414 research outputs found
EASILY VERIFIABLE CONTROLLER DESIGN WITH APPLICATION TO AUTOMOTIVE POWERTRAINS
Bridging the gap between designed and implemented model-based controllers is a major challenge in the design cycle of industrial controllers. This gap is mainly created due to (i) digital implementation of controller software that introduces sampling and quantization imprecisions via analog-to-digital conversion (ADC), and (ii) uncertainties in the modeled plant’s dynamics, which directly propagate through the controller structure. The failure to identify and handle these implementation and model uncertainties results in undesirable controller performance and costly iterative loops for completing the controller verification and validation (V&V) process.
This PhD dissertation develops a novel theoretical framework to design controllers that are robust to implementation imprecision and uncertainties within the models. The proposed control framework is generic and applicable to a wide range of nonlinear control systems. The final outcome from this study is an uncertainty/imprecisions adaptive, easily verifiable, and robust control theory framework that minimizes V&V iterations in the design of complex nonlinear control systems.
The concept of sliding mode controls (SMC) is used in this study as the baseline to construct an easily verifiable model-based controller design framework. SMC is a robust and computationally efficient controller design technique for highly nonlinear systems, in the presence of model and external uncertainties. The SMC structure allows for further modification to improve the controller robustness against implementation imprecisions, and compensate for the uncertainties within the plant model.
First, the conventional continuous-time SMC design is improved by: (i) developing a reduced-order controller based on a novel model order reduction technique. The reduced order SMC shows better performance, since it uses a balanced realization form of the plant model and reduces the destructive internal interaction among different states of the system. (ii) developing an uncertainty-adaptive SMC with improved robustness against implementation imprecisions. Second, the continuous-time SMC design is converted to a discrete-time SMC (DSMC). The baseline first order DSMC structure is improved by: (i) inclusion of the ADC imprecisions knowledge via a generic sampling and quantization uncertainty prediction mechanism which enables higher robustness against implementation imprecisions, (ii) deriving the adaptation laws via a Lyapunov stability analysis to overcome uncertainties within the plant model, and (iii) developing a second order adaptive DSMC with predicted ADC imprecisions, which provides faster and more robust performance under modeling and implementation imprecisions, in comparison with the first order DSMC.
The developed control theories from this PhD dissertation have been evaluated in real-time for two automotive powertrain case studies, including highly nonlinear combustion engine, and linear DC motor control problems. Moreover, the DSMC with predicted ADC imprecisions is experimentally tested and verified on an electronic air throttle body testbed for model-based position tracking purpose
Adaptive Discrete Second Order Sliding Mode Control with Application to Nonlinear Automotive Systems
Sliding mode control (SMC) is a robust and computationally efficient
model-based controller design technique for highly nonlinear systems, in the
presence of model and external uncertainties. However, the implementation of
the conventional continuous-time SMC on digital computers is limited, due to
the imprecisions caused by data sampling and quantization, and the chattering
phenomena, which results in high frequency oscillations. One effective solution
to minimize the effects of data sampling and quantization imprecisions is the
use of higher order sliding modes. To this end, in this paper, a new
formulation of an adaptive second order discrete sliding mode control (DSMC) is
presented for a general class of multi-input multi-output (MIMO) uncertain
nonlinear systems. Based on a Lyapunov stability argument and by invoking the
new Invariance Principle, not only the asymptotic stability of the controller
is guaranteed, but also the adaptation law is derived to remove the
uncertainties within the nonlinear plant dynamics. The proposed adaptive
tracking controller is designed and tested in real-time for a highly nonlinear
control problem in spark ignition combustion engine during transient operating
conditions. The simulation and real-time processor-in-the-loop (PIL) test
results show that the second order single-input single-output (SISO) DSMC can
improve the tracking performances up to 90%, compared to a first order SISO
DSMC under sampling and quantization imprecisions, in the presence of modeling
uncertainties. Moreover, it is observed that by converting the engine SISO
controllers to a MIMO structure, the overall controller performance can be
enhanced by 25%, compared to the SISO second order DSMC, because of the
dynamics coupling consideration within the MIMO DSMC formulation.Comment: 12 pages, 7 figures, 1 tabl
MIMO First and Second Order Discrete Sliding Mode Controls of Uncertain Linear Systems under Implementation Imprecisions
The performance of a conventional model-based controller significantly
depends on the accuracy of the modeled dynamics. The model of a plant's
dynamics is subjected to errors in estimating the numerical values of the
physical parameters, and variations over operating environment conditions and
time. These errors and variations in the parameters of a model are the major
sources of uncertainty within the controller structure. Digital implementation
of controller software on an actual electronic control unit (ECU) introduces
another layer of uncertainty at the controller inputs/outputs. The
implementation uncertainties are mostly due to data sampling and quantization
via the analog-to-digital conversion (ADC) unit. The failure to address the
model and ADC uncertainties during the early stages of a controller design
cycle results in a costly and time consuming verification and validation (V&V)
process. In this paper, new formulations of the first and second order discrete
sliding mode controllers (DSMC) are presented for a general class of uncertain
linear systems. The knowledge of the ADC imprecisions is incorporated into the
proposed DSMCs via an online ADC uncertainty prediction mechanism to improve
the controller robustness characteristics. Moreover, the DSMCs are equipped
with adaptation laws to remove two different types of modeling uncertainties
(multiplicative and additive) from the parameters of the linear system model.
The proposed adaptive DSMCs are evaluated on a DC motor speed control problem
in real-time using a processor-in-the-loop (PIL) setup with an actual ECU. The
results show that the proposed SISO and MIMO second order DSMCs improve the
conventional SISO first order DSMC tracking performance by 69% and 84%,
respectively. Moreover, the proposed adaptation mechanism is able to remove the
uncertainties in the model by up to 90%.Comment: 10 pages, 11 figures, ASME 2017 Dynamic Systems and Control
Conferenc
Discrete Adaptive Second Order Sliding Mode Controller Design with Application to Automotive Control Systems with Model Uncertainties
Sliding mode control (SMC) is a robust and computationally efficient solution
for tracking control problems of highly nonlinear systems with a great deal of
uncertainty. High frequency oscillations due to chattering phenomena and
sensitivity to data sampling imprecisions limit the digital implementation of
conventional first order continuous-time SMC. Higher order discrete SMC is an
effective solution to reduce the chattering during the controller software
implementation, and also overcome imprecisions due to data sampling. In this
paper, a new adaptive second order discrete sliding mode control (DSMC)
formulation is presented to mitigate data sampling imprecisions and
uncertainties within the modeled plant's dynamics. The adaptation mechanism is
derived based on a Lyapunov stability argument which guarantees asymptotic
stability of the closed-loop system. The proposed controller is designed and
tested on a highly nonlinear combustion engine tracking control problem. The
simulation test results show that the second order DSMC can improve the
tracking performance up to 80% compared to a first order DSMC under sampling
and model uncertainties.Comment: 6 pages, 6 figures, 2017 American Control Conferenc
An Overview of Studies Conducted on Washback, Impact and Validity
This article aimed at presenting a comprehensive overview of three interrelated concepts of washback, impact and validity in language testing and a myriad of studies conducted at different places to investigate the influence of testing on teachers and teaching, textbooks, learners and learning, attitudes toward testing, test preparation behaviors, etc.. Some of these studies present the results of various investigations on the influence of a national English examination on the local English language teaching and learning due to its high-stakes nature in particular countries such as Brazil, China, Hong Kong, Iran, Israel, Japan, Romania, Sri Lanka, and Taiwan. Some others cover a wide range of worldwide investigation on English testing such as the IELTS, TOEFL, and MECC. Moreover, there is a complete report of several important projects appointed by major testing agencies such as Cambridge ESOL and Educational Testing Services (ETS) on washback and impact studies. The article proceeds by reviewing the relevant literature on test validation which is a key concept in language testing domain since it is concerned with test interpretation and use. This domain is characterized and enriched by studies of washback and impact
Single Coronary Artery with Anomalous Origin of the Right Coronary Artery from the Distal Portion of Left Circumflex Artery: A Very Rare Case
Congenital anomalies of coronary arteries, albeit rare, may be significant contributors to angina pectoris, hemodynamic
abnormalities, and sudden cardiac death. A 47-year-old man referred to us with atypical chest pain. Electrocardiography
demonstrated no significant ischemic changes, but cardiac troponin I test was positive. The patient underwent coronary
angiography, which revealed a single coronary artery from the left Valsalva sinus. In addition, the left anterior descending
(LAD) and the left circumflex (LCx) arteries were in normal position with significant stenosis in the mid-portion of the
LAD and the distal portion of the LCx. A large branch originated from the distal portion of the LCx and tapered toward the
proximal portion as the right coronary artery (RCA). This is a rare coronary anomaly that has no ischemic result. Coronary
lesions were the cause of the patient’s angina pectoris. Angioplasty and stenting of the LAD and LCx was done, and medical
therapy (Clopidogrel, Aspirin, Atorvastatin, and Metoprolol) was continued. The patient was asymptomatic at 8 months’
follow-up.
J Teh Univ Heart Ctr 2013;8(3):161-163
This paper should be cited as: Pourbehi MR, Amini A, Farrokhi S. Single Coronary Artery with Anomalous Origin of the Right
Coronary Artery from the Distal Portion of Left Circumflex Artery: A Very Rare Case. J Teh Univ Heart Ctr 2013;8(3):161-163.
Keywords: Coronary angiography, Coronary vessel anomalies • Angina pectori
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