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Release 2020 R1

AVL Virtual Battery Development - Components and Systems

Highlights of the latest range of improvements across the AVL battery portfolio

At AVL we engage in a constant program of updates and improvements to all of our products and services. This is to address the changing needs of our customers, the end users, and the transformation of the global automotive landscape.

A wide range of updates have been made in all our disciplines and competencies. Below you will find some of the highlights of the latest release in our battery solution area.
 

 

Solution: Battery Thermal Analysis


This latest release of AVL FIRE™ M offers a variety of new features and functions. These enhance its capabilities and improve usability for battery-related applications. The following list contains a selection of those features:
 

New Selection and Defeaturing Functions

The defeaturing and selection functions in SHAPE™ have been enhanced. This makes surface preparation and CAD data simplification faster and more user friendly. In addition, SHAPE’s viewer performance has been improved.
 

Figure: Defeaturing in SHAPE™
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Extension of Battery Meshing Capabilities

Electrothermal and electrochemical battery models require special meshing techniques. In this latest release of FIRE M, features such as automatic volume embedding, and thin-layer meshing have been improved. Their functionalities have been extended to meet requirements for battery meshing and ease of use.
 

Figure: Prismatic Battery Cell Mesh
 

Changes in Mesh Preparation

The function known as mesh decoupling is required for multi-material meshes, in order to make them compatible with the FIRE M solver. In previous versions of FIRE M this step was performed automatically during meshing, but had to be done manually in some applications like battery venting. In the latest release, mesh decoupling has been moved to the solver start to be completed automatically, hence no user interaction is required anymore.
 

Import/Export of Model Setup

In FIRE M 2020 R1, the model setup can be imported/exported. This functionality allows an easier and more lightweight sharing of model setups while still retaining their parameters and data pool links. This functionality also offers full compatibility between the different versions of FIRE M.
 

Figure: Import/Export Model Setup
 

Volumetric Heat Sources

In release 2020 R1, Volumetric Heat Sources have been introduced in the FIRE M solver GUI as “Sources”, which can be activated within the “Additional Terms” section.

The user can now define global (domain-based) and/or cell selection-based source(s), as either a heat rate (W) or a volumetric heat rate (W/m3). Volumetric Heat Sources can be used in various cases, such as when no electrical properties (resistance) of a current-carrying part are known.
 

Global Ohmic Sources

Global Ohmic Heat Sources can now be defined for individual components. These heat sources are generated by a user-prescribed resistance and by detecting the current flowing through the component. Global Ohmic Heat Sources replace the local ohmic heat sources generated by the distributed current density and the electrical conductivity of the material.
 

Figure: Battery Module Cooling simulated with Global Ohmic Heat Sources

 

 

Variable Contact Resistances

Variable thermal contact resistances have been introduced to FIRE M 2020 R1. This is to meet the needs for various types of simulations, such as battery thermal runaway, in which the contact resistance can change significantly due to high temperature fluctuations.
 

Conversion of 3D Model to Equivalent 0D System Model

The latest release now includes an algorithm to support the conversion of FIRE M models to CRUISE™ M. The algorithm extracts the necessary data to build a physics-based thermal network from a steady-state CFD simulation. Through this process, a 3D component-model can be transferred to a 1D/1D system-level model while still retaining predictive capabilities.
 

Figure: Thermal Network Model Generator Interface
 

Thermal Domain for Multi Rate Simulations

Within CRUISE M 0D simulation the thermal domain can now be treated as a separate time domain in multi-rate simulations. This enables faster models by increased accuracy in electro-thermal simulations of battery systems.
 

Discretized Solid Extensions

The Discretized Solid element has been extended in CRUISE M 2020 R1 to allow the modelling of solid cylindrical elements. Furthermore, the Discretized Solid element now handles anisotropic material properties, which takes battery module modelling to a new level. Several usability improvements now allow the Discretized Solid element for battery modelling on cell, module or pack level to be used even more effectively.
 

 

Solution: Battery Safety Analysis

 

Flammability Index for Venting Gas

To evaluate the flammability of venting gas (which is mixed with ambient air after venting), the flammability index has been introduced as an additional, optional output in the Species Transport module. The upper and lower flammability limit of the species being considered are used to form the flammability index. This provides information on whether the current mixture in the computational cell is flammable or not, and how easy/difficult it is to ignite.

Furthermore, the cell temperature is checked and an autoignition index indicates whether the venting gas will auto ignite or not. The current implementation features seven additional output scalars. These are:

  • Flammability Index of CH4
  • Flammability Index of H2
  • Flammability Index of CO
  • Total Flammability Index
  • Autoignition Index of CH4
  • Autoignition Index of H2
  • Autoignition of CO

 

Figure: Flammable spots can easily be assessed spatially and temporally resolved. Flame barriers, that are meltable as shown in the image, can be used in combination.
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Solution: Vehicle Integration

 

Battery Management System Component

A new Component Battery Management System has been introduced in this latest update. The control component limits battery system power and current output and, depending on temperature and SOC, different maps for continuous and peak performance can be implemented. An integrated derating algorithm is used to switch between the maps. The component can be used to assess battery performance and lifetime prediction in a Vehicle or Subsystem context.
 

Figure: Battery Management System Parameterization
 

 

Solution: Power Electronics Functional Analysis

 

Electric Networks Improvements

Several improvements have been made to the CRUISE Solver, to enable more robust simulations of electrical networks. This allows investigation into pre-charge units, safety functions, charging systems and power electronics.
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Thermal Network Generator

On system-level simulation, the setup of thermal networks can be a challenging modeling task. The 3D complexity of i.e. battery-packs or inverters needs to be broken down into a network of fundamental 0D building blocks such as lumped masses, different heat transfer components, boundary conditions and source terms. To facilitate this effort, this version of CRUISE M releases a Thermal Network Generator (TNG) that takes advantage of FIRE M and its capability of 3D-modeling and simulation. FIRE M supports the conversion and export of a 3D-CFD model into an equivalent 0D network with dedicated functions that can be customized by the user. CRUISE M loads the exported model and builds automatically the corresponding thermal network. Here, it is key that also the parametrization of the individual components is done based on results gained from CFD simulations.
 

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Figure: Thermal Network Generator and Inverter Power Module Result Validation


The predictability of the CRUISE M results is validated on the inverter example with the help of CFD simulations at different operating conditions. The TNG breaks the complexity of 0D modeling by automating the effort to create and parametrize detailed, high fidelity, equivalent 0D models.