A low power and high performance design scheme of solar controller based on STC89C52 microcontroller is introduced. The system consists of solar cell module, thermostatic element storage battery, charge and discharge circuit, voltage acquisition circuit, MCU control circuit and optocoupler drive circuit. Using pulse width modulation technology, the charging and discharging of batteries can be controlled by controlling the opening and closing of MOSFET tubes. The whole design has the characteristics of stable performance, reliable operation, low cost and prolonging the service life of batteries. In recent years, due to the problems of resources and environment, many countries in the world begin to attach importance to the development and utilization of new renewable energy.
Among all renewable energy sources, solar energy is developing effectively with its unique characteristics. In order to make more efficient use of solar energy and effectively alleviate the problem of power supply in scarce resources, serious environmental pollution and remote areas, the utilization of solar energy has great practical significance. This system takes STC89C52 as the control center, combines hardware and software, and uses voltage dividing circuit to sample the voltage and current of storage battery and solar cell. After A/D conversion, the sampled data are input to the single chip computer for processing. The output of MCU is controlled by optocoupler driving MOSFET tube to open and close the external circuit. The system can control the optimal charging and discharging of the battery. When the battery voltage is 14.4V 0.5, the solar battery stops charging the battery.
When the battery voltage is 10.9V 0.
5, the battery stops discharging the load. The load current detection circuit can protect the overcurrent and detect the load power.
The system structure diagram is shown in Figure 1. The circuit includes solar cell, DC-DC conversion circuit, battery, data acquisition circuit, a / D conversion circuit, MCU control circuit and status display part. In this design, ATMEL series AT89S51 single chip computer is used as the control center of the combination of hardware and software. Two series resistors connected in parallel at both ends of the battery are used to sample the voltage of the storage battery and solar cell in a voltage dividing way. The voltage value of a digital signal is converted to A/D, and then the signal is sent to the single chip computer for processing. The output of MCU is controlled by optocoupler circuit. Pulse width modulation (PWM) is used to control the on-off of MOSFET. The bias of MOSFET gate is modulated according to the load variation of program design to achieve switching function. According to the program design, when the voltage of the battery is less than 12V, the charging mode is uniform charging, Q1 is fully conducting, that is, the pulse duty ratio of conduction is the largest; when the voltage of the battery is detected at 12V-14.5V, the charging mode is floating charging, the duty ratio of Q1 conduction and non-conduction becomes smaller; when the voltage of the battery is detected equal to 15V, the Q1 stop charging. When the battery voltage was detected to be less than 10.8V, Q2 was turned off and discharged. The software of the system is designed in embedded C language. When the system starts to run, the microcontroller initializes the parameters, then enters the main cycle program, collects the battery voltage, solar cell voltage and the environment temperature of the battery in real time, enters the charging mode when the solar panel voltage is larger than the terminal voltage of the battery, and the charging mode adopts the intelligent control mode. When the battery voltage is less than the normal working voltage, the microcontroller charges in time and during the charging process. The charging mode can be intelligently controlled. For example, when the working voltage is greater than 10.
8V, the fast charging mode is adopted; when the working voltage is greater than 12V, the charging mode is converted to floating charging mode; when the working voltage is greater than 14.5V, the charging mode is stopped. When the battery is full, the LED display prompt is full. Batteries are allowed to discharge. This paper presents a design method of intelligent solar controller based on STC MCU.
The system works stably, the conversion efficiency is high and the control is accurate. It can complete the three-stage charging curve of the battery and prolong the service life of the battery. It is suitable for popularization and application in small power generation system.