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Research Papers

Robust Nonlinear Disturbance Observer Design for Estimation of Ammonia Storage Ratio in Selective Catalytic Reduction Systems

[+] Author and Article Information
Jinbiao Ning

Department of Mechanical Engineering,
McMaster University,
Hamilton, ON L8S 4L7, Canada
e-mail: ningj4@mcmaster.ca

Fengjun Yan

Department of Mechanical Engineering,
McMaster University,
Hamilton, ON L8S 4L7, Canada
e-mail: yanfeng@mcmaster.ca

1Corresponding author.

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received March 17, 2015; final manuscript received September 9, 2015; published online October 5, 2015. Assoc. Editor: Zongxuan Sun.

J. Dyn. Sys., Meas., Control 137(12), 121012 (Oct 05, 2015) (8 pages) Paper No: DS-15-1118; doi: 10.1115/1.4031595 History: Received March 17, 2015; Revised September 09, 2015

Urea-based selective catalytic reduction (SCR) system is a promising way to obtain high NOx reduction and commonly adopted in diesel engine aftertreatment systems. The ammonia storage ratio is critical for SCR feedback control but it is difficult to be directly measured by sensors. This paper aims to effectively estimate the ammonia storage ratio on line and reduce the cost of using ammonia sensors. In the proposed method, the ammonia storage ratio is treated as an external disturbance in the NOx dynamic model and estimated by the nonlinear disturbance observer (NDO) methods. Furthermore, to reduce estimation errors of ammonia storage ratio caused by the high-frequency measurement noises, a novel robust nonlinear disturbance observer (robust NDO) is proposed and compared with a typical design method (regular NDO). Both the NDOs are developed based on part of the three-state SCR model and cost-effective, since NOx sensors are only used. The stability and noise attenuation properties of both estimations were also analyzed in the paper. The simulation results based on the full-vehicle simulator of FTP-75 test demonstrate that the regular NDO and the robust NDO can effectively estimate the ammonia storage ratio even in cases where ammonia cross-sensitivity affects the response. Among the two observers, the robust NDO has better noise attenuation properties.

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Figures

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Fig. 1

Urea-based SCR system for diesel engines

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Fig. 3

NOx sensors only for SCR system

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Fig. 2

Sensors for SCR system

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Fig. 4

The temperature and the total NOx out of the engine

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Fig. 5

Estimation performance of regular NDO without measurement noise

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Fig. 6

Estimation performance of robust NDO without measurement noise

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Fig. 7

Estimation performance of regular NDO with measurement noise

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Fig. 8

Estimation performance of robust NDO with measurement noise

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Fig. 9

NOx slip and NH3 slip

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Fig. 10

Estimation performance of regular NDO with ammonia cross-sensitivity

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Fig. 11

Estimation performance of robust NDO with ammonia cross-sensitivity

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Fig. 12

Estimation performance of regular NDO with ammonia cross-sensitivity and measurement noise

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Fig. 13

Estimation performance of robust NDO with ammonia cross-sensitivity and measurement noise

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