Simplified electric vehicle powertrain modelling

Abstract

Rapid development and adoption of electric vehicle technology has driven the requirement for simplified powertrain models. In this thesis, a simplified electric vehicle powertrain (SEVP) model, which calculates energy consumption for a battery electric vehicle (BEV) based on the minimum number of published vehicle parameters, is presented. The SEVP utilises published coast-down coefficients to model the tractive force and simplifies the traction motor model by using a surface-mounted permanent (SPM) motor. The SEVP is benchmarked for energy consumption estimation, with two industry-standard vehicle simulators, ADVISOR and FASTSim. The comparison is enabled by combining all three simulators in a single MATLAB model, which permits the interchange of the individual powertrain component models and establishes their impact on the cumulative energy consumption in a drive cycle. The three simulators are validated for ten BEVs using dynamometer test data from Argonne National Laboratory. Energy consumption estimation deficiencies of the SEVP are addressed by; (i) a simple cabin thermal load model, and (ii) including machine saturation and flux weakening in the SPM model. For electrical circuit simulation, the ideal battery model of the SEVP was expanded to include a Lithium-ion (Li-ion) battery pack model and the SPM motor was replaced with a more complex internal permanent magnet (IPM) design. In the Li-ion model, the output voltage is a function of the depth of discharge and a simple ageing function is included to estimate battery capacity over the lifetime of the vehicle. A comparison of the choice of internal impedance network on the dynamic performance of the battery model is conducted. The IPM motor model parameters are derived based on finite element analysis (FEA) of five traction motor designs, rated from 50 kW to 165 kW. The FEA models are validated based on test data from Oakridge National Laboratory. Finally, an energy management strategy (EMS) for a fuel cell electric vehicle (FCEV) is proposed. The EMS minimises the fuel consumption and the overall operating costs. Prerequisites for achievement of the minimum overall operating costs are minimising the battery and the fuel cell degradation.