Output current measurement of solar cells based on Hall current sensor

Renewable energy solar power generation can be divided into two categories: solar photovoltaic power generation (also known as photovoltaic) and solar thermal power generation. The latter is relatively complex in technology and can only be used for relatively large capacity. Its application is subject to certain restrictions, so it is currently less used in practice. Solar photovoltaic power generation has many advantages such as inexhaustible, inexhaustible, and pollution-free, and has become a hot spot for humans to seek new energy. But at the same time, it also has the disadvantages of intermittent application and the power generation being related to climatic conditions. Therefore, in order to improve the utilization rate of solar cells, it is necessary to monitor the power generation in real time, so as to detect abnormal conditions in the operation of solar cells as early as possible. Here, a design scheme for a real-time monitoring system for solar cell power generation is proposed. The system is controlled by the AT89S52 single-chip microcomputer and uses a Hall current sensor to measure the output current of the solar cell. Its outstanding advantage is that it can convert current into voltage for measurement without consuming almost any energy.

1 System hardware design

The system hardware circuit is shown in Figure 1. It mainly consists of five parts: a solar cell group, a Hall current sensor, an I/U conversion circuit, a display device composed of a liquid crystal 1602, a control system composed of an AT89S52 single-chip microcomputer, and an energy storage system composed of a lead-acid battery. Its working process: When the solar cell receives light, it generates current to charge the battery. The microcontroller uses the voltage stabilizing device to provide driving voltage from the battery to collect real-time signals of the amount of electricity generated by the solar cell. Since the microcontroller can only receive voltage signals, the I/U and U/U conversion modules adjust the signal to a suitable voltage before receiving the signal. After internal calculation processing, the result is sent to the 1602 LCD display device to display the battery power generation.


1.1 A/D conversion module

After the analog signal is input into the microcontroller, it needs to be converted into a digital signal. Since the output voltage and current of the solar cell need to be measured at the same time, ADC0832 is an 8-bit serial dual-channel A/D converter. The A/D conversion accuracy depends on the reference voltage with high stability. The reference voltage is set to 5 V and is generated by TL431. The analog signal is sent to the AD input terminal after RC filtering, and then the analog-to-digital conversion is performed and the serial output is output.

1.2 I/U conversion module

Because the I/O interface of the microcontroller can only receive 0-5 V voltage signals, the real-time acquisition of the output current of the solar cell requires the current signal to be converted into a voltage signal. Since this system is an auxiliary device for the photovoltaic power generation system, reducing energy consumption as much as possible is the primary issue. Therefore, the Hall current sensor becomes the first choice. It works according to the Hall effect principle and can convert the current signal into a voltage signal without consuming almost any energy. This system uses the TBCl0SY type Hall current sensor with a rated output voltage of (±4±0.5%)V, ±15 V dual power supply, and a measurement current range of 0-15 A, which basically meets the application of small off-grid photovoltaic systems. [page]

1.3 Power supply design

For the normal operation of the single-chip microcomputer, it is necessary to supply power to the transistors or field effect tubes in the chip so that they can work in the corresponding state. AT89S52 requires a 5 V power supply (the actual working voltage is 3.6~6.0 V). It can be powered by rectification and voltage regulation to obtain a voltage of about 4.5 V. Because this system is an independent power generation and is used for a long time, considering the life of the power supply, it is not practical for the device to be driven by the mains or dry batteries. Therefore, the best solution should be powered by the battery of the solar cell inside the system, which is stabilized to 5 V by the voltage regulator integrated block 7805 and input to the Vcc pin of the single-chip microcomputer to drive the single-chip microcomputer and the liquid crystal display device. The TBCl0SY Hall current sensor requires a ±15 V dual power supply, which is also powered by the battery in the system. It is stabilized at ±15 V by the voltage regulator integrated blocks 7805 and 7915, thereby driving it to work.

1.4 Output display module

The power calculation formula is Q=UIT, where the time T can be determined by the software programming according to the needs, such as sampling every 3 minutes, and sending it to the 1602 LCD to display the power generation after internal calculation. In order to save energy, the LCD display is set to automatically turn off after 10 seconds.

2 System software design

The system software design is mainly completed by the single-chip microcomputer, which mainly realizes data acquisition and control display. The entire software system design adopts modularization thinking. The measurement and display program flow is shown in Figure 2.


3 System test analysis

Take a 200 W small off-grid photovoltaic system as an example, with a rated voltage of 24 V, a maximum current of 6.18 A, and a battery of 200 Ah. The normal discharge time is designed to be 2 to 3 days. The current of 0 to 6.18 A is converted into a voltage of 0 to 5 V in proportion. The attenuator is composed of two resistors. The output voltage amplification ratio is determined by the ratio of resistors R1 and R2. The U/U conversion ratio is set to 5/24, then R7=10 kΩ, R6+Rp2=48 kΩ. According to the power calculation formula Q=UIT, the experimental time is from 12 noon to 2 pm. Starting from the display of power, the actual power and the data displayed by the monitoring system are recorded every 3 minutes. The error of each time is less than 3%. Table 1 shows the initial 10 measurement errors. As the power gradually increases, the error range gradually decreases.


4 Conclusions

The real-time monitoring system of solar cell power generation composed of AT89S52 microcontroller, Hall current sensor and 1602 LCD has a simple structure, low cost, maintenance-free, low power consumption, and can effectively monitor the power generation of solar cells in real time, and detect abnormal conditions in the operation of solar cells as soon as possible. The system is designed as an auxiliary component of a photovoltaic system and is suitable for small off-grid photovoltaic systems. At the same time, the system devices have a long life, are durable and reliable, and are widely used in off-grid photovoltaic systems.