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As we all know, the auto market has not performed well this year, and the overall situation is in a slow growth or even a partial decline. But the new energy sector is just the opposite, and the trend is bullish. According to the data of the China Automobile Association, the production and sales of new energy vehicles in November 2018 were 1.054 million and 1.03 million respectively, an increase of 63.6% and 68% respectively over the same period of the previous year. Among them, the production and sales of pure electric vehicles were 807,000 and 791,000, respectively, up 50.3% and 55.7% over the same period of the previous year; the production and sales of plug-in hybrid vehicles were 247,000 and 239,000 respectively, up from the same period of the previous year. 130.3% and 127.6%.
As the core component of new energy vehicles, the power battery pack accounts for a very high proportion of the cost of vehicle manufacturing, and its performance also affects the vehicle's endurance performance and safety performance. The power battery also has an indispensable component, which is the BMS management system. So what is the BMS management system? The tram resources will be used to take a look at everyone.
The battery management system, BMS (Battery Management System) in English, is an important part of the electric vehicle battery system. It can detect and collect the battery real-time status parameters, and control the on/off of the power supply circuit according to the comparison between the detected value and the allowable value. In addition, it will feed back the collected key data to the vehicle controller and receive the controller. The instructions work in coordination with other systems on the car. Different battery types have different requirements for management systems. The lithium-ion battery used in electric vehicles has a large capacity, a large number of series-parallel joints, a complicated system, and high requirements for safety, durability, and power performance, and is difficult to implement. Therefore, it has become a bottleneck affecting the popularization of electric vehicles. The safe working area of a lithium-ion battery is limited by the temperature and voltage window. When the window is exceeded, the battery performance will accelerate and even cause safety problems.
The main purpose of the battery management system is to ensure the design performance of the battery system, providing functions in terms of safety, durability and power. In terms of safety, the BMS management system protects the battery cells or battery pack from damage and prevents safety accidents. In terms of durability, the battery life is extended even if the battery operates in a reliable and safe area. In terms of power, it is necessary to maintain the working state of the battery while satisfying the requirements of the vehicle.
The BMS management system is mainly composed of various sensors, actuators, controllers, and signal lines. In order to enable new energy vehicles to travel safely and comply with relevant standards and regulations, the BMS management system should have the following functions:
Battery parameter detection: including total voltage, total current, single cell voltage detection (to prevent overcharging, overdischarging, and even reverse polarity), temperature detection (preferably each string of batteries, critical cable connectors, etc.), smoke Detection (monitoring electrolyte leakage, etc.), insulation detection (monitoring leakage), collision detection, etc.
Battery state estimation: including state of charge (SOC) or depth of discharge (DOD), state of health (SOH), functional state (SOF), energy state (SOE), fault and safety state (SOS).
Online fault diagnosis: including fault detection, fault type judgment, fault location, fault information output, etc. Fault detection refers to the diagnosis of fault types and early warning through the collected sensor signals. Battery failure refers to sensor failures of various subsystems such as battery packs, high-voltage electrical circuits, and thermal management, actuator failures (such as contactors, fans, pumps, heaters, etc.), as well as network failures, various controller hardware and software failures. Wait. The fault of the battery pack itself refers to overvoltage (overcharge), undervoltage (overdischarge), overcurrent, ultrahigh temperature, internal short circuit fault, loose joint, electrolyte leakage, and insulation reduction.
Battery safety control and alarm: including thermal system control, high voltage power safety control. After the BMS diagnoses the fault, the vehicle controller is notified through the network, and the vehicle controller is required to perform effective processing (the BMS can also cut off the main loop power when a certain threshold is exceeded) to prevent high temperature, low temperature, overcharge, over discharge, and over Flow, leakage, etc. damage to the battery and the human body.
Charge Control: The BMS has a charge management module that controls the charger to safely charge the battery based on the characteristics of the battery, the temperature and the power level of the charger.
Battery equalization: The presence of inconsistencies makes the capacity of the battery pack smaller than the capacity of the smallest single cell in the group. Battery balance is based on single battery information, using the main
Thermal management: According to the temperature distribution information and charging and discharging requirements in the battery pack, the intensity of active heating/heat dissipation is determined, so that the battery works as much as possible at the most suitable temperature, and the performance of the battery is fully exerted.
Network communication: BMS needs to communicate with network nodes such as vehicle controllers. At the same time, BMS is inconvenient to disassemble on the vehicle, and online calibration, monitoring, automatic code generation and online program download (program update) are required without removing the shell. The general vehicle network uses CAN bus technology without disassembling the product.
Information storage: used to store key data such as SOC, SOH, SOF, SOE, cumulative charge and discharge Ah number, fault code and consistency. The real BMS in the vehicle may only have some of the hardware and software mentioned above. Each battery unit should have at least one battery voltage sensor and one temperature sensor. For a battery system with dozens of batteries, there may be only one BMS controller, or even a BMS function integrated into the vehicle's main controller. For a battery system with hundreds of battery cells, there may be one master controller and multiple slave controllers that manage only one battery module. For each battery module with dozens of battery cells, there may be some modular circuit contactors and balancing modules, and the slave controller manages the battery modules like measuring voltage and current, controls the contactors, equalizes the battery cells and works with the main controller Communication. Based on the reported data, the primary controller will perform battery state estimation, fault diagnosis, thermal management, and more.
Electromagnetic compatibility: Due to the harsh environment of electric vehicles, BMS is required to have good anti-electromagnetic interference capability, and BMS is required to radiate externally.
As the monitoring and management center of the new energy vehicle power battery pack, the BMS management system must monitor the temperature, voltage, charge and discharge current and other related parameters of the battery pack in real time, and take emergency measures to protect each single battery when necessary. Avoid battery packs with overcharge, over discharge, over temperature and short circuit safety issues. In addition, the BMS management system must accurately estimate the SOC of the battery during the entire life cycle of the battery pack, and timely feedback key information such as remaining power, driving range and fault abnormality to the driver in a suitable manner, and simultaneously A suitable way to complete the data exchange function between the system and the vehicle ECU or the host computer.
