Concept of battery models

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This information is part of the Modelica Standard Library maintained by the Modelica Association.

The core of the cell models is a signal voltage controlled by a look-up table OCV (open circuit voltage) dependent on SOC (state of charge).
However, other dependencies (e.g., on temperature) are not implemented yet.

Current flowing to or from the battery is measured and integrated, thus calculating the charge contained in the battery. The charge contained in the battery with respect to nominal charge Qnom gives SOC.
The look-up table is parameterized for one cell, therefore input has to be scaled by 1/(Np*Qnom), and the output has to be scaled by Ns*OCVmax.

To model self-discharge, a conductor in parallel to the signal voltage and the current sensor is implemented. If self-discharge is specified as zero, the conductor is omitted.

A resistor r0 is connected in series to the signal voltage, representing the inner resistance of the battery. The resistance can be specified as linearly dependent on temperature.

If CellRCStack instead of CellStack is chosen, RC-elements are connected in series to model the transient behaviour of the battery.
Both models can be used for a single cell Ns = Np = 1 as well as a stack built from identical cells.
Note that the total inner resistance Ri is the sum of the resistance of resistor r0 and the sum of the resistances of the resistors of the RC-elements.

Additionally to these batteries that model a single cell scaled by the number of series connected cells Ns and the number of parallel connected cells Np, single cell models and stacks are provided in BatteryStacksWithSensors. The cells are equipped with sensors, the measured signals are provided in the CellBus. The stack models contain a matrix of Ns x Np single cells which can be parameterized differently to investigate the influence of a degraded cell on the behaviour of the whole stack, as well as to design battery management systems. The stack provides the StackBus which contains Ns x Np cell buses of the cells. Additionally, the signals of the whole stack - the same signals as of a single cell - are provided in the BatteryBus.

There are two options of series and parallel connections of cells in stacks:

  • useAllParallelConnections=true : Np cells are connected in parallel, and these groups are connected in series.
  • useAllParallelConnections=false: Ns cells are connected in series, and these groups are connected in parallel.

For convenience, a block BusTranscription transfers the signals of all cell buses in the stack bus to the StackBusArrays, arranged as Ns x Np matrix per measurement signal.

For details of parameterization, see UsersGuide.Parameterization.