Interview with Anja Fenske from Rohde & Schwarz

Ms. Fenske, where and why are battery management systems needed?

Anja Fenske: Battery management systems are essential wherever rechargeable batteries are used. This is why BMSs are used in nearly all electrical devices—from smartwatches, smartphones, and laptops to e-bikes and electric cars. In all these cases, the charging and discharging behavior of a battery directly influences a device’s service life. The BMS ensures the correct state of charge, thereby preventing dangerous conditions such as overheating or deep discharge. In electric car batteries, which consist of several hundred or even thousand cells, BMSs ensure that the charge is distributed evenly across the battery cells and that the entire system works safely and efficiently. We have all heard reports of electric cars catching fire, usually caused by individual battery cells overheating. Intelligent management ensures that the cells are always in the safe operating area (SOA). BMSs also play a decisive role in the performance and longevity of a battery. They ensure that battery cells work optimally, last a long time, and, especially in the case of electric vehicles, facilitate the maximum range and optimum charging cycles.

Do BMSs also contribute to predictive maintenance?

Anja Fenske: In the area of predictive maintenance, BMSs go one step further: They continuously monitor the condition of individual cells and can detect early on if a cell is weakening or failing. In this case, they issue a warning, for example, recommending that the affected cell be replaced before it impairs the entire system. The scope of these functions varies depending on the intelligence and complexity of the BMS. Sophisticated systems, such as those used in electric vehicles, feature technologies such as active cell balancing, which enable precise control and optimization of the cells. However, the following also applies: The more powerful the BMS, the more complex and costly both its development and testing are.

What solutions are available for the development and verification of BMSs?

Anja Fenske: High-precision power supplies are available for BMS development and testing. Rohde & Schwarz offers the R&S®NGM200 and R&S®NGU series. These measuring devices can accurately set and precisely measure very low currents and voltages. In addition, both devices have dedicated battery simulation software that can be used to simulate charging and discharging curves precisely. Our solutions also make it possible to simulate individual battery cells at the cell level, which is particularly important for the development of complex BMSs. For example, a battery pack with twelve cells can be tested without having to connect the physical battery cells. In this way, it is possible to specifically test how a BMS reacts to different states of charge, for example, to a single, almost empty cell in an otherwise well-charged battery pack. There is also a software solution that makes it easier to create a battery model. Batteries can be repeatedly charged and discharged while data on open-circuit voltage, charging voltage, and internal resistance are recorded as a function of the charged and discharged capacity. On this basis, a precise battery model can be created that enables realistic tests.

Please list a few of the common test cases for testing the BMS

Anja Fenske: Tests focus on two central areas: security and performance. When it comes to safety, the aim is to check whether the battery cells are healthy. We are talking about a battery’s state of health (SOH). Similar to a person's vital signs, SOH describes certain limit values for batteries that must be adhered to. A BMS continuously monitors these values to prevent overheating, overcharging, or deep discharging because this is where the greatest risks arise, such as fires or harm to people and damage to materials. Performance is all about using the battery efficiently and extending its service life. Various operating states and scenarios are tested for this purpose. In other words, how fast and with what voltage and current is the battery being charged? What happens if the current is too high? How does the BMS react in the event of a sudden voltage drop or if the temperature rises sharply? And finally, how does the system behave when individual cells are out of balance? Our solutions can accurately simulate many of these test cases. Test engineers evaluate the results and optimize the BMS where necessary. The BMS can then be retested to validate the improvements.

How do you think the technical development of BMSs and BMS test solutions will progress?

Anja Fenske: I think that the management of batteries—and energy storage systems in general—will continue to gain importance, especially with regard to renewable energies. In order to solve the challenges of the energy transition, it must be possible to store large amounts of energy efficiently and make it available in line with the demand. It is also to be expected that future standards and safety regulations will prescribe even more detailed tests for BMSs. As a result, BMS test systems also need to be further developed to measure more precisely and make more extensive test scenarios possible. I am also convinced that AI will revolutionize battery management by not only optimizing the energy flow, but also by detecting problems preventively and thus extending the service life of batteries. In summary, it can be said that BMSs and their test procedures will play an increasingly important role in a future in which more and more technologies rely on electric drives.

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