New Way to Determine Amount of Charge Remaining in Battery

Currently in the United States, consumers are slow to embrace electric vehicles. One prime factor against resistance to the electric car is buyers' anxiety over finding a charging station. It is very tough to sell an electric vehicle that needs to be plugged in overnight as the thought of being stranded with few charging stations haunts the motorist.

But the newly developed technique by the team of researchers from the North Carolina State University comes as good news for electric vehicle consumers. The researchers have developed a new technique that allows users to check the amount of charge remaining in a battery in real time. Even the battery developers benefit from this new study.

The lead author of the paper is Habiballah Rahimi-Eichi, a Ph.D. student at NC State. 

"This improved accuracy will also give us additional insight into the dynamics of the battery, which we can use to develop techniques that will lead to more efficient battery management," says Dr. Mo-Yuen Chow, a professor of electrical and computer engineering at NC State and co-author of the paper. "This will not only extend the life of the charge in the battery, but extend the functional life of the battery itself."

With the existing computer models the drivers find it very difficult to estimate the remaining charge, and the number they get is not accurate. The inaccuracy stems, in part, from the number of variables that must be plugged in to the models. 

The researchers stated an example, the capacity of a battery to hold a charge declines with use, so a battery's history is a factor. Other factors include temperature and the rate at which a battery is charged, among many others.

The drawback with the existing model is that they allow data on these variables to be plugged in to the model once. But variables such as, temperature constantly keeps altering. With this the models can get highly inaccurate. T

The newly designed technique identifies and processes data that can be used to update the computer model in real time, allowing the model to estimate the remaining charge in a battery much more accurately. Specially designed for batteries in plug-in electric vehicles, the approach is also applicable to battery use in any other application.

With the help of the new technique models are able to estimate remaining charge within 5 percent of accuracy.  If a model using the new technique estimates a battery's state of charge at 48 percent, the real state of charge would be between 43 and 53 percent (5 percent above or below the estimate).

The research was supported by the National Science Foundation, in collaboration with the foundation's Engineering Research Center for Future Renewable Electric Energy Delivery and Management, which is based at NC State.

The paper, "Adaptive Parameter Identification and State-of-Charge Estimation of Lithium-Ion Batteries," will be presented at the 38th Annual Conference of the IEEE Industrial Electronics Society in Montreal, Oct. 25-28.