Battery Stack Monitor Maximizes Performance of Li-Ion Batteries in Hybrid and Electric Vehicles: Page 8 of 8

April 29, 2020 //By Cosimo Carriero, Analog Devices
Battery Stack Monitor Maximizes Performance of Li-Ion Batteries in Hybrid and Electric Vehicles
Lithium-ion (Li-Ion) batteries offer a high energy density, but to maximize performance, a battery monitoring system (BMS) is mandatory. A state-of-the-art BMS not only allows you to extract the highest quantity of charge from your battery pack, but also lets you manage the charge and discharge cycles in a safer way, which results in an extended life.

Advantages of the dissipative technique are low cost and low complexity. Disadvantages are high energy loss and a more complex thermal design. Active balancing, on the other hand, redistributes the excess energy between the other cells of the module. This way the energy is recovered and less heat is generated. The disadvantage of such a technique is a more complex hardware design.


Figure 9. A 12-cell battery stack module with active balancing

Figure 9 shows an active balancing implementation using the LT8584. This architecture solves the problems of passive shunting balancers by actively shunting the charging current and returning the energy back to the battery stack. Instead of the energy being lost as heat, it is reused to charge the rest of the batteries in the stack. The architecture of the device also solves the problem of reduced run time when one or more of the cells in the stack reaches the lower safety voltage threshold before the entire stack capacity is extracted. Only active balancing can redistribute the charge from the stronger cells to the weaker cells. This allows the weaker cells to continue to supply the load, extracting the highest percentage of energy from the battery. The flyback topology allows the charge to return between any two points in the battery stack. Most applications return the charge to the module cells (12 or more), others return the charge to the entire battery stack, and some applications return the charge to an auxiliary power rail.

Conclusion

Electrification is the key for lower emission vehicles, but requires a smart management of the energy source—the Li-Ion battery. If not managed properly, a battery pack can become unreliable, and drastically reduce the safety of the automobile. High accuracy helps maximize the performance and the life of the battery. Active and passive cell balancing allow a safe and efficient battery management. Distributed battery modules are easily supported, and a robust communication of the data to the BMS controller, both wired and wireless, allows reliable SOC and SOH calculations.

References

1 Greg Zimmer. “Wireless Battery Management Systems Highlight Industry’s Drive for Higher Reliability.” Linear Technology, February 2017.

2 “Wireless BMS Concept Car.” Lion Smart, June 2017.

3 Michael Kultgen and Jon Munson. “Battery Stack Monitor Extends Life of Li-Ion Batteries in Hybrid Electric Vehicles.” LT Journal, Vol. XIX No. 1, March 2009.

4 Mike Kultgen and Greg Zimmer. “Maximizing Cell Monitoring Accuracy and Data Integrity in Energy Storage Battery Management Systems.” Analog Devices, Inc., 2019.

5 Stephen W. Moore and Peter J. Schneider. “A Review of Cell Equalization Methods for Lithium Ion and Lithium Polimer Battery Systems.” SAE 2001 World Congress, March 2001.

About the Author

Cosimo Carriero joined Analog Devices in 2006, as a field applications engineer, providing technical support to strategic and key accounts. He holds a Master’s of Science in physics from Università degli Studi of Milan, Italy. Past experiences include INFN, the Italian Institute for Nuclear Physics, defining and developing instrumentation for nuclear physics experiments, collaboration with small companies, developing sensors and systems for factory automation, and Thales Alenia Space as a senior design engineer for satellite power management systems. He can be reached at cosimo.carriero@analog.com.

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