Texas Instruments was at CES 2023 this week, where it introduced its latest battery cell and battery pack management tools. The company says its new battery management system products could increase the range of an electric vehicle by as much as 20%. How can BMS technology do that? Read on.
The technical details will make fascinating reading for you tech types who enjoy reading wiring diagrams and exploring the intricacies of transistor design. Basically, it comes down to the new TI components being able to better understand what is actually happening inside that container we call a battery pack and using that information to more accurately predict its performance and range.
In a press release, the company says its new automotive battery cell and pack monitors have the most accurate measurement capabilities available on the market. As EVs grow in popularity, advanced battery management systems (BMS) are helping overcome critical barriers to widespread adoption. By focusing on solving complex system design challenges, TI provides the most advanced, comprehensive portfolio of BMS devices, enabling automakers to create a safer, more reliable driving experience and accelerate EV adoption.
TI’s latest battery controls are the BQ79718-Q1 battery cell monitor and the BQ79731-Q1 battery pack monitor. These devices provide an unprecedented level of accuracy and precision in measuring battery voltage, current, and temperature to determine the true range of a vehicle and increase the overall life and safety of the battery pack.
“Automakers aim to get the most range possible out of their EVs, and accurate state of charge estimations are vital to achieve this,” said Sam Wong, general manager for BMS at TI. “Our new devices bring substantially higher precision to voltage and current measurement, giving automakers confidence to accurately measure an EV’s true range.”
Critical Battery Management System Functions
As electric vehicles become more popular, the challenge for automakers is to reflect true range while making the vehicle more affordable. This translates into making the battery packs lower cost with higher energy densities. Every single watt-hour stored and retrieved from the cells is critical to extending the driving range, the company says.
The BQ79718-Q1 allows automakers to maximize the true range of their EV with high performance battery cell voltage measurements down to 1 mV of accuracy, and the BQ79731-Q1 allows measurement of the battery pack current down to 0.05% of accuracy. Such precision provides the clearest way possible to accurately measure state of charge and state of health at the individual cell and pack level. That in turn allows drivers to have better information about the true range of their cars at any moment in time.
Best in the industry voltage and current synchronization enables instantaneous monitoring of battery pack power, which provides a real time snapshot of battery health. This level of synchronization enables electrochemical impedance spectroscopy, which provides vital insight into the cell core temperature, battery aging, and state of charge of the battery.
The BQ79718-Q1 battery cell monitoring integrated circuit achieves an unprecedented Automotive Safety Integrity Level (ASIL) accuracy, giving automakers the ability to charge and discharge a vehicle battery pack beyond any cell monitor previously on the market.
Figure 1 presents a typical BMS architecture containing a battery management unit (BMU), a cell supervisor unit (CMU), and a battery junction box (BJB). A BMU typically has a microcontroller (MCU), which manages all of the functions within the battery pack. The traditional BJB is a relay box or a switch box with power contactors that connects the entire battery pack to the load inverter, motor, or battery charger.
Figure 1a shows the traditional BMS with no active electronics inside of the junction box. All of the measurements in the BJB are measured at the BMU. There are wires connecting the BJB into the analog-to-digital converter (ADC) terminals.
Figure 1b shows the intelligent BJB. There is a dedicated pack monitor inside the box that measures all voltages and currents and passes the information to the MCU using simple twisted pair communication. It helps eliminating wires and cabling harnesses and improves voltage and current measurements with lower noise.
Figure 2 shows the different high voltages, current, and temperatures that the pack monitor measures inside a BJB enabled by the BQ79731-Q1 battery pack monitor.
- Voltage: The high-voltage is measured using divided-down resistor strings. These voltage measurements monitor the state of high-voltage components in the system.
- Temperature: The temperature measurements monitor the temperature of the shunt resistor so that the MCU can apply compensation, as well as the temperature of the contactors to make sure that they are not stressed beyond the normal operating conditions.
- Current: The current measurements are based on either:
- A shunt resistor — because the currents in an EV can go up to thousands of amperes, the shunt resistance values are extremely small — in the range of 25 µOhms to 50 µOhms; or
- A hall effect sensor — Used to measure the EV current on the high voltage rail while still being isolated. Its dynamic range is typically limited, thus there can be multiple sensors in the system to measure the entire range.
The main function of a battery management system is to monitor cell voltages, pack voltages, and pack current. In addition, due to the high-voltage design of the BMS, insulation resistance measurement between the high-voltage domain and low-voltage domain is needed in order to catch defects in the battery structure and protect against hazardous conditions.
No Supply Chain Issues
Automakers can jumpstart their designs by purchasing the battery cell monitor BQ79718-Q1 evaluation module for $399. Also available is the battery pack monitor BQ79731-Q1 evaluation module priced at $199. All products featured for BMS are immediately available for purchase from Texas Instruments. Availability is a crucial factor in the world of manufacturing today, where shortages of computer chip based components are preventing automakers from meeting the explosion of demand for electric cars.
We have no way of knowing how these new battery management system tools from Texas Instruments compare with those used by industry leading companies like Tesla, but we can presume TI would not be investing time and money into making more accurate systems if there was not a need. Accurate information about the status of individual battery cells and a battery pack as a whole should enable drivers to maximize charging performance and range — two of the most important factors driving the EV revolution.
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