Sharif Digital Repository

In this paper, an algebraic tuning rule is presented for fractional PI controllers to control first order plus dead-time processes. By using the performance map (PM) method, this tuning rule is derived in order to set the gain margin of the control system close to 3 and the phase margin close to 60 degrees. The robustness and performance of this tuning rule are compared with some well-known PI tuning rules. Simulation results are brought to demonstrate the effectiveness and robustness of this tuning formula against process dynamic uncertainties in comparison with the other tuning methods  

In this paper, a new approach is presented for optimal control of large-scale chemical processes. In this approach, the chemical process is decomposed into smaller sub-systems at the first level, and a coordinator at the second level, for which a two-level hierarchical control strategy is designed. For this purpose, each sub-system in the first level can be solved separately, by using any conventional optimization algorithm. In the second level, the solutions obtained from the first level are coordinated using a new gradient-type strategy, which is updated by the error of the coordination vector. The proposed algorithm is used to solve the optimal control problem of a complex nonlinear... 

In this paper, the axiomatic design is introduced for controlling a power electronic converter. The main idea of axiomatic design is to introduce variables affecting the desired performances of the system most independently possible. The control process is presented for a Buck converter to achieve constant efficiency and output voltage ripple. ©2008 IEEE  

Manipulation of a quantum system requires the knowledge of how it evolves. To impose that the dynamics of a system becomes a particular target operation (for any preparation of the system), it may be more useful to have an equation of motion for the dynamics itself, rather than the state. Here we develop a Markovian master equation for the process matrix of an open system interacting with a reservoir, which resembles the Lindblad Markovian master equation. We employ this equation to introduce a scheme for optimal local coherent process control at target times and extend the Krotov technique to obtain optimal control. We illustrate utility of this framework through several quantum... 

Co/Cu multilayers were deposited in a sulfate solution by controlling the current and potential for the deposition of cobalt and copper layer respectively. The electrochemical behavior of these multilayers was studied by cyclic voltammetry and current transients. In addition, a mathematical analysis was used to characterize the electrodeposition system. Simultaneously, the nucleation and growth mechanisms were monitored by these techniques. In this case, the results clearly showed that electrodeposition of cobalt layers was a kinetically controlled process while the reduction of copper ions was a diffusion-control process. Although nucleation mechanism of the single Co deposit was found as a... 

Fuzzy sliding mode control (FSMC) as a robust and intelligent nonlinear control technique is proposed to control processes with severe nonlinearity and unknown models. The performance of the proposed method has been evaluated for both single input single output (SISO) and MIMO nonlinear systems through its application in three severely nonlinear processes that are frequently used as benchmarks of nonlinear process control strategies. The evaluation shows that, despite its lack of dependence on the process model, the proposed method performs almost the same as conventional sliding mode control alternatives that utilize all the information that exists in the mathematical model of the process.... 

This paper deals with introducing non-fragile algebraic tuning rules for fractional-order PD controllers where they are used in controlling processes modeled in Integral Plus Delay (IPD) forms. These tuning rules are obtained based on a recently introduced approach, named as the centroid approach, which results in non-fragile tuning methods. Based on this approach, the centroids of two-dimensional admissible regions or the center of gravity of three-dimensional admissible regions in controller parameter space give non-fragile options for choosing controller parameters. © 2013 IFAC  

In process planning, determining feature's machining precedence is an essential step. The task becomes more difficult if features interact with each other, in which case the feature precedence information may suggest multiple machining sequences of the features. This paper considers interacting features in a feature-based model for process planning tasks. For each feature, precedence information is generated considering both roughing and finishing operations. A rule-based system is developed and implemented based on the information about machining precedence of the interacting features. The STEP-NC data model is used as the underlying data model. This model is object-oriented and compliant... 

It has been well documented that multivariate systems will benefit from application of advanced control strategies. The application of these methods has thus far been hindered for a variety of reasons which range from complexity of the design methodologies to the cost associated with implementation of these solutions. This paper shows that there exist alternative means by which existing control strategies of a multivariate system could be extended, thereby leading to increased efficiency, without the need to remove and implement a new control system installation. A realistic model of an entire pulping mill is used in this paper to show that by careful selection of only a few additional... 

Loop restoration scheme (LRS) is a special feeder automation (FA) scheme, which is used by utilities to improve distribution system reliability. The LRS is controlled and managed by its automatic control system (ACS). The impacts on distribution system reliability indices of implementing LRS mainly depend on the type of its ACS. Two common types of ACS of LRS are presented and used in this study. Successful operation of ACS is dependent on the protection and automatic control functions of switching devices of LRS. Different failure modes of these switching devices can therefore affect the procedure of ACS in fault detecting, isolating and service restoration. The impacts of failure of... 

There is a great deal of interest in the manufacturing industry for quantitative measures of process performance with multiple quality characteristics. Unfortunately, multivariate process capability indices that are currently employed, except for a handful of cases, depend intrinsically on the underlying data being normally distributed. In this paper, we propose a general multivariate capability index based on the Mahanalobis distance, which is very easy to use. We also approximate the distribution of these distances by the Burr XII distribution and then estimate its parameters using a simulated annealing search algorithm. Finally, we give an example, based on real manufacturing process... 

Multivariate monitoring techniques such as multivariate control charts are used to control the processes that contain more than one correlated characteristic. Although the majority of previous researches are focused on controlling only the mean vector of multivariate processes, little work has been performed to monitor the covariance matrix. In this research, a new method is presented to detect possible shifts in the covariance matrix of multivariate processes. The basis of the proposed method is to eliminate the correlation structure between the quality characteristics by transformation technique and then use an S chart for each variable. The performance of the proposed method is then... 

This study proposes a multi-objective control algorithm for simultaneous process and quality control in non-Gaussian stochastic batch processes. The objective is to control a non-Gaussian process so that each batch is delivered within a pre-specified time. During each batch, the process is controlled by a fixed-parameter PI controller. Between any two adjacent batches the controller parameters are updated by a differential evolution algorithm so that the integral squared of tracking error, entropy of tracking error, integral of absolute processing time error and entropy of processing time error are minimised. the proposed algorithm is applied to a batch continuously stirred tank reactor... 

Finding an optimal control strategy for a nonlinear uncertain system is a challenging problem in the area of nonlinear controller design. In this paper, a two-level control algorithm is developed for robust optimal control of large-scale nonlinear systems. For this purpose, using a decomposition/coordination framework, the large-scale nonlinear system is first decomposed into several smaller subsystems, at the first level, where a closed-form solution as a feedback of states and interactions is obtained to optimize each subsystem. At the second level, a substitution-type prediction method, as a coordination strategy, is used to compensate the nonlinear terms of the system and to predict the... 

The electrocatalytic oxidation of methanol was studied over Ni, Co and Cu binary or ternary alloys on graphite electrodes in a NaOH solution (0.1 mol/L). The catalysts were prepared by cycling the graphite electrode in solutions containing Ni, Cu and Co ions at cathodic potentials. The synergistic effects and catalytic activity of the modified electrodes were investigated by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). It was found that, in the presence of methanol, the modified Ni-based ternary alloy electrode (G/NiCuCo) exhibited a significantly higher response for methanol oxidation compared to the other samples. The anodic peak... 

The electrodeposition of nickel was studied using electrochemical techniques in different electrolytes and various agents. The voltammetry analysis clearly showed that the electrodeposition of nickel was a diffusion-controlled process associated with a typical nucleation process. The current transients represented instantaneous nucleation with a typical three-dimensional (3D) growth mechanism. Scharifker's equations were derived for instantaneous and progressive nucleation of the 3D growth of the spherical centers under diffusion-controlled condition. The number of nucleation sites increased with the increment in overpotential and Ni 2+ concentration. Atomic force microscopy was used to... 

The capability analysis of production processes where there are more than one correlated quality variables is a complicated task. The problem becomes even more difficult when these variables exhibit nonnormal characteristics. In this paper, a new methodology is proposed to estimate process capability indices (PCIs) of multivariate nonnormal processes. In the proposed methodology, the skewness of the marginal probability distributions of the variables is first diminished by a root transformation technique. Then, a Monte Carlo simulation method is employed to estimate the process proportion of nonconformities (PNC). Next, the relationship between PNC and PCI is found, and finally, PCI is... 

Process planning (PP) has an important role in manufacturing systems design and operations. Volume decomposition and machinable volumes (MVs) or machining features determination is the core activity in process planning. This process requires extraction of elementary volumes (EVs), merging or clustering EVs to construct feasible MVs and finally selecting an optimal combination of MVs. Development of MVs is an important activity, so that better solution is obtained by better developed MVs. Generation of limited number of MVs or machining features, which is often performed by experts may miss the optimal solution. Also, using exact methods such as combinatorial optimization not only generate... 

The paper presents a comprehensive electric arc furnace (EAF) model, developed for simulation and model-based control of the EAF processes. The model consists of three sub models, i.e., (i) arc model; (ii) chemical and slag model; and (iii) heat-transfer model. Arc model predicts the amount of energy dissipated from the arcs using arc currents and arc lengths; chemical and slag model calculates chemical energy and changes of elements/compounds, slag height and slag quality; while the heat-transfer model uses calculations of the other two models in order to establish a reference energy system (RES) for each zone in the EAF due to the variations in arc length, slag height, and bath height. The... 

Determining the precedence of machining features is a critical issue in feature-based process planning. It becomes more complex when geometric interaction occurs between machining features. STEP-NC, the extension of STEP (ISO 10303) standard developed for CNC controllers, is a feature-based data model. It represents all the geometric and topological product data minus feature interactions. In this paper, machining precedence of interactive and non-interactive STEP-NC features is discussed. Local and global precedence of machining features are defined on the basis of geometric constraints, such as geometric interaction of features and feature approach face and technological constraint such as...