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TECHNICAL PAPERS

Model-Based Fuel Optimal Control of Hybrid Electric Vehicle Using Variable Structure Control Systems

[+] Author and Article Information
X. Wei, V. I. Utkin, G. Rizzoni

Center for Automotive Research, The Ohio State University, Columbus, OH 43212

L. Guzzella

Swiss Federal Institute of Technology, (ETH), Zurich, Switzerland

J. Dyn. Sys., Meas., Control 129(1), 13-19 (Jun 26, 2006) (7 pages) doi:10.1115/1.2397148 History: Received May 11, 2004; Revised June 26, 2006

Abstract

Hybrid electric vehicles provide promising alternatives to conventional engine-powered vehicles with better fuel economy and less emission. Realization of these benefits depends, in part, on proper control of the vehicle. This paper examines a variable structure control that switches between two operating points. The resulting sliding optimal control provides a better energy management strategy than that obtained conventionally from Pontryagin’s minimum principle. Since one of the operating points is at zero engine power, this sliding optimal control is also referred to as engine start-stop strategy. Contrary to the general understanding that the engine should only stop at low speeds or during decelerations, it is shown that engine start-stop also improves fuel economy during highway cruising. The main contribution of this paper is to theoretically prove that this “duty-cycle” operation mode is indeed optimal using Pontryagin’s minimum principle.

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Figures

Figure 1

Example 1: Sliding optimal control and state trajectory: (a) state trajectory under sliding optimal control and (b) sliding optimal control trajectory

Figure 2

Example 2: Hamiltonian and state trajectories under sliding optimal control: (a) Sliding optimal control exists: u1=0, u2=1 when λ=0; and (b) state trajectories under sliding optimal control

Figure 3

Battery equivalent circuit

Figure 4

Hamiltonian versus engine power: (a) Sliding optimal control exists: Pice1=0 and Pice2>Preq when Preq=5.35KW and λ=−0.693; and (b) sliding optimal control does not exist: Pice=Preq when Preq=22KW and λ=−0.497

Figure 5

Optimal control for vehicles with batteries of different internal resistance

Figure 6

State trajectories under sliding optimal control when vehicle is cruising at 29m∕s(65mph)

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