Keywords: Control Education, Modelling, Identification and Signal Processing, Linear Control Systems
Abstract: The Benchmark proposed for the 3rd IFAC Conference on Advances in Proportional-Integral-Derivative Control (PID'18) held in July 2017 is described. This facilitates researchers to test their recent developments in the design of PID controllers on a challenging control problem. The paper focuses on the control of refrigeration systems: the canonical vapour-compression cycle is first described and then the MIMO control problem selected for the Benchmark PID 2018 is addressed, where the cooling power (through the outlet temperature of the evaporator secondary fluid) is intended to be controlled, as well as the degree of superheating at the evaporator outlet, using the compressor speed and the expansion valve opening as manipulated variables. The control systems described in this paper are ready to test other multivariable control strategies, despite being focused on PID regulators. Full documentation about the Benchmark was linked on the website of PID'18 and it will remain in http://www.dia.uned.es/~fmorilla/benchmarkPID2018/.

Keywords: Control Design, Non Linear Control Systems
Abstract: In this paper, decentralized linear active disturbance rejection control (LADRC) method is applied to the benchmark refrigeration system presented at the 3rd IFAC Conference on Advances in Proportional-Integral-Derivative Control (PID18). Two second-order LADRCs are tuned by trial and error without the knowledge of the benchmark refrigeration system. To overcome the saturation of the actuators, an anti-windup scheme for LADRC is adopted. Simulation results show that LADRC technique is simple to apply in practice and can achieve good performance compared with the given PID controllers for the benchmark system.

Keywords: Adaptive and Learning Systems, Control Design
Abstract: In the present work, an evolutionary tuning is used to determine in a coupled manner the controllers of a refrigeration system (VCRS) proposed in the challenge of the 2018 IFAC Conference on Advances in PID Control. The evolutionary strategy finds the parameters of the controllers that best satisfy the problem, fulfilling all the requirements and restrictions imposed by the challenge. The evolutionary strategy is independent of the structure and domain of the model, both the plant and the controllers.

Keywords: Control Design
Abstract: This work presents an application of the Virtual Reference Feedback Tuning (VRFT) method to a multivariable refrigeration system benchmark. For the Benchmark PID 2018 problem, two approaches are developed: decentralized and centralized multivariable PID controllers are designed using only open-loop collected data. In order to cope with the saturation of the process’ input variables, an anti-windup strategy is associated with the PID controllers. Finally, the closed-loop behavior achieved with VRFT is compared with the reference controller originally provided by the problem, where it can be noted that the performance is considerably enhanced by both proposed designs, with obtained combined indexes of 0.4134 and 0.3635 for the decentralized and centralized controller, respectively.

Keywords: Control Design, Linear Control Systems, Modelling, Identification and Signal Processing
Abstract: In this paper a proportional-integral-derivative (PID) autotuning control strategy is presented and applied to the benchmark system presented at the 3rd IFAC Conference on Advances in Proportional-Integral-Derivative Control (PID18). The automatic tuning of controller gains is based on a single sine test, with user-defined robustness margins guaranteed. Its performance is compared against a model based designed controller with computer-aided design tool based on frequency response (FRtool) and against the benchmark reference controller. The closed loop control simulations, applied on the benchmark, indicate that the method properly performed.

Keywords: Non Linear Control Systems, Control Design, Automotive Control
Abstract: A model-free adaptive control (MFAC) is applied to the Refrigeration Systems based on Vapour Compression of the BENCHMARK PID 2018. A SISO MFAC controller and a MIMO MFAC controller are designed to control the outlet temperature of evaporator secondary flux and the superheating degree of refrigerant at evaporator outlet by manipulating the expansion valve opening and the compressor speed. The two designed controllers are the pure data driven control methods without using any model information of the refrigeration process in the control implementation by virtue of the dynamic linearization technique, and the PID controllers can be considered as special cases of the two designed controllers. The qualitative and quantitative comparison results between the MFAC schemes and the default PID controllers given in the simulation platform provided by the Benchmark PID 2018 demonstrate the effectiveness of the two designed controllers.

Keywords: Control Design, Modelling, Identification and Signal Processing, Linear Control Systems
Abstract: Structural vibration is a highly studied topic, especially in civil structures. Unwanted earth vibrations during seismic activity endanger life and often destroy buildings. In this paper, a Fractional Order Proportional Derivative controller is designed with the purpose of vibration mitigation in a three-story building. The experimental setup consists of a third floor building equipped with an active pendulum attached to the last floor. The controller is designed for the fractional order mathematical approximation of the structure by imposing frequency domain constraints such as gain crossover frequency, phase margin and robustness to gain variations. The validity of the controller is analyzed considering the simulated behavior of the compensated building to the El Centro earthquake and experimental disturbance rejection performance.

Keywords: Control Design, Linear Control Systems, Modelling, Identification and Signal Processing
Abstract: A stunning outcome of fractional calculus for control practice are fractional-order PID (FOPID) controllers. Based on their experimental and numerical results, several studies have reported improvements in control performance of closed loop control systems by FOPID controllers compared to classical PID controllers. However, the industry at large is still cautious about adopting FOPID controllers because of the lack of concrete data about the related cost-benefit trade-off. Main concerns arise at the point that there have not been a quantitative evaluation scheme that clearly demonstrates for which concrete cases FOPID controllers can provide considerable improvements in control. Therefore, there is a need for more thorough theoretical and quantitative demonstrations. To that end, this study presents a plant function independent evaluation methodology to reveal inherent advantages of FOPID control. Impacts of two additional controller coefficients, namely fractional orders of differentiator and integrator, are analyzed in the frequency domain and their contributions to open loop gain maximization, phase margin and Reference to Disturbance Rate (RDR) performance are investigated.

Keywords: Control Education, Control Design, Mechatronic Systems
Abstract: A novel toolbox named FLOreS is presented for intuitive design of fractional order controllers (FOC) using industry standard loop shaping technique. This will allow control engineers to use frequency response data (FRD) of the plant to design FOCs by shaping the open loop to meet the necessary specifications of stability, robustness, tracking, precision and bandwidth. FLOreS provides a graphical approach using closed loop sensitivity functions for overall insight into system performance. The main advantage over existing optimization toolboxes for FOC is that the engineer can use prior knowledge and expertise of plant during design of FOC. Different approximation methods for fractional order filters are also included for greater freedom of final implementation. This combined with the included example plants enables additionally to be used as an educational tool. FLOreS has been used for design and implementation of both integer and fractional order controllers on a precision stage to prove industry readiness.

Keywords: Control Design
Abstract: In this paper we assess the performance improvement achievable by using one-degree-of-freedom fractional-order proportional-integral-derivative controllers (FOPI/FOPID) instead of their integer-order counterparts (PI/PID). To this end, we take into account a single-pole fractional-order model, which has the advantage of representing a wide variety of process dynamics, ranging from over-damped (first-order models) to under-damped behaviors, depending on the fractional order alpha. In the proposed analysis we consider a combined performance index which deals with the trade-off between servo and regulatory control modes. Moreover, the performance of the closed-loop system is optimized subject to a robustness constraint, expressed as a target maximum sensitivity of either 1.4 or 2.0. The obtained performance assessment results are shown for different values of the fractional order alpha of the model and for different normalized dead times, thus quantitatively evaluating the benefits achievable with fractional controllers on a wide variety of process dynamics.

Keywords: Linear Control Systems, Control Design
Abstract: This paper proposes a method for designing robust fractional-order proportional-integral (FOPI) controllers to be employed in a cascade control system. The FOPI controllers are employed for controlling two nested loops. The design is based on performance and robustness specifications in the frequency domain. Taking inspiration from well-known tuning rules, the open-loop frequency response in the two nested loops is shaped around the gain crossover frequency to obtain a nearly flat phase diagram, then a nearly constant phase margin. The method is tested to control the speed and position of a linearly sliding motor.

Keywords: Control Design, Control Education, Linear Control Systems
Abstract: The purpose of this paper is to introduce an advanced virtual tool for fractional PID (FPID) controller design. It implements generic Nyquist plot shaping and/or sensitivity functions shaping capabilities. In this context, one can define e.g. gain and phase margins, sensitivity functions limits or loop bandwidth. The procedure relies on generalized robustness regions method for fractional PID controllers. The technique is best applicable namely for any non-oscillatory or slightly oscillatory linear system even with dead time, both integer and fractional order. The robustness regions can be computed and painted for more system models hence the robust controller design can be done. Here the method is validated on three illustrative examples. The author believes, that the virtual lab will be worthwhile for both researchers and industrial practitioners and will help to boost the employment of fractional order PID controllers.

Keywords: Control Design, Linear Control Systems, Optimal Control
Abstract: This work presents some guidelines for tuning PID controllers in order to increase robustness within a hierarchical control structure focused on load disturbance rejection, in which the process' mathematical model is unknown. The proposed structure consists in two control loops: an inner PID control layer tuned using only data collected from the process, whose set point signal is governed by an outer predictive control layer, with the purpose of increasing closed-loop performance and enabling the specification of constraints. Some simulation results are presented, in which it is shown that the appropriate tuning of the PID controller allows the outer loop to correctly predict the inner loop behavior and therefore provide better disturbance rejection than the data-based tuned PID alone.

Keywords: Control Design, Linear Control Systems, Optimal Control
Abstract: In industrial applications, it is possible to encounter processes that have an integrator in its transfer function. The most widely used controllers in the control of these processes are Proportional-Integral-Derivative (PID) controllers. However, it is well known that PID controllers do not perform well in controlling integrating processes. Hence, in this study, the use of I-PD controllers for controlling integrating processes has been given. Optimal and analytical tuning rules have been derived to identify tuning parameters of the I-PD controller. Simulation examples have been provided to show the use of the proposed optimal I-PD tuning formulas. Comparisons with existing PID and I-PD design methods to control integrating processes have been supplied to illustrate the closed loop performance of the proposed optimal I-PD design approach.

Keywords: Control Design, Adaptive and Learning Systems, Optimal Control
Abstract: A cascade control system consists of inner and outer loops, where the update interval of the inner controller is shorter than that of the outer controller. In the present study, a new data-driven approach is applied for such a dual-rate cascade control system. In the proposed method, the fictitious reference iterative tuning method is used for optimizing the cascade control system. Hence, the control system is designed using only the control data, and the modeling procedure is omitted. In the present study, the controller parameter in the inner loop is optimized firstly, and next that in the outer loop is also optimized. Because the inner loop is updated faster that the outer loop in the dual-rate system, the control performance of the proposed dual-rate design is superior to that of the conventional single-rate systems. The effectiveness of the proposed method is shown through numerical examples.

Keywords: Control Design, Optimal Control, Linear Control Systems
Abstract: The proposed tuning method for integrating processes, which is based on Magnitude optimum criterion, has been extended to PID types of controllers. The method requires either the process transfer function (in frequency-domain) or the measurement of process steady-state change (in time-domain). The PID controller parameters are calculated analytically by solving fourth-order polynomial. By changing refer-ence-weighting parameter b, the user can favour tracking (higher b) or control performance (lower b). The proposed method has been tested on several process models (lower-order with delay, higher order with delay, and a phase non-minimum process) and the closed-loop responses were relatively fast and non-oscillatory. The comparison with other tuning method based on process step-response data results in favourable tracking and control performance.

Keywords: Linear Control Systems, Control Design, Optimal Control
Abstract: In this paper it is described a new method to design PID controllers using a linear programming approach for optimizing performance subject to robustness constraints. It is based on the shaping of a reference loop gain transfer function which forms a convex region on the Nyquist diagram which contains and bounds the designed loop gain Nyquist plot. The convex region is approximated by a set of lines in order to formulate a linear optimization problem. It is also presented an optional performance specification related to the crossover frequency of the designed loop gain. The class of stable linear time-invariant single-input simple-output (SISO) systems is considered and the optimization problem is proposed, solved and analyzed.

Keywords: Optimal Control, Control Design, Linear Control Systems
Abstract: In this paper, a structurable robust output-feedback infinite horizon LQR design toolbox for Matlab and Octave is introduced. The aim of the presented toolbox is to fill the gap between available toolboxes for Matlab/Octave by extending the standard infinite horizon LQR design (from Matlab/Control System Toolbox, Octave/Control package) to robust and structurable output-feedback LQR design. The toolbox allows to design a robust infinite horizon output-feedback controller in forms like proportional (P), proportional-integral (PI), realizable proportional-integral-derivative (PID), realizable proportional-derivative (PD), realizable derivative (D), dynamic output-feedback (DOF), dynamic output-feedback with integral part (DOFI), dynamic output-feedback with integral and realizable derivative part (DOFID), and dynamic output-feedback with realizable derivative part (DOFD). In addition, the controller structure for all supported controller types is fully structurable. The toolbox relies on Yalmip (A Matlab/Octave Toolbox for Modeling and Optimization) and on linear matrix inequality solvers like SeDuMi, SDPT3, etc. Notions like "simple", "highly customizable", and "user-friendly" have been used and considered as main terms during the development process.

Keywords: Control Education, Control Design
Abstract: In this paper, a brief literature review for the design of a PID controller for load frequency control (LFC) in power systems is presented. The transfer function models for various configurations of power systems are developed. For a systematic presentation of the review, the PID tuning schemes are categorised into soft computing techniques, robust control schemes, fractional order based PID design and internal model control (IMC) based PID design approaches. Due diligence has been taken to include all the design schemes. Further, the paper also enlists various future challenges that are still unresolved and can form the basis of future research work.

Keywords: Control Design
Abstract: This paper presents a new technique for the design of an optimal fractional order PID controller for Load frequency control (LFC) in power systems. The proposed approach utilizes a unique combination of Big Bang Big Crunch (BB-BC) algorithm which is a recent soft computing technique and internal model control (IMC) scheme for the design of a fractional order PID controller and it also unifies the notion of order diminution with controller design. A detailed mathematical description of the proposed approach is elucidated in the paper. Since BB-BC is a stochastic search technique, hence a thorough statistical analysis of the response specifications is performed. To demonstrate the effectiveness of the proposed approach, an exhaustive comparative analysis in terms of time response specifications and performance indices is also carried out. It is inferred that the proposed approach is highly efficient and outperforms the existing techniques in the literature.

Keywords: Control Design, Linear Control Systems, Large Scale Complex Systems
Abstract: This paper proposes a robust CDA-PIDA control scheme for load frequency control problem. The proportional integral derivative acceleration (PIDA) controller is a variant of PID and it is used to cope with large overshoot and settling time in higher order systems. The tuning of PIDA controller is based on coefficient diagram algorithm (CDA). The CDA is based on algebraic design approach and it is demonstrated sufficient condition for stability. In this paper, CDA-PIDA control scheme is designed for two area interconnected power system. The overall closed loop system stability is guaranteed in case of two area power system because each area CDA-PIDA controller is designed independently. The robustness of the proposed control scheme is demonstrated in presence of parametric uncertainty, load disturbances and physical constraint. The robustness and eminence of CDA-PIDA control scheme is proved through comparison between the CDA-PIDA and recently published control schemes.

Keywords: Control Design, Linear Control Systems, Networked Systems
Abstract: The modern power systems are becoming complicated day by day because of the delays introduced by the communication networks. Due to this reason, the traditional load frequency control (LFC) design scheme depicts a destabilizing impact and an unacceptable performance. Therefore, this paper proposes an analytico-graphical approach for designing PI controller for a single-area LFC system having communication delay. The concept is based on extracting stability region in parameter space (kp; ki) with predened gain and phase margins. Further, the values of optimal kp and ki are selected using integral error criterion. The proposed scheme gives faster disturbance rejection response as compared to the recently developed LFC scheme. The controller also works well when the system parameters are perturbed from their nominal values.

Keywords: Control Design, Linear Control Systems
Abstract: In interconnected power systems, the load frequency control (LFC) is considered a hugely beneficial ancillary service. The goal of the LFC in an interconnected power system is to limit the frequency of each area within certain bounds and to maintain the tie-line power flows within some pre-specified latitudes by balancing the power outputs of the generators so as to satisfy ever changing load demands. In the classical control theory, PID controller is said to be robust if it provides some specific gain and phase margin. In this paper, a novel methodology is proposed for the robust PID controller design having specific gain and phase margins for LFC in a multi-area power system. The proposed technique is based on stability boundary locus and PID controllers are designed for four-area power system having different types of turbines. The simulations are carried out using MATLAB and effectiveness of the proposed methodology is verified by the comparison with a recently published approach.

Keywords: Linear Control Systems, Control Design
Abstract: In this paper, some detrimental time-domain characteristics (zero-crossings, overshoot(due to zeros) and initial undershoot) are analyzed using the system transfer function model, for identifying the presence of these effects in step response of non-minimum phase linear systems. Moreover, regarding initial undershoot, a theorem for detection using the state-space model, without the need to obtain transfer function, is proposed. In addition to detection, a theorem for estimating the percentage of initial undershoots is also proposed. Applications of these theorems are carried out on load frequency control of hydro-electric power plant which employs hydro-turbine, a non-minimum phase system. Moreover, the effect of a PI controller on initial undershoot is discussed for a general non-minimum phase linear system and illustrated for load frequency control of hydro-electric power plant.

Keywords: Control Design
Abstract: This paper presents a non-ideal model of DC-DC PWM buck converter considering the parasitic elements (or non-idealities) such as equivalent series resistances (ESRs) of inductors and capacitors, parasitic resistances of semiconductor devices (diode, MOSFET) during conduction and the forward voltage drop of the diode. Incorporating this non-ideal model, a proficient PID control technique is proposed based on the internal model control (IMC) strategy. The salient features of proposed control methodology are: (i) tuning is such that the controller yields the desired bandwidth; (ii) unlike the conventional IMC-PID, the PID parameters are obtained by direct formula without trial and error. The proposed control scheme is simulated in MATLAB/SIMULINK and validated on a hardware setup using DSPACE DS1104 to confirm the superior results under variation of input voltage, reference voltage and load.

Keywords: Modelling and Control of Biomedical Systems, Control Design, Optimal Control
Abstract: This study investigates the computer-regulated propofol administration in anesthesia during medical interventions considering output feedback and robust PID control. The paper applies the Affine Tensor Product Model Transformation to derive the appropriate polytopic quasi-LPV representation of the closed-loop dynamics. This model form enables the use of LMI-based optimisation techniques to evaluate the closed loop performance. Despite the highly non-convex nature of this output feedback problem, the PID gains can be locally tuned through simplex optimisation. The proposed method provides a systematic way of tuning PID-controlled propofol administration for individual patients with theoretically established worst-case performance measures.

Keywords: Control Design, Linear Control Systems
Abstract: In this paper, a new approach is proposed to design optimal PID controller for load frequency control (LFC) problem. This scheme is based on Quadratic Regulator Approach with Compensating Pole (QRAWCP) technique. Application of this control law is done to both single area and multi-area power system based load frequency problem. In addition to the nominal situation, robustness of this controller is also tested on the same systems with respect to parametric uncertainty, external disturbances, and non-linearities like Generation Rate Constraint (GRC) and Governor Dead Band (GDB). The performance evaluation is done using Matlab & Simulink based simulations and the obtained results are compared with the performance achieved using the recent control strategies designed for LFC.

Keywords: Non Linear Control Systems, Control Design, Linear Control Systems
Abstract: Conventional PID controllers have been a practical solution when controlling linear processes but its response is degraded considerably in strongly nonlinear processes. Fuzzy control presents an improvement in the response because its nonlinear nature. However, there is no absolute tuning methodology, with solutions ranging from trial and error to sophisticated computational methods. In this paper, we present a simple but effective systematic approach for the tuning of several direct fuzzy PID controllers, based on the calculation of static gains of linear sub-models and controller scaling factors. The proposed methodology was successfully tested in a nonlinear process model and a CSTR model.

Keywords: Adaptive and Learning Systems, Control Design, Chemical Process Control
Abstract: The design and application of learning feedforward controllers (LFFC) for the one- staged refrigeration cycle model described in the PID2018 Benchmark Challenge is presented, and its effectiveness is evaluated. The control system consists of two components: 1) a preset PID component and 2) a learning feedforward component which is a function approximator that is adapted on the basis of the feedback signal. A B-spline network based LFFC and a low-pass filter based LFFC are designed to track the desired outlet temperature of evaporator secondary flux and the superheating degree of refrigerant at evaporator outlet. Encouraging simulation results are included. Qualitative and quantitative comparison results evaluations show that, with little effort, a high-performance control system can be obtained with this approach. Our initial simple attempt of low-pass filter based LFFC and B-spline network based LFFC give J=0.4902 and J=0.6536 relative to the decentralized PID controller, respectively. Besides, the initial attempt of a combination controller of our optimized PI controller and low-pass filter LFFC gives J=0.6947 relative to the multi-variable PID controller.

Keywords: Control Design, Optimal Control, Chemical Process Control
Abstract: In this paper, the reduced model of the Pressurized Water Nuclear Reactor (PWR) is derived based on the point kinetics equations and thermal equilibrium relations. The power level of the nuclear reactor is controlled by adjusting the insertion reactivity of the rod. Several controllers such as Genetic Algorithm based PID controller (GAPID), Fractional Order PID controller (FOPID) and Genetic Algorithm based Fractional Order PID Controller (GAFOPID) are used to control the power level of the PWR reactor. The simulation results depict that the Genetic Algorithm based Fractional Order PID Controller (GAFOPID) shows the satisfactory response than other control techniques.

Keywords: Control Design, Linear Control Systems, Optimal Control
Abstract: To improve the control performance and robustness of fractional order PID (FOPID) controller for the uncertainty model, a tuning method for FOPID controller based on probabilistic robustness is proposed in this paper. Based on the Monte Carlo simulation, a probabilistic robustness index is formulated to represent the controller sensitivity to the uncertainty model. Stability boundaries of FOPID is depicted to provide the search space, in which the optimal group of parameters are selected based on the probabilistic robustness index. The procedure of the proposed method is designed to obtain the optimal controller parameters for the uncertainty model. Numerical examples are performed to verify the efficacy of the proposed method, and simulation results show that the proposed method has better performance, stronger robustness and ability of handling uncertainties.

Keywords: Control Design, Optimal Control
Abstract: An improved frequency-domain design method is proposed to design the fractional order PID controller. Using this improved method, the parameters of the fractional order PID controllers can be obtained immediately according to the model characteristics and design specifications. A proportional relation between the integral gain and derivative gain is built, while the derivative order is set to be equal to the integral order. The proportional coefficient between integral gain and derivative gain is studied and modeled based on priori knowledge and data fitting, and then the estimation model for the optimal proportional coefficient is built. The proposed tuning method is applied to design a fractional order PID controller for a permanent magnet synchronous motor servo system. Motor speed control simulations are performed to verify the proposed method. Simulation results show that the obtained control system can achieve robustness and the optimized step response performance.

Keywords: Modelling, Identification and Signal Processing, Non Linear Control Systems, Control Design
Abstract: The nonlinear behavior of gas turbine engines has motivated the development of advanced controllers for ensuring their safe and reliable operation. In this paper, the problem of controller design for a two-shaft industrial gas turbine is addressed. Specifically, a transient dynamic engine model has been developed in MATLAB/Simulink for assessing the performance behavior of the engine. Observed engine behavior during transient maneuvers has enabled the development of a PI controller capable of ensuring a smooth gas turbine operation. The performance of the gas turbine engine implementing the developed PI controller has been also compared to a fractional PI controller. Results demonstrate and illustrate the remarkable impact that transient engine simulation has in the developement of robust controllers.

Keywords: Networked Systems
Abstract: In the paper the Cucker-Smale type models with a fractional variable order operator are considered. The asymptotic stability of a class of linear fractional variable order discrete-time systems is used to study a consensus in the nonlinear fractional variable order discrete-time systems. Basing on a linearization method of the considered multi-agent system we give the sufficient conditions that guarantee the consensus. Finally, an example illustrates our results.

Keywords: Control Design, Linear Control Systems, Modelling, Identification and Signal Processing
Abstract: This paper presents a combined approach to the design of PID control applied to vapour-compression refrigeration systems. The underlying controller consists of two decentralised PIDs, aiming to control both the reference on the temperature of the evaporator secondary fluid, imposed by the cooling demand, and the degree of superheating, by manipulating the compressor speed and the expansion valve. A partial decoupling matrix is calculated to reduce the high coupling between the controlled variables, while the PIDs are tuned applying affine parameterisation and considering the condition for robust stability given by the study on the uncertainty sources and the estimation of the uncertainty region around a nominal linear model. The designed controller is applied to the system proposed in the Benchmark process challenge and some comparative simulations are presented and discussed, while the performance indices of the proposed controller with respect to the reference one are analysed.

Keywords: Optimal Control, Control Design
Abstract: This paper deals with data-driven control design in a Model Reference (MR) framework for multivariable systems. Based on a batch of input-output data collected on the process, a fixed structure controller is estimated without using a process model, by embedding the control design problem in the Prediction Error (PE) identification of an optimal controller. A multivariable extension of the OCI (Optimal Controller Identification) method is applied in the design of PID controllers for a refrigeration system based on vapor compression, which is the subject of the benchmark process challenge of the IFAC PID 2018 conference. Simulation results show the obtained controllers perform significantly better than the ones provided by the benchmark challenge.

Keywords: Control Design, Optimal Control
Abstract: This paper deals with the control problem of a refrigeration vapor compression system proposed as a benchmark for the IFAC Conference on Advances in PID Controllers (PID’18). This refrigeration system is a multivariable nonlinear process that shows interactions and is subjected to input constraints. In this work, a decentralized PID control with inverted decoupling is proposed as control structure. The inverted decoupling is designed from an approximated multivariable linear model. Then, the PID controllers are tuned by genetic algorithms to minimize a performance index. In addition, a superheat reference generation is developed to achieve stationary operation points with maximum coefficient of performance which is a widespread efficiency measurement in these systems. Simulations considered in the benchmark show that the proposed design achieves better performance than the reference case.

Keywords: Non Linear Control Systems, Control Design, Chemical Process Control
Abstract: There are different ways in making nonlinear PID controllers. In this paper, a kind of nonlinear PID controller designed by special usage of nonlinear function is introduced, which is called Han's nonlinear PID controllers for short according to the name of the original inventor. Typically, a fal function based nonlinear PID controller has been taken as an example for performance verification upon the Benchmark PID 2018 platform. The simulation results prove that, by parameters tuning for the performance of minimal control efforts, the fal function based nonlinear PID controller can achieve the desired cooling goal under more stable operating conditions yet holding nearly the similar quality steady-state performance.

Keywords: Chemical Process Control, Control Design
Abstract: In this work a tuning procedure by means of multi-objective optimization techniques is used for a refrigeration system based on vapour compression, stated as the benchmark process control challenge organized by the IFAC Conference on Advances in Proportional- Integral-Derivative (PID) Control. The advantage of such a procedure lies in the capacity to perform an analysis on the trade-off among con icting design objectives. The resulting controller fullls the requirements of the contest, and gets and overall performance index of 0.4028 outperforming the base line controller.

Keywords: Control Design, Linear Control Systems, Modelling, Identification and Signal Processing
Abstract: In this paper an Internal Model Control (IMC) based proportional-integral-derivative (PID) control is presented and evaluated on the benchmark system presented at the 3rd IFAC Conference on Advances in Proportional-Integral-Derivative Control (PID18). The controller is designed based on the model of the benchmark system. Its performance is compared with a computer-aided design tool based on frequency response (FRtool) and against the benchmark reference controller. The results show that the proposed method has a better performance due to the fact that IMC based PID parameters depend totally on the model.

Keywords: Control Design, Automotive Control, Control Education
Abstract: In this paper, the standard PID controller and the fractional first generation CRONE controller are applied on the anti-roll moment system to improve ride comfort for passengers in the frame of global chassis control of electric vehicles. A comparative study is done showing the performance and the robustness of the two controllers, in frequency and time domain. It is shown that the first generation CRONE control-system is able to provide robust fractional order controller for uncertain perturbed plants.

Keywords: Control Design, Linear Control Systems
Abstract: A new Fractional Order Proportional-Integral (FOPI) controller is proposed in this paper for process control systems. This is achieved by combining Biggest Log-modulus Tuning (BLT) method and Internal Model Control (IMC) method of designing conventional PID controllers to tuning FOPI controllers for multivariable processes. Unlike the conventional PID case, internal model control method is first used to design the FOPI controller and obtain preliminary values of controller parameters. This yields simple formulae for setting controller gains. Thereafter, the FOPI controller gains are adjusted using a single detuning factor (F) until a biggest log modulus of 2n dB is obtained where n is the number of loops. Extended simulation studies show that good compromise between performance and robustness can be achieved for multiloop process control applications with the proposed FOPI controller.

Keywords: Control Design
Abstract: In this paper the authors present a novel control algorithm based on control error sign--dependent variable-fractional-order PI controller. The algorithm is being optimized via ITSE criterion for control error. It is tested both for unconstrained control signal and a more real-case scenario, i.e. +/-2.5 saturation on control signal. The algorithm is tested for A-,B-,D- and E-type variable-order PI controllers and compared to basic PI and fractional-PI (FPI) controllers. Important parameters, including rise and settling time, overshoot and peak time of unit-step response, as well as graphical representation of unit-step response are presented. Conducted numerical simulations show some interesting behaviour of the A-type definition both in non-limited and limited control signal cases, i.e. switching between derivation and integration action. Moreover, collected unit-step response parameters indicate the A-type definition to be the best behaving in all considered criteria. However, some unwanted minor oscillations in the unit-step response are to be observed, whose origin will be investigated in further research.

Keywords: Linear Control Systems, Control Design
Abstract: Fractional-order PID controllers have been introduced as a general form of conventional PID controllers and gained considerable attention latterly due to the flexibility of two extra parameters (fractional integral order λ and fractional derivative order µ) provided. Designing fractional controllers in the time domain has still difficulties. Moreover, it has been observed that the techniques based on gain and phase margins existing in the literature for integer-order systems are not completely applicable to the fractional-order systems. In this study, stability regions based on specified gain and phase margins for a fractional-order PI controller to control integrating processes with time delay have been obtained and visualized in the plane. Fractional integral order λ is assumed to vary in a range between 0.1 and 1.7. Depending on the values of the order λ, and phase and gain margins, different stability regions have been obtained. To obtain stability regions, two stability boundaries have been used; RRB (Real Root Boundary) and CRB (Complex Root Boundary). Obtained stability regions can be used to design all stabilizing fractional-order PI controllers.

Keywords: Control Design
Abstract: In this paper, we propose an optimization-based tuning methodology for real and complex Fractional-Order Proportional-Integral (FOPI) controllers. The proposed approach hinges on a modified version of the Integral Absolute Error (IAE) sensitivity-constrained optimization problem, which is suitably adapted to the design of fractional controllers. As such, it allows the exploitation of the potentiality of the (possibly complex) fractional integrator. We also propose a method, based on the well-known CRONE approximation, which delivers a band-limited real-rational approximation of the real part of the complex-order integrator. Finally, based on a First-Order-Plus-Dead-Time (FOPDT) model of the process, we use our design and approximation techniques to find an optimal tuning for real, complex fractional-order, and integer PI controllers and we provide a quantitative performance assessment.

Keywords: Linear Control Systems, Control Design, Optimal Control
Abstract: Recently, PID tuning rules based on integer-order model set approach has been developed. This paper shows how they can be enhanced through extending the set of a priori admissible systems to fractional-order form. Firstly, such set covers wider range of real process plants. Secondly, a new parameter affecting the model set span was introduced. It can help to reach the proper robustness/performance ratio especially in the case when the system has a lower order which is known. The authors believe that the procedure of fully automatic computing of robust PI/PID parameter surfaces will in the future lead to huge dataset that will serve as a base for deriving mature 2DOF PI/PID tuning rules based on various requirements.

Keywords: Control Design, Chemical Process Control, Optimal Control
Abstract: The PI/PID controller is the most used controller in industry. However, for processes with large time delays, the common belief is that PI and PID controllers have sluggish performance, and that a Smith Predictor or similar dead-time compensator can give much improved performance. We claim in this paper that this is a myth. For a given robustness level in terms of the peak sensitivity (Ms), we find that the performance improvement with the Smith Predictor is small even for a pure time delay process. For other first-order processes a PID controller is generally better for a given robustness level. In addition, the Smith Predictor is much more sensitive to time delay errors than PI and PID controllers.

Keywords: Control Design
Abstract: This paper treats development and research at the regulatory control layer in process control. It is noticed that very little attention is payed to this subject, with the exception PID controller tuning. The reason for this is discussed. Two examples of recent advances in the field treating feedforward control and ratio control, respectively, are presented. A goal of the paper is to point out the need for further research in the area. One reason for this is the great industrial impact such research may have, since the functions appearing in this layer are used at so many places in so many industries. A second reason is the need for well functioning regulatory control layers to form solid foundations for the advanced process control layers.

Keywords: Non Linear Control Systems, Control Design
Abstract: In this paper we present a study of the appearance of limit cycles in event-based PID control systems. Our approach is based on the extension of the Tsypkin method, which has been widely used to study the relay control systems. A new margin has been obtained to measure the robustness to limit cycles of continuous controllers when applied on event based control loops. The margin has been calculated to characterize some well known PID controllers tuning methods applied to the control of FOPTD systems with SSOD sampling strategy.

Keywords: Control Design, Chemical Process Control, Linear Control Systems
Abstract: One of the recurrent topics in the PI/PID literature of recent years is the incorporation of the tradeoff between the two possible modes of closed-loop operation: servo and regulation. Tuning rules are usually provided as for servo or regulation. Operator should choose which one to apply depending on the most usual loop operation. As an alternative, the so called tradeoff tunings provide a controller tuning that is not optimal in either of the operation modes but aims to provide a reasonable (in fact, the best) tradeoff among both in such a way that the loss of performance is minimised with respect to the corresponding optimal tunings. In this paper the use of the I-PD controller structure is proposed as an structural solution to the tradeoff tuning. The proposal states that a direct, simple and efficient solution is found if the controller tuning is addressed for the servo mode but using the I-PD controller structure. This is the feedback error just drives the integral mode or, if preferred, a two degrees of freedom controller with the set-point weight to zero.

Keywords: Control Design, Linear Control Systems
Abstract: Dead times affect many industry processes and are mainly caused by the time required to transport mass, energy or information. In process with dead times the performance of classical PID controllers may be significantly decreased, especially when the dead times are large and higher than the dominant time constant of the process. Several solutions have been presented over the years to improve the control in such cases. The paper contributes in this direction by presenting an extension to second order stable processes of the predictive PI controller introduced by Hagglund in 1996 for first order processes. Both real and complex poles cases are considered. The solutions are derived in special forms in which the classical PID controller is maintained and a new linear block, which just requires one additional parameter, is inserted. In this way, the flexibility of the PID is conserved and control performances improve. For the sake of coherence with respect to the Hagglund's controller, the proposed solutions are called Predictive PID controllers (PPID). Simulation examples show the good performance of the PPID controllers.

Keywords: Chemical Process Control, Control Design, Non Linear Control Systems
Abstract: It is well-known that valve stiction causes sustained oscillations on process variables when a traditional PID controller is implemented in the feed-back loop. In the literature, there is a vast collection of solid techniques to compensate for valve stiction which employ different approaches and require various prior knowledges on process and stiction dynamics. Among others methods, PID retuning or changes to the traditional algorithm and structure of PID can be useful solutions to mitigate or remove negative effects of valve stiction. Appropriate controller retuning can reduce significantly amplitude and frequency of oscillation, but it cannot remove the problem permanently. Modifying traditional PID algorithm or augmenting standard structure of the controller are also robust approaches for the scope. This paper briefly revises some PID-based stiction compensation techniques and illustrates a new version of stiction-aware PID. A standard PI(D) controller is augmented with a two-move compensator and, by monitoring the control error, it is able to remove effect of valve stiction and to guarantee set-point tracking and disturbance rejection. This PID-based structure requires the estimation of controller output associated with the desired valve position at steady-state and the estimate of valve stiction parameters.

Keywords: Computer and Telematics, Control Design
Abstract: Applying controls to manage and optimise the behaviour of computers and networks is an important research field. In recent years, controllers have been gaining a role not only as add-ons to improve the efficiency of already functioning systems, but also as core components of those system themselves, and of their design. This paper provides a brief but reasoned review on the matter, evidencing the preminent role of PID-centred control solutions, and outlines some open issues for future research directions.

Keywords: Networked Systems
Abstract: A new constrained predictive PID controller is presented to achieve stability and performance robustness in Wireless Networked Control Systems (WNCS), where the communication is subject to dropouts in both communication directions: sensor to control and control to actuator transmission. The control strategy is based on a new PID controller with similar properties to Model-Based Predictive Control (MBPC). A Kalman filter used for output prediction and a consecutive dropouts compensator have also been added to the control scheme. The purpose of this approach is to develop an estimation algorithm and a control system that maintain information of the sensor packets and the control actions. Several experiments using the TrueTime network simulator showed that the predictive PID controller performs as good as the MBPC scheme with the advantage of having a simple structure.

Keywords: Control Design, Linear Control Systems, Non Linear Control Systems
Abstract: Although PID control has been widely used in practical engineering, its ability to reject external disturbance and to handle severe nonlinearities should be further enhanced. In this paper, we present a simple robust unknown dynamics estimation, which can be easily incorporated into PID control to achieve satisfactory control for a rotor plant subject to period disturbance. The use of this estimator together with PID control leads to a feedforward like composite control framework. Unlike other estimators (e.g. DOB, ESO), only low-pass filter operations on the input and output and simple algebraic operations are needed to construct our estimator, while exponential convergence can be guaranteed. Numerical simulations are given to show the validity of the proposed estimator and composite PID control.

Keywords: Chemical Process Control, Mining, Mineral and Metal Processing
Abstract: Control loop performance monitoring methods to detect problems in PID loops are developed and tested using industrial data sets. The data is captured from the process, passed on to the researcher who tries out new detection and diagnosis methods. The data is not generally shared with other researchers working on similar problems. The authors therefore have implemented a data repository to categorise and store the data so that it becomes accessible to all researchers. Existing methods can be compared and enhanced using the data sets. This paper describes the context of CPM as well as the data repository. The repository is set up, hosted and maintained by the South African Council for Automation and Control using a professional web developer.

Keywords: Control Design
Abstract: Small-scale experiments allow to reproduce and understand phenomena and to draw inferences about large-scale processes. In this paper, we consider a peculiar experimental apparatus which is aimed at reproducing a typical lagoonal environment subject to tidal forcings. This apparatus is useful for performing morphometric analyses of synthetic tidal networks. The quality of these kind of experiments strongly depends on the behaviour of the artificial tide that has to exhibit predefined characteristics. To this aim, the height of the artificial water wave is controlled in real-time. Due to the intrinsic complexity of the system, the development of a control algorithm as simple as possible but able to ensure suitable control performance over a wide range of operative conditions, is a non-trivial task. In this paper, we have developed and tested a model-free control algorithm, that is the intelligent-PI (i-PI). Finally, the performance of the i-PI controller are compared with those of a standard regulator for different type of experiments.

Keywords: Control Design, Chemical Process Control, Linear Control Systems
Abstract: This paper considers the case of averaging level control, where the main objective is to reduce flow variations by using varying liquid levels. However, to avoid overfilling or emptying the tank, the liquid level needs to satisfy safety-related constraints. In the simplest case, a P-controller can be used, but may not give acceptable averaging of the flow, especially if the surge tank is relatively small. In addition, the P-controller does not allow the level setpoint to be adjusted. We propose a simple scheme with a PI-controller for normal operation and two high-gain P-controllers to avoid the liquid level constraints, which is compared with a benchmark MPC strategy. We demonstrate that the proposed method has similar performance, but with less modeling effort, less computational time and simpler tuning.

Keywords: Control Design, Linear Control Systems
Abstract: In control systems, controller preference and design is an important issue for meeting the desired design criteria. In this paper, PI controller design was performed by using optimization method for fractional order systems. First, all the PI controller parameters that make the control system stable are calculated by using the stability boundary locus method. However, each controller parameter selected in the stability region may not be able to optimally control the system. Optimal controller parameters that provide the best control from the PI controller parameters that make the system stable by using the optimization method are obtained. In the optimization process, the optimal PI controller parameters are calculated by using the integral performance criterion based on the error. Simulation studies have been done for closed loop control system including a fractional order transfer function with time delay. It has been shown that the presented method can be successfully applied to fractional order control systems.

Keywords: Control Design, Linear Control Systems
Abstract: Internal model control (IMC) structure is derived from classical control by introducing the model of plant in the control loop and thereby having significant advantages over classical control such as dual stability, perfect control and zero-steady state offset. The basic one degree of freedom (ODF) IMC provides good compromise between set-point tracking and disturbance rejection and works well for non-minimum phase (NMP) systems. In this work, an IMC based fractional order (FO) controller is designed for NMP system which satisfy desired phase margin (fm) at a desired gain-crossover frequency(wg). The domain of desired fm and wg is provided from which they can be selected. Simulation studies are done for (i) DC-DC boost converter which is a NMP system with one zero in right half of s-plane and (ii) first order plus time delay (FOPTD) system which is also a NMP system because of the delay. Significance of the proposed methodology is verified by comparing with other well-known techniques in IMC based on the performance measures, such as rise time (Tr), settling time (Ts) and overshoot (%Mp) and performance indices such as integral square error (ISE), integral absolute error (IAE) and integral of the time weighted absolute error (ITAE).

Keywords: Linear Control Systems, Modelling, Identification and Signal Processing
Abstract: The objective of the paper is to present the method of fitting finding constant lambda coefficient and a parameter of an order function of the processes described by variable-, fractional-order backward difference of the Grunwald-Letnikov-type. As a qualitative criterion of the estimation the Coefficient of Determination (which we mark as R^2) and the Mean Square Error are used. All the numerical experiments were done with MATLAB.

Keywords: Optimal Control, Control Design, Control Education
Abstract: This paper has propounded the notion of the design of cascaded integer order (IO) PID - fractional order (FO)PI D controller by evolutionary multi-objective based optimization approach for a synchronous generator excitation system. The three contradicting performance indices have been framed in time domain as well as in frequency domain to minimize error, escalate the robust stability and to minimize the energy consumption. This paper propounded the issue of contradiction in minimizing error, escalation of robust stability and minimization of energy consumption by framing cascaded IO PID - FO PID controllers as multi-objective optimization problem. The optimization problem is solved to generate the design parameter that meets the competitive multi-objective specifications relating to performance, robust stability and to optimal control by making trade-off between them and respective weightage given to each objective function. The solution generates the non-dominated set of Pareto-optimal solutions and allows the designer to select a particular controller configuration with respective weightages. With the application of this proposed design to the excitation system of synchronous generator to a power plant’s, the dynamic robust stability enhanced explicitly with minimum energy consumption.

Keywords: Control Design, Linear Control Systems
Abstract: In this paper the application of robust Fractional Order Proportional-Integral (FO-PI) autotuning control strategy is presented and applied to heterogeneous dynamic systems using decentralized control. The automatic tuning of controller gains is based on a single sine test, with user-defined robustness margins guaranteed. Its performance is compared against two other fractional order controllers based on PI gain-crossover autotuning method and Internal Model Control (IMC). The closed loop control simulations applied on the heterogeneous dynamic systems indicate that the proposed method performs properly.

Keywords: Control Design, Non Linear Control Systems, Linear Control Systems
Abstract: In this paper, an original method for the design of PID Controller for MIMO application is presented. The proposed method is based on the CRONE MIMO approach which makes easier the design of MIMO robust controllers. The problem treated here is the control of a refrigeration system based on vapour compression in order to achieve high energy efficiency and to satisfy the cooling demand. Simulation results show the good control performance and robust stability for a wide set of operating points.

Keywords: Chemical Process Control, Control Design, Optimal Control
Abstract: This paper presents a multi-objective stochastic optimization method for tuning of the controller parameters of Refrigeration Systems based on Vapour Compression. Stochastic Multi Parameter Divergence Optimization (SMDO) algorithm is modified for minimization of the Multi Objective function for optimization process. System control performance is improved by tuning of the PI controller parameters according to discrete time model of the refrigeration system with multi objective function by adding conditional integral structure that is preferred to reduce the steady state error of the system. Simulations are compared with existing results via many graphical and numerical solutions.

Keywords: Optimal Control, Control Design, Chemical Process Control
Abstract: This paper presents a multi-variable Model Predictive Control (MPC) based controller for the one-staged refrigeration cycle model described in the PID2018 Benchmark Challenge. This model represents a two-input, two-output system with strong nonlinearities and high coupling between its variables. A general purpose optimal control problem (OCP) solver Matlab toolbox called RIOTS is used as the OCP solver for the proposed MPC scheme which allows for straightforward implementation of the method and for solving a wide range of constrained linear and nonlinear optimal control problems. A conditional integral (CI) compensator is embedded in the controller to compensate for the small steady state errors. This method shows significant improvements in performance compared to both discrete decentralized control (C1) and multi-variable PID controller (C2) originally given in PID2018 Benchmark Challenge as a baseline. Our solution is introduced in detail in this paper and our final results using the overall relative index, J, are 0.2 over C1 and 0.3 over C2, respectively. In other words, we achieved 80% improvement over C1 and 70% improvement over C2. We expect to achieve further improvements when some optimized searching efforts are used for MPC and CI parameter tuning.

Keywords: Chemical Process Control, Linear Control Systems, Control Design
Abstract: Since proportional-integral-derivative (PID) controllers absolutely dominate the control engineering, numbers of different control structures and theories have been developed to enhance the efficiency of PID controllers. Thus, it is essential and inspiring to operate different PID control strategies to the PID2018 Benchmark Challenge. In this paper, a novel control strategy is designed for this refrigeration system, where a feedforward compensator and a conditional integrator are utilized to compensate the disturbances and remove the steady-state error in the benchmark problem, respectively. The simulation results given in the benchmark problem show the straightforward effectiveness of the proposed control structure compared with the existing control methods.

Keywords: Modelling and Control of Biomedical Systems, Control of Biotechnological Systems, Control Design
Abstract: The usability of advanced control methods of physiological processes have been several times demonstrated. Advanced (i.e. MPC) control approaches cope with practical difficulties of limited measurability of the state variables, model-imprecisions, significant interpatient variability of the available model's parameters and limitations in the sampling frequency of the variables that at least in principle can be directly measured. However, the lack of the necessary information prevents the use of state estimators. Compensation of the effects of the presence of model-imprecisions needs the application of robust control methods or adaptive techniques. The Proportional-Derivative (PD) control completed with Robust Fixed Point Transformation (RFPT)-based adaptive control was invented for tackling such difficulties. The current paper investigates the applicability of this technique in case of angiogenic growth of tumors using different scenarios of tumor volume measurement. Conclusions are drawn on the basis of numerical simulations.

Keywords: Modelling and Control of Biomedical Systems, Control Design, Control of Biotechnological Systems
Abstract: In the past few decades cancer research has delivered several new treatment options, of which can be highly expensive thus reducing its applicability in medical practice. However, advances in control engineering can tackle this issue by the use of an appropriate optimal controller. In this paper a Computed Torque Control (CTC) based PID controller was designed for the Hahnfeldt tumor growth model which can provide an optimal administration protocol for every individual patient. The paper contains the system model in conjunction with the detailed design steps of the controller. The control strategy was tested by numerical simulations which can be found at the end of the paper together with the conclusions.

Keywords: Adaptive and Learning Systems, Modelling and Control of Biomedical Systems, Control Design
Abstract: The operation of the nervous system, consequently the various dynamic neuron models, show strong nonlinearities. Their control, that may result in the treatment of various diseases, have to cope with the essential difficulties as the great deviations/uncertainties in the parameters of the available models, and the time-delay related to the observations of the measurable quantities, the computation, and the exertion of the control signal. For tackling model uncertainties a novel, fixed point transformation (FPT)-based adaptive control approach was suggested that generally works by the use of fresh observations on the behavior of the controlled system, therefore its operation may be degraded by time-delay effects. Furthermore, in the practice time-delay effects can be reduced by using model-based extrapolation of the motion of the controlled system for the “dead period” spanned between the observation and the actual appearance of the control action. In the lack of reliable dynamic model such an extrapolation may be questionable. In this research, up to or knowledge, at first time, time-delay effects are studied in the FPT-based adaptive control of the FitzHugh-Nagumo Neuron Model using novel fractional order kinematic feedback terms. This neuron is a relevant paradigm because showing very sharp nonlinearities in its dynamics. It is concluded that the use of an approximation-based extrapolation in a control of this special fractional order PID-type feedback can considerably reduce the consequences of the time-delay problems.

Keywords: Control Design, Non Linear Control Systems
Abstract: Due to adding the extra degree of freedom, the fractional order PID controllers can achieve better control performance than the integer order PID controllers. The present paper proposes a novel fractional order controller design method, inspired by the Kessler’s optimum magnitude method. The explicit tuning rules are accessible even to less experienced users in fractional calculus, taking only the advantages of the controller and not the disadvantage of complex mathematical background. The advantages of the method are demonstrated by a case study.

Keywords: Linear Control Systems, Control Design
Abstract: Dominant roots of the closed loop characteristic equation play a crucial role in terms of the performance of Linear Time Invariant (LTI) systems. Within the scope of this study, a dominant pole placement approach which has two main phases is proposed for PI/PID type controllers. In the first phase, characteristic equation is partitioned into its dominant and non-dominant polynomial pairs and dominant poles are placed to predetermined locations. In the second phase, it is required to determine how far the non-dominant poles can be placed. In the current study, this requirement is transformed into a stability problem and Lyapunov Equation-based stability mapping approach is used. This combined approach creates a more flexible design environment compared to the currently existing approaches in literature. In order to demonstrate this flexibility, two benchmark case studies are included with different definitions of dominant pole placement problem.

Keywords: Linear Control Systems, Control Design
Abstract: This paper proposes a method so that all PID controller tuning parameters, which are satisfying stability of any integrating time delay processes, can be calculated by forming the stability boundary loci. Processes having a higher order transfer function must first be modeled by an integrating plus first order plus dead time (IFOPDT) transfer function in order to apply the method. Later, IFOPDT process transfer function and the controller transfer function are converted to normalized forms to obtain the stability boundary locus in , and planes for PID controller design. PID controller parameter values achieving stability of the control system can be determined by the obtained stability boundary loci. The advantage of the method given in this study compared with previous studies in this subject is to remove the need of re-plotting the stability boundary locus as the process transfer function changes. That is, the approach results in somehow generalized stability boundary loci for integrating plus time delay processes under a PID controller. Application of the method has been clarified with examples.

Keywords: Control Design, Linear Control Systems, Optimal Control
Abstract: Robust PID controller design methods are proposed for linear single-input single-output systems. Non-parametric models represented by a finite number of frequency responses are used for them. Sufficient conditions for closed-loop stability are derived based on the Nyquist stability criterion and the sufficient conditions are reduced to convex constraints. Together with the convex constraints and closed-loop model matching problems the robust PID controller design problems are formulated as convex optimization problems. A important feature of the proposed design methods is that they can be applied to delay-free and time-delay systems in the same manner. Moreover, the proposed methods are extended to two-degree-of-freedom PID controller design methods.

Keywords: Control Education, Control Design, Components and Instruments
Abstract: A major challenge of higher education institutions is to prepare professionals capable of learning by building effective solutions that are able to integrate different disciplines and knowledge areas. With this in mind, academics and researchers from ESPOL university in Ecuador, have designed laboratory experiments for a digital control class that introduces students to a modular design of embedded feedback controllers using Field Programmable Gate Array (FPGA) technologies. The proposed experiment includes the design of direct discrete time PID controllers, for an existing speed control system with three different sampling times, to test and compare their performance. The obtained controllers are implemented using a prototyping strategy that relies on FPGA development boards. The prototype controller is tested using the experimental plant, and the system performance is contrasted with results from simulations under realistic conditions.

Keywords: Control Education, Control Design, Linear Control Systems
Abstract: The problem of designing a pole placing PID type (ppPIDt) controller is considered, motivated by educational considerations. Effectively, the number of controller zeros, integrators and filtering poles can be extended to aid in the response shaping and stabilizing of the closed loop, while simultaneously avoiding spikes in the control signal. In contrast to the state feedback observer-controller, we do not emphasize maintaining the original systems order, rather we utilize the increased order of the closed loop to shape its response by a suitable choice of poles in the closed loop. This is similar to the classical PID which typically increases the order of the original system by two in the closed loop. We also propose a prefilter to cancel stable system zeros and ppPID zeros and replace them by new zeros if desirable. This results in a new overall transfer function of the controlled system, with full pole placement including good input tracking and disturbance rejection properties and guaranteed closed loop stability. The material is presented in a tutorial way suitable for basic undergraduate control courses and has been used successfully by the first author in such a course.

Keywords: Linear Control Systems, Control Education
Abstract: This work presents an analysis of the effect of measurement noise on the closed-loop performance for three anti-windup strategies, used together with a PID controller. The study is done both analytically and experimentally and considered stable, integrating and unstable processes with dead time subjected to saturation of the actuator. The PID tuning rule, used for all the presented case studies, is based in a low-order approximation of the filtered Smith predictor. The analysis shows that the error recalculation anti-windup technique gives better reference tracking performance when compared to the incremental algorithm and back-calculation techniques, being able to reduce the effects of noisy measurements on the calculation of the control action, thus resulting in lower control and process variable variability. In addition, it is shown that when the process operating point is near a saturation limit, noise can cause an offset between the process variable and the reference and it is also proven that the error recalculation anti-windup strategy can significantly attenuate this behavior.

Keywords: Control Design, Optimal Control, Control Education
Abstract: The aims of the paper are: (a) to extend the 2DOF PI and PID controller design for the first order time-delayed (FOTD) plant by the multiple real dominant pole method to the 2DOF PIDD^2 control, (b) to modify for this controller augmented by an nth order series binomial filter required for the derivative action implementation and measurement noise attenuation the simple integrated tuning procedures known already for the PI and PID control. (c) to align all the filtered controllers as for the guaranteed stability range in case of unstable plants, and (d) to compare the performance limits expressed in terms of the integral of absolute error (IAE) and (e) to discuss the corresponding closed loop robustness by a simple test based on comparing impacts of ``exact'' and simplified tunings based on the integral + dead time (IPDT) models.

Keywords: Control Design, Optimal Control, Control Education
Abstract: The paper discusses performance measures used dominantly in the robust and optimal control design. By simple examples of the first order time delayed (FOTD) system control it illustrates that the usually prescribed levels of the maximal and complementary sensitivity functions indeed define situations with interesting loop properties, but may not be universally applied to the robust and optimal design of systems with an uncertain feedback variable in a broader range. For this purpose the shape related measures based on deviations from monotonicity yield results matching the technological requirements of practice in a much more appropriate way. It is also shown that in an optimal nominal controller design the monotonicity based performance measures nearly coincide with the multiple real dominant pole (MRDP) method. For the loop optimization using a broader spectrum of different performance measures, the performance portrait method may be recommended. It avoids the problems of convergence to the absolute optimum and, once generated, the performance portrait may repeatedly be used with a limited effort for a broader spectrum of different cost function specifications.