Vehicle Performance Simulations in Open Modelica: Case Study of Battery and Fuel Cell Electric Buses

In a world characterized by themes like decarbonization and pollution reduction receiving increasing attention, the automotive industry is experiencing a revolution. Manufacturers are striving to achieve new eco-friendly solutions capable of reducing environmental impact whilst remaining cost-competitive for the consumer. To achieve such goals, increasingly complex propulsion systems are being developed that aim to minimize energy consumption whilst ensuring good, or improved performance. Traditional approaches heavily based on procurement and testing of physical hardware are no longer a viable option for the development of these new solutions since they would be too slow and expensive. This is especially true when all the steps normally needed to find the best solution starting from draft designs are considered. In this context, numerical simulation represents a key element capable of supporting the entire development process from the concept phase up to the validation one, reducing the need for physical prototypes. This is possible through CAE tools capable of facilitating the testing of several powertrain solutions and predicting a wide range of performance indicators, from fuel consumptions to failure points. With the help of computers, complex calculations and simulations can be performed, allowing the exploration of trade-offs for a huge set of solutions in a reduced timeframe. This work aims to explore the viability of an open-source software such as OpenModelica as an alternative to costly commercial licenses. OpenModelica is a tool developed in the Modelica programming language, which has been developed by the Modelica Association for simulation environments. Since the software is open source, information is openly shared by OpenModelica users online, whilst pre-existing models and libraries can be found online for a variety of applications. An advantage of such is that users can easily build upon pre-existing libraries built by previous developers such as to create models for systems and set-ups that hadn’t previously been considered or built. Consequently, the focus of this work is to create an ad-hoc model library for PUNCH Torino for modeling battery electric vehicles and fuel cell electric vehicles. The custom library aims to evaluate vehicle performance parameters such as acceleration times and fuel economy, whilst the choice to create a library from the ground up allows to optimize models running time, whilst simultaneously ensuring an appropriate model accuracy. In order to validate the tool, vehicle models are created, assembled and simulated, with results being compared directly with those from models already available and developed in GT-SUITE. The slight deviations detected between the simulation results, with errors ranging from zero to ten percent due to differences between the software and the modeling approaches taken, confirm the reliability of the models developed and provide an initial point from which the project can be expanded upon.