BMS is the core and brain of the lithium battery pack, and its performance determines the intelligence level and performance of the lithium battery pack. As a manufacturer with nearly 20 years of customized lithium battery R&D and manufacturing, SES Power is very familiar with BMS. For example, we use 12V100Ah, 12V200Ah, 24V100Ah, 24V200Ah, 36V100Ah, 48V50Ah, 48V100Ah, etc. Lead-acid replacement, wall-mounted home energy storage, mobile home energy storage, etc., all use high-precision and high-intelligence BMS. In addition to traditional RS485 and CAN communication, we also added Bluetooth communication. As for special customized lithium batteries such as 12V30Ah, 12V50Ah, 12V60Ah car start-up batteries (maximum peak current can reach 1500A) using high-performance lithium batteries, and lithium battery systems normally used in -40°C environment, because the parameters fluctuate greatly, the design requirements of BMS are higher.

　　Below we will explain some of the functions and design concepts of BMS for you.

　　The core function of lithium battery BMS is to collect data such as voltage, temperature, current, insulation resistance, and high-voltage interlock status of the system, and then analyze the data status and battery use environment, and monitor and control the charging and discharging process of the battery system. Under the premise of ensuring the safety of the battery, the energy stored in the lithium battery system is maximized. According to the function, BMS can be divided into battery data acquisition, battery status analysis, battery safety protection, battery system energy management control, data communication and storage, fault diagnosis and management and other parts.

　　1. Battery data collection

　　Data acquisition includes the acquisition of data such as voltage, temperature, current, insulation resistance, and high-voltage interlock status, which can provide BMS with real-time data of the battery system and provide a basis for subsequent status analysis, control and protection of the battery system.

　　The voltage collection includes the voltage of each string of cells, the total internal voltage Vbat of the battery system, and the total external voltage Vlink of the battery system. The temperature collection includes the temperature of the surface of the cell and the tab, the temperature of the liquid cooling water inlet and outlet, the interface temperature of the fast-charging pile, and the working internal temperature of the BMS. The current acquisition mainly collects the current of the main circuit of the battery system through a shunt or a Hall current sensor, and uses the ampere-hour integration and other estimation methods to estimate the state of the battery system. Insulation resistance mainly collects the insulation resistance between the total positive of the battery system and the box, and the insulation resistance between the total negative of the battery system and the box. The high-voltage interlock includes the interlock state of the high-voltage air plug and the interlock state of the MSD.

　　2. Battery status analysis

　　Estimation of the state of charge (SOC) of a lithium battery system: SOC is defined as the percentage of the battery's remaining charge to the battery's capacity.

　　Estimation of the state of health (SOH) of a lithium battery system: SOH is defined as the percentage of the number of times the battery has been fully charged to the number of available charges over the battery life cycle.

　　The estimation of SOC and SOH is the core technology of BMS and the main parameters for evaluating the performance of lithium batteries in all aspects. Typical algorithms for SOC estimation include open circuit voltage method (OCV method), ampere-hour integration method, impedance method, extended Kalman filter method and neural network method.

　　At this stage, most BMSs use the optimized ampere-hour integration method. On the basis of the ampere-hour integration method, cell parameters such as open circuit voltage, rated capacity at different temperatures, and charge-discharge efficiency at different currents are added. SOC is corrected.

　　In order to reduce the SOC estimation error, some BMS manufacturers have studied artificial intelligence SOC estimation methods: on the basis of the weighted ampere-hour integration method, real-time OCV estimation is performed by collecting real-time data (cell voltage, current, temperature, etc.) of the battery system, so as to achieve dynamic OCV correction SOC.

　　3. Battery safety protection

　　When the battery system has faults such as overvoltage, undervoltage, ultra-high temperature, ultra-low temperature, overcurrent, low insulation, disconnection of the voltage collection line, disconnection of the temperature collection line, abnormal high-voltage interlock, etc., the BMS needs to protect the battery system in time. According to the severity of the fault, protection measures such as power limitation and immediate power-off are adopted in stages, so as to ensure that the battery system can maximize the use of its stored energy under the premise of safety.

　　In a low temperature or high temperature environment, when the battery system needs to be charged and discharged, the BMS will first report the cell surface temperature and the ambient temperature to the system. The system will heat or dissipate the battery system by analyzing the temperature data reported by the BMS, so that the battery system is in Charge and discharge at suitable ambient temperature.

　　4. Battery system energy management

　　4.1 Charge Management

　　The BMS performs a linear look-up table for the charging power MAP of the battery system according to the current cell temperature and SOC of the battery system, thereby determining the current maximum allowable charging current of the system.

　　When charging, the BMS communicates information with the charging equipment such as the highest voltage of the battery system, the highest total voltage, the highest temperature, the current maximum current allowed for charging, the nominal energy, the SOC, and the current battery voltage, so that the battery can be charged. The system charges according to the adapted charging voltage, charging current and charging method to ensure that the battery is fully charged. At the same time, the remaining charging time is estimated according to the maximum output capacity of the charger and the state of charge of the battery system.

　　4.2 Discharge Management

　　Discharge management is that the BMS performs a linear look-up of the 10s/30s peak discharge power MAP and continuous discharge power MAP of the lithium battery system according to the real-time collected temperature and estimated SOC, and obtains the current 10s/30s peak discharge power value and continuous discharge power value of the battery system. The discharge power value is reported to the system MCU.

　　The MCU compares the motor requested power P1 with the peak discharge power Pmax and continuous discharge power Pc reported by the BMS. When P1>Pmax, take the peak discharge power Pmax of the battery system to discharge and time it, and after the timeout, it will drop to the continuous discharge power Pc to discharge; when P1

　　4.3 Balanced management

　　The main function of balance management is to reduce the voltage difference between the cell voltages, so as to maintain the consistency of cell discharge and ensure that the battery system can maximize the use of its stored energy under the premise of safety.

　　Balance is divided into active balance and passive balance. Active balance is when the pressure difference between the monomers is too large, the energy in the high-voltage monomer is transferred to the low-voltage monomer, so as to achieve balance; passive balance is when the pressure difference between the monomers is too large. When it is too large, a resistor is connected in parallel at the strings of monomers with high voltage, so as to consume part of the energy and finally achieve the equalization function.

　　5. Data Communication and Storage

　　The BMS reports the cell voltage, temperature, total voltage, current, SOC, SOH and fault alarm data of the battery system to the system through CAN communication. After the system receives the data, it first displays the real-time total voltage, current and SOC on the The second is to analyze the fault alarm information, and then send commands to the BMS through CAN communication, so that the BMS can protect and control the battery system.

　　6. Troubleshooting and Management

　　According to the cell parameters and the function of the battery system, the corresponding fault threshold table is formulated, including the fault name, fault threshold, fault hysteresis, fault detection time and response time, as well as the protection measures taken by the BMS and system protection measures and other information.