As the “heart monitor” of EV, the core task of BMS is to ensure that the battery pack works safely, efficiently and for a long time. The foundation of all this begins with the precise perception of the most basic parameters of the battery monomer: voltage, current, temperature and so on.
Among them, voltage monitoring is the most important, which is not only the basis of calculating the total voltage and evaluating the battery status, but also the key first step to achieve battery balance and ensure safety.
The most basic function of the battery management system is to measure the voltage, current, temperature, insulation detection and high-voltage interlock detection of the battery monomer, which is the basis of the top-level calculation, control logic and high-voltage safety of the power battery of all battery management systems.
- Battery voltage monitoring
Monitoring the voltage of the monomer (or unit, module) has the following three functions for the battery management system:
① It can be used to accumulate and obtain the voltage value of the whole power battery;
(2) that monome (or unit, module) difference can be judged accord to the voltage difference of the monomer (or unit, module);
③ It can monitor the operation status of monomer (or unit, module).
- Battery voltage monitoring circuit
① Resistance voltage division method
Battery resistance divider detection is a commonly used battery detection method, which calculates the voltage of the battery by measuring the voltage across the resistance divider. This method has its own advantages and disadvantages, and the following is a detailed introduction.
Advantag:
The principle is simple: the principle of the resistance voltage division method is similar to pouring a bottle of water into two cups. You only need to know the amount of water in one of the cups to know the amount of water in the whole bottle. This approach is easy to understand and implement. Applicable to high voltage: The resistance voltage division method is applicable to high voltage, which can divide the high voltage into low voltage within a safe range for easy measurement.
Quick estimation: The resistive divider method provides a quick, approximate estimate for situations where a quick understanding of the battery voltage is required.
Shortcomin:
The measurement accuracy is affected by the divider resistor: if the divider resistor is aged or faulty, the measurement accuracy will decrease. At the same time, the resistance divider is used to detect its low internal resistance and large dissipation. Cannot provide detailed battery status information: The resistance voltage division method can only provide a rough estimate of the battery voltage, and cannot provide detailed battery status information like the cell voltage accumulation method. Complicated acquisition circuit is required: although the principle of resistance voltage division method is simple, in practical application, in order to improve the accuracy and stability, complex acquisition circuit may be required.
② Level shift method
Battery level shift detection is a technology used in battery management system (BMS), which is mainly used to detect and adjust the voltage level of each battery cell in the battery pack to ensure the balance and safety of the battery pack.
We can summarize the advantages and disadvantages of battery level shift detection as follows:
Advantage
(1) Improve the balance of the battery pack:
Through the level shift detection, the voltage difference of each battery unit in the battery pack can be found and adjusted in time, thereby improving the overall balance of the battery pack.
(2) Extend the service life of the battery pack:
A balanced battery pack can avoid overcharge or overdischarge of some battery cells, thus prolonging the service life of the whole battery pack.
(3) Improve the safety of the battery pack:
By monitoring and adjusting the voltage of the battery unit in real time, we can prevent dangerous situations such as overcharge and overdischarge in the battery pack, and improve the safety of the battery pack.
(4) improve energy utilization rate:
Active equalization technology can transfer the energy of high-energy battery cells to low-energy battery cells, thereby improving the energy utilization of the battery pack.
Shortcoming
(1) Complicated technology:
Battery level shift detection technology is relatively complex, which requires precise circuit design and control algorithm, and is difficult to implement.
(2) High cost:
Due to the complexity of the technology, the realization of battery level shift detection requires high cost, including hardware cost and research and development cost.
(3) Impact on battery life:
Frequent charging and discharging operations in the active equalization process may cause additional burden on the battery unit and affect the life of the battery.
(4) Difficult to realize:
Battery level shift detection needs to be balanced in the charging, discharging and static process, which is difficult to achieve.
Battery level shift detection technology has significant advantages in improving the balance of battery pack, prolonging the service life, improving safety and energy efficiency. However, its technical complexity, high cost, and potential impact on battery life are also drawbacks that cannot be ignored. In practical applications, it is necessary to weigh the pros and cons according to the specific needs and conditions, and select the appropriate battery level shift detection scheme.
With the rapid development of EV industry, the requirements for BMS voltage monitoring technology will only be higher and higher.
In the future, we may see the emergence of more accurate, efficient and cost-effective monitoring schemes, which will continue to push the boundaries of battery technology and make our travel and energy use safer, more reliable and more intelligent.