Online Estimation of Battery Resistances in a Battery Integrated Modular Multilevel Converter

For lifetime-optimized control of a modular multi-level converter battery energy storage system, determining the current state of health is crucial. Due to the degrees of freedom within the control of such a system, the utilization of dedicated test signals is possible without interrupting operation. In this paper, a method to determine internal battery resistance is described and implemented in the control structure of a prototype converter. The method is verified by measurement, and the results are validated by electrochemical impedance spectroscopy.