The hottest solar panel automatic tracking system

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Research on automatic tracking system of solar panel based on OMRON PLC

1 introduction

solar energy has become one of the most promising new energy at home and abroad with its inexhaustible and environmental protection advantages. Photovoltaic (PV) power generation technology has been deeply studied and promoted abroad, and China has basically matured in technology, and has entered the stage of promotion and application [1]. However, solar energy has the problems of low density, intermittent, and the light direction and intensity change with time, which puts forward higher requirements for solar energy collection and utilization devices. At present, many solar panel arrays are basically fixed, which can not make full use of solar energy resources and low power generation efficiency [2]. If we can always keep the solar panel vertical to the light and make it receive solar energy to the greatest extent, we can make full use of abundant solar energy resources. According to experiments, in solar power generation, under the same conditions, the power generation capacity of automatic tracking power generation equipment is about 35% higher than that of fixed power generation equipment [3]. Therefore, it is a very valuable research topic to design and develop a control system that can automatically track the sunlight

the sunlight automatic tracking system of a new programmable logic controller PLC (programmable logic controller) can not only automatically adjust the orientation of solar panels according to the direction of sunlight, but also has simple structure and low cost. In the tracking process, it can automatically remember and correct the coordinate positions at different times without manual intervention. It is especially suitable for the situation of complex weather changes and unattended, It effectively improves the utilization rate of solar energy, and has good popularization and application value and market application prospect. This research takes the first and second phases of the "photovoltaic and power generation demonstration project of the Ministry of science and technology" of our university as the research basis and research platform, and the power generation of the control system is 75kwp

2 composition and working principle of automatic tracking system

the sun has no new large mining capacity in a short time. The automatic tracking control system of battery panel is composed of PLC main control unit, sensor and signal processing unit, photovoltaic module, electromagnetic mechanical motion control module and power supply module. The composition block diagram of the system is shown in Figure 1

Figure 1 system composition block diagram

the photosensitive detector head (sensor) of the automatic tracking system of solar photovoltaic power generation equipment is used to detect the solar intensity. When there is a deviation, the deviation signal passes through the tracking PLC main control unit (controller) and adopts the principle of high Pseudo differential pressure comparison of mold equipment stiffness to calculate, compare and issue instructions, so as to make the electric actuator act, drive the mechanical part to rotate, drive the whole device to rotate, adjust the deviation, ensure that the solar cell array is facing the sunlight, and achieve the purpose of automatically tracking the sun. The solar cell array generates photovoltaic power under the sunlight, and charges the battery through the controller. The system is equipped with an automatic protection line, which will automatically start when the wind force reaches level 8, cut off the tracking solar system, so that the battery array can be quickly flattened. When the wind force drops, it will delay 10 minutes, remove the wind protection system, and resume the tracking process. The data of fixed light intensity, tracking light intensity, battery temperature and natural wind speed are collected by microcomputer, and the charging and discharging of battery are controlled hierarchically

the system has two control modes: automatic and manual. SB1 and SB2 are control buttons for manual operation. Q0 or Q1 output by PLC are respectively connected to two relay coils to control the positive and negative motion directions of the sun plate. In the automatic operation mode, PLC first compares the values of two analog inputs from the signal processing unit, and then decides to output Q0 or Q1

2.1 PLC unit

the tracking controller adopts PLC, which is the control core of solar panel tracking system and the focus of system research. The system adopts the technology developed by OMRON in recent years α Series PLC, which is a small and medium-sized machine between mainframe and minicomputer, with the maximum control i/o points of 1184. In application, the central processing unit (CPU) adopts c200hx-cpu43-e, which has a programming port and an RS232C port. The CPU has rich instruction functions and programming is very convenient; The switching value input module is c200h-id212; The switching value output module is c200h-oc225; The communication with the upper computer is realized by inserting the communication board c200hw-com06-e (the board has an RS232C and an rs-422/485) into the CPU. Due to the use of RS-422 interface and balanced transmission, the data transmission rate is high, the crosstalk is small, and the transmission distance can reach 500m. Especially for the tracking system control of series parallel photovoltaic solar cell array, it can give play to the advantages of PLC field bus control for centralized control. After research and optimization design, the integrated standard circuit is applied, and the analog differential pressure comparison principle is adopted. The controller has the functions of high tracking accuracy, wide range and automatic return. The limit device has the limit limit function in four directions: East, West, up and down. The double limit control structure, namely, the control signal limit and the drive motor limit, is adopted to ensure the reliable operation of the equipment. Figure 2 shows the PLC input/output hardware configuration diagram

Figure 2 PLC input and output hardware configuration figure

2.2 sensor detection and signal processing unit

the orientation of the sun varies with the observation position and observation time. Therefore, to track the sun, you must first detect and locate the sun. The methods to detect the solar light intensity include timing method, coordinate method, solar panel light intensity comparison method and photosensitive resistance light intensity comparison method [4]. After comparing and screening these four control methods, it is considered that although the circuit of timing method is simple, the control accuracy of the system is poor due to the influence of season; The control accuracy of coordinate method is high, but the control circuit is complex; The light intensity comparison method makes the solar energy utilization rate of the system unable to reach the best; The circuit of photosensitive resistance comparison method is the simplest to realize, and the utilization rate of solar energy is the largest. Based on this, the photosensitive resistance light intensity comparison method with high control accuracy and easy circuit implementation is selected as the detection scheme of this research system. The photosensitive detector head (sensor) is the optical signal receiver of the solar panel tracking system. It uses the principle that the resistance value of the photosensitive resistor changes during illumination to place two identical photosensitive resistors under the East-West edge of a panel respectively (when the light is perpendicular to the panel, half of the light can be received and half of the light is below). If the sun shines vertically on the solar panel, the two photoresistors receive the same light intensity, so their resistance values are completely equal, and the motor does not rotate at this time. When there is an included angle between the sunlight direction and the vertical direction of the battery board, the resistance value of the photoresist with more received light intensity decreases, driving the motor to rotate until the light intensity on the two photoresistors is the same. The control sensitivity directly affects the tracking accuracy. The advantage of photosensitive resistance light intensity comparison method is that the control is accurate and the circuit design is relatively easy to realize. After experimental research, aluminum alloy materials with light weight, beauty and corrosion resistance are selected, and the photoelectric receiver tube is strictly calculated and positioned to ensure its detection sensitivity

Figure 3 shows the top view of the photoelectric detection circuit in the solar photoelectric positioning device, which is composed of 9 photoelectric triodes. There is one in the center and eight next to it in a circle. Cover the test plate with an opaque cylinder with an opening below, and the diameter of the cylinder is slightly larger than the outer circle of the test plate. A hole with the same diameter as the photodiode used for detection is opened in the upper center of the cylinder so that light can pass through. The whole photoelectric detection device is installed on the solar photovoltaic panel, and the detection surface of the photodiode is parallel to the panel. A photodiode is also installed at the place outside the cylinder that is not covered by the cylinder (to ensure that it will be illuminated by light), and its orientation is the same as that of the photodiode in the cylinder, which is used to detect the ambient brightness, and forms a comparison circuit with each photoelectric diode and operational amplifier in the cylinder (one of LM324 integrated circuits can be used). In this way, when the photodiode in the cylinder is not illuminated by light, the op amp will output a low level, which can be connected to the input end of the for detection. Each photoelectric diode in the cylinder uses a PLC input end, a total of 9. In this way, the direction of the sun's rays can be detected to determine which motor rotates and in which direction. In addition, in order to increase the detection range of photodiodes, depending on the actual situation, another circle of closely arranged photodiodes can be added, and the photodiodes in the outer ring are connected in parallel with the photodiodes in the corresponding positions of the inner ring

Figure 3 photoelectric detection arrangement

Figure 4 shows the signal processing unit circuit. When the solar radiation intensity increases, the resistance value of the photoelectric resistance decreases, and the voltage drop of the 1K variable resistance increases, thereby generating a voltage signal directly related to the solar radiation intensity. The output signals of the two sensors are connected with the PLC Analog input port, and the two analog signals are compared and calculated, so as to output the correct signal to drive the electromagnetic mechanism of the solar panel tracking system

Figure 4 signal processing unit

2.3 photovoltaic module

the photovoltaic module adopts Mitsubishi photovoltaic intelligent power module PV IPM (pm50b4la060), and its technical parameters mainly include peak power Pmax = 85W, the best working voltage 17.5V. These parameters are tested under standard test conditions (solar intensity 1000w/m3, solar panel temperature 25 ℃, air quality 1.5)

2.4 electromagnetic mechanical motion control module

the anti wind automatic sail release function is to ensure that the tracking power generation device, when the wind reaches a certain strength, the wind protection system starts, and automatically adjust the wind receiving surface to prevent the equipment from being damaged by the wind. After experimental research, the windproof sensor is imported from Germany, and the windproof system adopts the priority working mode. Once it is started, it will cut off the tracking solar system and automatically release the sail

mechanical transmission mechanism is the actuator of tracking control. It not only bears the weight and wind force of the device, but also works outdoors, and directly affects the accuracy of the whole machine. After research, the horizontal transmission adopts motor, harmonic reducer and two-stage worm gear reducer. The elevation transmission adopts motor, harmonic reducer and ball screw to ensure mechanical accuracy and transmission efficiency

2.5 the system power module

power circuit adopts the design of switching power supply, which has the characteristics of high efficiency and low loss. The switch control chip L4960 can provide an output voltage of 5.1 ~ 40V and an output current of 2.5A. The power circuit is shown in Figure 5. By adjusting the two resistors R3 and R4, 12~24v DC voltage is generated. 24V (DC) is used for PLC power supply, and 44V (DC) is directly supplied to DC motor from rectifier bridge side. If it is used in the tracking system of photovoltaic inverter system, 220V (AC) can be directly taken from photovoltaic inverter power supply

Figure 5 switching power supply design

3 photovoltaic system software design

and the photovoltaic power generation system control software adopts modular design, including PLC control and monitoring program, PC monitoring and data processing program

3.1 PLC control and monitoring program

plc control statement is an important part of the whole solar panel tracking system. The software programming adopts CX programmer 7.1 of OMRON company. Cx-p ladder programming support software provides users with a full Chinese operating environment from the operating interface to program notes, supports windows drag and paste operations, as well as complete retrieval functions and simple input functions of common standard bits, It creates an efficient programming environment for users.

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