Electric Drive Transient Behavior Modeling: Comparison of Steady State Map Based Offline Simulation and Hardware-in-the-Loop Testing

Electric drives, whether in battery electric vehicles (BEVs) or various other applications, are an important part of modern transportation. Traditionally, physics-based models based on steady-state mapping of electric drives have been used to evaluate their behavior under transient conditions. Hardware-in-the-Loop (HIL) testing seeks to provide a more accurate representation of a component’s behavior under transient load conditions that are more representative of real world conditions it will operate under, without requiring a full vehicle installation. Oak Ridge National Laboratory (ORNL) developed such a HIL test platform capable of subjecting electric drives to both conventional steady-state test procedures as well as transient experiments such as vehicle drive cycles. This facility was used to compare the behavior of an electric drive installed in a BEV with the two methods: offline simulation built from the experimental steady state efficiency map, and HIL experimentation of the same electric drive simulating the same BEV. The aim of this study is to evaluate the accuracy of steady state map based simulation against experimental HIL results in the case of an electric drive. This paper first outlines HIL test procedures as well as the key aspects of utilizing steady-state maps to develop a model of the drive. Then both quantitative and qualitative differences in the experimental results obtained from the two processes are presented. Differences in specific transient behaviors between the two methods are discussed. Although both methods agree well in most transient situations, direct comparison of the offline simulation against the HIL results demonstrates that transient behaviors are not captured entirely by simulation alone.