Current sensing and coulomb counting

Overview
current voltage

Current sensing in BMS is used to accurately predict the State of Charge (SoC). That is because of the high flat nature and sensitivity of the SoC curve to the cell state (e.g. voltage, temperature, age, etc.) As such deducing the SoC accurately from the cell voltage alone would not be possible. Therefore, a current sensor is used for predicting the SoC using Coulomb counting, by measuring the charges that enter or leave a battery cell.

Additionally, the current sensor is also used to detect current events (OCD). An OCD event implies that the cells and the load need to be protected by disconnecting the battery. Fast OCD event detection is crucial to protect the passengers, the load, and the battery.

 

The most common ways to measure current are with shunt resistors and/or hall sensors. Infineon as such offers:

  • Shunt Resistor Sensing ICs: The PSoC™ 4 HV PA 144k is a fully integrated programmable embedded system for battery monitoring and management and a subfamily of the PSoC™ 4 HV PA. The system features an Arm® Cortex® M0+ processor running at up to 48 MHz and programmable and reconfigurable analog and digital blocks. In terms of memory, it offers 128 KByte of code flash with ECC protection. The family is offered in a 32-QFN package with wettable flanks.
  • Hall sensors: The automotive XENSIV™ TLE4972 is a magnetic coreless current sensor that provides an analog sensor signal proportional to the measured current as well as two fast overcurrent detection pins.  Due to its differential measurement principle, it is robust against stray fields and suited for current measurements in EMC-prone environments, e.g. in-phase current sensing in a motor application. The digitally assisted analog concept of TLE4972 offers superior stability over temperature and lifetime thanks to the proprietary stress and temperature compensation and the well-established and robust Hall technology. The core-less design avoids negative effects (saturation, hysteresis) commonly known from sensors using iron cores for flux concentration. 
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