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-charging, 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 basic functions of three important subsystems of the battery management system (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 related 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. 1. What is a battery? What is its function? Let’s talk about the pool first. Water cups, buckets, water cylinders, pools, cups, buckets, ponds, and ponds here all have a common feature. Their basic function is to hold water. The difference is in the volume. Water is a liquid and has a basic property: it can flow from high places to low places. Basic common sense is that people may not think about it. The pool is empty originally, and the water in the pool is poured in by people. If a hole is drilled in the lower part of the pool, the water in the pool will eventually drain out. What is the scientific reason behind this process? a) In an empty pool, only the empty volume can hold water; b) Water cannot enter the pool on its own, people pour it in; c) Only with the existence of water pressure, water will flow from high places to the ground. In the same way, the battery is the capacity to hold "electricity". The battery is originally "empty" and has no electricity. The electricity is charged by people. The reason why the battery can be discharged is because there is a voltage difference in the battery. The pool is based on the principle of physics, it contains liquid, and water has a molecular structure; the battery is based on the principle of electrochemistry, and it contains "charged" ions, which are smaller than molecules. 2. Basic knowledge about dry batteries. Batteries commonly found in radios, radios, cameras, electronic clocks, toys, etc. are classified as dry batteries. The electrolyte in a dry battery is a non-flowable paste, which is called a dry battery (see Figure 1). This is relative to batteries with a flowable electrolyte. The basic knowledge of the power battery is a cylindrical container made of zinc. A carbon rod stands in the center of the zinc cylinder, and a copper cap is fixed on the top of the carbon rod. The carbon rod and zinc cylinder are called the electrodes of the dry battery. The carbon rod that collects positive charges is called the positive electrode, (the symbol + represents the positive electrode of the battery), and the zinc cylinder that collects negative charges is called the negative electrode (the symbol - represents the negative electrode of the battery). The basic principle of discharge: the carbon electrode is filled with magnesium dioxide, the zinc electrode forms the outer shell of the dry battery, and the carbon electrode is placed in the center. The electrons are given by the electronized zinc metal (oxidation) and flow into the external circuit to reach the carbon electrode. The magnesium dioxide close to the carbon electrode gains electrons (reduction) to generate hydroxide ions, and forms a new compound called magnesium oxide. Oxidation reactions push electrons out of the battery's negative electrode, while reduction reactions absorb them at the positive electrode. Dry batteries do not have the ability to be recharged by users and are single-use batteries. 3. Power batteries must be rechargeable batteries (1) The biggest difference between dry batteries and current power batteries is: a) the electrolyte of dry batteries is an immovable paste and does not have rechargeability; b) the power battery is an electrolyte with lithium ion energy. The electrolyte that can flow in it can be charged thousands of times; (2) The basic similarities between dry batteries and current power batteries: a) There is a positive electrode, a negative electrode, a shell, and it is an electrochemical reaction; b) Dry batteries and power batteries On a single body, the physical properties are basically the same, including cylindrical and square. Basic knowledge of power batteries 4. What does a power battery pack mean? Why should one section be connected in series (parallel) to form a battery pack? To the engineers of the OEM, a fuel vehicle is a fuel tank, which is a liquid volume. But when you see electric vehicles, there are power battery packs one after another. When you open the battery pack, there are countless batteries one by one. Can the power battery be directly made into a large battery pack? Flashlights are usually equipped with 2 dry batteries, some are equipped with 3 cells, and some are equipped with 5 cells. Dry battery specifications include No. 1, No. 2, and No. 5. In power batteries, one battery is called a cell, a group connected in parallel is called a module, a group of modules connected in series is called a battery pack, and a group of battery packs connected in series is called a battery system. A single cell (or single cell) is the smallest unit of a battery product. Can the electric battery be made larger? For example, make three dry batteries into one and put them in the flashlight. In fact, it cannot be done. This is a shortcoming of the electrochemical battery principle. One dry cell can only produce 1.5V. If people want a 3V power supply, they must connect two dry cells in series. The capacity of a single cell cannot be very high. If people want a power supply with a large capacity, they must connect individual batteries in parallel.

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