Abstract To better utilize solar energy, automatic tracking systems are increasingly being applied in the solar energy industry. An automatic solar panel tracking system based on a programmable logic controller (PLC) consists of two parts: hardware and software. The hardware includes PLC input/output ports, signal processing units, and drive components; the software includes the PLC control and monitoring programs. This automatic solar panel tracking system enables photovoltaic panels to track solar radiation in real time, thereby maximizing solar energy acquisition, effectively improving solar energy utilization and the efficiency of photovoltaic power generation systems, and reducing the cost of grid-connected photovoltaic power generation. It has both theoretical research significance and application promotion value.
Keywords: LM PLC, solar automatic tracking system
The solar panels Automatic Tracking system based on LM PLC
Fanzhansong
(Beijing Hollysys Automation & Drive Ltd.,Co, 100176)
Abstract In order to make better use of solar energy, more and more automatic tracking system are used in the solar industry. The solar panels tracking system based on programmable logic controllers including hardware and software parts. The hardware input and output ports of hardware, signal processing unit, driving part; software include two parts which PLC control and monitoring program. reduced the cost of grid-connected PV power generation with significances of theories research and application values of applications promotion.
Key Words LM PLC Solar Automatic Tracking system
1 Introduction
Developing new and renewable resources is a common challenge facing the world. Among new energy sources, solar power generation has become the fastest-growing technology globally. Solar energy, as a clean and pollution-free energy source, has a very broad development prospect. However, due to the intermittent nature of sunlight and the constantly changing intensity of sunlight over time, higher demands are placed on solar energy collection and utilization devices. Currently, many solar panel arrays are basically fixed, which cannot fully utilize solar energy resources and results in low power generation efficiency. Tests have shown that, under the same conditions, solar panel arrays using automatic tracking systems generate approximately 35% more power than fixed systems.
A solar tracking system is a power device that ensures solar panels are always directly facing the sun, allowing sunlight to hit them perpendicularly, significantly improving the power generation efficiency of solar photovoltaic modules. Currently, tracking systems on the market are categorized into single-axis and dual-axis automatic solar tracking systems based on their driving mechanism. Single-axis systems can only track the sun horizontally, requiring manual adjustment of the altitude based on geographical and seasonal changes. This increases workload and reduces tracking accuracy. Dual-axis tracking, on the other hand, can track the sun's trajectory in both horizontal and vertical directions, making it clearly superior to single-axis tracking.
From a control perspective, the system can be divided into sensor tracking and apparent solar motion trajectory tracking (programmed tracking). Sensor tracking uses photoelectric sensors to detect whether sunlight deviates from the normal to the solar panel. When sunlight deviates from the normal, the sensor sends a deviation signal, which, after amplification and processing, controls the actuator to re-align the tracking device with the sun. This type of tracking device has high sensitivity, but its operation will be affected by prolonged cloud cover. Apparent solar motion trajectory tracking adjusts the tracking device according to a predetermined program based on the actual trajectory of the sun. This tracking method can track in real time around the clock. Its accuracy is not very high, but it meets operational requirements and is more widely used.
Based on the type of main control unit, control systems can be divided into PLC control and microcontroller control. Microcontroller control programs are written and developed by professionals at the factory, and it's generally not easy for equipment manufacturers to redevelop and configure parameters. Learning to use a PLC is much easier. With training from the PLC manufacturer's technicians, the equipment manufacturer's technicians can easily learn simple debugging and programming. Furthermore, PLCs provide multiple communication interfaces, making communication networking relatively convenient and simple.
2 System Hardware Design
This system is a dual-axis automatic tracking system based on the apparent solar motion trajectory control (program control) of the PLC main control unit. The apparent solar motion trajectory tracking uses the corresponding formulas and algorithms of the PLC control unit to calculate the real-time position of the sun: the solar azimuth angle and the solar altitude angle, and then sends instructions to the actuator to drive the solar tracking device to achieve the purpose of real-time tracking of the sun.
2-1 Schematic diagram of azimuth and elevation angles: α - elevation angle β - azimuth angle
The sun's position in the sky can be determined by its solar altitude angle and solar azimuth angle. The solar altitude angle, also known as solar elevation angle or solar pitch angle, is the angle between the sun's rays and the horizontal plane of the Earth's surface. The solar azimuth angle, or the direction of the sun, is the angle between the projection of the sun's rays onto the horizontal plane and the local meridian; it can be approximated as the angle between the shadow of a straight line erected on the ground and the direction due south. The real-time values of the solar azimuth angle and altitude angle can be calculated using formulas based on geographical latitude and longitude and time zone parameters.
The main control unit is the core component of the solar tracking system, and the system utilizes a compact, flexible, and instruction-rich Hollysys LM PLC. The selected configuration includes the LM 3108 CPU module and the LM 3310 expansion module. The LM3108 integrates 24 digital inputs (DI) and 16 digital outputs (DO), meeting the requirements. It integrates both RS232 and RS485 communication interfaces; RS232 is used for communication with the host text display, and RS485 can be used for networking. The LM 3310 is a four-way AI module, used to collect protection data such as wind speed. When used with the Hollysys HD2400L text display, it can monitor the operating status and change parameter settings to achieve control objectives.
2-2 Selection of System Control Components
Table 2-1 System Signal Table
Serial Number | signal type | Input/output signal description |
1 | DI | Altitude Angle Origin Limit |
2 | DI | Altitude angle upper limit |
3 | DI | Lower limit of elevation angle |
4 | DI | Azimuth origin limit |
5 | DI | Eastern limit of elevation angle |
6 | DI | Western limit of elevation angle |
7 | AI | Wind speed sensor |
8 | DO×2 | Altitude angle forward/reverse |
9 | DO×2 | Azimuth forward/reverse |
The tracking and adjustment device designed in this paper has the following structure as shown in the figure below: It mainly consists of a base, a vertical shaft, a horizontal shaft, two rotary motors, and transmission gears. Rotary motor 1 drives the horizontal shaft, supporting the solar panel's movement around the horizontal shaft to track the elevation angle. Rotary motor 2 drives the horizontal shaft to track changes in azimuth angle.
2-3 Schematic diagram of the mechanical structure of the tracking system
Throughout the day, the tracker obtains the optimal altitude and azimuth angles, allowing the solar panels to receive maximum solar radiation. The system uses a set of formulas, with the PLC calculating the actual altitude and azimuth angles of the sun at any given moment. Based on the difference between the real-time solar altitude and azimuth angles and the actual altitude and azimuth angles of the tracking device, as well as the operating speed of the drive unit, the tracking time of the actuator is calculated. Finally, the program executes the drive motor to reach the required position, achieving the tracking of the altitude and azimuth angles.
3 System Software Design
The tracking mode determination process is entirely software-driven, offering high flexibility and allowing adjustments for different regions and climates to improve the power generation efficiency of photovoltaic power plants. Furthermore, additional sensors such as light intensity sensors and wind power sensors can be added as needed to enhance safety and improve control.
Through program control, the system can automatically determine whether operating conditions are met, thereby automatically starting, stopping, and returning to the initial state. A wind sensor is added for system protection; when the wind speed exceeds a certain value, the system stops working and resets to its origin. When the wind speed meets the operating conditions, the system automatically starts working. The solar panel has two degrees of freedom, with the control mechanism adjusting the elevation and azimuth angles. When the panel reaches its maximum position, the tracking device, equipped with limit sensors, automatically cuts off the output and stops the motor at the limit contact.
Figure 3-1 Control System Flowchart
4. Conclusion
This paper introduces a dual-axis automatic solar tracking system based on Hollysys LM PLC control. The system employs a solar motion trajectory tracking method to automatically detect operating conditions and achieve real-time solar tracking. Using a Hollysys PLC as the main control unit, the PLC program calculates the angular difference between the real-time solar position and the system position using an algorithm, and then calculates the running time based on the speed of the rotating motor. Through the logic control relationship of the PLC program, the motor is driven to rotate, achieving the function of automatically tracking the solar position. Therefore, this automatic tracking system has high accuracy and reliability, and can operate normally even under complex weather conditions, improving the utilization efficiency of solar energy. Because PLCs have strong programmability, customers can modify and write control programs according to their own requirements to achieve optimal control effects. For the control of large-scale photovoltaic solar array systems connected in series and parallel, a communication network can be formed through the communication of the LM PLC for centralized control. It is evident that the automatic solar tracking system developed based on Hollysys LM PLC has the characteristics of high accuracy, real-time tracking of solar changes, and convenient communication networking, which can meet customer needs.
References
[1] Hollysys LM PLC Hardware Manual
[2] Wang Xuewen. Design of automatic tracking system for solar panels [J]. Journal of Northwest University
[3] Chen Wei. Research on tracking control methods in solar energy utilization [J]. Energy Engineering
