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Measuring and Balancing Li-Ion Cell Stack Voltages

Developing and validating battery management algorithms

Application Areas

  • Developing and validating battery management systems and algorithms
  • Battery stress tests (deep discharge and overload)
  • Test of cell chemistry and cell geometry
  • End-of-line and approval tests for batteries and battery controllers

Key Features

  • Scalable modular system, supporting up to 846 V (around 200 cells)
  • Measuring range from 0 to 5 V
  • Accuracy of down to ±2 mV
  • Very high measurement frequency of up to 1 kHz
  • Absolute synchronous measurement for all cell voltages (independent of the count), cell temperatures and battery currents with the EV1093 board
  • Monitoring of isolation status
  • Real-time state of charge (SOC) algorithms for battery cells  

Lithium-ion (Li-ion) batteries typically consist of up to several hundred interconnected cells with an operation range of around 2.5 to 3.8 V. As the voltage curve is rather flat, a small cell voltage change causes a relatively great change in the state of charge (SOC).

Therefore, one of the many algorithms needed for managing batteries is the state of charge algorithm for balancing the battery cell voltages. For this, the cell voltages have to be measured and monitored with a high precision.

Since an individual cell voltage is much lower than the voltage a complete battery provides (up to and beyond 500 V), measuring the individual cell voltages is necessary. For this, dSPACE offers the EV1093 Battery Cell Measurement and Balancing Board. One board covers 24 cells, and you can easily add further boards for more channels, if necessary. The EV1093 supports the passive balancing of battery cells, where energy is drawn from the most charged cell and disposed of as heat through resistors. Due to the high technical production quality of today’s Li-ion batteries, active balancing, where energy is drawn from the most charged cell and transferred to the least charged cells, is often not required.

The EV1093 can be used either in a 19'' rack in the laboratory or in an in-vehicle housing. In both cases, the measurement channels for the cell voltages are isolated from the measurement channels for the temperature due to the high difference between the cell and the system voltages. Any Ethernet-capable dSPACE platform, such as MicroAutoBox II, MicroLabBox® or the DS1007 PPC Processor Board, can be used to control the board. The Ethernet connection lets you use distributed intelligence via the EV1093's FPGA and the high-performance processor on the dSPACE platform.

For different configuration and implementation requirements, the specialized dSPACE Battery Cell Voltage Measurement and Balancing Blockset provides maximum flexibility for accessing the battery directly. You can fully control the balancing process and the algorithms.

For example, to passively balance the cells while the battery is being recharged, you can define a target voltage, i.e., the minimum voltage which the EV1093 will always maintain. For passive balancing, resistors with a wide range of resistor values can be added to the EV1093 via a plug-on module.

Although the system comes with integrated safety mechanisms, these can be disabled to discharge the cells completely or create an overload. As each cell is monitored individually, battery stress tests or tests of a new cell chemistry and cell geometry are supported. Additionally, the EV1093 provides numerous temperature sensors that give you detailed information on which temperatures occur where, making it easy for you to identify hot spots.

To give you a boost start, the blockset also includes ready-to-use, configurable real-time-capable SOC algorithms that are based on Kalman filters.