuit begins to detect the external interrupt signals P1.0 and P1.7. The external interrupt signal is the level signal of the silicon photovoltaic cell sensor and its variation. If there is an external interrupt When the signal meets the adjustment conditions, the adjustment subroutine is entered to adjust the angle of the battery panel. In order to meet the needs of full automation, the system also determines whether it is daytime by detecting external interrupt signals and automatically turns on or off the tracking mode. This can prevent meaningless tracking at night and reduce battery consumption. If the battery voltage is lower than a certain value, the system will sound an alarm and cut off the power supply circuit to meet its own needs.

　　Once the interrupt condition is established, the system begins to enter the adjustment subroutine. The adjustment subroutine will first detect the last recorded horizontal azimuth angle α and vertical azimuth angle β, and then perform horizontal summing based on the detected signals of P1.0 and P1.7. Vertical azimuth adjustment. The adjustment process is mainly completed by controlling the A and B motors of the dual-axis mechanical tracking and positioning system. After the adjustment is completed, it returns to the main program of the system.

　　The solar automatic tracking system does not require additional energy input and can automatically detect day and night. It has the characteristics of low cost, high accuracy, and flexible use. Even in the case of complex weather changes, the system can work normally and improve the utilization efficiency of solar energy.

　　3. Application of solar power generation system in urban gardens

　　The device has practical value and is especially suitable for urban garden facilities and traffic lighting. Urban gardens, especially public green spaces, are the main places for urban residents' activities. They are equipped with a large number of public service facilities, so they have become a large energy consumer. The garden green space occupies a wide area. If wires are laid to supply power to the facilities in the garden, the cables will hinder the view and increase the burden of daily maintenance. Using solar power generation systems to supply power to public facilities in gardens and green spaces not only eliminates many troubles and disadvantages caused by laying wires and cables everywhere, but also facilitates daily maintenance and reduces maintenance costs.

　　Solar power generation facilities in gardens and green spaces are generally used for night lighting and greenhouse power supply. Inverters can be used for power supply in greenhouses and greenhouses. The system structure is shown in Figure 3.

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