Loop Shaping Controller Research Articles

Active Vibration Control of Beams by Combining Precompressed Layer Damping and ACLD Treatment: Performance Comparison of Various Robust Control Techniques

It is a well known fact that system parameters of the flexible structures keep on changing due to several reasons. Ordinary controllers lose their effectiveness in changed situations and do not guarantee the stability of the closed loop system. However, controllers designed based on robust control theory not only maintain the closed loop stability of the perturbed system with a large variation in system parameters but also maintain the best performance. H∞ loop shaping controller is designed and implemented experimentally on a smart flexible beam treated with precompressed layer damping and ACLD treatment. It outperforms linear quadratic Gaussian and standard H∞ controller both in terms of robust stability and robust performance. Relative merits and demerits of the μ-synthesis based controller are also discussed. Afterwards, these controllers were digitized at certain sampling frequencies and applied to the experimental flexible structure. Certain time domain parameters of the closed loop system discuss the relative superiority of these controllers which otherwise cannot be captured using frequency domain results alone.

State-space solution to weight optimization problem in [formula omitted] loop-shaping control

This paper proposes a state-space solution to weight optimization problem in ℋ∞ loop-shaping control. A pointwise-in-frequency weight optimization framework is transformed into convex optimization searches that are independent of frequency. The introduced optimization problem therefore avoids gridding of the frequency space and consequently, the inaccuracies attributed to fitting transfer functions to magnitude data. In this optimization problem, the order of the weight is specified ‘a priori’, thus facilitating the synthesis of low-order controllers, which is desirable from an implementation perspective. The proposed solution algorithm simultaneously synthesizes a robust stabilizing controller and a loop-shaping weight (pre-compensator) that maximize the robust stability margin subject to constraints on the performance and the singular values of the weight. Three numerical examples are given to illustrate the effectiveness of the technique.

선박용 대형 디젤 기관의 강인 속도 제어기 설계

Abstract: Energy saving is one of the most important factors for profits in marine transportation. In orderto reduce the specific fuel oil consumption, the ship's propulsion efficiency must be increased as much aspossible. The propulsion efficiency depends upon a combination of propulsion engine and propeller that hasbetter efficiency as lower rotational speed. As the engine has lower speed the variation of rotational torquebecome larger because of the longer delay time in fuel oil injection process. In this study, robust control theory is applied to the design of engine speed controllers which are sub-optimal  ∞ controller,  ∞ loop-shaping controller and -synthesis controller considering robust stability and robust performance. Andthe validity of these three controllers is investigated through the results of computer simulation. Key words: Specific fuel oil consumption, Sub-optimal  ∞ control,  ∞ loop-shaping, -synthesis †교신저자(한국해양대학교 해사대학 기관공학부, E-mail: bgjung@hhu.ac.kr, Tel: 051-410-4269)1 MAN Diesel & Turbo2 한국해양수산연수원3 경남정보대학 전자정보계열

Shape Detecting and Shape Control of Cold Rolling Strip

Based on the shape detecting principle and the DSP (Digital Signal Processing) technology, a high-precision shape detecting system of cold rolling strip is developed to meet industrial application. It was successfully used in Angang 1250 mm HC 6-high reversible cold rolling mill. The precision of shape detecting was 0.2 I, the shape deviation was controlled within 6 I after the close loop shape control was input.

Robust control of Cassette Multi-functional Mover for ITER remote handling tasks

The Cassette Multi-functional Mover (CMM) is designed for performing safety-critical divertor cassettes movements in ITER. Therefore, special attention should be paid to the design and analysis of its feedback controllers. Firstly, the design of the multivariable tracking controller possesses many challenges. The hydraulic manipulator dynamics are highly nonlinear; moreover, the loaded mass spans a wide range. Secondly, a number of test runs (even a large number) do not necessarily reveal the controller sensitivity to all the system uncertainties. Thus, some theoretical tools are needed to assess the robustness of the controller. H ∞-based approach is a reasonable choice since it provides a set of metrics to evaluate the controller robustness which can be validated in tests. In this paper, the dynamic model of CMM is first derived, characterizing the nominal system model and the model uncertainties. Then, a multivariable H ∞ loop-shaping controller is synthesized which ensures both the robust stability and robust performance. Finally, the designed controller is validated by simulation results.

A linear matrix inequality approach to parametric H ∞ loop shaping control

The parametric H ∞ loop shaping technique explores more design flexibility by introducing a free parameter that ensures robust stabilization with regard to normalized coprime factor uncertainty of the shaped plant. This paper addresses a design framework for parametric H ∞ loop shaping control using linear matrix inequality (LMI) approach that provides a new set of solvability condition along with the larger feasibility region of solution space over the work of Gu et al. (1999) [6]. An equivalence between the Riccati equation based state-space approach and the proposed LMI framework is established and subsequently, an observer-based structure for parametric H ∞ loop shaping controller has been realized. A numerical example is considered to demonstrate the effectiveness of the proposed method and the results therein are compared with the work of Gu et al. (1999) [6].

Load Varying Polytopic Based Robust Controller Design in LMI Framework for a 2DOF Stabilized Platform

This paper tackles the problem of payload uncertainties through polytopic system formulation and robust controller design for a 2DOF parallel manipulator. Typically, such platforms are used as a base for different payloads, e.g. satellite antenna and camera in oceangoing crafts. Traditionally, these kinds of manipulators are modeled through a time varying nonlinear model, thus providing the rationale for a nonlinear or adaptive controller. Uncertainties due to load variations present a significant challenge for robust control design. In this paper, the authors have proposed a novel and practical approach to solve the variant payload dilemma for the stabilized platform. The novelty lies in extracting different linear models with distinct load conditions using the system identification method and quantifying them into a convex hull to formulate a polytopic system. A regulator is then designed by mixed H 2/H ∞ synthesis with pole-placement constraints in a linear matrix inequality (LMI) framework to compensate output disturbances. The results are compared with a Riccati-based H ∞ loop shaping controller. It is shown through simulations and experiments that an LMI design is a better choice for achieving robustness as well as performance. The hallmark of this work is the successful testing of the control strategy on a stabilized platform with heavy asymmetric satellite antenna to reject the tides’ effect in a deep, turbulent sea.

ROBUST STATE FEEDBACK CONTROL DESIGN VIA PSO-BASED CONSTRAINED OPTIMIZATION

Computational intelligence has been successfully applied to many engineering applications including control engineering problems. In this paper, a robust state feedback control design using particle swarm optimizer based constrained optimization is proposed. The feedback controller is optimized based on state space model of the plant with structured uncertainty such that the closed-loop system would have maximum stability radius. A wedge region is assigned as a constraint to locate the desired closed-loop poles, which correspond to time-domain control system performance. The proposed controller design is applied to anti-swing control for a gantry crane system. The experimental result is shown, and comparison with that of conventional linear quadratic regulator based controller and H ∞ loop shaping controller are made. The proposed method achieves a satisfactory robust performance based on the structured singular value analysis and the experimental results.

Turbofan aero-engine full flight envelope control using H<SUB align=right>∞ loop-shaping control technique

A full flight envelope turbofan aero-engine control is developed by H ∞ loop-shaping control concept in this paper. First, H∞ loop-shaping control concept which is carried out in frequency domain is introduced and used to aero-engine control design. In order to meet the maximum robustness, multi-objective genetic algorithm is proposed creatively to obtain the global optimum loop-shaping weights. Second, considering the finite robustness of H ∞ loop-shaping controller while implementing the task of flight envelope turbofan engine control, the full flight envelope is divided to eight sub-regions and gain-scheduled control system where the sub-region controller could be switched with the change of the engine Mach number and altitude is constructed as the original work. The simulation results show the ability of the proposed control system in tracking the flight command, it is also verified that switching process has only slight effects on the engine condition under the control of the designed flight envelope controller.

Weight optimization for maximizing robust performance in ℋ∞ loop-shaping design

AbstractThis paper proposes a design framework that maximizes the robust performance of a closed-loop system via weight optimization in ℋ∞ loop-shaping control. In line with design objectives, frequency-dependent optimization problems are formulated in LMI framework to maximize robust performance at low and high frequencies, and directly improve the robust stability margin at mid frequencies. The philosophy of the work thus gives the best robust performance that can be achieved on a particular problem once a level of robust stability margin is demanded. Loop-shaping weights and controller are simultaneously synthesized from the proposed algorithm.

Artificial Neural Networks, Adaptive and Classical Control for FTC of Linear Parameters Varying Systems

AbstractThree different schemes for Fault Tolerant Control (FTC) based on Adaptive Control in combination with Artificial Neural Networks (ANN), Robust Control and Linear Parameter Varying (LPV) systems are compared. These schemes include a Model Reference Adaptive Controller (MRAC), a MRAC with an ANN and a MRAC with an H∞ Loop Shaping Controller for 4 operating points of an LPV system (MRAC-4OP-LPV, MRAC-NN4OP-LPV and MRAC-H∞4OP-LPV, respectively). In order to compare the performance of these schemes, a coupled-tank system was used as testbed in which two different types of faults (abrupt and gradual) applied in sensor and actuators in different operating points were simulated. The simulation results showed that the use of ANN in combination with an adaptive controller for LPV-based system improves the FTC scheme, delivering a robust FTC system against abrupt and gradual sensor faults. For actuator faults, the only schemes that were fault tolerant were the MRAC-H∞4OP-LPV and the MRAC-4OP-LPV (i.e. the MRAC-H∞4OP-LPV was fault tolerant for actuator faults varying from 0 to 0.5 of magnitude).

Design of H∞ Loop-Shaping Controller for LTI System With Input Saturation: Polytopic Gain Scheduled Approach

This paper demonstrates the design of H∞ loop-shaping controller for a linear time invariant (LTI) system with input saturation constraint. The design problem has been formulated in the four-block H∞ synthesis framework, which is equivalent to normalized coprime factor robust stabilization problem. The shaped plant is represented as a polytopic linear parameter varying (LPV) system while saturation nonlinearity is considered. For a polytopic model, the LTI H∞ loop-shaping controllers have been designed at each vertex of the polytope using linear matrix inequalities, and subsequently controllers are scheduled by adopting a certain interpolation procedure. The proposed controller ensures the stability and robust L2-performance of the closed-loop system due to vertex property of the polytopic LPV shaped plant. The effectiveness of the design method has been illustrated through a numerical example.

Smooth weight optimization in loop-shaping design

Abstract Smooth variation in the magnitude response of weights facilitates ℋ ∞ loop-shaping design, as it prevents the cancellation of important modes of the system, for example, lightly damped poles/zeros of flexible structures, when the shaped plant is formed based on closed-loop design specifications. For accurate fitting of transfer functions to magnitude data, smooth weights also allow low-order transfer functions to be used when such smooth variations in their magnitude responses are computed point-wise in frequency. In this paper, smoothness constraints for weights, expressed as gradient constraints on a log scale in dB/decade, which is intuitive from a design perspective, are imposed in a weight optimization framework for ℋ ∞ loop-shaping control. This work builds on [A. Lanzon, Weight optimization in ℋ ∞ loop-shaping, Automatica 41 (1) (2005) 1201–1208], where additional constraints are formulated in linear matrix inequality (LMI) form to cast a complete weight optimization framework. The resulting algorithm thus maximizes the robust stability margin and simultaneously synthesizes smooth weights along with a stabilizing controller. A numerical example is given to elucidate the efficacy of the smoothness constraints in ℋ ∞ loop-shaping control.

Unified ${\mathscr H}_\infty$ Control to Suppress Vertices of Plant Input and Output Sensitivity Functions

This note presents a discrete-time H∞ controller to attenuate effects of external disturbances introduced from both plant input and plant output. In this note, two stage control structure is constructed so that state variable dependent conventional controllers and H∞ loop shaping controllers are simultaneously utilized, which is a different approach from previous methods. For the loop shaping controller, a new weighting function derived from an open loop transfer function of fictitious state-feedback systems is proposed. Since the weighting function inherits implicit stability margins, sufficiently stable closed loop systems are designed, therefore well damped transient responses are achieved.

Structure-Specified H∞ Loop Shaping Control for Balancing of Bicycle Robots: A Particle Swarm Optimization Approach

The Particle swarm optimization (PSO) approach is an efficient meta-heuristic search method that can be used to solve the multi-objective and non-convex optimization problems that are normally generated when designing structure-specified H∞ loop shaping controllers. In this study, PSO is used to design the controllers able to balance a bicycle robot, with a model-based systematic procedure for the controller design being proposed. Simulation and experimental results are presented that show that superior robustness and efficiency properties were obtained using the structure-specified H∞ loop shaping controllers compared to those obtained using the proportional plus derivative as well as conventional H∞ loop shaping ones. In comparison with the solutions obtained based on genetic algorithms, the use of PSO has a better efficiency in term of the computational time.

Pre-compensator selection for H ∞ loop shaping control

In this paper, an attempt has been made to address on the design of pre-compensator to obtain the solution of H∞ loop-shaping control problem. Two different design techniques have been proposed where the first one is based on singular value decomposition (SVD) technique along with the matrix perturbation approach; the other one is focused in linear matrix inequality (LMI) framework leading to minimize the condition number of the pre-compensator that, in turn, reduces loop deterioration. A numerical example has been considered to illustrate the effectiveness of the proposed method.

Formula omitted] control of active magnetic suspension

A robust control of an active magnetic suspension requires an accurate plant model and proper model uncertainties. Moreover, the selection of control design performance weighting functions is not straightforward. In this paper, the design of a centralized H ∞ controller of an active magnetic suspension is considered. Two design approaches are examined: an H ∞ loop-shaping control design procedure and a signal-based H ∞ control. The tuning of the design performance functions is carried out applying a genetic algorithm. The robust stability of the gain-scheduled H ∞ controller is verified in the presence of real parametric and non-parametric frequency-dependent uncertainties. Accurate models of the system and its uncertainties can be obtained using engineering models and frequency response functions of the test-rig. Finally, simulations and experimental results confirm the effectiveness of the signal-based H ∞ approach.

Application of electrolyzer system to enhance frequency stabilization effect of microturbine in a microgrid system

Abstract It is well known that the power output of microturbine can be controlled to compensate for load change and alleviate the system frequency fluctuations. Nevertheless, the microturbine may not adequately compensate rapid load change due to its slow dynamic response. Moreover, when the intermittent power generations from wind power and photovoltaic are integrated into the system, they may cause severe frequency fluctuation. In order to study the fast dynamic response, this paper applies electrolyzer system to absorb these power fluctuations and enhance the frequency control effect of microturbine in the microgrid system. The robust coordinated controller of electrolyzer and microturbine for frequency stabilization is designed based on a fixed-structure H ∞ loop shaping control. Simulation results exhibit the robustness and stabilizing effects of the proposed coordinated electrolyzer and microturbine controllers against system parameters variation and various operating conditions.

Robot-assisted Active Catheter Insertion: Algorithms and Experiments

Angioplasty is a frequently performed clinical procedure in which a catheter is inserted into a blood vessel under image guidance to open narrowed or blocked arteries and to allow normal blood flow to resume. This paper is concerned with the development of algorithms for a robot-assisted method for a more accurate, safer and more reliable approach for catheter insertion that can reduce the potential for injury to patients and radiation exposure or discomfort to clinicians. A force control algorithm is presented for a robot to control the force of insertion of a catheter and prevent the catheter from buckling or “bunching up” during insertion. In addition, the paper also describes a master—slave control strategy to precisely control the bending angle of the tip of an active catheter instrumented with Shape Memory Alloy (SMA) actuators. A novel model for SMAs and a robust H∞ loop-shaping controller have been implemented to guarantee robust performance of the active catheter. The algorithms for catheter insertion developed in this paper may help to prevent damage to the epithelial cells of an artery and enable easier guidance of the catheter into appropriate branches. In addition, a robotics-based approach could make it possible for a clinician to remotely perform the insertion of the active catheter from a safe and comfortable environment, thereby reducing exposure to harmful X-ray radiation. Experimental results are presented to illustrate the performance of the algorithms.

Missile Autopilot Design: Gain-Scheduling and the Gap Metric

This paper presents a systematic methodology for the synthesis of global gain-scheduled controllers for nonlinear time-varying systems. A controller of this type is used to compute the pitch-axis autopilot of an air-air missile. The missile model used is considered a benchmark for testing autopilot controllers in the academic and industrial communities. The missile's dynamics are linearized at a small set of operating points for which proportional― integral/proportional-type controllers are designed, to shape the frequency response of the linear plants' dynamics. A new set of operating points is computed afterward using the connection between the gap metric and the H ∞ loop-shaping theory. Then, reduced-order, static, H ∞ loop-shaping controllers are designed for this set of points using linear matrix inequality optimization techniques. Finally, the global gain-scheduled controller is obtained by interpolating the proportional―integral/proportional and the loop-shaping controllers' gains over the missile's flight envelope. The simulation results given show the generality and effectiveness ofthe proposed control strategy in terms of the operating point selection, stability, performance and robustness, of the closed loop.