Showing papers by "Cristina I. Muresan published in 2019"

A Survey of Recent Advances in Fractional Order Control for Time Delay Systems

Abstract: Several papers reviewing fractional order calculus in control applications have been published recently. These papers focus on general tuning procedures, especially for the fractional order proportional integral derivative controller. However, not all these tuning procedures are applicable to all kinds of processes, such as the delicate time delay systems. This motivates the need for synthesizing fractional order control applications, problems, and advances completely dedicated to time delay processes. The purpose of this paper is to provide a state of the art that can be easily used as a basis to familiarize oneself with fractional order tuning strategies targeted for time delayed processes. Solely, the most recent advances, dating from the last decade, are included in this review.

Tuning of fractional order proportional integral/proportional derivative controllers based on existence conditions:

Abstract: Fractional order proportional integral and proportional derivative controllers are nowadays quite often used in research studies regarding the control of various types of processes, with several pa...

Identification for control of suspended objects in non-Newtonian fluids

Abstract: This paper proposes a framework for modelling velocity profiles and suspended objects in non-Newtonian fluid environment. A setup is proposed to allow mimicking blood properties and arterial to venous dynamic flow changes. Navier-Stokes relations are employed followed by fractional constitutive equations for velocity profiles and flow. The theoretical analysis is performed under assumptions of steady and pulsatile flow conditions, with incompressible properties. The fractional derivative model for velocity and friction drag effect upon a suspended object are determined. Experimental data from such an object is then recorded in real-time and identification of a fractional order model performed. The model is determined from step input changes during pulsatile flow for velocity in the direction of the flow. Further on, this model can be employed for controller design purposes for velocity and position in pulsatile non-Newtonian fluid flow.

Universal Direct Tuner for Loop Control in Industry

Abstract: This paper introduces a direct universal (automatic) tuner for basic loop control in industrial applications. The direct feature refers to the fact that a first-hand model, such as a step response first-order plus dead time approximation, is not required. Instead, a point in the frequency domain and the corresponding slope of the loop frequency response is identified by single test suitable for industrial applications. The proposed method has been shown to overcome pitfalls found in other (automatic) tuning methods and has been validated in a wide range of common and exotic processes in simulation and experimental conditions. The method is very robust to noise, an important feature for real life industrial applications. Comparison is performed with other well-known methods, such as approximate M-constrained integral gain optimization (AMIGO) and Skogestad internal model controller (SIMC), which are indirect methods, i.e., they are based on a first-hand approximation of step response data. The results indicate great similarity between the results, whereas the direct method has the advantage of skipping this intermediate step of identification. The control structure is the most commonly used in industry, i.e., proportional-integral-derivative (PID) type. As the derivative action is often not used in industry due to its difficult choice, in the proposed method, we use a direct relation between the integral and derivative gains. This enables the user to have in the tuning structure the advantages of the derivative action, therefore much improving the potential of good performance in real life control applications.

An Autotuning Method for a Fractional Order PD Controller for Vibration Suppression

Abstract: Fractional order controllers are receiving an ever-increasing interest from the research community due to their advantages. However, most of the tuning procedures for fractional order controllers assume a fully known mathematical model of the process. In this paper, an autotuning method for the design of a fractional order PD controller is presented and applied to the vibration suppression in airplane wings. To validate the designed controller, an experimental unit consisting of a smart beam that simulates the behaviour of an airplane wing is used. The experimental results demonstrate the efficiency of the designed controller in suppressing unwanted vibrations.

Robust Estimation of a SOPDT Model from Highly Corrupted Step Response Data

Abstract: Most industrial processes, even though complex in nature, can be represented using second order plus dead-time models, usually determined from step response data, which capture the essential process dynamics. The parameters of these models are computed based on specific algorithms. However, the great majority of these algorithms require system identification basic knowledge and are thus difficult to be used by the process engineer. The focus of this paper is to introduce a new method for computing the parameters of such models. The major advantage over existing methods is that it does not require any system identification expertise, being fully automatic. Additional advantages include robustness to noise, disturbances and system order. All of these are emphasized through several numerical examples, as well as an experimental validation.

Robust Fractional Order Control of LPV Dynamic Mechatronic Systems

Abstract: This paper introduces the application of a robust fractional order control method to control a highly linear parameter varying (LPV) mechatronic system. We validate the proposed methodology on the study case of the Stewart platform, which is representative for docking systems in aerospace engineering. The application has been inspired by a collaborative master thesis work with research teams involved in aerospace engineering projects for European Space Agency. The novelty of the proposed methodology is the high degree of autonomy in tuning controller parameters and high degree of robustness to varying dynamics profiles of the system under test. The controller design, analysis, stability and implementation are discussed, along with simulation results on two mimicked cases of extreme LPV dynamics encountered in real life of such complex mechatronic systems.

Design and Practical Implementation of a Fractional Order Proportional Integral Controller (FOPI) for a Poorly Damped Fractional Order Process with Time Delay

Abstract: One of the most popular tuning procedures for the development of fractional order controllers is by imposing frequency domain constraints such as gain crossover frequency, phase margin and iso-damping properties. The present study extends the frequency domain tuning methodology to a gen-eralized range of fractional order processes based on second order plus time delay (SOPDT) models. A fractional order PI controller is tuned for a real process that exhibits poorly damped dynamics characterized in terms of a fractional order transfer function with time delay. The obtained controller is validated on the experimental platform by analyzing staircase reference tracking, input disturbance rejection and robustness to process uncertainties. The paper focuses around the tuning methodology as well as the fractional order modeling of the process’ dynamics.

Approximation methods for FO-IMC controllers for time delay systems

Abstract: Fractional Order Internal Model Control (FO-IMC) is among the newest trends in extending fractional calculus to the integer order control. Approximation of the FO-IMC is one of the key problems. Apart from this, when dealing with time delay systems, the time delay needs also to be approximated. All these approximations can alter the closed loop performance of the controller. In this paper, FO-IMC controllers will be tested in terms of the approximation accuracy. The case study is a first order system with time delay. Several scenarios will be considered, aiming for a conclusion regarding the choice of the approximation method as a function of the process characteristics, closed loop performance and FO-IMC fractional order. To approximate the time delay, two extensively used techniques will be considered, such as the series and Pade approximations. These will be compared to a novel approximation technique. An analysis of the test cases presented show that the series approximation proves more suitable in a single scenario, whereas the novel approximation method produces better results for the rest of the test cases.

Alternative Approximation Method for Time Delays in an IMC Scheme

Abstract: Internal Model Control (IMC) algorithms have proven to be quite efficient in designing PID type controllers for time delay systems. However, to compute the equivalent PID controller in a feedback loop, using the IMC tuning approach, implies the approximation of the process time delay. Two of the most widely used approximation methods (first order or series and Pade) are used in this paper and compared to a new approximation method, the Non Rational Transfer Function (NRTF) approximation. In the current paper, the NRTF approximation is presented as an alternative method to the series/Pade approximation techniques for time delay systems in an IMC closed loop design. It is shown that for first order and second order processes, given a certain ratio of the IMC filter time constant and process time delay, the NRTF method could produce better closed loop dynamics, compared to the series/ Pade approximations. Several numerical examples are presented, as well as a case study.

Experimental Validation of an Efficient Disturbance Rejection Method for Dead-Time Processes using Internal Model Control

Abstract: When controlling industrial processes, setpoint tracking and disturbance rejection play an important part in the design and tuning of the PID controller parameters, especially since most of these processes exhibit dead-times. Internal Model Control (IMC) algorithms have proven to be quite efficient in setpoint tracking issues. However, the basic tuning rules for IMC lead to PID controllers that cause a sluggish disturbance rejection, especially for delay dominant processes (i.e. with big ratio of dead-time versus the process time constant). In the current paper, the experimental validation of a novel idea for tuning IMC controllers for improved disturbance rejection is presented. The method is based on using a disturbance filter that compensates for the dead-time, provided that the process is affected by stochastic disturbances having their spectral energy in a narrow frequency band (such as quasi-periodic disturbances). Diophantine equations are used to compute the disturbance filter coefficients. The exaperimental case study consists in the Quanser six tanks process.

Experiment Design and Estimation Methodology of Varying Properties for Non-Newtonian Fluids

Abstract: This paper provides an overview of the distributed parameter properties of non-Newtonian fluids and a proposal for identifying them. A low cost setup is described along with a proposed methodology protocol. The paper introduces the problem of moving from a linear framework of fluid properties towards a nonlinear one and motivates the choice for lumped nonlinear parameter model structures. It follows identification using nonlinear least squares in various liquids. The results obtained suggest that parameters of the proposed fractional order impedance model are susceptible to changes in density as being one important feature of non-Newtonian fluids. Further use of these findings across disciplines is given in the conclusion section of the paper.

Fractional-order modeling of impedance measurements in a blood-resembling experimental setup *

Abstract: In this paper we analyze the opportunity to provide a methodology and signal processing algorithm to model and quantify drug concentrations in blood. The properties of blood as a non-Newtonian fluid are used to develop a physiologically based model using fractional calculus tools, which provide natural solutions to derivatives which no longer limit their order to integer numbers. In vitro tests support our mathematical model development. A prospective use for continuous monitoring of drug concentration profiles during anesthesia or other interventions is proposed. The proposed solution is based on fractional order impedance models.