Today's batteries are far more powerful, providing extended driving range and fast charging for cars, trains, and even airplanes, all while remaining completely safe. Dedicated circuitry, known as a Battery Management System (BMS), extends battery life and enhances its safety during use and charging. The battery type most affected by BMS is rechargeable batteries, particularly lithium-ion batteries, which are 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.
introduce
To ensure the long-term safe and efficient operation of batteries, a Battery Management System (BMS) is required. It performs many functions, some of which are quite complex. The first function is battery monitoring, which collects a wealth of information in real time about key battery parameters. These include output current, charging current, current-voltage ratio, temperature, and state of charge. This information is used to assess the battery's health and check for any anomalies.
A crucial function is controlling charging and discharging current to prevent energy overload or deep discharge, as these can shorten the battery's lifespan. Temperature is also strictly monitored to avoid overheating and potential explosions or fires. The most sophisticated models involve independently delivering current to each individual cell to ensure optimal balance. The battery management system also implements various safety measures to prevent damage, malfunctions, and failures. It intervenes in cases of abnormal distribution or charging, and immediately interrupts 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 capability is particularly useful if the battery is located in an area difficult for the operator to access. The simplest systems monitor voltage and current and check for any overloads, while more advanced systems offer battery balancing, communication with other systems, and advanced diagnostics.
Improve battery management
Electronic and automated battery management in electric vehicles is one of the most challenging issues today, and one of the most critical factors is the selection of integrated circuits to implement many of the functions. A good system must first understand the battery pack architecture of an electric vehicle. Typically, they consist of a number of cells connected in series, parallel, or in a hybrid configuration to increase voltage or current and obtain more energy.
Each battery typically has an electronic module for continuous monitoring. The system collects all information to ensure safe battery operation. The BMS performs multiple tasks, such as precise thermal management, accurate voltage and current measurement, excellent balance of individual battery charge, and a series of system safety procedures. In fact, the main functions of a BMS are as follows:
• Battery protection: Ensures normal operation and prevents any accidental operation within its operating area.
• Battery monitoring: Continuously checks the battery's charging status and health condition during charging and discharging.
• Battery optimization: Ensure a good balance of batteries, improve battery life and capacity, thereby optimizing the autonomy of electric vehicles.
A detailed analysis reveals the valuable role of the Battery Management System (BMS), which performs undervoltage and overvoltage control. Lithium-ion batteries can be damaged if charged and discharged outside a certain voltage range, typically between 10.5V and 14.8V. In such cases, the BMS automatically stops the battery. Furthermore, it implements automatic protection against high continuous and pulsed maximum discharge currents. It automatically protects the system from short circuits, which can easily cause explosions and fires, and it performs effective and continuous monitoring of operating temperature, as lithium-ion batteries cannot be charged below 0°C and above 55°C, and cannot function properly below -20°C and above 60°C.
The BMS also plays a fundamental role in controlling the maximum charging current, as LiFePO4 batteries charge faster than lead-acid batteries, but must always adhere to limits. Finally, the battery management system balances the batteries, a topic we will explore in more detail in the next section. A prime example of a BMS is the battery management solution manufactured by STMicroelectronics. Based on the L9963E integrated circuit, it provides the highest accuracy measurement of up to 14 series-connected cells in unidirectional or bidirectional configurations and enables highly sophisticated battery monitoring and diagnostic functions.
Another example of a BMS is Texas Instruments' BQ76905, which integrates battery monitoring for 2 to 5 series-connected batteries; including protection circuitry for 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
Compared to traditional batteries, lithium batteries offer numerous advantages and superior performance. However, during manufacturing, it's impossible to guarantee that all cells will have identical nominal capacity, internal resistance, and self-discharge. Over time, these minute differences can cause battery cells to become unbalanced, reducing efficiency and accelerating aging. Internally, battery cells are connected in series, using the same energy for charging and discharging. Without a proper balancing system, these differences can grow larger, effectively damaging the battery. Therefore, if you charge a battery unbalanced, the weaker cells will reach full capacity before the stronger ones. Common problems often stem from the presence of the weakest cell.
Balancing functions extend battery life because they perform a comprehensive and independent check on each component. This function maximizes the overall battery capacity and prevents localized undercharging or overcharging. Through this technology, the BMS ensures that all cells comprising the battery have the same state of charge. Depending on the technology used, passive balancing exists, where overcharged cells dissipate power (and heat) using power resistors to equalize the state of charge of all cells. This method involves dissipating the energy of the most charged cells by connecting them to a power load (such as a passive regulator). Therefore, a common BMS system applies a resistor to the most charged cells, waiting for the least charged cells to reach the same energy level. This method is inefficient, the balancing process is extremely long, sometimes lasting tens of hours, and while very economical, it does not extend battery life.
On the other hand, active balancing is more complex and costly, but it yields excellent results because the current is independently redistributed among the individual cells during charge and discharge cycles; moreover, it is implemented very quickly, sometimes in just a few minutes. This method transfers energy from more charged cells to less charged cells, or reduces the charging current to a level low enough that fully charged cells are not damaged, while less charged cells can continue charging. Therefore, autonomy is increased, and no significant increase in system temperature is generated. However, with passive or active battery balancing, each cell in the battery pack is monitored to maintain a good state of charge.
Therefore, balancing extends the average battery life and provides additional protection against damage from deep discharge or overcharging. Analog Devices provides an example of an active battery balancing circuit. It is a monolithic flyback converter with a discharge current of 2.5 A, used in conjunction with the LTC680x series battery monitor.
in conclusion
With a proper Battery Management System (BMS), battery life can be significantly increased. It helps prevent damage caused by improper battery use, such as overcharging or deep discharging. The BMS is the true brain of the battery; if designed with cutting-edge electronics, it can perform many additional functions, controlling and monitoring battery behavior in real time.
