Electrical and Electrochemical Modeling

Electrical simulations are used at Fraunhofer ISE in various fields. In addition to the simulation of inhomogeneities in PV modules, the simulation of batteries - on cell and system level - as well as their production processes is a main focus.

Batteries are rapidly gaining in importance for the success of the further expansion of fluctuating renewable energies (PV, wind). Also they represent the foundation for the transport transition, as a highly efficient mobile storage system. The complex behavior of the electrical performance and its sensitive dependencies on temperature, constructive, mechanical and chemical parameters as well as, in particular, the aging mechanisms and their interactions are the subject of extensive scientific and technical research. Modeling and simulation of batteries as well as their production processes (e.g. welded joints or interface formation) are substantial tools for their efficient processing. The scope of time-consuming tests in the laboratory, which are associated with high safety precautions, can thus be significantly reduced, enabling cost-optimized development towards the product (time to market).

R&D Services for Electrical and Electrochemical Modeling

In the business area Hydrogen Technologies and Electrical Energy Storage and the research topic Photovoltaic Modules and Power Plants we offer the following services in the field of electrical and electrochemical modeling.

• Representation of any battery cells or battery systems in an FEM model or in an equivalent circuit model, depending on the respective scientific-technical issue
• Material characterization to determine the model parameters
• Experimental validation in the test laboratory
• Simulation of battery pack interconnection
• Simulation of welding processes
• Simulation of battery cells and battery systems in different applications
• Virtual product development and optimization
• Virtual analysis of critical operating conditions
• Simulation of inhomogeneities in PV modules

Simulation of Battery Cells and Battery Systems

Fraunhofer ISE creates highly accurate, locally resolved models of battery cells. These are necessary to understand the close interplay between temperature and temperature distribution, pressure and pressure distribution, cell voltage or efficiency and aging. In this way, local differences in the various aging mechanisms can be understood, leading to a better understanding of the overall aging process. Based on this, for example, the cell design (e.g., thicknesses, design of connections) can be optimized or cooling can be adjusted to minimize temperature differences in the battery cell.

In order to minimize temperature differences in the entire battery system, to achieve an efficient coupling to the heating and cooling system and thus to be able to guarantee the performance, reliability and safety of the system, the battery system is transferred to a CFD model, analyzed and optimized.

Electrochemical Modeling of Battery Cells

In addition to electrical equivalent circuit models, models based on actual electrochemical processes are also developed and applied at Fraunhofer ISE. These models reproduce the electrical and also thermal behavior of the battery cell. Among others, the pseudo two-dimensional battery model (P2D model) is used, which provides reliable values and is widely applied. However, both the equivalent circuit model and the P2D model require cell-specific parameters, including cell chemistry and cell geometry. Fraunhofer ISE can create and parameterize different battery models and verify their precision over all operating ranges (temperatures, current rates) in experimental tests. In addition to commercially available lithium-ion battery cells, alternative cells based on zinc or sodium ions, for example, are also developed, tested and simulated at Fraunhofer ISE.

Simulation of the Connection of Battery Packs

The core property of a PV module is the power generation, which can be analyzed very well, e.g. with SmartCalc.CTM. If, on the other hand, inhomogeneities play a role, this is often difficult to capture analytically. Therefore, we also use the finite element method to simulate currents and high voltages in PV modules. We also apply FEM simulations for interconnection technologies, such as resistance welding.

Battery packs are now frequently used as intermediate storage for regeneratively generated energy. Here, individual battery cells are connected to each other, e.g., by means of a welding process. In the research projects ElVis and Leopard, on the one hand the welding process for the production of the battery packs is investigated by means of FEM. On the other hand, both the vibration and the impact test according to UN38.3 are simulated in order to analyze the mechanical stability of the battery packs and to uncover any weak points at an early stage.