CR1625 battery.Intelligent lead-acid battery management system

　　Intelligent lead-acid battery management system

　　Introduction The lead-acid battery industry is closely related to the development of electricity, transportation, information and other industries. It plays a controlling role in transportation vehicles such as automobiles and forklifts and large-scale uninterruptible power supply systems. It is indispensable in social production and business activities and human life. my country's battery industry is quite large and has a wide range of applications. In view of the problems caused by improper use of lead-acid batteries (such as vulcanization, reduced capacity, shortened service life, etc.), it is very necessary to realize intelligent management of batteries, and currently in China There are very few embedded system products used in this field. This design uses the 8-bit microcontroller MB95F136 to realize intelligent management of lead-acid batteries, including battery charge and discharge monitoring and control, battery capacity detection, display and alarm, etc., thereby effectively realizing intelligent management of lead-acid battery systems. Improved battery life and reduced maintenance costs.

　　1 System Overview This design makes full use of the characteristics of MB95F136 to achieve real-time online monitoring of battery voltage, current and temperature. The charging and discharging process of the intelligent control system can display the battery's power, control and provide alarm prompts for incorrect or usage conditions that greatly damage the battery life, and can remind the user to charge in time or switch to a backup power supply when the battery needs charging. , to prevent overcharge and overdischarge, etc. In order to realize intelligent management of lead-acid batteries, the system automatically corrects the dynamic parameters of the battery in real time to obtain accurate calculation basis, thereby calculating the accurate power and battery status information, and obtaining the battery charging parameters. The battery management system designed in this article mainly has the following functions: ① Monitor the temperature of the battery in real time, calculate the charging and discharging parameters of the battery through temperature and other parameters, and avoid shortening the life of the battery due to improper use or excessive battery temperature. ② Monitor the terminal voltage and current of the battery in real time. If the battery capacity is found to be less than the warning threshold, it will remind you to charge or automatically switch to the backup battery. ③The remaining capacity of the battery can be calculated through parameter analysis and displayed in real time through the digital tube. ④The system can automatically correct the internal parameters of the battery to adapt to some changes caused by use of the battery, and can also obtain better charging effects by controlling the charge and discharge circuit. The structure of this system is shown in Figure 1.

　　2 System Hardware Design 2.1 System Control Core This system is designed to use F2MC-8FX series microcontroller MB95F136 as the control core of the system. In the system, MB95F136 must not only monitor the current, voltage, temperature and other parameters of the battery as well as the system operating status in real time, but also process the collected data and output control signals to the charging control module to achieve intelligent management of the battery system; At the same time, it is also responsible for realizing button control and system status output display. Fujitsu's MB95F136 uses O. Using 35μm low-leakage process technology, mask products can operate in low-power operating modes (clock mode) of 1.8V and 1μA. The pipeline bus architecture can provide double execution speed, with a minimum instruction cycle of 62.5ns. While it has fast processing and low power consumption characteristics, it is equipped with rich timers; it integrates an 8-channel 8/10-bit optional A/D converter, which can be easily used in the system to control voltage and current. collection. Dual-operation flash memory is also one of the features of the F2MC-8FX series 8-bit microcontroller. When a program is running in one storage area, it can be rewritten in another storage area, thereby reducing the number of external memory parts and shrinking the circuit. The surface area of the plate. In addition, LVD (low voltage detection) and CSV (clock monitor) functions can improve the stability and reliability of the system. 2.2 Power supply circuit design In this system, in order to enhance the flexibility of system application, the system power supply is taken from the managed battery. For this purpose, DC-DC modules must be used for isolation. Since the selected DC-DC module requires an input voltage of ≥24V, the battery managed by the system must be a battery pack of more than 2 cells with a nominal 12V, otherwise an additional power supply circuit needs to be designed; in order to enhance the reliability of the system, the system can set up a The 3V battery box is used for backup batteries. Once the power source from the battery fails, the system can still operate as usual. The schematic diagram of the system power supply circuit is shown in Figure 2.

　　2.3 The main objects monitored by the current and voltage acquisition circuit are the voltage and current of the battery pack. The voltage is obtained by the voltage dividing precision resistor, and then sent to the A/D port of the microcontroller after corresponding amplification. The charging and discharging current of the battery passes through O. 01Ω sampling resistor samples, amplifies, and then sends it to the A/D port pOl of the microcontroller. The key to battery detection lies in the accuracy of voltage sampling, so whether the sampling circuit is appropriately designed is crucial to the entire system. Since the A/D converter embedded in MB95F136 can operate at a 5V reference voltage, the current and voltage acquisition circuit shown in Figure 3 is used. The biggest benefit of this circuit is that it not only ensures that the sampling value changes in real time as the battery terminal voltage changes, but also makes the data more accurate and reliable. This circuit is a typical linear circuit. According to the characteristics of the operational amplifier, the output voltage after passing through the sampling circuit can be calculated to be O. 01Q×I×23.

　　2.4 Parameter storage module Before the system is put into operation, parameters (such as product sequence, zero point adjustment, battery standard voltage, etc.) must be set, and the system will write these parameters into EE-pROM. In order to reduce the number of times of reading/writing EEpROM, the data is read from EEpROM when the system is turned on and stored in the RAM of the microcontroller. The main function of EEpROM is the storage and quantitative backup of parameter data. It is mainly used to store some system operating parameters, such as reference data for calculating battery power, correction coefficients, etc. This system uses EEpROMAT24C02 with 2Kb capacity. The chip is serial using the I2C bus protocol. EEp-ROM can store important data in the system reliably for a long time without power supply, and its working life can reach 1 million times. The I2C bus greatly facilitates the design of the system, eliminating the need to design a bus interface, and helps reduce the PCB area and complexity of the system. 2.5 Temperature acquisition module design This design uses the DSl8820 single-bus digital intelligent temperature sensor produced by the American Dallas Company, which directly converts the temperature physical quantity into a digital signal, and transmits it to the controller in a bus mode for data processing. DS18B20 provides 9 to 12 bits of data and alarm temperature registers for the measured temperature. The temperature measurement range is -55 to +125°C, and the measurement accuracy is ±0.5°C in the range of -10 to +85°C. This sensor can be applied to automated measurement and control systems in various fields and environments. It has the advantages of miniaturization, low power consumption, high performance, strong anti-interference ability, and easy integration with microprocessors. In addition, each DSl8820 has a unique serial number, so multiple DSl8820s can exist on the same single-wire bus, which brings great convenience to applications. The temperature measurement circuit design is shown in Figure 4. The system uses thermally conductive adhesive to adhere the device to the surface of the battery. The difference between the die temperature and the surface temperature is approximately 0. Within 2℃. When the ambient air temperature is different from the battery temperature being measured, the backside and leads of the device should be isolated from the air. The ground pin is the main heat path leading to the die. It must be ensured that the ground pin also has good thermal contact with the battery being measured.

　　2.6 Controllable charge and discharge module This module is a hardware difficulty in actual design. It is connected to the external power grid to charge the vehicle battery; it can charge the battery with different currents in stages according to the instructions or flags issued by the control circuit; and it has an automatic power-off function to realize intelligent charging. This system is mainly designed to manage electric vehicle battery packs, and the current used to charge the battery packs is relatively large. To this end, an IGBT-based intelligent power module (IntelligentpowerModule, IpM) was selected for high-current charge and discharge management. IpM is an advanced hybrid integrated power device, consisting of high-speed, low-power IGBT, drive circuit and protection circuit. It has fault detection circuits such as overvoltage, overcurrent, short circuit and overheating, and has automatic protection function. The main circuit of battery charging and discharging is shown in Figure 5.

　　In Figure 5, Q1 and Q2 are integrated into an IpM. When Q2 is turned on, the battery pack is charged, and when Q1 is turned on, the battery pack is discharged through R1; when the battery pack supplies power to the load, both Q1 and Q2 are closed. In order to improve the working status of the power switching device, soft switching technology is used in the main circuit. In the case of high current charging, due to long-term charging of the battery pack, charge accumulates on the battery electrodes and generates reverse voltage, which actually manifests as an increase in the internal resistance of the battery. Not only the effective chemical substances in the battery cannot fully participate The chemical reaction reduces the capacity utilization of the battery pack, and also causes severe heating of the battery pack, which affects the charging speed and quality, and in turn affects the performance and life of the battery pack. An effective way to eliminate it is to use the negative pulse method: instantaneous discharge at both ends of the battery to remove the charge accumulated on the electrodes, thereby changing the inherent exponential curve form of the charge acceptance characteristics of the battery and improving the battery's ability to receive electricity. To this end, the charging strategy of "charge-stop-release-charge-stop-release" cycle charging is adopted. Its pulse charging characteristics are shown in Figure 6, and the time parameters are determined by the parameters of the battery.

　　2.7 Power and status output indication and alarm module In order to reduce system complexity and cost, this design uses three 8-segment digital tubes to display the system status. Simple parameter settings can be performed, and status, temperature and other data can be displayed in real time to achieve better human-computer interaction. This design adopts the solution of debounce processing of input in software, and continuously judges the button status until the button is released, and then executes the corresponding processing program. The data display adopts 3-digit 7-segment digital tube dynamic display mode, and uses 74HC595 to latch the dynamic display data. This design cleverly shares the key input and dynamic display digital selection ports, thereby reducing the application of microcontroller ports and achieving the purpose of system optimization and product cost reduction. The alarm uses a buzzer.

　　3 System software design The system software design process is shown in Figure 7. After the system starts, it immediately executes the system initialization program and reads the parameters obtained from the last run from EEpROM. Then start reading the data in the temperature sensor to obtain the current system temperature, and then call the A/D sampling subroutine to obtain 10-bit precision voltage and current signal data. After processing, the final battery operating status can be obtained. According to different statuses, respective processing procedures are performed, and the status data is output to the digital tube display. When the system is running, it will automatically correct the parameters based on existing data and monitored data to accurately reflect the internal parameters of the battery and realize intelligent system management.

　　Conclusion This system uses MB95F136 as the controller, making full use of its advantages of multiple peripheral interfaces, strong functions, integrated high-precision A/D converter, easy operation, low actual cost, and easy system modularization and miniaturization. The system can monitor the status of the battery and display the battery's power in real time and accurately. When the power is insufficient, it can automatically switch the power system to implement self-protection. The update of parameter data is based on the results of multiple experiments, comparisons and calculations of measured parameters. Through experiments, the calculated remaining power value is closer to the actual value than when the parameters are not updated. Practice has proven that this intelligent lead-acid battery management system is highly intelligent and accurate in measurement. It can promptly detect and control improper use of batteries, provide self-protection, and accurately judge the operating status of the system. It not only greatly improves the efficiency of the power supply System stability, and help improve battery life and efficiency.

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