Electrochemical impedance spectroscopy for online battery monitoring - power electronics control

Online diagnostics for monitoring of battery cells in a battery pack is necessary in order to determine the state of the battery pack, like its age and safe operation. It could also provide the possibility to adjust the operation strategy of the battery management system and the load to increase the battery lifetime and safety. Impedance spectroscopy is a well-known measurement technique for electrochemical systems, such as a battery half-cell. Once the method is implemented in the battery management system and performed online during operation it could provide a monitoring system for the whole pack. Current solutions are either inaccurate or too big, expensive and energy inefficient. The presented approach proposes a dual use of the battery charger which incorporates a switched mode amplifier to generate the stimuli current necessary to perform an electro impedance spectroscopy. A suitable control is designed to overcome the non-linearities and instabilities introduced by the output filter and the current crossover effects of the electronic switches. This inexpensive, energy efficient technology could allow impedance monitoring of every cell in the battery pack and make a better prediction of the state of the battery possible.