Novel methode of state-of-charge estimation using in-situ impedance measurement: Single cells in-situ impedance measurement based state-of-charge estimation for LiFePO 4 — Li 2 TO 3 Battery Cells with a real BMS

The major tasks of Battery Management Systems (BMS) are to guaranty safe operation conditions and to maintain every single cell of the whole battery pack. These tasks require measurements and balancing processes for each cell. Especially new lithium ion cell chemistries reveal hard conditions on the BMS to estimate hardly measurable state variables like the State of Charge (SoC) or the State of Health (SoH). The capability to exactly estimate these conditions represents the fundamental requirement for the economical operation of the battery pack This paper describes a method to estimate the SoC for every single cell based on impedance spectroscopy measurements. For that purpose a genetic algorithm (GA) is developed running on an electronic control unit (ECU) of the BMS to determine significant parameters which offer the opportunity to estimate the actual SoC. In this paper the impedance spectroscopy is measured in the laboratory. Future work will include an measurement electronic on the BMS to determine the impedance in-situ.