Signal isolation performance significant optocoupler enhances EV battery safety
At present, in the all-electric (BEV) or hybrid electric vehicle (HEV) applications, the management of high-voltage Lithium Battery packs faces many challenges. In addition to the need to monitor the charging and discharging loops, it is necessary to provide hundreds of volts for safety considerations. The Battery pack is isolated. This article specifically discusses lithium battery monitoring needs and discusses the architecture and components used in battery monitoring systems, digital communication systems, and isolation interfaces. In the management system, the battery monitoring board uses two key subsystems to monitor battery status and provide digital results to the master processor that controls the operation of the system. To separate these subsystems, an optically isolated signal interface is used between the high voltage battery sensing circuit and the communication components of the board to ensure that high voltages do not affect the digital subsystem. Keep the lithium battery stable and operate the battery management system Complex electronic systems must meet the performance, safety and reliability requirements of electric vehicles and are affected by the characteristics of lithium batteries. When a lithium battery is discharged, the lithium material is usually ionized at the graphite anode, and then the lithium ions move through the separator to the cathode to cause charge flow. The charging process reverses the entire program, and the lithium ions pass through the separator through the separator. Bring back the anode. The performance and reliability of this chemical inversion program is controlled by the temperature and voltage of the battery unit. At lower temperatures, the chemical reaction is slower, causing the cell voltage to be lower; as the temperature increases, the reaction rate increases until the lithium ion unit begins to collapse. When the temperature exceeds 100 ° C, the electrolyte begins to decompose, releasing the gas generated by the battery unit designed without pressure relief mechanism. At high enough temperatures, the lithium battery unit may release oxygen due to thermal runaway due to oxide decomposition, further accelerating the temperature rise. Therefore, maintaining the optimal operating conditions of the lithium battery is a key requirement of the battery management system. The main challenge in designing the control and management system is to ensure reliable data acquisition and analysis to monitor the status of the lithium battery in the car. It is the characteristic problem of the lithium battery itself. In the Chevy electric Volt, the battery pack contains 288 prismatic lithium batteries, divided into ninety-six battery packs, which provide a DC system voltage of 386.6 volts. These battery packs combine temperature sensors and cooling units. Forming four main battery modules, connected to the voltage sensing lines of each battery group, and then connected to each battery module for terminal processing, and connected to each battery module through a voltage sensing band combination connector The battery interface module above the group. Four color-coded battery interface modules operate at different locations in the battery pack, corresponding to the low, medium, and high voltage ranges of the four module DC voltage bias bits. The data provided by the battery interface module will be sent to the battery energy control module. The module will then provide the fault condition, status and diagnostic information to the hybrid control module as the vehicle diagnostic master Controller. More than 5,000 system diagnostics were run, 85% of which focused on battery pack safety and others as target battery performance and life control. Ensuring signal integrity multilayer boards are a must Battery performance analysis begins with the battery interface control module used in the Chevy electric vehicle Volt (Figure 1). The control module is designed for high signal integrity using a four-layer design board that uses a combination of trace layout techniques, isolation techniques, and ground planes to help ensure signal integrity in challenging environments. Among them, the uppermost layer contains most components, such as optical isolators, ground planes and signal traces with multiple through holes, providing a connection path to the lower layer; the second layer is distributed on the circuit board using the power and ground planes. Below the high voltage area; the third layer contains signal traces through these areas; the other side of the printed circuit board (PCB), the fourth layer is the ground plane and signal traces, and includes some additional components. Figure 1 Each of the four battery interface control module boards in the Chevy Volt electric vehicle contains multiple sensing circuits and CAN communication circuits, and is isolated by optocouplers at the edge of the communication subsystem. In electric vehicle applications, communication and control are important cornerstones of vehicle operation. In Volt electric vehicles, multiple network isolation and protection of independent subsystems are used, complex algorithms are used to manage independent lithium battery groups, and special battery interfaces are monitored. Controls the battery pack in each sensing subsystem on the module. However, key information on overall battery management is included in the controller area network (CAN) bus signal interface, as well as a high voltage fault signal, while the system's safety and reliability also depends on the CAN bus network and high voltage. Safe isolation between sensing circuits. While isolation can be achieved using a variety of methods and components, the harsh environment and multiple safety regulations make optocouplers the preferred solution for this type of application. Achieve the best signal isolation optocoupler hot Optocouplers provide high common-mode noise suppression and high electrical noise environments, such as electromagnetic compatibility (EMC) and electromagnetic interference (EMI) immunity in automobiles; in addition, the high isolation provided by this type of component provides It is important to face the DC voltage stress of the battery pack for a long time, as well as the rapid high voltage transients that may occur during testing, charging connections and removal, and DC-to-DC conversion. When selecting this critical component, the main requirements for automotive applications include proper package and operating voltage specifications. While performance specifications such as speed, data rate, and power consumption are still important, consider the EMI caused by fast switching and high current variations. This will limit the need for ultra-high-speed components and thus shift to higher flexibility requirements for adjusting slew rate and limiting EMI performance. Optocouplers play a very important role in all-electric and hybrid automotive electronic systems, providing signal isolation, high noise suppression and system protection, avoiding high voltages entering paths that may cause injury or electric shock to the driver or occupant. Volt electric vehicles are just one practical example of how optocouplers can be used to assist in battery pack management.
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