62 Chapter 6 representative model of the battery can be created and material properties can be applied. From this model different stresses and forces can be applied to the product in order to find failure modes and weak spots in the mechanical design. Another tool that some thermal engineers use to evaluate the performance of energy storage systems is the lumped parameter model or lumped capacitance model.
The lumped parameter model is a useful tool because instead of defining each and every characteristic and material type as is required in an FEA or CFD analysis, the lumped parameter model “lumps” the characteristics together into categories and makes the assumption that the differences within each of these groups is not important. The benefit of this model is that it can be very quickly developed and is quick to run and will provide directionally correct estimates of the thermal performance of the energy storage system.
During the design process, it is very easy to continually make changes to your lumped parameter model in order to evaluate the impacts of those different changes on the thermal performance of the system. In this case, approxima- tion will offer a good estimate of a system’s performance while minimizing the number of complex calculations that must be made. One of the benefits of this model is that it can be developed using a simple Excel spreadsheet rather than needing to use a specialized software tool.
Hardware-in-the-loop (HIL) and software-in-the-loop (SIL) simulations are yet another set of tools that can help to quickly evaluate different performance profiles and different system designs in a safe laboratory-type environment. A HIL system uses a series of tools which could include some of the actual hardware but more likely the hardware will be represented by a mathematical simulation model. In the case of the battery pack, the hardware might include BMS controllers, electric motors, switches, and contactors or even a partial or complete battery pack. But for rapid turnaround most HIL engineers will create simulation models for many of the components.
In this type of system, it is possible to test literally hundreds of different situations, failure modes, and performance models in a matter of hours. In the case of a battery controller, you may create simulations of the battery pack and then you can run each and every different fault code situation that has been developed by your software team to ensure that the system responds correctly and as it was designed. As a final thought, it is important to note that none of these tools are intended for the typical sales person but instead a good thermal or mechanical engineer should be engaged to develop and use these tools due to the complexities involved.
Battery Sizing Tools When it comes to lithium-ion battery sizing tools, there are not currently any industry stan- dards developed in order to assist the system designer in generating an initial specification for a lithium-ion-based energy storage system. This is a weakness in the current literature on the