Robust control systems

International Journal of Electrical and communication engineering (IJECE) is an open access peer-reviewed journal that publishes quality articles contributing new results in all areas of Applied Control Systems, Electrical Engineering and Electronics Engineering. The Journal of Electrical and communication engineering (IJECE) is an abstracted and indexed international journal of high quality devoted to the publication of original research papers from Control Systems, Electrical Engineering, Power Systems, Automation, Electronics Engineering, Networks and Communication Systems and their broad range of applications.

Une alternative, consiste à exploiter les énergies renouvelables qui offrent la possibilité de produire de l’électricité et surtout dans une moindre dépendance des ressources à condition d’accepter leurs fluctuations naturelles. Ce mémoire présente une étude et commande d'un système éolien basé sur un générateur asynchrone à double alimentation (GADA), pour améliorer les performances de régulation de cette dernière est associée à un contrôle des puissances active et réactive, basée sur une commande à flux statorique orienté selon un repère diphasé.
Dans ce travail, une technique de contrôle non linéaire robuste d'une génératrice asynchrone à double alimentation destiné aux systèmes éoliens a été proposée. L'idée principale dans ce mémoire est de découpler la puissance active et réactive de la GADA avec une grande robustesse en utilisant la stratégie de backstepping. Le principe de cette méthode de contrôle repose sur la fonction de Lyapunov, afin de garantir la stabilité asymptotique globale du système. Enfin, nous présentons quelques résultats de simulation afin de vérifier l'efficacité et la robustesse de la technique de contrôle proposée.

This paper presents the simulation of real time data acquisition of a solar panelin LabVIEW. A prototype model has been made where two Arduino were used. One is used for interfacing the solar panel with the PC for acquisition of data and the other one isused with the servomotor. The servomotor is linked with the solar panel with the help of a shaft and is rotated according to the LDR output. Two LDR is fixed on both the sides of the solar panel for tracing the sunlight. The whole simulation is performed with the help of LINX firmware wizard, which is available in LabVIEW Maker's Hub. Data were collected of different days in different duration of time. According to the collected data, behaviour and the voltage of the solar module was analysed. This paper describes the design of a low cost, solar tracking and real time data acquisition system.

This paper demonstrates a multi-input multi-output (MIMO) robust control approach where multiple scheduled designs are merged to produce a
smooth control law. The design is verified using software-in-the-loop (SIL) testing based on blade element theory (BET) for highly realistic flight simulations.
An inner-loop attitude controller balances performance and robustness, achieving a fast response time, low overshoot, good noise rejection and
minimal lateral–longitudinal coupling. The controllers are formed at several predetermined grid points so the design covers a wide flight envelope.
Blade element SIL testing shows that the flight control system preserves stable flight and follows the references well, even under tough weather conditions.
The proposed strategy is also compared with a classical autopilot design procedure and is seen to be superior.

This research work is developed with two AT89C52 microcontrollers from Atmel. The microcontrollers provide all the functionality of the display notices and wireless control. The Display is obtained on a 7X96 Light Emitting Diode (LED) dot matrix display, arranged on a Vero board. A desired text message from a mobile phone is sent via a Global System for Mobile Communication (GSM) to the GSM module located at the receiving end. The GSM modem is connected, through MAX 232 Integrated Circuit (MAX 32 IC), to the AT89C52 microcontroller. The message that is stored in the Electrically Erasable Programmable Read Only Memory (EEPROM) is then displayed on the LED dot matrix display. This hardware uses regulated 5V, 500mA power supply. A three-terminal LM7805 is employed for regulation of the voltage. A bridge type full-wave rectifier is used to rectify the AC output of the secondary of 230/12V step down transformer. The system was tested to work according to specification.

Unstable wheel inverted pendulum is modelled and controlled deploying Kane's method and optimal partial-state PID control scheme. A correct derivation of nonlinear mathematical model of a wheel inverted pendulum is obtained using a proper definition of the geometric context of active and inertia forces. Then the model is decoupled to two linear subsystems namely balancing and heading subsystems. Afterward partial-state PID controller is proposed and formulated to quadratic optimal regulation tuning method. It enables partial-state PID to be optimally tuned and guarantees a satisfactory level of states error and a realistic utilization of torque energy. Simulation and numerical analyses are carried out to analyse system's stability and to determine the performance of the proposed controller for mobile wheel inverted pendulum application.

The article addresses a robust control strategy for efficient path tracking of nonholonomic wheeled mobile robot (WMR) based on time delay approach. Depending on the application requirements, nonholonomic WMR system might be subjected to various payloads, which affects the overall system mass, inertia, position of center of mass and other hardware parameters statically or dynamically. Under such circumstances, accurate modeling of nonholonomic robots is difficult and challenging. The proposed controller negotiates uncertainties caused due to payload variations as well as associated disturbances and reduces modeling effort through approximation of the overall uncertainties with a composite function. It has been shown that the controller does not require any bounds on the uncertainties, thus providing unconstrained working paradigm. The controller is proposed for a nonholonomic WMR and its effectiveness is verified through simulation and experimentally while WMR is commanded to track various paths. The superior performance is also noted against adaptive sliding mode control law

The aim of this paper remains to introduce the extensive application of a state-of-the-art autonomous underwater vehicle (AUV-150) capable of operating up to a depth of 150 meters, without any human intervention. The AUV-150 has been developed to perform seabed mapping and collect oceanographic data like salinity, temperature and conductivity at various depths. In this regard, various functional aspects of the system shall also be discussed in this paper. Considering navigational and guidance issues relating AUV-150 as well as the images obtained on an account of underwater terrain mapping done employing the payload sensors as the pioneer space; the paper also includes the plots generated as a result of post-processing algorithms applied on the raw data obtained from the scanning sensors used typically for seabed mapping.

The process of identifying the central nodes in complex networks research has remained interesting and
very important issue for network analysis. The identification of main nodes in the network can lead to many
answers for the solution of security and other problems depending on the type of complex networks under
analysis. Different topological metrics of the network can be used to locate the major nodes in the network
but the degree and betweenness (Load) centralities perform very important role in evolution and
communication of nodes in growing networks. Unfortunately, these metrics have been analyzed in different
complex systems mainly either on the bases of the number of links to nodes in the network or with much
focused from the perspective of weights of links. Therefore, locating the main nodes in the network not
only depends on links but majorly on weight of links. Routers network of the internet is an example of
scale-free nature which follow power-law distribution and causes inhomogeneous structure with some
nodes with large number of links while many with a few. Further, in this type of distribution few nodes
become very important. In this paper, we analyze the behavior of routers network by using two metrics of
centralities with weighted and un-weighted links based on the dataset of PTCL routers network in Pakistan.
Furthermore, by using centralities measures we try to show that weight of links is important as compare to
number of links by following the concept from “rich get richer” to “fit get richer” in routers network.
Moreover, we prove that weighted routers network is very close to scale-free networks as compared to unweighted,
and due to this phenomenon these networks sustain their robustness.

The work proposed in this paper aims to design a robust stabilization of an underactuated quadrotor UAV system in presence of sensor failures. The dynamical model of quadrotor while taking into account various physical phenomena, which can influence the dynamics of a flying structure is presented. Subsequently, a new control strategy based on backstepping approach is developed. Lyapunov based stability analysis shows that the proposed control strategy design keep the stability of the closed loop dynamics of the quadrotor UAV even after the presence of sensor failures. Numerical simulation results are provided to show the good tracking performance of proposed control laws.

This article studies the problem of designing robust control laws to achieve multiple performance objectives for linear uncertain systems. Specifically, in this study we have selected one of the control objectives to be a closed-loop pole placement in specific regions of the left-half complex plane. As such, a guaranteed cost-based multi-objective control approach is proposed and compared with the H_2 / H_∞ control by means of an application example.

This paper presents a method for the estimation of unknown disturbances for high
precision gimbal systems. Alternative to the classical methods of model inversion and filtering, we
employ an asymptotically stabilizing controller which achieves the estimation process even in the
presence of unstable zeros. The architecture provides an input equivalent disturbance which can be
thought to capture all real disturbances in the system as well as virtual ones such as unmodelled
dynamics and nonlinearities. The proposed method is illustrated on a 2-axis gimbal system where
system identification is followed by the design on an integral linear quadratic regulator as the
stabilizing controller which forms the base of the disturbance observer. It is seen that a random
unknown disturbance is estimated successfully in the presence of additional gyro noise.

Minh et al (2003) and Toshihiro Abe et al (2010) proposed a new method to derive circular distributions from the existing linear models by applying Inverse stereographic projection or equivalently bilinear transformation. In this paper, a new circular model, we call it as stereographic circular normal moment distribution, is derived by inducing modified inverse stereographic projection on normal moment distribution (Akin Olosunde et al (2008)) on real line. This distribution generalizes stereographic circular normal distribution (Toshihiro Abe et al (2010)), the density and distribution functions of proposed model admit closed form. We provide explicit expressions for trigonometric moments.

Analytical optimisation design methods generally have weights which are adjusted by the designer to get a good design. To combine analytical and numerical methods, one can simply use numerical search techniques to find 'good' weighting parameters for the analytical optimisation problem. This note briefly describes how one such numerical search technique, the method of inequalities (MOI), can be combined with analytical optimisation design methods such as McFarlane and Glover's loop-shaping design procedure (LSDP) to provide a multi-objective mixed optimisation robust controller design method. Its application to the design of an unknown plant is described.

We consider methods for synthesizing robust controllers that can be directly implemented in the Internal Model Control (IMC) scheme. We show how to put H∞ design methods into the IMC scheme to improve its robustness. These methods include one degree-of-freedom (one d.o.f.) and two degrees-of-freedom (two d.o.f.) H∞ designs. Explicit state-space formulae for the H∞ one d.o.f. and two d.o.f. IMC-based controllers are derived in discrete time. We show that the IMC controller solves a special H∞ control problem, namely a disturbance feedforward control problem, and it proves robust stability against coprime factor uncertainty and with a degree of robust performance for the two d.o.f. case, in the sense of making the closed-loop system match a pre-specified reference model. A design for a glass tube production process is presented as an illustrative example.

In this paper a two-degree-of-freedom (2 DOF) controller is designed for an industrial MIMO process. The design tech nique used is Discrete-Time H∞ control (via a coprime factor framework [4]) with the Method of Inequalities [7] and the pro cess is a glass tube shaping plant. The purpose of the study is to investigate the performance and robust stability char acteristics of ten different models derived from experiments carried out on the process. It is desired to control all the models with one controller, and it is shown that an accept able performance/robustness trade-off can be obtained by a loop-shaping technique built into a 2 DOF design as described in [2].

This paper presents results on the output regulation of a single-input multi-output (SIMO) rotationaltranslational actuator (RTAC) system. The results focus primarily on stability and robustness, which are studied in light of the presence of externally generated exogenous input signals. Two exosystem types were investigated and tested. Obtained results answers the question of asymptotic stabilization and tracking of a desired trajectory in the presence of a dynamic exosystem. The results confirmed the working theory of robust stabilization using output feedback techniques, borne out of differential-geometric observer design principles. The utilized design showed good stability results which compares favourably with existing works on RTAC stabilization.

In the paper a velocity-based linearisation approach for the design of a gain-scheduling controller for ship steering is presented. While ship steering and gain-scheduling are well known problems with well-developed solutions, the described method differs from previous approaches to gain-scheduled controller design in that the closed-loop system with nonlinear controller retains properties of the linearised system with linear controller designed in one of the design stages. Stochastic robustness with Monte Carlo simulations is applied to confirm performance of the nonlinear control which was the objective for control design

Unstable wheel inverted pendulum is modelled and controlled deploying Kane's method and optimal partial-state PID control scheme. A correct derivation of nonlinear mathematical model of a wheel inverted pendulum is obtained using a proper definition of the geometric context of active and inertia forces. Then the model is decoupled to two linear subsystems namely balancing and heading subsystems. Afterward partial-state PID controller is proposed and formulated to quadratic optimal regulation tuning method. It enables partial-state PID to be optimally tuned and guarantees a satisfactory level of states error and a realistic utilization of torque energy. Simulation and numerical analyses are carried out to analyse system's stability and to determine the performance of the proposed controller for mobile wheel inverted pendulum application.

Paper introduces extensive application of a state-of-the-art Autonomous Underwater Vehicle (AUV-150) capable of operating up to a depth of 150 meters, without any human intervention. Considering navigational and guidance issues relating AUV-150 as well as the images obtained on an account of underwater terrain mapping done employing the payload sensors as the pioneer space; the paper also includes the plots generated as a result of post-processing algorithms applied on the raw data obtained from the scanning sensors used typically for seabed mapping.

Robust fixed-gain controllers were sattsfactordy designed for stress levels 1 and 2 of the benchmark process using H® loop-shaping and a numerical approach to the selection of weights At stress level 3, it was found that the performance of a fixed-gain controller was Improved usmg a simple adaptive gain scheme.

Explicit state-space formulae for an H∞ two degrees-of-freedom (2-DOF) Internal Model Control (IMC)-based controller are derived. The IMC controller solves a special H∞ control problem directly in discrete-time, providing robust stability against coprime factor uncertainty, and a degree of robust performance in the sense of making the closed-loop system match a pre-specified reference model. The IMC controller structure is shown to comprise a plant state observer, an on-line step response model, and a generalised state-feedback law associated with the plant and model states. A design for a binary (methanol/water) distillation column is presented as an illustrative example.

In a special glass factory of a well-known engineering company, glass tubes are manufactured on so-called SQ (Sulvanian Quartz) furnaces. Each furnace is equipped with a MIMO control device which is used for controlling the wall thickness and external diameter of tubes. When these glass tubes are used in the production of gas-discharge lamps, the internal diameter is very important since the volume of gas to be filled in the lamp very much determines the characteristics of the lamp. It is not possible to measure the internal diameter directly. Two external diameter sensors placed vertically on top of each other and four wall thickness sensors each displaced by 90 degrees with respect to each other are used for measuring the dimensions of the glass tube. It is possible to deduce the internal diameter from the average of two external diameters and the average of four wall thicknesses. This process takes account of the fact that it is not possible for these dimensions to be measured at the same time. The particular glass tube production process studied in the paper is used for the production of three different types of tube which differ in dimensions. Specifications on these products differ significantly and some are difficult to achieve. The specifications are on the average external diameter and the average wall thickness of the tubes. The objective is to design and test a control law in the internal model control scheme for controlling the average external diameter and the average wall thickness for the three types of tube which are used for the production of gas-discharge lamps.

El enfoque probabilista para el control de un robot combina elementos probabilistas con
arquitecturas de control diversas. Las arquitecturas de control que incorporan modelos de
creencia probabilista renuncian a prever todos los patrones de interacción entre un robot y
su ambiente En este trabajo se presenta un modelo para el control de un robot hexápodo
hexagonal, i.e. un robot hexápodo cuya base tiene la forma de un hexágono regular con
extremidades rodeando la base, usando un Proceso de Decisión de Markov (MDP por sus
siglas en inglés) de tipo jerárquico, el cual es un modelo probabilista. Se utiliza un enfoque
descentralizado, un MDP formado a su vez por 2 MDPs que controlan acciones básicas del
robot, como levantar o apoyar una pata, y un tercer MDP que coordina a los anteriores,
para atacar un problema complejo. Se obtuvieron resultados satisfactorios al aplicar este
modelo para controlar un robot hexápodo simulado en el ambiente Webots©. Dicho control
permite que el robot se mantenga y se desplace de manera estable dentro de diversos
ambientes. Además, el control obtenido le permite al robot desplazarse en un ambiente
distinto al ambiente en el que fue entrenado.

Linear systems controlled by a nonlinear version of the PI algorithm are under study. The modified PI controller in question is known in the literature as the Super-Twisting (STW) algorithm (see ), and it belongs to the family of second order sliding mode controllers. The considered closed-loop system exhibits self-sustained stable oscillations (chattering) when the relative degree of the linear plant is higher than one (see ) and it is the task of the present paper to present a systematic yet simple procedure for tuning the STW algorithm parameters in order to obtain pre-specified frequency and magnitude of the resulting chattering oscillation. The proposed methodology is based on the Describing Function (DF) approach. The approach is theoretically illustrated and verified by means of, both, simulation analysis and experiments carried out by making references to a DC motor.

The work proposed in this paper aims to design a robust stabilization of an underactuated quadrotor UAV system in presence of sensor failures. The dynamical model of quadrotor while taking into account various physical phenomena, which can influence the dynamics of a flying structure is presented. Subsequently, a new control strategy based on backstepping approach is developed. Lyapunov based stability analysis shows that the proposed control strategy design keep the stability of the closed loop dynamics of the quadrotor UAV even after the presence of sensor failures. Numerical simulation results are provided to show the good tracking performance of proposed control laws.

This paper is concerned with discrete-time model reduction via order-reduction of a discrete-time left coprime factor representation of a given model or controller. The proposed model reduction scheme is suitable for both, stable and unstable models, and for non-minimal state-space systems. Balanced singular perturbation approximation is considered rather than balanced truncation. Numerical issues are also considered.

Many control design specifications, such as the IFAC 1993 benchmark, include stringent closed-loop performance requirements, which are required to be met in the face of uncertainties. Such problems can be effectively designed by a combination of the method of inequalities, which designs for explicit closed-loop performance, and analytical optimization techniques, from which robustness is obtained. This paper describes how to combine the method of inequalities with a variety of analytical optimization methods. An introduction to μ synthesis is also included. The design of robust controllers for the benchmark problem using these methods is described, and a simple adaptive gain scheme to improve the performance is suggested.

In this paper a comparison between various advanced multivariable identification techniques and a description of various control design methods, all applied to a glass tube production process, will be discussed. The main features such as accuracy, user-friendliness and speed, will be presented for each identification technique. Also, the differences between the identified models with respect to order, static-gains and dynamical behaviour will be discussed. Starting with a nominal model derived via advanced identification, a robust controller is designed based on an Internal-Model Control (IMC) scheme. The control objectives together with the controller design results, will be presented. It will be shown that the application of advanced identification techniques and robust control design methods can achieve high levels of performance specifications in industrial processes.

In this paper a two-degree-of-freedom (2 DOF) controller is designed for an industrial MIMO process. The design technique used is H∞ control (via a coprime factor framework (McFarlane, 1990)} and the process is a glass tube shaping plant. The purpose of the study is to investigate the performance and robust stability characteristics of ten different models derived from experiments carried out on the process. It is desired to control all the models with one controller, and it is shown that an acceptable performance/robustness trade-off can be obtained by a loop-shaping technique built into a 2 DOF design as described in (Limebeer et al, 1991).

: Linear systems controlled by a nonlinear version of the PI algorithm are under study. The modified PI controller in question is known in the literature as the Super–Twisting (STW) algorithm (see Levant (1993)), and it belongs to the family of second order sliding mode controllers. The considered closed–loop system exhibits self–sustained stable oscillations (chattering) when the relative degree of the linear plant is higher than one (see Boiko and Fridman (2005)) and it is the task of the present paper to present a systematic yet simple procedure for tuning the STW algorithm parameters in order to obtain pre–specified  requency and magnitude of the resulting chattering oscillation. The proposed methodology is based on the Describing Function (DF) approach. The approach is theoretically illustrated and verified by means of, both, simulation analysis and experiments carried out by making references to a DC motor.

Identification of uncertainty bounds in robust control design is known to be a critical issue that attracts the attention of research in robust control field recently. Nevertheless, the practical implementation involves a trial and error procedure, which depends on the designer prior knowledge and the available information about the system under study. Artificial intelligent techniques provide a suitable solution to such a problem. In this paper a new intelligent identification method of uncertainty bound using an adaptive neuro-fuzzy inference system (ANFIS) in an enhanced feedback scheme is proposed. The proposed ANFIS structure enables accurate determination of the uncertainty bounds and guarantees robust stability and performance. In our proposed technique, the validation of the intelligent identified uncertainty weighting function is based on the measurement of both the v-gap metric and the stability margin that result from the corresponding robust controller design. Additionally, these two indices are used to improve the accuracy of the intelligent estimation of uncertainty bound in conjunction with the robust control design requirements. The enhanced intelligent identification of uncertainty bound is demonstrated on a servo positioning system. Simulation and experimental results prove the validity of the applied approach; more reliable and highly efficient estimation of the uncertainty weighting function for robust controller design.

The article addresses a robust control strategy for efficient path tracking of nonholonomic wheeled mobile robot (WMR) based on time delay approach. Depending on the application requirements, nonholonomic WMR system might be subjected to various payloads, which affects the overall system mass, inertia, position of center of mass and other hardware parameters statically or dynamically. Under such circumstances, accurate modeling of nonholonomic robots is difficult and challenging. The proposed controller negotiates uncertainties caused due to payload variations as well as associated disturbances and reduces modeling effort through approximation of the overall uncertainties with a composite function. It has been shown that the controller does not require any bounds on the uncertainties, thus providing unconstrained working paradigm. The controller is proposed for a nonholonomic WMR and its effectiveness is verified through simulation and experimentally while WMR is commanded to track various paths. The superior performance is also noted against adaptive sliding mode control law.

Unstable wheel inverted pendulum is modelled and controlled deploying Kane's method and optimal partial-state PID control scheme. A correct derivation of nonlinear mathematical model of a wheel inverted pendulum is obtained using a proper definition of the geometric context of active and inertia forces. Then the model is decoupled to two linear subsystems namely balancing and heading subsystems. Afterward partial-state PID controller is proposed and formulated to quadratic optimal regulation tuning method. It enables partial-state PID to be optimally tuned and guarantees a satisfactory level of states error and a realistic utilization of torque energy. Simulation and numerical analyses are carried out to analyse system's stability and to determine the performance of the proposed controller for mobile wheel inverted pendulum application.

This paper presents results on the output regulation of a single-input multi-output (SIMO) rotationaltranslational actuator (RTAC) system. The results focus primarily on stability and robustness, which are studied in light of the presence of externally generated exogenous input signals. Two exosystem types were investigated and tested. Obtained results answers the question of asymptotic stabilization and tracking of a desired trajectory in the presence of a dynamic exosystem. The results confirmed the working theory of robust stabilization using output feedback techniques, borne out of differential-geometric observer design principles. The utilized design showed good stability results which compares favourably with existing works on RTAC stabilization.

This paper considers the design problem of integrated controls and diagnostics. The foundation for such an integrated approach was presented in (Nett et al., 1988), where the approach made use of the so-called four degrees-of-freedom (4-DOF) controller. This controller has 2-inputs and 2-outputs (rather than one). The additional controller output was viewed as a diagnostic output which is monitored to detect and isolate sensor and actuator failures. It will be shown that the 4-DOF controller is a simple case of the standard regulator framework. The design of the integrated controls and diagnostics can thus be done in the framework of robust control theory. This gives the advantage of synthesizing the 4-DOF controller in a single step approach. The effect of model uncertainty is directly incorporated in the synthesis so that when uncertain plants are used, the diagnostic performance should remain reasonable. An example will be presented to demonstrate the proposed design approach.