These improvements all enhance efficiency and reduce operating costs. The gradual transition to a 48V power bus for vehicles and the introduction of high-voltage batteries necessitate appropriate thermal management technologies. Continuous monitoring and control of the temperature of critical components, such as the battery and charging system, can improve vehicle reliability, increase driving range, enhance driving comfort, and reduce charging time.
Thermal management of electric vehicles is more complex than that of traditional internal combustion engine vehicles. The electric motor must be constantly cooled, while the battery must be cooled or heated depending on environmental conditions. Furthermore, unlike in conventional vehicles, there is no immediately available waste heat to heat the passenger compartment. Therefore, it is necessary to provide appropriate energy-saving measures, such as heat pumps. Cooling circuits are essential for maintaining the motor and battery at appropriate temperatures and can be flexibly used for heat distribution within the vehicle.
When the cooling circuit absorbs heat, its temperature rises, necessitating a heat exchanger in which liquid or gaseous refrigerant circulates. The refrigerant must have a high heat capacity to absorb as much heat as possible within the same space. The battery can be cooled to a temperature lower than ambient temperature through the refrigerant evaporation process (the transition from liquid to gas). The heat generated during condensation (the transition from gas to liquid) can be used to heat the passenger compartment during cold periods. Efficient thermal management solutions enable greater autonomy, meeting the current and future needs of electric vehicles.
Monitoring EV battery cells
The battery pack installed in an electric vehicle consists of multiple battery modules connected in series and parallel. The electronic circuitry required to manage these battery modules is called the BMS (Battery Management System). The BMS includes one or more power conversion stages and a microcontroller-based embedded system that handles all aspects related to the power subsystem. During the charging or discharging process of an electric vehicle battery, the state of each cell belonging to the battery pack must be monitored.
Electric vehicle batteries pack a large amount of energy into a small volume. If left unmanaged, overvoltage or undervoltage conditions can lead to thermal runaway, damaging the battery. To address this, a special circuit called a BMIC (Battery Monitoring Integrated Circuit) is introduced to monitor the voltage and temperature of each battery. This information is sent to the Battery Management Controller (CMC) and, depending on the system's complexity, to a higher-level Battery Management Controller (BMC).
The BMC aggregates information about the battery voltage monitored by the CMC to calculate the battery's current state of charge (SOC). SOC is a fundamental parameter for assessing the battery's remaining autonomy, thus determining when to request a new charge. Another parameter is state of health (SOH), which provides crucial information from which remaining battery life can be derived. Particularly deceptive is thermal runaway, triggered by various types of faults, including excessively rapid charging or discharging processes. To avoid these phenomena, communication between the BMS, CMC, and BMC must be performed with as little latency as possible.
Business Solutions
Solutions exist for monitoring the performance of electric vehicle batteries, and these solutions are available for purchase from organizations such as STMicroelectronics, Analog Devices, and NXP.
STMicroelectronics offers a broad portfolio of EV battery monitoring solutions, providing high-precision measurements in 48V and high-voltage battery packs. A typical BMS architecture uses multiple battery management ICs to monitor the voltage, current, and temperature of each cell in the battery pack. An example of an AEC-Q100 compliant IC for EV battery management is the L9963, a lithium-ion battery monitoring and protection chip for high-reliability automotive applications and energy storage systems. It can monitor up to 14 stacked cells to meet the requirements of 48V and higher voltage systems. Information can be transmitted via SPI communication or an isolated interface. Multiple L9963s can be daisy-chained and communicate with a host processor via a transformer-isolated interface, featuring high-speed, low-EMI, long-distance, and reliable data transmission.
Analog Devices (ADI) offers a broad portfolio of battery management system devices, providing the flexibility to support virtually any EV battery system architecture. For example, the LTC6810 can measure up to six cells in series with a total measurement error of less than 1.8mV. Its 0V to 5V battery measurement range makes the LTC6810 suitable for most battery architectures. Multiple devices can be connected in series, allowing simultaneous monitoring of long, high-voltage battery packs. Each LTC6810 has an isoSPI interface for high-speed, RF-immune, long-distance communication.
NXP provides robust, secure, and scalable BMS ICs for a variety of automotive applications. One example is the MC33771, a lithium-ion battery controller IC designed for automotive applications such as HEVs, EVs, e-bikes, and e-scooters. This device features differential battery voltage and current ADC conversion, as well as coulomb counting and temperature measurement capabilities. It also supports standard SPI and transformer-isolated daisy-chain communication with MCUs for processing and control.
