In this monitoring system, current sensors play a crucial role. Taking an open-loop Hall effect sensor as an example, it acts like a keen current detective, monitoring the battery's charging and discharging current in real time with extremely high accuracy, with errors controllable within ±1%. This means that even extremely minute changes in current can be quickly detected and promptly transmitted this critical information.
Temperature sensors act like "little guardians" distributed across the battery surface, closely monitoring temperature changes. Typically, one temperature sensor is installed for every 10-20 batteries, evenly distributed across the battery surface to form a robust temperature monitoring network, providing real-time feedback on the battery's temperature distribution. If an abnormal temperature is detected in any area, these "little guardians" will immediately issue an alarm, alerting the BMS to take appropriate measures.
The voltage acquisition module, with its high-precision measurement capabilities, has become a key component of the BMS monitoring system. Through a high-precision AD converter, it can achieve a measurement accuracy of ±1mV for individual cell voltages, much like using a high-precision ruler to accurately measure the voltage of each battery, ensuring that no minute voltage change is missed.
The data collected by these sensors requires an efficient transmission channel to be transmitted to the BMS's central processing unit (MCU) in a timely and accurate manner. CAN bus or LIN bus undertakes this important transmission task. Like high-speed information highways, they update and transmit the data collected by the sensors at a high frequency of 10-50 times per second, ensuring that the MCU can obtain the latest battery status in real time and provide timely and accurate information for subsequent decisions.
Once the Battery Management System (BMS) collects massive amounts of battery data through sensor networks, the key lies in how to analyze and process this data to make sound and rational decisions. This crucial task falls on the BMS's central processing unit, which is equipped with complex and sophisticated control algorithms. Like an experienced commander, it quickly makes correct strategic decisions based on real-time intelligence from the battlefield.
Among numerous control algorithms, SOC estimation and fault diagnosis algorithms are core components. Taking SOC estimation as an example, the Extended Kalman Filter (EKF) and the Ampere-Hour Integral (AHI) method are two commonly used algorithms. The EKF acts like an intelligent data analysis master, accurately estimating the remaining battery capacity by fusing multi-dimensional data such as voltage, current, and temperature. The advantage of this algorithm lies in its ability to fully consider the impact of various factors on battery capacity, thereby controlling the estimation error to within 3%, significantly better than the traditional open-circuit voltage method. The traditional open-circuit voltage method is like a simple estimation tool; it estimates the remaining capacity solely based on the battery's open-circuit voltage, ignoring the influence of other factors, thus resulting in a larger estimation error.
The fault diagnosis algorithm acts like a keen doctor, promptly identifying potential problems in the battery system. When the system detects three consecutive instances where the cell voltage exceeds the safety threshold, it quickly triggers a three-level fault response mechanism. This mechanism is like a progressively stronger safety net: the first-level warning is like a doctor's verbal reminder, alerting the user to potential battery issues through dashboard prompts; the second-level limitation is like a doctor's initial treatment plan, reducing charging and discharging power to decrease the battery's workload and prevent further deterioration; the third-level cutoff is the final emergency measure, forcibly disconnecting power when the problem becomes severe, much like a surgeon's operation in an emergency to ensure the safety of the battery and the entire system.
Battery Management System (BMS) is closely connected to the power battery of electric vehicles, and its core task is to scientifically and efficiently manage and control the battery pack. So, how does it achieve this function? Specifically, the BMS workflow is as follows: Real-time monitoring: Through sensors, the BMS can continuously monitor key parameters such as battery voltage, current, and temperature. State management: Based on monitoring, the BMS further manages the battery's operating state, including leakage detection, thermal management, battery equalization, and alarm reminders. Simultaneously, it can calculate and report the battery's remaining capacity (SOC) and state of decay (SOH). State prediction and control: Based on real-time battery data, the BMS uses algorithms to predict the battery state and control the maximum output power to ensure optimal driving range. Furthermore, it can intelligently control the charger to achieve optimal charging current.
All this information interacts in real time with the vehicle's main controller, motor controller, energy control system, and vehicle display system via the CAN bus interface, enabling comprehensive monitoring and management of the battery pack. To ensure stable operation of the BMS within the vehicle, several key points need to be considered. First, to avoid interference between BMS modules, an isolated DC-DC power supply is required at the power input front end. In electric vehicles, multiple BMS modules typically operate simultaneously, all drawing power from the battery. The use of an isolated DC-DC power supply is crucial to ensure the independent power supply of each module and prevent crosstalk. Furthermore, the input voltage range of this power supply should be sufficiently wide to accommodate different operating requirements.
Secondly, to ensure real-time communication between the BMS and the electric vehicle, we need to implement CAN isolation at the communication front end. Due to the complex communication environment inside a vehicle, which is susceptible to interference signals such as surges and pulses, we also need to adhere to the principle of low coupling between systems and implement safety regulations for the power supply to ensure normal communication. This means that the CAN terminal also needs isolation, while placing higher requirements on protection levels and transmission rates.
Finally, we also need to consider the personal safety of the driver, therefore, high-strength power isolation protection measures are required. With multiple batteries connected in series, the battery pack voltage can reach around 500VDC, which poses a safety threat to humans. To ensure the safety of the low-voltage side of the battery, we typically use isolated DC-DC technology to separate the high-voltage and low-voltage sides. Given the critical importance of BMS safety, power and signal isolation between systems is particularly necessary. The power supply to the BMS mainboard usually comes from the battery pack, with a voltage typically of 12V (or 24V), and often uses 2W/3W isolated DC-DC power modules. In some applications with higher power requirements, 6W isolated DC-DC power modules are also selected. Furthermore, for environments with high electromagnetic interference (EMI) requirements, a π-type filter circuit can be added to the input of the isolated DC-DC power module to further improve system stability. The BMS, or Battery Management System, is figuratively described as the battery's "nanny" or "housekeeper." Its core responsibility is to intelligently manage and maintain battery cells. Through precise monitoring and protection measures, it effectively prevents overcharging and over-discharging, thereby ensuring the safety and longevity of the battery. Simultaneously, the BMS can track and provide real-time feedback on the battery's status, offering comprehensive monitoring and protection for the battery's health.
Ten major functions of BMS
(1) Battery terminal module: responsible for data acquisition, covering key parameters such as voltage, current, temperature and communication signals.
(2) Intermediate control module: communicates with the vehicle system in real time and controls key equipment such as the charger.
(3) Display module: Presents data in an intuitive way to enable efficient interaction between users and the system.
In addition, BMS also has the following core functions:
(1) Comprehensive detection of battery parameters: Real-time monitoring of total voltage, total current, individual cell voltage, etc. by sensors to ensure safe operation of the battery.
(2) Accurate battery status estimation: Real-time estimation of key indicators such as state of charge and health status, providing a scientific basis for battery management.
(3) Online fault diagnosis and alarm: Intelligent diagnostic algorithm is adopted to detect and handle various faults in a timely manner to ensure battery safety.
(4) Battery safety control: Through measures such as thermal system control and high voltage safety control, potential risks such as high temperature and overcharging are effectively prevented.
(5) Intelligent charging management: Based on battery characteristics and charger power level, the charging process is intelligently controlled to ensure safe and efficient charging.
(6) Battery balancing technology: Through active or passive balancing methods, the capacity difference of the battery pack is minimized as much as possible, and the battery life is extended.
(7) Thermal management system: Based on the temperature distribution within the battery pack and the charging and discharging requirements, the intensity of active heating or heat dissipation is intelligently adjusted to ensure that the battery operates within the optimal temperature range, thereby maximizing its performance.
(8) Network Communication Function: The BMS needs to communicate in real time with network nodes such as the vehicle controller. Furthermore, considering the inconvenience of disassembling the BMS on the vehicle, online calibration, monitoring, upgrades, and maintenance operations need to be performed without disassembling the casing. The vehicle network typically uses the CAN bus for data transmission.
(9) Information storage capacity: The BMS should have the function of storing key data, such as the battery's state of charge (SOC), state of health (SOH), state of fault (SOF), as well as accumulated charge and discharge Ah, fault codes and battery consistency information.
(10) Electromagnetic compatibility: Electric vehicles are often used in harsh environments, so the BMS is required to have good electromagnetic interference resistance and reduce electromagnetic radiation to the outside world.
