Modelica.Electrical.Batteries.UsersGuide

This library provides battery models, based on the electrical behaviour at the terminals.

Battery characteristics

All battery models rely on existing components like voltage source, resistor and capacitor models provided in the Analog package of the Modelica Standard Library.
Explore the concept of the battery models as well as parameterization. Both are based on the references.

Each battery is equipped with an optional heat port which can be enabled by the parameter useHeatPort; the heat flow of the battery heat port is determined by the sum of all heat flows of all resistive elements.
This enables coupling with external thermal models to investigate thermal management issues. However, thermal models are not included yet.

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Package Content

Name	Description
Concept	Concept of battery models
Parameterization	Parameterization of battery models
Contact	Contact
ReleaseNotes	Release Notes
References	References

Modelica.Electrical.Batteries.UsersGuide.Concept

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.

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Modelica.Electrical.Batteries.UsersGuide.Parameterization

A stack from BatteryStacks is built from Ns*Np identical cells, where Np describes the number of parallel connected cells and Ns the number of series connected cells.

The parameters of a stack built from Np*Ns identical cells are calculated as follows:

Cell parameters

The parameters of one cell are summarized in the parameter record cellData. Dependency of OCV on SOC can be chosen either linear (useLinearSOCDependency=true) or based on a look-up table.
By default, a linear OCV versus SOC characteristic is defined (like a capacitor), i.e. OCV_SOC[:,2]=[SOCmin,OCVmin/OCVmax; SOCmax,1].
The OCV versus SOC table has to be specified with 1st column = SOC values in ascending order, 2nd column = corresponding OCV values with respect to OCVmax.
Be careful using parameter smoothness for table interpolation, check the resulting characteristic.
Further dependencies of OVC (e.g. on temperature) are not taken into account, this would require a 2-dimensional table look-up.

Self-discharge is specified as discharge current Idis at SOC = SOCmax. From that values, a self-discharge conductance is calculated.
If self-discharge should be neglected, set Idis=0.

Linear temperature dependency of inner resistance can be specified by reference temperature T_ref and temperature coefficient alpha:
R = R_ref*(1 + alpha*(T - T_ref)).

Transient parameters

The parameter record for one cell of a transient battery model cellData extends from the basic cellData record, and adds the parameters of the additional RC-elements. These are specified by an array of parameter records rcData:

• R .. Resistance of RC-element
• C .. Capacitance of RC-element

The size of the array rcData has to be defined as parameter nRC. The parameters of these RC-elements are results of sophisticated measurements, e.g. cell impedance spectroscopy.
Temperature dependency of the resistors is assumed to be the same as inner resistance Ri.

Typical parameters of a Li-Ion cell

Capacity (i.e. nominal charge) Qnom, inner resistance Ri and short-circuit current Isc depend on the cell size.
Typical (estimated) values for a certain cell size are, as an example:

Self-discharge rate is typically 1%/month.

Parameters of stacks built from a matrix of Ns x Np cells:

A stack from BatteryStacksWithSensors is built from Ns*Np cells arranged in a matrix, where Np describes the number of parallel connected cells and Ns the number of series connected cells. The parameters of such a stack are summarized in the parameter record stackData. Here the matrix of Ns x Np cell parameters records is compiled. The parameters of original cell data are propagated to all cells except those whose indices are specified in the array kDegraded[:,2]. For these degraded cells the parameters of degraded cell data are propagated.
Note: Any members of the parameter array kDegraded[:,2] outside the range 1≤kDegraded[:,1]≤Ns and 1≤kDegraded[:,2]≤Np are ignored.

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Modelica.Electrical.Batteries.UsersGuide.Contact

Main authors

Anton Haumer
Technical Consulting & Electrical Engineering
D-93049 Regensburg, Germany
email: a.haumer@haumer.at

Dr. Christian Kral
Electric Machines, Drives and Systems
A-1060 Vienna, Austria
email: dr.christian.kral@gmail.com

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Modelica.Electrical.Batteries.UsersGuide.ReleaseNotes

Version 2.5.0, 2019-12-24

• Extension with stack models built from a matrix of different cells
• Cell and stack models with sensors

Version 1.1.0, 2019-07-17

• Agreement on consistent naming

Version 1.0.0, 2019-07-14

• First tagged version

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Modelica.Electrical.Batteries.UsersGuide.References

References

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