What is battery management system(BMS)?

What is battery management system (BMS)?

The full name of BMS is Battery Management System, battery management system. It is a device that cooperates with monitoring the state of the energy storage battery. It is mainly for the intelligent management and maintenance of each battery unit, to prevent the battery from overcharging and over-discharging, to prolong the service life of the battery, and to monitor the state of the battery. Generally, BMS is represented as a circuit board or a hardware box.

 BMS is one of the core subsystems of the battery energy storage system. It is responsible for monitoring the operating status of each battery in the battery energy storage unit to ensure the safe and reliable operation of the energy storage unit.  The BMS can monitor and collect the state parameters of the energy storage battery in real-time (including but not limited to the voltage of the single battery, the temperature of the battery pole, the current of the battery circuit, the terminal voltage of the battery pack, the insulation resistance of the battery system, etc.), and make necessary According to the analysis and calculation of the system, more system state evaluation parameters are obtained, and the effective control of the energy storage battery body is realized according to the specific protection control strategy, so as to ensure the safe and reliable operation of the entire battery energy storage unit. At the same time, BMS can exchange information with other external equipment (PCS, EMS, fire protection system, etc.) through its own communication interface, analog/digital input, and input interface, and form the linkage control of various subsystems in the entire energy storage power station to ensure the safety and reliability of the power station, Efficient grid-connected operation.

What is the function of BMS?

There are many functions of BMS, and the most core ones, which we are most concerned about, are nothing more than three aspects: status management, balance management, and safety management.

State management function of battery management system

We want to know what is the state of the battery, what is the voltage, how much energy, how much capacity, and what is the charge and discharge current, and the BMS state management function will tell us the answer.  The basic function of BMS is to measure and estimate battery parameters, including basic parameters and states such as voltage, current, and temperature, and the calculation of battery state data such as SOC and SOH.

Cell measurement

 Basic information measurement: The most basic function of the battery management system is to measure the voltage, current, and temperature of the battery cell, which is the basis of the top-level calculation and control logic of all battery management systems.

 Insulation resistance detection: In the battery management system, insulation detection of the entire battery system and the high-voltage system is required.

SOC calculation

 SOC refers to the State of Charge, the remaining capacity of the battery. Simply put, it is how much power is left in the battery.

 SOC is the most important parameter in BMS, because everything else is based on SOC, so its accuracy is extremely important. If there is no accurate SOC, no amount of protection functions can make the BMS work normally, because the battery will often be protected, and the life of the battery cannot be extended.

 The current mainstream SOC estimation methods include the open circuit voltage method, current integration method, Kalman filter method, and neural network method. The first two are more commonly used.

The balance management function of the battery management system

Each battery has its own "personality". To talk about balance, we have to start with the battery. Even batteries produced by the same manufacturer in the same batch have their own life cycle and their own "personality"-the capacity of each battery cannot be exactly the same. There are two types of reasons for this inconsistency:

Inconsistency in cell production and inconsistency in electrochemical reactions

production inconsistency

 Production inconsistency is well understood. For example, in the production process, the separator, cathode, and anode materials are inconsistent, resulting in inconsistency in the overall battery capacity.

 Electrochemical inconsistency means that in the process of battery charging and discharging, even if the production and processing of the two batteries are exactly the same, the thermal environment can never be consistent during the electrochemical reaction.

 We know that over-charging and over-discharging can do great damage to the battery. Therefore, when battery B is fully charged when charging, or the SOC of battery B is already very low when discharging, it is necessary to stop charging and discharging to protect battery B, and the power of battery A and battery C cannot be fully utilized. This results in:

 Firstly, The actual usable capacity of the battery pack is reduced: the capacity that batteries A and C could have used, but now there is nowhere to exert force to take care of B, just like two people and three legs tie the tall and the short together, and the tall one's steps are slow. Can't make big strides.

 Secondly, The life of the battery pack is reduced: the stride is small, the number of steps needed to be walked is more, and the legs are more tired; the capacity is reduced, and the number of cycles that need to be charged and discharged increases, and the attenuation of the battery is also greater. For example, a single battery cell can reach 4000 cycles under the condition of 100% charge and discharge, but it cannot reach 100% in actual use, and the number of cycles must not reach 4000 times.

  There are two main balancing modes for BMS, passive balancing and active balancing.
  The current for passive equalization is relatively small, such as the passive equalization provided by DALY BMS, which has a balanced current of only 30mA and a long battery voltage equalization time.
  The active balancing current is relatively large, such as the active balancer developed by DALY BMS, which reaches a balancing current of 1A and has a short battery voltage balancing time.

Protection function of battery management system

 The BMS monitor matches the hardware of the electrical system. According to the different performance conditions of the battery, it is divided into different fault levels (minor faults, serious faults, fatal faults), and different processing measures are taken under different fault levels: warning, power limit or cutting off the high voltage directly. Faults include data acquisition and plausibility faults, electrical faults (sensors and actuators), communication faults, and battery status faults.

A common example is that when the battery is overheated, the BMS judges that the battery is overheated based on the collected battery temperature, and then the circuit controlling the battery is disconnected to perform overheating protection and send an alarm to the EMS and other management systems

Why to choose DALY BMS?

DALY BMS, is one of the largest battery management system (BMS) manufacturers in China, has more than 800 employees, a production workshop of 20,000 square meters and more than 100 R&D engineers. The products from Daly are exported to more than 150 countries and regions.

Professional security protection function

The smart board and hardware board contain 6 major protection functions:

 Overcharge protection: When the battery cell voltage or battery pack voltage reaches the first level of overcharge voltage, a warning message will be issued, and when the voltage reaches the second level of overcharge voltage, DALY BMS will automatically disconnect the power supply.

 Over-discharge protection: When the voltage of the battery cell or the battery pack reaches the first level of over-discharge voltage, a warning message will be issued. When the voltage reaches the second level of over-discharge voltage, DALY BMS will automatically disconnect the power supply.

 Over-current protection: When the battery discharge current or charging current reaches the first level of over-current, a warning message will be issued, and when the current reaches the second level of over-current, DALY BMS will automatically disconnect the power supply.

 Temperature protection: Lithium batteries cannot work normally under high and low temperature conditions. When the battery temperature is too high or too low to reach the first level, a warning message will be issued, and when it reaches the second level, DALY BMS will automatically cut off the power supply.

  Short-circuit protection: When the circuit is short-circuited, the current increases instantaneously, and DALY BMS will automatically disconnect the power supply

Professional balance management function

 Balanced management: If the battery cell voltage difference is too large, it will affect the normal use of the battery. For example, the battery is protected from overcharge in advance, and the battery is not fully charged, or the battery is protected from over-discharge in advance, and the battery cannot be fully discharged.  DALY BMS has its own passive equalization function, and has also developed an active equalization module. The maximum equalization current reaches 1A, which can prolong the service life of the battery and ensure the normal use of the battery.

Professional state management function and communication function

 The status management function is powerful, and each product undergoes strict quality testing before leaving the factory, including insulation testing, current accuracy testing, environmental adaptability testing, etc.  BMS monitors battery cell voltage, battery pack total voltage, battery temperature, charging current and discharging current in real time. Provide high-precision SOC function, adopt the mainstream ampere-hour integration method, the error is only 8%.

 Through the three communication methods of UART/ RS485/ CAN, connected to the host computer or the touch display screen ,bluetooth and light board to manange lithium battery. Support mainstream inverters communication protocols, such as China Tower, GROWATT, DEY E, MU ST, GOODWE, SOFAR ,SRNE,SMA,etc.

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Post time: May-14-2023