A new type of management system about lithium ion battery

With the development of society, lithium ion batteries are widely used in the production and life. The application and management of batteries have become a very key technology for the development of various equipment. Based on the study of lithium-ion battery technology, a new type of lithium-ion battery management system is designed and the realization method is introduced. The design and implementation of the lithium battery management system are designed in a distributed structure, including power estimation, battery charging and discharging, the balance between individual battery functions and other local measurement modules. The hardware design of the realization module is analyzed in detail.

Since the turn of the century, lithium battery production and research, obtained the very big breakthrough, because it has many good advantages, such as stable discharge voltage, low self-discharge rate, wide working temperature range, no memory effect, long storage life, light weight, small size and other characteristics, has gradually replaced the traditional nickel cadmium battery and lead acid battery, in the field of social production and life of the application is more and more wide, into the main stream Power battery. Because in the lithium battery inside, the chemical reaction is very complex, while people are constantly perfecting the battery itself performance, also used in the management of the battery technology and continuous research, to increase the battery life, improve the efficiency of the battery, the most earth battery performance.

Battery management system (Battery Management System, BMS), which involves the microcomputer technology and detection technology, implement dynamically monitoring the running state for battery unit and battery pack, can accurately calculate the battery remaining power, for the battery charge and discharge protection, at its best working condition, reduce running cost, improve the service life.Combines the advanced achievements of home and abroad, this paper designs and realizes a new kind of lithium battery management system.The management system adopts modular structure, the design of the distributed, the control structure of a system contains 2 levels of the local measurement module and the central processing module.Among them, the function of the central processing module is mainly to use RS232 interface implementation and the upper machine communication, in order to CAN bus network form and local measurement module connected;Local measurement module main functions as data acquisition (mainly for data acquisition of temperature, current and voltage), charge and discharge control, electricity measurement, a single battery equalization and using CAN bus technology and the central processing module communication, etc.

1 management system hardware design

Design of battery management system, this paper is mainly used in electric vehicles and some underwater equipment, so the system design to reasonable structure, advanced technology, strong scalar ability ;The various parameters of the system accuracy is higher.Therefore, this design of battery management system, to achieve the following functions:

1) real-time acquisition battery information, contains the battery voltage, single battery voltage, charge and discharge parameters such as current and temperature;

2) measurement and display of remaining power;

3) CAN provide data transmission interface, complete part and CAN bus and PC communication;

4) good human-computer interaction function, system safe, reliable, strong anti-jamming.

Battery management system block diagram is shown in figure 1.

A kind of new type of lithium battery management system design and implementation scheme

CAN see in figure 1, the lithium battery management system includes 2 levels of control structure, respectively is the central processing module (Central Electric Control Unit CECU), local measurement module (Local Electric Control Unit, LECU), the central processing module and the local measurement module is implemented in the form of CAN bus communication connection. The battery management system structure is shown in figure 2.In figure 2, the local measurement module's main function is to the battery charging, the modules are: data collection module (as for current, voltage, temperature data acquisition), the equilibrium module, the charging module, power measuring module, etc.; The central processing module is mainly to the management of local measurement module, using the CAN bus communication mode, to control the information sending and receive battery status information. This article only for some of the key modules are introduced.

A kind of new type of lithium battery management system design and implementation scheme

2 the local measurement module hardware design

2.1 voltage acquisition module

Single voltage of the battery, as the implementation of the battery remaining power calculation, charging and discharging mode choice, and one of the main to the evaluation of the running state, so to monitor battery condition, is to have a reasonable method of single battery voltage measurement. Numbers because the batteries in the battery pack, however, the total voltage is higher, measurement accuracy is high, thus the difficulty of the implementation of the power measurement is larger. Voltage monitoring program working principle is: the first step, MCU control of mufti-channel switch Kn - 1, Kn - 2 (n) between a 1 to 7, the synchronization of the capacitance and ends with the matching unit cell implement docking, start capacitor charging, achieve the goal of capacitor voltage and cell battery voltage is the same; The second step, the MCU control mufti-channel switch Kn - 1, Kn - 2 to disconnect, and close the switch K1 and K2, from single chip A/D module implement measures. At the time of measurement, based on the prevent caused by unstable voltage of the battery to affect the outcome of consideration, module of the average measurement by selecting multiple methods. The solution can be easily used microprocessor internal A/D unit, not an additional A/D module, improves the design efficiency, save the cost. In the actual circuit, usually can use the relay to realize analog switch.

2.2 current acquisition module

For measuring dynamic current charge and discharge process, in this paper, by using the LEM company LTSR25 - NP current sensor. This element is based on hall effect with compensating closed-loop multiracial current sensor, through single polarity voltage of power supply in the form of having good measuring precision, no insertion loss, good linearity, current overload ability is better. In below 25 degrees Celsius, its measuring accuracy can reach + / - 0.2%.The rated current is 25, the largest measurable current is 80 a, can well realize the system design requirements. The current sensor to be able to charge and discharge current into 0 to 5 v voltage signal, and then access to the single chip microcomputer A/D unit, can charge and discharge current can be measured.

2.3 temperature acquisition module

Temperature acquisition module through Dallas semiconductor companies are in the United States DS620 programmable intelligent digital temperature sensor. Its chip contains registers, A/D converter and the interface circuit, can the digital signal directly to the output. Its and MCU interface circuit is simple, long transmission distance and control function is good, the rest of the world strong anti-interference ability, especially suitable for low power consumption micro temperature measuring system. The DS620 digital temperature sensor, can provide the 1.7 to 3.5 v low voltage temperature measurement, in 0 to 70 degrees Celsius, the measurement precision can be up to + / - 0.5 degrees Celsius, the sensor can work scope for minus 55 to 125 degrees Celsius above freezing. Can be used in a distributed sensing system for multiple spot connection, and a bus can be connected at the same time eight DS620 work at the same time, based on the SPCE061A IOA2 and IOA3 interface, analog I2C bus, and DS620 communication.

2.4 equilibrium module

Implementation of cascade connection of battery charging, because of the battery pack, the differences of chemical properties, a full battery if some unit, but some cell battery did not charge, that will happen is fully charged battery charging unit produced phenomenon, it will be a great influence on the battery. On the contrary, if the battery is not enough electricity for a long time, and can increase the resistance, reduce the capacity of battery, lead to the battery is easy to damage. Some solution in the process of charging battery charging and charge problem one of the most effective way, is the implementation of the equalization charging the battery, let all the battery can achieve the same state. The battery management system adopted by the equilibrium solution, which adopts two-way reversible DC/DC the principle of dynamic equilibrium method, through the DC/DC switching power supply, according to the detected in the process of charging and discharging voltage value of each single cells of the single section must charge battery charging, dynamic equilibrium with battery power for the batteries additional equalizing charge. DC/DC switching power supply using the star of the DOM - 24 d15s5 chip, its input voltage is between 18 and 36 v, output voltage between 4.6 to 5.5 v.

2.5 charging module

At present, most of the charging curve for the combination of constant voltage and constant current charging curve. Lithium battery in the late charge, based on considerations of ensure the security of the battery, the battery needs to adopt the way of constant voltage charging. General method of charging of the battery charging process is divided into three parts, namely: early charging, constant current and constant voltage, its principle and control process is simple, in the early stages of charging, charging fast, high charging efficiency. However, the charging way of heat is very big.In order to solve this problem, this article through early charging and constant voltage charge into intermittent charging, constant current charging way of charging current limit control of the power adapter. Intermittent charging sequence diagram is shown in figure 3.

A kind of new type of lithium battery management system design and implementation scheme

Lithium-ion battery pack is recharged, if there is a battery management system, the battery installation must be an external one and its matching of constant voltage current limiting type power adapter. Calculation of constant pressure value U expression is: U = 4.2 * N + voltage loss; On the type of N said the section of the battery, and loss of voltage is obtained through experiments. In this system, using the lithium-ion battery is Shenzhen thunder TS - LCP50AHA type, the type of battery current limit value of the Ic is between 0 and 0.5 C, C said battery capacity. In computing, take the best charging current TS - LCP50AHA battery 0.3 C. The battery recharged before, must first implement the system initialization, and then early charging, constant current and constant voltage charging, charging the three steps for battery charging.

3 conclusion

To sum up, this paper designs and realizes a new kind of lithium ion battery management system, introduces the system hardware design and design of each function module in detail. In the process of test, this system operation is normal, the technical indicators, including single battery voltage measurement, the total current, total voltage, and temperature measurement, meet the requirements , so that the system has good reliability and practicability.

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