Electrical & Computer Engineering, Department of


Date of this Version

Winter 11-18-2010


A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Engineering (Electrical Engineering), Under the Supervision of Professors Dean J. Patterson and Jerry L. Hudgins. Lincoln, Nebraska: November, 2010.
Copyright 2010 Liqin Ni.


Plug-in hybrid electric vehicles (PHEVs) are gaining increasing interest for both residential and commercial transportation applications. In PHEV design, energy storage system (EES) is a critical component which will impact the overall design efficiency, performance, cost and etc. This dissertation aims to design an advanced energy storage system for a small plug-in hybrid electric vehicle, whose performance will approach very closely to the optimal possible, in terms of energy efficiency and acceleration, for passenger road vehicles application. Moreover, practical automotive requirements are considered during ESS design, such as cost, life time, safety and volume.

This dissertation utilizes ultracapacitors in conjunction with Lithium-ion batteries to combine the power performance ability of the former with the greater energy storage capability of the latter. This combination can improve vehicle performance, battery life time and safety issue with appropriate design. This dissertation describes the entire ESS design, from energy storage size optimization (determination of power and capacity), multi-source control strategy, to associated power electronics design and testing.

An economical 16-phase interleaved bidirectional DC/DC converter connected between ultracapacitors and batteries, is presented featuring smaller input/output filters, faster dynamic response and lower device stress advantages, which are highly preferable in high power applications. Discontinuous conduction mode (DCM) methodology is applied in the proposed converter to reduce imbalance current between phases so that the current control loop in each phase can be removed. The high current ripples associated with DCM operation are then alleviated by interleaving. The design, construction and testing of hardware prototype are presented with experimental results. Moreover, a novel ZVS/ZCS soft switch is proposed for the DC/DC converter based on DCM operation to improve efficiency, reduce spike voltage between MOSFET, and reduce Electromagnetic Interference (EMI). Both simulation model and experiment circuit have been built for one stage DC/DC converter to verify the proposed method.

In addition, a battery charger for residential application with power factor correction (PFC) capability is designed. A single stage of boost converter is proposed to achieve both PFC and battery charging control simultaneously. A modified charger system is proposed by utilizing ultracapacitor combined with bidirectional DC/DC converter, to remove large filtering capacitor requirement in traditional charger system, due to the fact that the power absorbed from the single phase AC supply has a large 120 Hz component.