Novel Implementation of an FPGA-based Real Time Impedance Spectroscopy for Highly Integrated Reliable Safety Systems

The power supply of battery-based safety systems is a highly critical component due to its influence on all system functions. To guarantee functionality the state of the battery must be known at any time. Especially the current State of Charge (SoC) and State of Health (SoH) must be monitored continuously to guarantee functionality during deployment. It is not possible to fully discharge the battery of a system that needs to provide energy to perform safety functions. This makes current state of the art methods like Voltage Analysis (DVA) or Coulomb Counting (CC) unusable. This especially is a problem in subsea systems where components cannot be easily exchanged, and a design life of 25 years is common. A solution for this problem is the Electrochemical Impedance Spectroscopy (EIS) which can be conducted at any SoC. The EIS provides impedance values over a defined set of frequencies that correspond to different chemical processes which can be used to accurately estimate the battery state.

A novel real time EIS implementation is proposed which uses the on-board charger of the Battery Management System (BMS) to perform the measurement. No additional components are required as the EIS is calculated on a Field Programmable Gateway Array (FPGA) in real time which makes it useable for embedded systems. The structure of the impedance measurement system is presented, and the functionality of the embedded impedance spectroscopy is proven using an RC-circuit as a reference load.

Keywords: EIS, FPGA, Impedance, Real-time, Reliability, Safety.

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