Battery management system is mainly applied to lithium batteries, traditional lead-acid batteries have limited-service life and low price, which is not suitable for using battery management system. Battery management system is a kind of electronic equipment to manage rechargeable batteries, which can protect the safe use of batteries and prolong the lifespan of batteries in practical applications, and at the same time monitor and evaluate the status of batteries, such as SOC (simply the amount of power stored in the battery), provide battery protection, continuously optimize the performance of batteries, report data, control the environment, and verify the identity.
The supervisory and control functions of a battery management system are typically applied to individual cells or battery packs called modules within a battery pack assembly. Lithium-ion batteries have high energy density and are used in many devices such as (cell phones, computers, electric vehicles) are the standard choice for modular battery packs for these products.
How Battery Management Systems Work?
There is no fixed or unique standard for battery management system, the main consideration is the cost of the battery pack, complexity, size, application of the battery, life span, etc. There are many functions of the battery management system, for the battery pack, the battery pack protection says the main function is to work through the battery management system with multiple sensors inside the battery management system, and then the data from the sensors will be transmitted to the BMS (Battery Management System).
1. Detecting the state of the battery
BMS (Battery Management System) can detect the state of the battery, such as the total voltage of the battery, the individual cell voltage, the connector voltage, the average temperature of the battery, the temperature of the coolant inlet and outlet, the temperature of the individual cell, the flow of current, etc., to protect the battery and prolong the service life of the battery.
2. Calculate battery data
Battery management system can calculate the maximum and minimum voltage, SOC (State of Charge), DOD (Depth of Discharge), SOH (State of Health of Battery), SOP (State of Power), SOS (State of Safety), the common state of safety are the maximum charging current, the maximum discharging current, the total number of cycles, the battery’s running time, temperature monitoring and so on.
3. Communication
The battery management system communicates internally with the hardware running the battery, so that the outside can know the running status of the battery, and there are different types of serial communication, CAN bus communication and so on.
4. Battery Protection
Battery protection mode is a function that mainly protects the battery by limiting the amount of battery charging, battery charging speed, etc. to prolong the life of the battery. Battery protection mainly protects against overcharging, overdischarging, charging and discharging currents, avoiding high or low temperatures, failure of the battery itself and related wiring, etc. Battery protection regulates the battery to ensure that the battery complies with the safety specifications and to ensure that the battery will not be damaged. If the battery management system monitors any abnormal state of the battery, it will enter the protection mode (over-voltage protection, under-voltage protection, high temperature protection, etc.) to maximize the service life of the battery.
Current Protection
The battery management system monitors the current of the battery pack, usually the battery management system usually prevents running outside the battery’s quota value to protect the battery, the charging current limit of lithium-ion batteries is different from the discharging current limit, both modes can deal with peak currents, but the duration is very short. When an electric vehicle accelerates suddenly, for example, the battery management system can integrate the peak current by reducing the available current or interrupting the battery pack current. It also enters a current protection state when the current is too high to maintain smooth battery operation.
Voltage Protection
Voltage protection has under-voltage protection and high-voltage protection. Under-voltage protection is mainly when the voltage of the battery is insufficient during charging, the battery management system (BMS) will enter into the under-voltage protection mode, and the battery will not be able to be charged, which will result in the insufficient power of the battery. We need to use a multimeter to measure the voltage at both ends of the battery to confirm that the battery voltage is too low, and then use a charger with an activation function to charge the battery to about 12V or 24V. If the charging voltage is too high or the voltage of the battery is too high, the battery management system (BMS) will also enter the battery high voltage protection mode, and it will cut off the function of the battery, so the battery will not overheat inside the battery due to the high voltage, and thermal runaway or fire will occur. If the voltage of the battery is too high, we need to disconnect the power supply to let the voltage of the battery return to a safe level.
Temperature protection
Generally lithium batteries have a battery temperature protection mode, we can view the battery through intelligent devices to see what temperature protection mode, under normal circumstances lithium batteries can withstand a short period of high temperature conditions, but if the temperature is too high will activate the battery management system’s high-temperature protection mode, to prevent the temperature from further increasing, the service life of the battery.
We can place the battery in a dry, well-ventilated area, and also reduce the load on the battery to allow the battery to return to normal temperature before use. In a low temperature environment, the capacity and discharge ability of the battery will be reduced, and in serious cases, it will lead to crystallization inside the battery, which will cause great damage to the battery. In the case of low temperature protection of the battery, the battery needs to be placed in a temperature environment until the battery returns to normal temperature can be used.
Energy recovery
Battery management system can guide the energy recovery, energy recovery refers to the braking energy recovery, braking energy recovery system is mainly to recover the excess energy released by the vehicle in braking or inertial skidding, and then through the vehicle generator into electrical energy, stored in the battery, reduce the vehicle engine fuel consumption and carbon dioxide emissions.
Balancing the overall state
Battery management systems maximize battery capacity and can prevent localized undercharging or overcharging. Battery management systems can ensure that all voltages within the battery pack are consistent through active balancing, and can also balance the battery by connecting the most charged battery to the load and transferring the most energy to the less energetic battery.
Types of Battery Management Systems
There are different types of battery management systems that can be implemented to protect the batteries through different technologies, battery protection systems are mainly categorized according to their topology.
1. Centralized Battery Management System
A single controller is connected to the battery cells through multiple wires, the advantage is that it is compact and the price is the most economical, but the disadvantage is that it requires a large number of ports to connect all the battery packs.
2. Distributed Battery Management System
Each battery cell has a BMS (Battery Management System), only one communication line is needed between the battery and the controller, which can simplify most of the wiring to a few sensor wires and communication lines between neighboring BMS modules, which is more independent, but more costly to use.
3. Modular Battery Management System
Modular Battery Management System, which is a combination of centralized BMS and distributed BMS, mainly has several BMAs, each BMS handles a certain number of cells, and these BMSs operate under the supervision of the main BMS, but the cost of use is slightly higher.
Conclusion
Battery management systems can maximize the protection of our batteries, maximize the best performance of our batteries when we use them, and prolong the life of our batteries. A good understanding of battery management systems will help us to make a better choice of batteries.
