Transactions of the Institute of Measurement and Control

Hamamci, Serdar Ethem; Tan, Nusret; Efe, Mehmet Onder; Soylemez, Mehmet Turan

doi: 10.1177/0142331215575469pmid: N/A

Dousti, Morteza; Baslamısli, S Caglar; Onder, E Teoman; Solmaz, Selim

doi: 10.1177/0142331214546522pmid: N/A

The purpose of this study is to design high-performance active braking control and observer algorithms for passenger vehicles equipped with electromechanical brake systems. These algorithms are designed to be adaptive with changing driving and road conditions in a switched multiple-model manner to ensure high performance and robustness. The effectiveness of a set of multiple-model switching lead-lag controllers is evaluated during transitions between different road friction coefficients. Meanwhile, a multiple-model switching observer algorithm is developed to estimate the shape of the tyre braking force curve with respect to the longitudinal slip. Each switched observer predicts signals according to its preset tyre model. The observers are designed based on different Burckhardt tyre models that are parameterized for different road conditions. In our simulations, the value of the friction coefficient is assumed to be unknown and our switching algorithms are observed to estimate successfully the varying friction coefficients by comparing a quadratic cost function of measured signals from the vehicle with signals generated by observers. We demonstrate that our algorithms provide high reliability and fast response, thus ensuring a stopping distance close to the theoretical minimum.

Taşçıkaraoglu, Fatma Yıldız; Ucun, Levent; Küçükdemiral, Ibrahim B

doi: 10.1177/0142331214538089pmid: N/A

This paper deals with the disturbance rejection problem for discrete-time linear systems having time-varying state delays and control constraints. The study proposes a novel receding horizon H∞ control method utilizing a linear matrix inequality based optimization algorithm which is solved in each step of run-time. The proposed controller attenuates disturbances having bounded energies on controlled output and ensures the closed-loop stability and dissipation while meeting the physical control input constraints. The originality of the work lies on the extension of the idea of the well-known H∞ receding horizon control technique developed for linear discrete-time systems to interval time-delay systems having time-varying delays. The efficiency of the proposed method is illustrated through simulation studies that are carried out on a couple of benchmark problems.

Deniz, Furkan Nur; Tan, Nusret; Hamamci, Serdar Ethem; Kaya, Ibrahim

doi: 10.1177/0142331214539991pmid: N/A

This paper deals with the stabilization problem of Smith predictor structures using a PI controller. Stability regions that include all stabilizing parameters of a PI controller for the case of perfect matching between the plant and model and for mismatched case are obtained. The models of the plant are assumed to be FOPDT (first-order plus dead time) and SOPDT (second-order plus dead time) transfer functions. Thus, the aim of this study is to determine all stabilizing PI controllers for the Smith predictor scheme and to compare the stability regions obtained for perfectly matched and mismatched models. It is observed that the stability regions obtained for both cases are quite different and the stability regions for FOPDT and SOPDT models are broader than the stability region of the actual model. Furthermore, an approach is presented to find different models of an actual system using the stability region and it is shown that the stability region of these models can fit the stability region of actual system. A simulation example is provided to illustrate the results.

Koksal, Muhammet; Koksal, Mehmet Emir

doi: 10.1177/0142331214532678pmid: N/A

After summarizing the commutativity results for analogue linear time-varying systems, the commutativity of cascade connected discrete-time linear time-varying systems is introduced. Some general open questions on the subject are stated and new results are presented, intended to answer some of them. Two examples are given to reinforce the concept and to show up its possible benefits in engineering to reduce noise effects and design robust systems.

Çakıroğlu, Osman; Güzelkaya, Müjde; Eksin, İbrahim

doi: 10.1177/0142331214536202pmid: N/A

In this study, a new serial cascade controller design methodology is proposed. The inner-loop process is taken as a stable first-order process with time delay and the outer-loop process as an integrating or non-integrating nth-order stable process with time delay. Classical Smith predictors are used to compensate for the time delay in each loop. In the outer loop when the process order is greater than 1, the process model transfer function is decomposed into first-order transfer functions of the required quantity. Next, for each first-order transfer function, a control loop is established and then for each loop an appropriate controller is built up. The controllers are designed to provide a simplified closed-loop transfer function for the existing loop using zero pole cancellation. The decomposed first-order transfer functions results in either an integrator form or a transfer function with one real pole. The resulting controller evolves to be a proportional-type controller for the loops involving the integrator and they appear as a PI-type of controller for the loops involving the real stable pole. To illustrate the effectiveness of the proposed methodology, it is compared with another method given in the literature via simulations.

Ablay, Günyaz

doi: 10.1177/0142331214534292pmid: N/A

U-tube steam generator level control systems are used to maintain the water level within prescribed narrow limits and to provide constant supply of high-quality steam during power demand variations. Traditional level control systems are often found to be unsatisfactory during low power operations and start-up conditions. Robust non-linear estimator-based optimal control systems are proposed for steam generator level control systems to solve the water level tracking problem during power (or steam) demand variations. It is shown that the proposed control strategies provide optimal and robust water level tracking with a single controller over the complete range of power operation with model and parameter uncertainties and noisy measurements.

Parlakçı, Mehmet Nur Alpaslan

doi: 10.1177/0142331214532305pmid: N/A

This paper is concerned with a state feedback controller design method for neutral systems with a time-varying delay, considering uncertainties in the plant parameters, as well as in controller gain. The uncertainties are in additive form, affecting both the system matrices of the plant and the controller gain. The uncertainties that are assumed admissible are time-varying and norm-bounded. The neutral system is also subject to external disturbances. A robust stabilizing H-infinity state-feedback controller is synthesized under several conditions that are presented in the form of matrix inequalities. A new generalized type of Jensen integral inequality has been introduced for utilization in the derivation of the aforementioned results, which could thus have been relaxed via that approach. A feasible solution set is obtained using the well-known cone complementarity technique by solving a non-linear minimization problem subject to linear matrix inequalities. A numerical example with case studies concludes the present work. The results of the minimum achievable attenuation rate indicate considerable improvement in comparison with those reported in the literature.

Alagoz, Baris Baykant; Ates, Abdullah; Yeroglu, Celaleddin; Senol, Bilal

doi: 10.1177/0142331214527476pmid: N/A

This experimental study investigates the practical benefits and drawbacks of error-cube control for closed-loop PID control structures. The error-cube control approach employs the cube power of the error signal for controllers and this causes variability in control characteristics due to the non-linearity of the cube power operation. The error-cube signal introduces attenuated and magnified error regions. These two characteristic error regions result in a tight control regime and a slack control regime, depending on magnitude of the error signal. The study presents a discussion on non-linear error signals in a practical aspect and demonstrates the effects of non-linear error signals on the step response of closed-loop PID control systems via simulation results and experimental measurements. An enhanced error-cube controller was proposed to improve the control performance of the error-cube control and results are discussed.

Evren, Sanem; Unel, Mustafa

doi: 10.1177/0142331214528351pmid: N/A

Research on swarm robotics has become increasingly important in the last three decades. One of the major research directions in swarm robotics is the control of the formation of swarm robots to perform various tasks in 2D or 3D environments. In this paper, we propose a new planar (2D) formation control framework based on a dynamic version of elliptic Fourier descriptors (EFDs) and develop formation controllers that enable robots to form the desired shapes. The main advantage of this method over more traditional approaches in the literature is its flexibility in the representation of the desired shape. The formation can be virtually any arbitrary planar closed curve. Representation by EFDs becomes much more powerful as the number of harmonics in the representation increases. Performance of the proposed formation controller is tested in three simulations where desired swarm formations modelled by EFDs with two, three and six harmonics are considered. Results are quite promising.