Abstract
Fast-switching semiconductors induce ripple currents on the high-voltage DC bus in the electric vehicle (EV). This paper describes the methods used in the project SiCWell and a new approach to investigate the influence of these overlaid ripples on the battery in EVs. The ripple current generated by the main inverter is demonstrated with a measurement obtained from an electric vehicle. A simulation model is presented which is based on an artificial reference DC bus, according to ISO 21498-2, and uses driving cycles in order to obtain current profiles relevant for battery cycling. A prototype of a battery cycling tester capable of high frequency and precise ripple current generation was developed and is used to cycle cells with superimposed ripple currents within an aging study. To investigate the impact of the frequency and the amplitude of the currents on the battery’s lifetime, these ripple parameters are varied between different test series. Cell parameters such as impedance and capacity are regularly characterized and the aging of the cells is compared to standard DC cycled reference cells. The aging study includes a total of 60 automotive-sized pouch cells. The evaluation of ripple currents and their impact on the battery can improve the state-of-health diagnosis and remaining-useful life prognosis. For the development and validation of such methods, the cycled cells are monitored with a measurement system that regularly measures current and voltage with a sampling rate of 2 MHz. The resulting dataset is suitable for the design of future ripple current aging studies as well as for the development and validation of aging models and methods for battery diagnosis.
Highlights
The vehicle model and current profiles can be used for further studies, the raw cycle measurements for the development of diagnostic and prognostic models, and the checkups of the battery cycles for modeling the aging process
If 45 A h is defined as the end of life (EoL) of the cells, the results shown in Figure 11 indicate a significant reduction in the lifetime of the cells when alternating currents (AC) or ripple currents are superimposed
In order to derive a realistic current profile for battery cycling, this study uses a simulation model which determines the DC current and its superimposed ripple depending on the operation point
Summary
The main traction inverter of an electric vehicle is the electric component with the highest power and highest energy throughput permanently connected to the HV battery and considered the dominant source for the ripple current. These measurements from a real electric vehicle strongly indicate that the ripple current should be considered, i.e., for the battery lifetime, as it exceeds a peak to peak value of 60 A
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