Safety of lithium battery for electric vehicles -Lithium - Ion Battery Equipment

Improve the safety of lithium battery for electric vehicles -Lithium - Ion Battery Equipment

At present, in the application of all electric or hybrid electric vehicles, the management of high voltage lithium-ion battery packs faces many challenges. In addition to monitoring the charging and discharging cycles, based on safety considerations, it is also necessary to isolate the battery packs that supply hundreds of volts. This paper discusses the monitoring needs of lithium-ion batteries, and discusses the architecture and components used in battery monitoring systems, digital communication systems and isolation interfaces.

In the management system, the battery monitoring circuit board uses two key subsystems to reliably monitor the battery status and supply digital results to the main control processor in charge of the operation of the control system. In order to separate these subsystems, optical isolation signal interfaces are used between the high-voltage battery sensing circuit and the communication devices of the circuit board to ensure that the high voltage will not affect the digital subsystem.(Lithium - Ion Battery Equipment)

Lithium ion battery characteristics

The complex electronic system that must meet the performance, safety and reliability requirements of electric vehicles is directly affected by the characteristics of lithium-ion batteries. When lithium-ion batteries discharge, lithium materials are usually ionized at the graphite anode, and then these lithium ions move through the separator to the cathode through the electrolyte to cause charge flow. The charging process reverses the entire process, bringing lithium ions back to the anode from the cathode through the separator.

The performance and reliability of this chemical reaction program are controlled by the temperature and voltage of the battery unit. At a lower temperature, the chemical reaction is slow, making the voltage of the battery unit low. With the temperature rising, the reaction speed will increase until the lithium ion unit starts to collapse. When the temperature exceeds 100 ° C, the electrolyte starts to decompose, releasing gas that may cause the pressure of the battery unit without pressure relief mechanism in design. At a sufficiently high temperature, Lithium ion battery cells may release oxygen due to thermal runaway of oxide decomposition surface, further accelerating the temperature rise.

Therefore, maintaining the optimal operating conditions of the lithium-ion battery is a key requirement of the battery management system. The important challenge in designing the control and management system is to ensure reliable data acquisition and analysis, so as to monitor the status of the lithium-ion battery in the vehicle. This is precisely the characteristics of the lithium-ion battery itself.

In the ChevyVolt electric vehicle, the battery pack contains 288 prismatic lithium-ion batteries, which are divided into 96 battery packs. The 386.6V DC system voltage is supplied through connection. These battery packs combine temperature sensors and cooling units to form four main battery modules. The voltage sensing lines connected to each battery pack conduct terminal processing when connected to the top of each battery module, It is connected to the battery interface module above each battery module through the voltage sensing strap combination connector. Four battery interface modules with color marks operate at different positions of the battery pack, corresponding to the low, medium and high voltage ranges of the DC voltage offset of the four modules.

The data supplied by the battery interface module will be sent to the battery energy control module, which will then supply the fault condition, status and diagnostic information to the hybrid power control module as the main controller of vehicle diagnosis. At any time, the whole system will run more than 5000 system diagnostics per second, of which 85% will focus on the safety of the battery pack, and the rest will be used as the target battery performance and life control.

Multilayer circuit board

The battery performance analysis starts from the battery interface control module used in the ChevyVolt electric vehicle. Please refer to Figure 1. The design is especially oriented to high signal integrity. The circuit board with a four layer design uses the combination of wiring layout technology, isolation technology and grounding plane to help ensure signal integrity in such a challenging environment. The top layer contains most components, including optical isolators The grounding plane and the signal wiring with multiple through holes supply the connection path to the lower layer. The second layer uses the power supply and grounding plane to distribute under the high-voltage area of the circuit board. The third layer contains the signal wiring passing through these areas. The other side of the printed circuit board, that is, the fourth layer, serves as the grounding plane and signal wiring, and contains some additional components.



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