Introduction
The lead-acid battery industry is closely related to the development of power, transportation, information and other industries. It is in a controlling position in transportation vehicles such as automobiles and forklifts and large uninterruptible power supply systems. It is indispensable for social production and management activities and human life. China's battery industry is quite large in scale and widely used. In view of the problems caused by improper use of lead-acid batteries (such as vulcanization, capacity reduction, and shortened service life), it is necessary to realize intelligent management of batteries. There are very few embedded system products used in this field. This design utilizes 8-bit microcontroller MB95F136 to realize intelligent management of lead-acid battery, including battery charge and discharge monitoring control, battery capacity detection, display and alarm, etc., thus effectively realizing intelligent management of lead-acid battery system. Increased battery life and reduced maintenance costs.
1 System Overview
This design makes full use of the characteristics of MB95F136 to realize 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, and control and alarm the incorrect use or damage to the battery life. It can remind the user to charge or switch the backup power when the battery needs to be charged. To prevent overcharge and over discharge. In order to realize the intelligent management of the lead-acid battery, the system automatically corrects the dynamic parameters of the battery in real time to obtain an accurate calculation basis, thereby calculating accurate electric quantity and battery status information, and obtaining the charging parameter of the battery.
The battery management system designed in this paper mainly has the following functions:
1 Real-time monitoring of the temperature of the battery, through the temperature and other parameters to calculate the battery charge and discharge parameters, to avoid the use of improper use or battery temperature is too high and other factors to shorten the battery life.
2 Real-time monitoring of the terminal voltage and current of the battery. If the battery capacity is found to be less than the warning threshold, it will remind the charging or automatically switch the backup battery.
3 The remaining capacity of the battery can be calculated by analyzing the parameters and displayed in real time through the digital tube.
4 The system can automatically correct the internal parameters of the battery to adapt to some changes caused by the use of the battery, and can also obtain better charging effect 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
The system uses F2MC-8FX series single-chip microcomputer MB95F136 as the control core of the system. In the system, MB95F136 not only needs to monitor the current, voltage, temperature and other parameters of the battery and the operating status of the system in real time, but also must process according to the collected data, and output control signals to the charging control module to realize intelligent management of the battery system; At the same time, it is also responsible for the implementation of button control and system status output display. Fujitsu's MB95F136 uses O. The 35μm low-leakage process technology allows mask products to operate in 1.8 V and 1 μA low-power modes of operation (clock mode), and the pipeline bus architecture provides double execution speed with a minimum instruction cycle of 62.5 ns. It has a fast processing and low power consumption, and is equipped with a rich timer. It integrates an 8-channel 8/10-bit optional A/D converter, which can be easily applied to voltage and current in the system. 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 memory area, it can be rewritten in another memory area, thereby reducing the number of external memory parts to reduce the circuit. The surface area of ​​the plate. In addition, LVD (Low Voltage Detection) and CSV (Clock Monitor) functions improve system stability and reliability.
2.2 Power circuit design
In this system, in order to enhance the flexibility of system application, the system power is taken from the managed battery. To do this, the DC-DC module must be used for isolation. Since the selected DC-DC module requires an input voltage of ≥24 V, the battery managed by the system must be a battery pack with a nominal voltage of 2 V or more. Otherwise, an additional power supply circuit is required. To enhance the reliability of the system, the system can Set a 3 V battery case for the backup battery, and if the power from the battery fails, the system will still operate as usual. The schematic diagram of the system power supply circuit is shown in Figure 2.
The main object of monitoring is the voltage and current of the battery pack. The voltage is obtained by the voltage divider precision resistor, and after being amplified accordingly, it is sent to the A/D port of the single chip microcomputer. The charging and discharging current of the battery passes through O. The 01Ω sampling resistor is sampled, amplified, and sent to the A/D port PO1 of the microcontroller. The key to detecting a battery is the accuracy of the voltage sampling, so whether the sampling circuit is properly designed is critical to the overall system. Since the A/D converter embedded in the MB95F136 can operate at a 5 V reference voltage, the current-voltage acquisition circuit shown in Figure 3 is used. The benefit of this circuit is that it not only ensures that the sample value can change in real time with the change of the battery terminal voltage, 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 the sampling circuit can be calculated as O. 01 Q × I × 23.
2.4 Parameter Storage Module
The parameters (such as product sequence, zero point adjustment, battery standard voltage, etc.) are set before the system is put into operation, and the system writes these parameters into the EE-PROM. In order to reduce the number of read/write EEPROMs, the data is read from the EEPROM when the system is powered on and stored in the RAM of the microcontroller. The main function of EEPROM is the preservation and quantitative backup of parameter data. It is mainly used to store some system operating parameters, such as reference data and correction coefficient for calculating battery power.
This system uses an EEPROMAT24C02 with a capacity of 2 Kb. The chip is a serial using the I2C bus protocol. EEP-ROM can store important data in the system for a long time and reliably without power supply, and the 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 helping to reduce the PCB area and complexity of the system.
The lead-acid battery industry is closely related to the development of power, transportation, information and other industries. It is in a controlling position in transportation vehicles such as automobiles and forklifts and large uninterruptible power supply systems. It is indispensable for social production and management activities and human life. China's battery industry is quite large in scale and widely used. In view of the problems caused by improper use of lead-acid batteries (such as vulcanization, capacity reduction, and shortened service life), it is necessary to realize intelligent management of batteries. There are very few embedded system products used in this field. This design utilizes 8-bit microcontroller MB95F136 to realize intelligent management of lead-acid battery, including battery charge and discharge monitoring control, battery capacity detection, display and alarm, etc., thus effectively realizing intelligent management of lead-acid battery system. Increased battery life and reduced maintenance costs.
1 System Overview
This design makes full use of the characteristics of MB95F136 to realize 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, and control and alarm the incorrect use or damage to the battery life. It can remind the user to charge or switch the backup power when the battery needs to be charged. To prevent overcharge and over discharge. In order to realize the intelligent management of the lead-acid battery, the system automatically corrects the dynamic parameters of the battery in real time to obtain an accurate calculation basis, thereby calculating accurate electric quantity and battery status information, and obtaining the charging parameter of the battery.
The battery management system designed in this paper mainly has the following functions:
1 Real-time monitoring of the temperature of the battery, through the temperature and other parameters to calculate the battery charge and discharge parameters, to avoid the use of improper use or battery temperature is too high and other factors to shorten the battery life.
2 Real-time monitoring of the terminal voltage and current of the battery. If the battery capacity is found to be less than the warning threshold, it will remind the charging or automatically switch the backup battery.
3 The remaining capacity of the battery can be calculated by analyzing the parameters and displayed in real time through the digital tube.
4 The system can automatically correct the internal parameters of the battery to adapt to some changes caused by the use of the battery, and can also obtain better charging effect 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
The system uses F2MC-8FX series single-chip microcomputer MB95F136 as the control core of the system. In the system, MB95F136 not only needs to monitor the current, voltage, temperature and other parameters of the battery and the operating status of the system in real time, but also must process according to the collected data, and output control signals to the charging control module to realize intelligent management of the battery system; At the same time, it is also responsible for the implementation of button control and system status output display. Fujitsu's MB95F136 uses O. The 35μm low-leakage process technology allows mask products to operate in 1.8 V and 1 μA low-power modes of operation (clock mode), and the pipeline bus architecture provides double execution speed with a minimum instruction cycle of 62.5 ns. It has a fast processing and low power consumption, and is equipped with a rich timer. It integrates an 8-channel 8/10-bit optional A/D converter, which can be easily applied to voltage and current in the system. 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 memory area, it can be rewritten in another memory area, thereby reducing the number of external memory parts to reduce the circuit. The surface area of ​​the plate. In addition, LVD (Low Voltage Detection) and CSV (Clock Monitor) functions improve system stability and reliability.
2.2 Power circuit design
In this system, in order to enhance the flexibility of system application, the system power is taken from the managed battery. To do this, the DC-DC module must be used for isolation. Since the selected DC-DC module requires an input voltage of ≥24 V, the battery managed by the system must be a battery pack with a nominal voltage of 2 V or more. Otherwise, an additional power supply circuit is required. To enhance the reliability of the system, the system can Set a 3 V battery case for the backup battery, and if the power from the battery fails, the system will still operate as usual. The schematic diagram of the system power supply circuit is shown in Figure 2.
The main object of monitoring is the voltage and current of the battery pack. The voltage is obtained by the voltage divider precision resistor, and after being amplified accordingly, it is sent to the A/D port of the single chip microcomputer. The charging and discharging current of the battery passes through O. The 01Ω sampling resistor is sampled, amplified, and sent to the A/D port PO1 of the microcontroller. The key to detecting a battery is the accuracy of the voltage sampling, so whether the sampling circuit is properly designed is critical to the overall system. Since the A/D converter embedded in the MB95F136 can operate at a 5 V reference voltage, the current-voltage acquisition circuit shown in Figure 3 is used. The benefit of this circuit is that it not only ensures that the sample value can change in real time with the change of the battery terminal voltage, 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 the sampling circuit can be calculated as O. 01 Q × I × 23.
2.4 Parameter Storage Module
The parameters (such as product sequence, zero point adjustment, battery standard voltage, etc.) are set before the system is put into operation, and the system writes these parameters into the EE-PROM. In order to reduce the number of read/write EEPROMs, the data is read from the EEPROM when the system is powered on and stored in the RAM of the microcontroller. The main function of EEPROM is the preservation and quantitative backup of parameter data. It is mainly used to store some system operating parameters, such as reference data and correction coefficient for calculating battery power.
This system uses an EEPROMAT24C02 with a capacity of 2 Kb. The chip is a serial using the I2C bus protocol. EEP-ROM can store important data in the system for a long time and reliably without power supply, and the 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 helping to reduce the PCB area and complexity of the system.
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