Abstract
This thesis aims to analyze the multi-disciplinary dynamics of key components in a hybrid electric vehicle (HEV) using bond graph unified approach. An element-oriented model simplification algorithm was also developed to enhance the computational ability for the HEV simulation but still remain the similar system dynamics of the original model. The key components including the direct injection spark ignition (DISI) engine, the brushless DC motor, the proton exchange membrane fuel cell (PEMFC) and the continuously variable transmission (CVT) have been modeled with a set of dynamic equations. Time-domain response and frequency-domain analysis for these key components (subsystems) then have been studied. These verified components were integrated into various types of HEVs, such as engine-motor HEVs or fuel cell HEVs. The highly-nonlinearity and high-order dynamics of a HEV make it improper for vehicle (high-level) controller designs or real-time simulation. A model simplification (order reduction) methodology was thereby proposed in this thesis using defined dynamics similarity, causality determination procedures and error dynamics modules to eliminate trivial states in the HEV bond graph model. Simulation results show that each subsystem can be modeled rapidly and multi-physical domains inside it can be integrated effectively using the bond graph approach. The dynamics analysis and controller designs for all bond graph models are accessible. Performance evaluations of hybrid vehicles are achieved by the combination of these subsystems and the developed rule-based control strategy. The proposed model simplification algorithm deduces complexity of HEV models systematically, enhances the computational efficiency and also keeps major characteristics of the original models. Results show that if the model fidelity of each subsystem in the automotive simulators is restricted within 5%, the computational time will decrease 40% via the proposed element-oriented model simplification algorithm. The automotive on-line simulators thus are completed.