A 12-meter electric bus generally requires 6-8 battery packs, and each battery pack contains thousands of cells connected in parallel (series). It is conceivable that how can a battery system composed of numerous individual cells with certain differences work in a coordinated and orderly manner? It's simple, organized, and managed, resulting in a battery management system. A single battery is a thing. Of course, the person who manages the battery must also be a "thing", not a person. This thing is naturally a computer management system. To sum up, the battery management system (BMS) is an intelligent management system using computer technology. Working process of lithium-ion power battery: During the process of charging and discharging, lithium ions pass through the separator through the electrolyte and constantly move back and forth between the positive and negative poles. The number of lithium ions to be moved back is no matter whether it is too much or too little. It must be controlled. If the control is good, it can be charged repeatedly without reducing the capacity. Otherwise, the battery capacity will permanently decrease or even explode. Basic knowledge of power batteries The battery management system is closely integrated with the power battery of electric vehicles. The battery management system usually has the function of measuring battery voltage to prevent or avoid abnormal conditions such as battery over-discharge, over-charge, and over-temperature. Appear etc. Its basic functions: real-time detection of battery voltage, current, and temperature through sensors, as well as leakage detection, thermal management, battery balance management, alarm reminders, calculation of remaining capacity (SOC), discharge power, and reporting of battery deterioration (SOH) ) and remaining capacity (SOC) status. It also uses an algorithm to control the maximum output power according to the voltage, current and temperature of the battery to obtain the maximum mileage. It also uses an algorithm to control the charger for optimal current charging. It communicates with the vehicle's main control through the CAN bus interface. devices, motor controllers, energy control systems, vehicle display systems, etc. for real-time communication. The three important basic functions of the battery management system are (1) SOC estimation function. It is very important to accurately estimate the SOC value change, and its algorithm is one of the core competitiveness of relevant companies. The SOC estimation accuracy is high, and for the same amount of battery, a higher cruising range can be achieved. Therefore, high-precision SOC estimation can effectively reduce the required battery cost. SOC is transmission information calculated based on monitored external characteristic information. SOC not only informs the car owner of the current power, but also allows the car to understand its own power, prevent overcharge and overdischarge, improve balance consistency, increase output power and reduce additional redundancy. The bottom layer of the system undergoes complex algorithm calculations to ensure the safe, continuous and stable operation of the car and improve safety. (2) Thermal management function Thermal management mainly includes determining the optimal operating temperature range of the battery, battery thermal field calculation and temperature prediction, heat transfer medium selection, thermal management system heat dissipation structure design and fan prediction stable point selection. Ensure batteries operate within the appropriate temperature range and reduce temperature differences between individual battery modules. (3) Balance control function Balance control is divided into active balance and passive balance. Active balancing is to equalize the capacity or voltage differences between battery cells during the charging, discharging or placement process of the battery pack to eliminate various inconsistencies generated within the battery. The balancing method is mainly passive balancing, which uses single cells connected in parallel to shunt energy consumption resistors, and the balancing work can only be done during the charging process. Its working principle is to discover the difference between the single cells in series by collecting the voltage. Based on the "upper limit threshold voltage" of the set charging voltage, any single cell will be the first to reach the "upper threshold voltage" when charging. "Upper Limit Threshold Voltage" and detect the difference with the batteries in the adjacent group, that is, the battery with the highest single voltage in the battery group will discharge the current through the energy consumption resistor connected in parallel to the single battery, and so on, until When the single cell with the lowest voltage reaches the "upper threshold voltage", it is a balancing cycle.

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