Today, modern batteries are far more powerful, allowing for extended autonomous and rapid charging, contributing to overall safety in cars, trains, and even airplanes. A dedicated circuitry called a battery management system (BMS) enables batteries to last longer and improves the safety of their use and charging. The battery type most affected by BMS is rechargeable batteries, particularly lithium-ion batteries, currently used in most applications, from smartphones to electric vehicles. These intelligent systems play a crucial role in monitoring, controlling, and optimizing battery performance and lifespan while ensuring the safety of users and loads.
Introduction
To ensure the long-term safe and efficient operation of batteries, a battery management system is required. It performs many functions, some of which are quite complex. The first function is battery monitoring, which collects a large amount of information in real time about key battery parameters. This includes parameters such as the current being transmitted, charging current, current-voltage ratio, temperature, and state of charge. This information is used to assess the battery's health and check for any abnormalities.
A crucial function is controlling charging and discharging current to prevent energy overload or deep discharge, which can shorten the battery's lifespan. Temperature is also carefully monitored to avoid overheating and potential explosions or fires. State-of-the-art models include the ability to independently deliver current to individual cells to ensure optimal balance. The battery management system also implements various safety measures to protect it from damage, malfunctions, and failures. It intervenes in cases of abnormal distribution or charging, immediately interrupting charging or discharging in hazardous situations.
Some models equipped with special circuitry can even transmit collected information to other systems via wired or wireless connections. This possibility is quite useful if the battery is located in a place difficult for operators to access. The simplest systems monitor voltage and current, checking for overloads, while more advanced systems perform battery balancing, communicate with other systems, and provide advanced diagnostics.
Improved battery management
Electronic and automatic battery management in electric vehicles is one of the most challenging aspects of modern engineering, and one of the most critical factors is the selection of the integrated circuitry to achieve a wide range of functions. A good system must first understand the battery pack structure of an electric vehicle. Typically, these consist of a number of batteries connected in series, parallel, or a hybrid configuration to increase voltage or current and extract more energy.
Each battery typically comes with an electronic module that continuously monitors it. The system collects all information to ensure the battery's safe operation. The system performs multiple tasks, such as precise thermal management, accurate voltage and current measurement, excellent balancing of charge levels in each battery, and a series of procedures for system safety. In fact, the main functions of the property management office are as follows:
• Battery protection: Ensures normal operation and prevents accidents in the work area.
• Battery monitoring: Continuously checks the battery's state of charge and health during charging and discharging.
• Battery optimization: Ensure a good balance in the battery, improve battery life and capacity, thereby optimizing the autonomy of the electric vehicle.
The crucial role of low or overvoltage control in battery operation is analyzed in detail. Lithium batteries can be damaged during charging and discharging if the voltage exceeds a certain range, typically between 10.5V and 14.8V. In such cases, the battery management system (BMS) automatically cuts off the battery. Furthermore, it provides automatic protection against high continuous and pulsed maximum discharge currents. It automatically protects the system from short circuits that could easily cause explosions and fires, and effectively and continuously monitors the operating temperature, as lithium batteries cannot be charged above 0℃ and 55℃, nor can they operate normally above 20℃ and 60℃.
The battery also plays a fundamental role in controlling the maximum charging current, as the Life4 battery charges faster than lead-acid batteries, but must always adhere to limits. Finally, the battery management system achieves battery balancing, a topic we will explore in more detail in the next section. A prime example is the battery management solution produced by STMicroelectronics. Based on the L9963E integrated circuit, it can provide measurement accuracy for unidirectional or bidirectional configurations of up to 14 cells in series and enables highly sophisticated cell monitoring and diagnostic functions.
Another example is the BQ76905 from Texas Instruments, which integrates battery monitoring for use with 2-5 battery banks in series; a protection circuit including voltage, temperature, current, and internal diagnostics. It implements a battery balancing function, which must be controlled to limit current and prevent exceeding the device's recommended operating temperature. This is achieved by correctly calculating the battery input resistance and limiting the number of batteries that can be balanced at a time.
Battery Balance
Lithium-ion batteries have many advantages over traditional batteries, but during production, it's impossible to guarantee identical and uniform models based on nominal capacity, internal resistance, and self-discharge. Over time, these minute differences cause the battery to become unbalanced, reducing efficiency and accelerating aging. Internally, the cells are connected in series, using the same energy for charging and discharging. Without a proper balancing system, the differences between cells will grow larger and larger, effectively destroying the battery. Therefore, if you charge batteries unbalanced, the weaker cell will reach full load before the stronger one. Common problems often stem from the presence of the weakest cell.
Balancing allows you to extend battery lifespan because it performs thorough and independent checks on each section. This function maximizes the overall battery capacity and prevents localized undercharging or overcharging. Using this technology, the system ensures that all cells constituting the battery have the same state of charge. Depending on the technology used, there is passive balancing, in which the overcharged battery dissipates power (and heat) using a power resistor to balance the state of charge of all cells. Using this method, the energy of the most charged battery is dissipated by connecting it to an electrical load, such as a passive regulator. Thus, a typical building management system waits for the fewest cells to reach the same energy level before balancing the most charged battery. This method can result in inefficient and extremely long balancing processes, even tens of hours, and does not extend battery life, although it is very economical.
On the other hand, active balancing is more complex and expensive, but it yields excellent results because the current is individually redistributed among the cells during charge and discharge cycles; moreover, it is implemented very quickly, sometimes even within minutes. This method allows energy to be transferred from more charged cells to less charged cells, or the current to charged cells to be reduced to a level low enough that fully charged cells are not damaged, while less charged cells can continue to charge. This increases autonomy without producing a specific rise in system temperature. However, when the cells are in passive or active balancing, each cell in the stack is monitored to maintain a good state of charge.
Therefore, balancing extends the average battery life and provides an extra level of protection against damage from severe discharge or overcharging. An example of an active battery balancing circuit is provided in the analog device, the LT8584. It is an overall recoil converter with a 2.5A discharge current, used in the LTC680X battery display family.
