Lithium iron phosphate battery acquisition system based on LTC6802 - Power Circuit - Circuit Diagram

Abstract: A lithium iron phosphate power battery state acquisition system based on battery monitoring chip LTC6802 is designed. The embedded microprocessor MC9S08DZ32 is used to collect the 12-string battery pack status data and upload it to the host through the CAN (Controller Area Network) bus. In this paper, the overall structure and working principle of the system are introduced, and the specific hardware and software design schemes are given.
Key words: LTC6802; MC9S08DZ32; lithium iron phosphate power battery; monitoring system

Introduction With the new energy and environmental pollution issues in the global economic development process is highly concerned, as a clean energy power battery is getting more and more attention. Lithium iron phosphate power battery has been rapidly applied in industrial and transportation fields due to its long life, safe use, high current 2C fast charge and discharge, high temperature resistance, large capacity, no memory effect and green environmental protection. The working state of the battery is a key link in the application. The intelligent battery state intelligent acquisition system based on embedded technology has also become a hot research topic. The traditional battery working state acquisition chip supports a small number of lithium battery cells in series. For example, bq2060 and bq2085, which are widely used in laptop battery cell working state collection, support up to 4 lithium battery cells in series. The power battery is often used as a power source. Generally, about 100 batteries are connected in series. For example, a pure electric bus battery requires 108 lithium iron phosphate batteries in series. If the traditional battery operating state acquisition chip is used, the number of chips required will be large, which will greatly increase the cost. Therefore, the world's leading chip manufacturers have begun to develop acquisition chips that support more than a dozen lithium battery cells in series. The LTC6802 developed by Linear is a dedicated battery condition monitoring chip that can measure up to 12 series cell voltages and complete all cell voltage detection in 13 ms. The overall measurement error is less than 0.25%, with high electromagnetic compatibility and low The advantages of power consumption.
This article uses the LTC6802 to collect 12 series cell voltages. The microprocessor MC9S08DZ32 uses the SPI bus to read the voltage of the series cells collected by the LTC6802 and controls the LTC6802 to equalize any one of the cells. At the same time, the surface temperature of 12 series cells is collected by the built-in ADC, and the voltage, temperature and equilibrium state of the 12 batteries collected are uploaded to the superior control system through the CAN bus, and the working status of 12 batteries is monitored in real time. . With this as a basic system, state monitoring of a battery pack composed of a large number of batteries connected in series is realized by using a plurality of basic systems.

1 system composition and working principle
1.1 System Composition The series lithium iron phosphate power battery collection system studied in this paper can realize on-line monitoring of 12 power batteries. The system includes the cell voltage acquisition and equalization part with LTC6802 as the core, and the temperature acquisition and CAN bus communication part with MC9S08DZ32 as the core, as shown in Figure 1.

1.2 Working principle Monitoring system The LTC6802 is used to collect the voltage of 12 batteries connected to it. The communication between MC9S08DZ32 and LTC6802 is completed by SPI bus, and the collected voltage value is read. The surface temperature of 12 cells is obtained by the thermistor NTC which is closely attached to each battery case, and the switching circuit of the 12 cells is determined according to the voltage and temperature of the 12 cells read. The SPI sets the corresponding register of the LTC6802 to initiate shutdown equalization. The entire system is implemented by embedded chips for centralized control and online monitoring of power battery packs.

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