Design Of Feedback Control Systems Research Articles

Adaptive output feedback control system design for nonlinear systems via neural networks

AbstractAdaptive output feedback control based on output feedback exponential passivity (OFEP) has a simple structure and strong robustness in regard to disturbances and system uncertainties. However, it is difficult for most nonlinear systems to satisfy the conditions of OFEP. Thus, the introduction of a suitable parallel feedforward compensator (PFC) to construct an OFEP‐augmented system with the controlled system has been used, but the control output cannot achieve perfect tracking because of the output of the introduced PFC. As a solution, introducing a feedforward (FF) input to build a 2 degree of freedom (2‐DOF) is a simple and effective way to solve this problem. In this paper, we propose the design schemes for suitable PFC and FF input of nonlinear systems via the use of neural networks (NN), respectively. Besides, to cope with possibly present input disturbances, we also provide a method to achieve disturbance compensation based on NN to reduce their interference. Finally, the effectiveness of all proposed design schemes is confirmed through numerical simulations.

Pole placement with minimum gain and sparse static feedback

The work addresses the issue of developing polar positioning algorithms for linear control systems with despotic thinning constraints on a static feedback matrix. The design of sparse-limiting feedback control systems is considered to be one of the more complex issues, but the issue of defining the sparse feedback matrix, which allows the selection of eigenvalues or, in other words, the placement of poles, has not been fully studied. Algorithms for determining the eigenvalues, i.e., solving the problem of pole placement and finding the optimal solution of the technological process control system are considered in the work. The results of numerical analysis confirmed the effectiveness of these algorithms, which allows them to be used in solving practical problems of synthesizing adaptive control systems for technological objects.

Feedback control system design for force-sensing concentric tube-based surgical robot: Kinematics using Bernstein polynomials

A novel force sensing module integrated into a concentric tube robot (CTR) was proposed for vitreoretinal surgery in our previous work, and this robot was able to provide tip force information to the operating surgeon. However, when the force-sensing module was integrated, the property of the tube changed, and the conventional modeling-based control algorithm proved to be unsuitable for the force-sensing concentric tube robot (FSCTR). In this work, we have proposed a shape optimization algorithm for the FSCTR to prevent snapping issue while providing an adequate workspace. A corollary actuation system was used to control the FSCTR. The forward kinematics of the FSCTR consisted of rigid body motion and shape variation, where the shape variation was determined using Bernstein polynomials. Inverse kinematics was derived using the Newton–Raphson method. A feedback controller was designed to compensate for the error caused by rigid body motion. Several experiments were conducted to evaluate the performance of the proposed control system. The experimental accuracy of the proposed forward kinematics was 0.15 ± 0.16 mm, and this result was superior to that of the torsionally compliant model. The accuracy of the inverse kinematics was 0.55 ± 0.24 mm, and the accuracy of point targeting under feedback control was 0.12 ± 0.05 mm. Overall, the results of this study indicate that the proposed motion control system satisfies the standards required for vitreoretinal surgery.

Design of power and phase feedback control system for ion cyclotron resonance heating in the Experimental Advanced Superconducting Tokamak

Ion cyclotron range of frequency (ICRF) heating system is an important auxiliary heating method in the experimental Advanced Superconducting Tokamak (EAST). In EAST, several megawatts of power are transmitted with coaxial transmission lines and coupled to the plasma. For the long pulse and high power operation of the ICRF waves heating system, it is very important to effectively control the power and initial phase of the ICRF signals. In this paper, a power and phase feedback control system is described based on field programmable gate array (FPGA) devices, which can realize complicated algorithms with the advantages of fast running and high reliability. The transmitted power and antenna phase are measured by a power and phase detector and digitized. The power and phase feedback control algorithms is designed to achieve the target power and antenna phase. The power feedback control system was tested on a dummy load and during plasma experiments. Test results confirm that the feedback control system can precisely control ICRF power and antenna phase and is robust during plasma variations.

Global regulation of large‐scale nonlinear systems via decentralized output‐feedback switching control

AbstractThis article concentrates on the global regulation problem for a class of large‐scale nonlinear systems with unknown growth rate and unknown external disturbances. In contrast to closely related works, the highlight of this article is that a novel decentralized output‐feedback switching control method is proposed for the first time to offset the serious uncertainties. By integrating logic‐based switching technique and gain scaling technique, this method can instantly adjust the controller parameters (that is, the scaling gain can be tuned online in a piecewise constant manner), and thus has strong adaptive capability as well as disturbance tolerance. Moreover, the decentralized output‐feedback switching controller designed by such the method has a concise linear‐like form and low complexity. It is shown that the objective of global regulation is finally achieved after a finite number of switching moments. Finally, two examples, including an engineering feedback control system design example, are given to verify the effectiveness of the proposed control method.

A novel robust extended dissipativity state feedback control system design for interval type-2 fuzzy Takagi-Sugeno large-scale systems

Recently, systems have become large in their model and dynamic. To apply control algorithms, serious problems appear that need to be solved. Two significant problems are modelling the dynamics of the large-scale system and reducing effects of perturbations. In this paper, we use the advantage of large-scale systems modelling based on the type-2 fuzzy Takagi–Sugeno model to cover the uncertainties caused by large-scale systems modelling. The advantage of using membership function information is the reduction of conservatism resulting from stability analysis. Also, this paper uses the extended dissipativity robust control performance index to reduce the effect of external perturbations on the large-scale system, which is a generalization of , , passive and dissipativity performance indexes and control gains can be achieved through solving linear matrix inequalities (LMIs). Hence, the whole closed-loop system is asymptotically stable. Finally, the effectiveness of the proposed method is demonstrated by two practical examples.

Efficient Numerical Solution of Coupled Axisymmetric Plasma Equilibrium and Eddy Current Problems

This paper presents an efficient numerical tool for solving the problem of transient nonlinear evolution of plasma equilibrium in presence of eddy currents. The code, named FRIDA-TD (FRIDA-Time Domain), and based on the existing FRIDA (FRee-boundary Integro-Differential Axisymmetric) code, exploits two different approaches for solving the elated nonlinear system of Partial Differential Equations (PDE): (i) Finite Element Method - Boundary Element Method (FEM-BEM) for plasma equilibrium, and (ii) Axisymmetric Volume Integral (AVI) formulation for eddy currents. The resulting FRIDA-TD is a fast and flexible tool suitable for engineering-oriented purposes, such as the design of Tokamak devices, set up of plasma operations, prediction of performance scenarios, and design of feedback control systems. FRIDA-TD is successfully validated at first with the well-established CarMa0NL code, and then against experimental data of the RFX-mod device.

Methodology of Plasma Shape Reachability Area Estimation in D-Shaped Tokamaks

This paper suggests and develops a new methodology of estimation for a multivariable reachability region of a plasma separatrix shape on the divertor phase of a plasma discharge in D-shaped tokamaks. The methodology is applied to a spherical Globus-M/M2 tokamak, including the estimation of a controllability region of a vertical unstable plasma position on the basis of the experimental data. An assessment of the controllability region and the reachability region of the plasma is important for the design of tokamak poloidal field coils and the synthesis of a plasma magnetic control system. When designing a D-shaped tokamak, it is necessary to avoid the small controllability region of the vertically unstable plasma, because such cases occur in practice at a restricted voltage on a horizon field coil. To make the estimations mentioned above robust, PID-controllers for vertical and horizontal plasma position control were designed using the Quantitative Feedback Theory approach, which stabilizes the system and provides satisfactory control indexes (stability margins, setting time, overshoot) during plasma discharges. The controllers were tested on a series of plasma models and nonlinear models of current inverters in auto-oscillation mode as actuators for plasma position control. The estimations were made on these models, taking into account limitations on control actions, i.e., voltages on poloidal field coils. This research is the first step in the design of the plasma shape feedback control system for the operation of the Globus-M2 spherical tokamak. The developed methodology may be used in the design of poloidal field coil systems in tokamak projects in order to avoid weak achievability and controllability regions in magnetic plasma control. It was found that there is a strong cross-influence from the PF-coils currents and the CC current on the plasma shape; hence, these coils should be used to control the plasma shape simultaneously.

Trunk Posture from Randomly Oriented Accelerometers.

Feedback control of functional neuromuscular stimulation has the potential to improve daily function for individuals with spinal cord injuries (SCIs) by enhancing seated stability. Our fully implanted networked neuroprosthesis (NNP) can provide real-time feedback signals for controlling the trunk through accelerometers embedded in modules distributed throughout the trunk. Typically, inertial sensors are aligned with the relevant body segment. However, NNP implanted modules are placed according to surgical constraints and their precise locations and orientations are generally unknown. We have developed a method for calibrating multiple randomly oriented accelerometers and fusing their signals into a measure of trunk orientation. Six accelerometers were externally attached in random orientations to the trunks of six individuals with SCI. Calibration with an optical motion capture system resulted in RMSE below 5° and correlation coefficients above 0.97. Calibration with a handheld goniometer resulted in RMSE of 7° and correlation coefficients above 0.93. Our method can obtain trunk orientation from a network of sensors without a priori knowledge of their relationships to the body anatomical axes. The results of this study will be invaluable in the design of feedback control systems for stabilizing the trunk of individuals with SCI in combination with the NNP implanted technology.

Observability-blocking control using sparser and regional feedback for network synchronization processes

The design of feedback control systems to block observability in a network synchronization model, i.e. to make the dynamics unobservable from measurements at a subset of the network’s nodes, is studied. First, a general design algorithm is presented for blocking observability at any group of m nodes, by applying state feedback controls at m+2 specified actuation nodes. The algorithm is based on a method for eigenstructure assignment, which allows surgical modification of particular eigenvectors to block observability while preserving the remaining open-loop eigenstructure. Next, a sparser design is obtained, which leverages low-cardinality vertex cutsets separating the actuation and measurement locations in the network’s graph to reduce the required number of actuation nodes for observability blocking. Also, the design is modified to encompass regional feedback controls, which only use data from accessible nodes. The regional feedback design does not maintain the open-loop eigenstructure, but can be guaranteed to preserve stability via a time-scale argument. The sparser and regional feedback designs are illustrated with numerical examples.

The Electronics Design of Real-Time Feedback Control System in KTX

A feedback control system has been designed for Keda Torus eXperiment (KTX) to achieve the following goals: 1) 3-D plasma stability control and 2) improvement of plasma discharge quality. The real-time electronics system which is the key unit of this feedback control system helps to resolve the lack of high-speed transmission and real-time processing capability of the previous data acquisition (DAQ) system. The electronics system is implemented in PXI Express using a modular, distributed architecture. Field-programmable gate array (FPGA) is the core component of the electronics system. This article describes in detail the reasons for the choice in the hardware components. Optical communication has been evaluated for real-time communication by using the Aurora protocol. Measurements have been executed on a prototype system. Results from several tests comparing the performance of different solutions are also provided. 2-D spatial Fourier analysis based on FPGA is first used on the reversed field pinch (RFP) fusion device. Results indicate that the system can control the whole process and calculation in low latency.

Real-Time Image-Based Feedback Control of Laser Powder Bed Fusion

Abstract This letter presents the design and experimental validation of a real-time image-based feedback control system for metal laser powder bed fusion (LPBF). A coaxial melt pool video stream is used to control laser power in real-time at 2 kHz. Modeling of the melt pool image response to changes in the input laser power is presented. Based on this identified model, a real-time feedback controller is implemented experimentally on a single track and part scales. On a single-track scale, the controller successfully tracks a time-varying melt pool reference. On a part-level scale, the controller successfully regulates the melt pool image signature to the desired reference value, reducing layer-to-layer signal variation and eliminating within-layer signal drift.

An Investigation into Accuracy, Computation, and Robustness of Stochastic Linearization of Systems with Saturation Nonlinearities

Quasilinear Control (QLC) is a theory with a set of tools that can be used for the analysis and design of stochastic feedback control systems with nonlinear actuators and sensors. It is based on Stochastic Linearization (SL), a method of linearization that approximates a nonlinearity with an equivalent gain and a bias using statistical properties of its input. While the QLC literature has studied many problems in controls (e.g., performance analysis and controller design), important issues such as accuracy, robustness, and computation of SL have not been fully investigated. This paper fills this gap, with a special focus on feedback systems with saturating actuators, which are commonly encountered in feedback control systems and the QLC literature. Specifically, the accuracy of SL in approximating the saturated response is investigated. A mathematical relationship is established between the saturation authority and the worst-case open-loop accuracy, and the implications on closed-loop accuracy are described. To study the robustness of SL in practical situations, the sensitivities of the equivalent SL gain and bias to system parameters are investigated. Finally, several root-finding algorithms are compared in terms of their computational speed in solving the SL equations, and a novel change of coordinates is presented to improve the performance. The results provide valuable insights into and methods for addressing the computational aspects of SL that are critical for proper design and analysis of nonlinear stochastic feedback control systems.

Inverse response behaviour in the bright ring radius measurement of the Czochralski process I: Investigation

This is the first part of a two-article series that deals with the investigation of the anomalous behaviour in the radius measurement signal of the Czochralski (Cz) process and its mitigation in a feedback control system. The inverse or anomalous behaviour is indeed a measurement signal response, which initially is opposite to that of the expected response. This is a crucial and limiting factor in feedback control system design. The paper presents the development of a rigorous 3D ray-tracing method to investigate the inverse response behaviour in the measurement signal. The results of this study provide an insight into the dynamic behaviour of the Cz growth process. It can serve as a guideline for achieving effective crystal radius control, which is addressed in the second part of this article series.

Boundary control design for conservation laws in the presence of measurement disturbances

Boundary feedback control design for systems of linear hyperbolic conservation laws in the presence of boundary measurements affected by disturbances is studied. The design of the controller is performed to achieve input-to-state stability (ISS) with respect to measurement disturbances with a minimal gain. The closed-loop system is analyzed as an abstract dynamical system with inputs. Sufficient conditions in the form of dissipation functional inequalities are given to establish an ISS bound for the closed-loop system. The control design problem is turned into an optimization problem over matrix inequality constraints. Semidefinite programming techniques are adopted to devise systematic control design algorithms reducing the effect of measurement disturbances. The effectiveness of the approach is extensively shown in several numerical examples.

A Reduced-order Model for Real-time NMPC of Ethanol Steam Reformers

One of the approaches to green energy of interest in recent years is through the use of hydrogen technologies in which the waste product of combustion is water rather than carbon dioxide, nitrous oxides, and other pollutants generated by the burning of hydrocarbon fuels. Ethanol steam reformers is one of the primary technologies with the potential to generate hydrogen efficiently and reliably. This article investigates the design of nonlinear optimal feedback control systems for ethanol steam reformers based on mechanistic models described by a system of nonlinear partial differential-algebraic equations, aka singular/descriptor systems. The mechanistic models are too complicated to simulate in real-time using the standard numerical discretization methods, much less to directly incorporate such models as nonlinear constraints into mechanistic model-based nonlinear model predictive control formulations. This article employs a rather sophisticated multivariate form of the method of characteristics to reformulate the nonlinear constraints into a much simpler form amenable to real-time control implementations.

Vibration control of a piezoelectric cantilever smart beam by ℒ 1 adaptive control system

In this paper, the modelling and design of an state feedback control system applied for vibration control of a smart piezoelectric flexible Euler–Bernoulli cantilever beam is presented. For a Single-Input Single-Output (SISO) case by retaining the first two dominant vibratory modes, the dynamics of the system is presented. Classical adaptive control law, with time-varying parameters and in presence of disturbance, is employed to suppress the vibration of the beam. Three Piezoelectric patches, two as actuators and the other as a sensor, are bonded to the structure at the support of the beam and along the length of the beam. The beam structure is modelled in the state space form using the concept of piezoelectric theory, the Euler–Bernoulli beam theory and the Finite Element technique. Also, for comparing the performance of the proposed controller, PID and LQR control systems are applied. Simulation results, first for constant parameters and then for time-varying parameters and disturbance, represent the better performance of the proposed control system in comparison to the other mentioned controllers.

Identification and Control of Counter-traction Mechanism to Finger Traps for Fracture Reduction

Finger traps are a valuable tool that can be maintained the traction. The devices stretch the thumb and other four fingers separately in order to achieve better reduction effect. These are applied individually to the fingers and the limb is suspended, with gravity providing counter-traction to disimpact the fracture by traction. However, personal gravity can’t be used to maintain the appropriate tension. This paper proposed an experimental study on the tension of counter-traction mechanism to finger traps for fracture reduction. This mechanism is particularly useful to help for the patients. Transfer function estimation from experimental data can improve the overall identification performance and the parameter. The feedback control system design for compensating tension that loses from disturbance tension consisted of the controller as PI controller and actuator as DC motor with counter-traction mechanism. Experimental results were demonstrated the efficiency of the proposed system to maintain the appropriate tension.

Proportional-integral-derivative controller parameter optimisation based on improved glowworm swarm optimisation algorithm

The proportional-integral-derivative (PID) controller parameters tuning, is seeking the optimal value in the space of three parameters to achieve the optimal control performance of the system. It is the core of contemporary feedback control system design. However, its easily falling into local optimum weakened its global search ability. To tackle this problem, this paper proposes an improved glowworm swarm optimisation algorithm, (D-AGSO) with the introduction of directed moving and adaptive step strategy. The simulation experimental results show that D-AGSO continuously adapts the tuning parameters, achieving lower fluctuations features, time settling and smaller steady state error, specially applied to the time delay in the case of inertia controlled system of industrial production.

Proportional-integral-derivative controller parameter optimisation based on improved glowworm swarm optimisation algorithm

The proportional-integral-derivative (PID) controller parameters tuning, is seeking the optimal value in the space of three parameters to achieve the optimal control performance of the system. It is the core of contemporary feedback control system design. However, its easily falling into local optimum weakened its global search ability. To tackle this problem, this paper proposes an improved glowworm swarm optimisation algorithm, (D-AGSO) with the introduction of directed moving and adaptive step strategy. The simulation experimental results show that D-AGSO continuously adapts the tuning parameters, achieving lower fluctuations features, time settling and smaller steady state error, specially applied to the time delay in the case of inertia controlled system of industrial production.