Modeling and Optimization of Power Management and Li-ion Batteries Health for Hydraulic-Electric Hybrid Vehicle.

Abstract

The main goal of this work is to develop a systematic methodology to improve the range of electric vehicle and protect the battery health. Several other objectives enable achieving the main goal, including modeling, and power management optimization of hydraulic electric hybrid system, and battery degradation investigation and optimization. In order to improve the electric vehicle range, the hydraulic hybridization of electric vehicle is proposed. Physics based models of hydraulic electric hybrid vehicle are developed and the performance is analyzed. A near optimal and vehicle implementable rule-based energy management strategy is developed for the hydraulic-electric hybrid vehicle. The all electric range is improved by 68.3% through hybridization and control optimization. To further improve the range, the battery health is identified to be the key issue. Electrochemistry-based battery models are developed to investigate the degradation of the graphite/LiMn_2 O_4 cell. Our degradation study shows that the capacity fade can be divided into three stages: acceleration stage (SEI growth on anode is dominant), stabilization stage (SEI growth slows down and cathode capacity fade continues), and saturation stage (cathode has poor capacity and becomes the limiting factor). Cathode LMO fracture is repeatedly observed and suspected to be one important degradation mechanism in the cathode. A single particle fracture model is developed to investigate capacity fade induced by cathode fracture. The study shows that fracture introduces a significant capacity loss. In a 5 um particle with fracture, the capacity loss can reach to 13.7%. The particle size is another key factor that affects the mass transportation in the particle. Larger particles lead to higher internal resistance for electron transportation; therefore, fracture-induced capacity fade is more severe than with particles of smaller size. Based on the degradation analysis, a general procedure is developed to optimize the battery health while fulfilling the energy and power requirements. In total, this dissertation provides a systematic way to improve the range of electric vehicle by hydraulic hybridization and battery optimal design. The methodologies developed in this dissertation can be used to provide guidance for development of strategies for hybrid propulsion and optimal design of the battery health.