How to use photocoupler to isolate high voltages to improve the safety of lithium-ion battery packs of electric vehicles

2022/04/08

  Author :Iflowpower – Portable Power Station Supplier

At present, in the use of all-electric or hybrid vehicles, the management of high voltage lithium-ion battery packs faces many challenges, in addition to non-monitoring and charging and discharging cycles, based on safety considerations, it is necessary to isolate battery packs from providing hundreds of voltages. This paper specially discusses the monitoring needs of lithium ion battery, and discusses architectural and zero components used by battery monitoring systems, digital communication systems, and isolation interfaces. In the management system, the battery monitoring board uses two key subsystems to reliably monitor the battery status and supply digital results to the main control system operated by the control system, in order to separate these subsystems, in high voltage battery induction circuits and boards The communication device uses an optical isolation signal interface to ensure that the high voltage does not affect the digital subsystem.

Lithium-ion battery characteristics do not match the complex electronic system of electric vehicles in performance, safety, and reliability requirements and this point straight from the characteristics of lithium ion battery, the lithium material is discharged, the lithium material is usually ionized in the graphite anode, then these The lithium ion is moved by the electrolyte by the electrolyte to reach the cathode, and the charging process is in reverse the entire program, and the lithium ions are brought back by the cathode through the separator. The performance and reliability of this chemical reaction program is controlled by the temperature and voltage of the battery unit. At a lower temperature, the chemical reaction is slow, so that the voltage of the battery unit is low, and the reaction speed increases until lithium as the temperature increases, the reaction speed increases until lithium The ion unit begins to crash, when the temperature exceeds 100°When C, the electrolyte begins to analyze, the release of gas that may cause the pressure of the battery cells in the design, at a high temperature, the lithium ion battery unit may release oxygen due to oxide analysis in the face of thermal out of control, further Accelerated temperature rise.

Therefore, the best operating conditions for maintaining the lithium ion battery are a key requirement of the battery management system. The critical challenge when designing control and management systems is to ensure reliable data acquisition and decomposition to monitor the status of lithium-ion batteries in the car. And this is the characteristic problem of lithium ion battery itself.

In the ChevyVolt electric vehicle, the battery pack contains 288 prism-shaped lithium-ion batteries, divided into 96 battery packs, and supplies 386.6V DC system voltages, which form four main batteries in conjunction with temperature sensors and cooling units. Module, the voltage sensing line connected to each battery group is connected to each battery module, and the terminal is solved and connected to the battery interface module above each battery module through the voltage sensing beam combined connector, 4 using color.

The indicated battery interface module operates at different positions of the battery pack, respectively corresponds to the low, neutralization high voltage range of 4 modules DC voltage offsets. The data supplied by the battery interface module will be sent to the battery energy control module, then supplied the fault situation, state, and diagnostic information to a hybrid control module as a vehicle diagnostic primary controller, at any time, the entire system will Run more than 5,000 system diagnostics, 85% diagnostic focuses on the security of the battery pack, other as the performance and life control of the target battery. The multilayer circuit board battery performance decomposition begins in the battery interface control module used in ChevyVolt electric vehicles, please refer to FIG.

1, specifically facing high signal integrity, using a four-layer design circuit board using a trace layout technology, isolation The combination of techniques and ground planes to assist in ensuring that the signal integrity in the challenging environment, where the uppermost layer contains most of the zero components, including optical isolators, ground planes, and signal traces with multiple through holes, The supply path to the lower layer is supplied with the second layer, and the power supply and the ground plane are distributed below the high voltage zone of the circuit board, and the third layer contains the signal line below these areas, the other side of the printed circuit board, that is The fourth layer is as a ground plane and signal trace and contains some extra zero components. Figure 1: Each of the four battery interface control module circuit boards in the ChevyVolt electric vehicle contains a plurality of induction circuits and CAN communication circuits, and isolates the photocoupler edges of the communication subsystem. Signal isolation In electric vehicle use, communication and control is a crimp of the vehicle, such as ChevyVolt, using multiple network isolation and protecting the independent subsystem, using complex algorithm to manage independent lithium ion battery groups and monitor special Battery Interface Control Module The battery pack in each induced subsystem, but the key data as an overall battery management is contained in the controller local area network (CAN, ControlraneNetWork bus signal interface and a high voltage fault signal, while the system security And reliability also releaves the safety isolation of the CAN bus network and the high voltage sensing circuit, although the isolation can be implemented using a variety of methods and zero components, but the demanding environment and multiple safety regulations require the optoelectronic coupler to be the preferred use of this type.

Method. The photocoupler supplies high coefficient noise suppression capabilities, and is fundamentally highly electrically noise enhancements such as EMC and EMI in the automotive, in addition, the height isolation of this type of device supply is related to the long-term facing battery pack DC voltage pressure. And the rapid high voltage transient change in the probe, charging connection, and removal, and DC-DC conversion is critical to.

When selecting this key zero component, the criticized requirements of the car include suitable package and operating voltage specifications, although the performance specifications such as speed, data rate and power consumption are still tight, but the EMI is considered for the fast switch and high current change The demand for ultra-high-speed devices will be restricted, thereby turning to improve the higher flexibility requirements for adjusting the compression wave rate and restriction EMI performance. In order to meet the strict requirements of the car usage environment, AVAGO supplies multiple series of photocoupleer products, which can be used on the voltage induction of the battery pack, which brings the data communication interface and other safety isolation, Table 1 Supply in line with various Optocoupler product for cars usage. Table 1: Various photoconductors suitable for automotive photocoupler examples, AVAGO's ACPL-M43T photocoupler supplies the battery interface control module circuit board to be separated, as a member of the Avagor2Coupler series, ACPL-M43T is a compact 5-pin SO-5JEDEC package, suitable for surface-mounted single-channel digital optocoupler.

In addition to strengthening insulation capabilities, Avago's R2Coupler products use double-line to enhance key functional connections, as shown in Figure 2. In addition, the sealing photocoupler exhibits stronger reliability and wider operating temperature range, which greatly exceeds the photocoupleer product using consumer grade LEDs. Specially designed for automotive use, AVAGO's products use car level LEDs, manufactured by the ISO / TS16949 quality system, and comply with the AEC-Q100 specifications.

Figure 2: Avago uses two-wire reinforced key function connection with ACPL-M43T photocondensor products. (Highlights in Figure) This device is ideal for electric vehicle battery pack requirements. The supply includes 567V continued working voltage, 6000V maximum transient overvoltage, 5MM creepage distance and 5mm electrical clearance, etc.

, when 10mA is input to the current, Whether there is a logic high or low level output having 30 kV / s common-mode instantaneous disturbance, it can reduce the chance of changes in other car systems into the CAN transmission line network.

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