Robust Hinfin Control Research Articles

Robust Control Technique in an Autonomous Microgrid: A Multi-stage $$H\infty$$ Controller Based on Harmony Search Algorithm

Microgrid (MG) control in off-grid mode of operation is one of the main challenges in MGs. Under different loading conditions, voltage and frequency deviate from their nominal limits. The droop control method that applied with the current control and voltage control loops can restore the MG voltage and frequency to their nominal limits. However, it can’t regulate these parameters to their specified values. Additionally, the droop control method can’t do well when the system supplies either nonlinear or unbalanced loads. This paper proposes a control technique for adjusting the voltage and frequency of an MG in islanded mode under different loading conditions. The proposed method is based on applying the H-infinity ($$H\infty$$) robust control as a secondary controller with the droop control method to improve its performance. The proposed method is composed of four stages including; droop control loop, voltage control loop, current control loop and control loop for inductance–capacitance–inductance (LCL) filter and coupling circuit. $$H\infty$$ control has an internal model that can control the frequency and improve the system power quality by decreasing the disturbance frequencies. Moreover, it has two weighted parameters $$\xi$$ and $$\mu$$ that must be correctly adjusted to improve the stability of the system. For a proper adjusting of these parameters, the Harmony Search (HS) optimization method is applied. To prove the effectiveness and superiority of the proposed method, it is applied on a test system with three different loading scenarios using MATLAB/Simulink program. The results are compared with those of droop controller and they confirm that the proposed control method is more effective in controlling the microgrids under islanded mode operation.

Master-slave H-Infinity robust controller design for synchronization of chaotic systems

This paper is devoted to robust master-slave controller design for generalized chaotic systems synchronization. The closed-loop system is asymptotically stable when the robust stability conditions hold and while the H-Infinity norm of the closed-loop transfer function with respect to defined output and input is strictly less than gamma>0. In this paper a modified L2 gain approach is used and an original design procedure is proposed to decrease the conservativeness of the former method. The effectiveness of the proposed method is shown in numerical examples.

Design and Implementation of DSP-Based H-Infinity Robust Controller for a Boost Converter

This work consists in synthesizing a H-infinity robust controller in a DC-DC Boost converter to minimize the system’s power loss effects on the converter output voltage. These power losses are caused by the uncertainties on the converter such as induction, switching and capacitive losses, which interferes directly on the converter duty-cycle. As the uncertainties, the power source and the output resistance variations also interferes on the converter output voltage. The main objective of the controller is to maintain the load voltage constant output regardless of these losses. Simulation results are performed in order to compare the stability, robustness and dynamics of the robust controller with a simple Proportional and Integrative controller. The H-infinity robust controller was implemented in a Digital Signal Processor and tested in a DC-DC boost converter in order to validate and confirm the performance, efficiency, transient response speed and robustness.

The robust H-infinity control of UUV with Riccati equation solution interpolation

The main purpose of this study was to develop a method for a robust H-infinity control of an unmanned underwater vehicle (UUV) based on the interpolation of the Riccati equation solution. This method combined the robust H-infinity control theory and results of the interpolation of the Riccati equation solution. The UUV's velocity, heading, and depth controllers were derived and obtained. A simulation and experiment in a lake were conducted to verify the effectiveness of the developed controllers. Results indicated that the controllers were feasible, effective, and robust in managing the control of a UUV.

Active vibration robust control for FGM beams with piezoelectric layers

The dynamic output-feedback robust control method based on linear matrix inequality (LMI) method is presented for suppressing vibration response of a functionally graded material (FGM) beam with piezoelectric actuator/sensor layers in this paper. Based on the reduced model obtained by using direct mode truncation, the linear fractional state space representation of a piezoelectric FGM beam with material properties varying through the thickness is developed by considering both the inherent uncertainties in constitution material properties as well as material distribution and the model error due to mode truncation. The dynamic output-feedback robust H-infinity control law is implemented to suppress the vibration response of the piezoelectric FGM beam and the LMI method is utilized to convert control problem into convex optimization problem for efficient computation. In numerical studies, the flexural vibration control of a cantilever piezoelectric FGM beam is considered to investigate the accuracy and efficiency of the proposed control method. Compared with the efficient linear quadratic regulator (LQR) widely employed in literatures, the proposed robust control method requires less control voltage applied to the piezoelectric actuator in the case of same control performance for the controlled closed-loop system.

Robust tracking and distributed synchronization control of a multi-motor servomechanism with H-infinity performance

The multi-motor servomechanism (MMS) is a multi-variable, high coupling and nonlinear system, which makes the controller design challenging. In this paper, an adaptive robust H-infinity control scheme is proposed to achieve both the load tracking and multi-motor synchronization of MMS. This control scheme consists of two parts: a robust tracking controller and a distributed synchronization controller. The robust tracking controller is constructed by incorporating a neural network (NN) K-filter observer into the dynamic surface control, while the distributed synchronization controller is designed by combining the mean deviation coupling control strategy with the distributed technique. The proposed control scheme has several merits: 1) by using the mean deviation coupling synchronization control strategy, the tracking controller and the synchronization controller can be designed individually without any coupling problem; 2) the immeasurable states and unknown nonlinearities are handled by a NN K-filter observer, where the number of NN weights is largely reduced by using the minimal learning parameter technique; 3) the H-infinity performances of tracking error and synchronization error are guaranteed by introducing a robust term into the tracking controller and the synchronization controller, respectively. The stabilities of the tracking and synchronization control systems are analyzed by the Lyapunov theory. Simulation and experimental results based on a four-motor servomechanism are conducted to demonstrate the effectiveness of the proposed method.

Robust control of dielectric elastomer diaphragm actuator for human pulse signal tracking

Human pulse signal tracking is an emerging technology that is needed in traditional Chinese medicine. However, soft actuation with multi-frequency tracking capability is needed for tracking human pulse signal. Dielectric elastomer (DE) is one type of soft actuating that has great potential in human pulse signal tracking. In this paper, a DE diaphragm actuator was designed and fabricated to track human pulse pressure signal. A physics-based and control-oriented model has been developed to capture the dynamic behavior of DE diaphragm actuator. Using the physical model, an H-infinity robust control was designed for the actuator to reject high-frequency sensing noises and disturbances. The robust control was then implemented in real-time to track a multi-frequency signal, which verified the tracking capability and robustness of the control system. In the human pulse signal tracking test, a human pulse signal was measured at the City University of Hong Kong and then was tracked using DE actuator at Wichita State University in the US. Experimental results have verified that the DE actuator with its robust control is capable of tracking human pulse signal.

Robust H-infinity Control of Discrete Time-delay Generalized System with Saturating Actuator

Robust H-infinity Control of Discrete Time-delay Generalized System with Saturating Actuator

Robust H-infinity Control of Building Structures with Time Delay

Robust H-infinity Control of Building Structures with Time Delay

Synthesis of Distributed Robust H-Infinity Controllers for Interconnected Discrete Time Systems

This paper presents an algorithm for the synthesis of robust distributed controllers for interconnected linear discrete-time systems. For a network of interconnected uncertain linear time-invariant systems, the distributed controller achieves robust stability and a guaranteed level of robust performance in a well-defined H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> sense. The setting of this paper is in discrete time. Based on the theory of dissipative dynamical systems, conditions for the analysis of robust stability and robust performance of networks are derived in terms of feasibility tests of linear matrix inequalities. From these conditions, computationally tractable synthesis conditions are derived. An iterative D-K type of synthesis algorithm is proposed that yields a robust distributed controller. Convergence properties of the algorithm are inferred.

Field Programmable Gate Array Implementation of Active Control Laws for Multi-mode Vibration Damping

A B S T R A C T This paper investigates the possibility and effectiveness of multi-mode vibration control of a plate through real-time FPGA (Field Programmable Gate Array) implementation. This type of embedded system offers true parallel and high throughput computation abilities. The control object is an aluminum panel, clamped to a Perspex box’s upper side. Two types of control laws are studied. The first belongs to non-model based control. This control law is designed to generate active damping within the designed bandwidth. The second control law is model based H-infinity robust control. A system identification process is needed before the controller comes out. Each of the control laws is implemented on a FPGA target, which is powerful enough to achieve high throughput control loop rates. The experimental control results demonstrate that the non-model based control law has sufficient authority to suppress the interesting modes. The model-based robust control law’s control performance is not so positive compared to the previous method. Therefore, it is not recommended for this application.

Robust H-infinity control for a class of neutral-type systems via sliding mode observer

In this paper, the problem of observer-based H-infinity integral sliding mode control (ISMC) is investigated for a class of uncertain neutral-type systems with time delay (NTSTD). An ISMC strategy is put forward based on the sliding mode observer. A new sufficient condition of robust asymptotic stability for the overall systems composed of the error system and sliding mode dynamics with disturbance attenuation level is derived via linear matrix inequality (LMI). Then, a SMC law is designed such that the reachability of the sliding surface defined in the state-estimate space can be guaranteed. Finally, a simulation example is presented to demonstrate the feasibility of the obtained result.

Robust H-Infinity Control for a Premium Pricing Model With a Predefined Portfolio Strategy

In this paper, the robust H-infinity (H∞) control problem for a premium pricing process is investigated with parameters uncertainty. A previous model is modified by taking into account a predefined risky investment strategy. A robust H∞ control problem for the reserve process is proposed using linear matrix inequality (LMI) criteria. Attention is focused on the design of a state feedback controller such that the resulting closed-loop system is robustly stochastically stable with disturbance attenuation level γ&amp;gt;0. Finally, a numerical example with colorful figures and tables based on the data from the Shanghai Stock Exchange market is provided illustrating clearly the impact of risky investment in the system. The MATLAB LMI Control toolbox is used for the numerical calculations.

Robust H-infinity Control for Stochastic Markovian Switching Systems Under Partly Known Transition Probabilities and Actuator Saturation via Anti-Windup Design

This paper deals with the problem of robust H-infinity control for stochastic Markovian switching systems with partly known transition probabilities and actuator saturation via anti-windup design. Under the assumption that output feedback controllers have been built to stabilize the stochastic Markovian switching system, anti-windup compensators are designed to expand the domain of attraction of the corresponding closed-loop system that contains admissible external disturbance, $$\hbox {It}\hat{o}$$Ito^-type stochastic disturbance, and norm-bounded parameter uncertainties. The procedure of deriving anti-windup compensation gain matrices is converted into an optimization problem with constraints of a set of linear matrix inequalities. Finally, numerical examples are given to demonstrate the validity of the main results.

A novel particle swarm optimization based robust H-infinity control for rotorcrafts

Purpose– The purpose of this paper is to present a novel optimization approach to design a robust H-infinity controller.Design/methodology/approach– To use a modified particle swarm optimization (PSO) algorithm and to search for the optimal parameters of the weighting functions under the circumstance of the given structures of three weighting matrices in the H-infinity mixed sensitivity design.Findings– This constrained multi-objective optimization is a non-convex, non-smooth problem which is solved by a modified PSO algorithm. An adaptive mutation-based PSO (AMBPSO) algorithm is proposed to improve the search accuracy and convergence of the standard PSO algorithm. In the AMBPSO algorithm, the inertia weights are modified as a function with the gradient descent and the velocities and positions of the particles.Originality/value– The AMBPSO algorithm can efficiently solve such an optimization problem that a satisfactory robust H-infinity control performance can be obtained.

A robust H-infinity controller design approach for neutral systems with time-varying delay and plant and controller uncertainties

This paper is concerned with a state feedback controller design method for neutral systems with a time-varying delay, considering uncertainties in the plant parameters, as well as in controller gain. The uncertainties are in additive form, affecting both the system matrices of the plant and the controller gain. The uncertainties that are assumed admissible are time-varying and norm-bounded. The neutral system is also subject to external disturbances. A robust stabilizing H-infinity state-feedback controller is synthesized under several conditions that are presented in the form of matrix inequalities. A new generalized type of Jensen integral inequality has been introduced for utilization in the derivation of the aforementioned results, which could thus have been relaxed via that approach. A feasible solution set is obtained using the well-known cone complementarity technique by solving a non-linear minimization problem subject to linear matrix inequalities. A numerical example with case studies concludes the present work. The results of the minimum achievable attenuation rate indicate considerable improvement in comparison with those reported in the literature.

An efficient reliability method for probabilistic H-infinity robust control of uncertain linear dynamic systems

Achieving balance between robustness and performance is always a fundamental challenge we are faced with in control design of systems in the presence of uncertainties. H∞ robust control theory has been extensively used to deal with the problems of robust stabilization and disturbance attenuation of uncertain systems. However, in traditional H∞ robust control, the most frequently used method for dealing with uncertainties is adopting the assumption of norm-bounded perturbations of arbitrary structure about a nominal plant and the design techniques are based on the deterministic worst-case scenarios that may never occur in a particular control system and thus often led to over-conservative results. In this paper we focus on developing a reliability method for probabilistic H∞ robust control of linear uncertain systems by describing the uncertain parameters as random variables. A new efficient reliability method for robust control of dynamic systems with probabilistic parametric uncertainties is presented systematically. Robust control design is carried out by solving a reliability-based optimization problem where the disturbance attenuation and control cost are minimized under the condition that reliability requirement is satisfied. One of the advantages of the presented reliability method is that it can be used directly for robust control design of parametric uncertain systems. Another advantage of the presented method is that it makes it possible to consider the factors such as system performance, control cost, and reliability simultaneously in an integrated framework and provides an essential basis for the coordination and tradeoffs between these important factors in control design of uncertain systems. Compared to traditional H∞ robust control, the presented method is less-conservative and more reasonable for dealing with probabilistic uncertainties. The presented formulations are within the framework of linear matrix inequality and thus can be carried out conveniently. Two numerical examples are investigated to demonstrate the effectiveness and feasibility of the presented method.

Robust control of exciting force for vibration control system with multi-exciters

Due to the dynamical character of electromagnetic exciter and the coupling between structure and exciter(s), the actual output force acting on the structure is usually not equal to the exact value that is supposed to be, especially when multi-exciters are used as actuators to precisely actuate large flexible structure. It is necessary to consider these effects to ensure the force generated by each exciter is the same as required. In this paper, a robust control method is proposed for the multi-input and multi-output (MIMO) structural vibration control system to trace the target actuating force of each exciter. A special signal is designed and put into the coupled mul-ti-exciter-structure system, and the input and output signals of the system are used to build a dynamic model involving both the dynamical characters of the exciters and the structure using the subspace identification method. Considering the uncertainty factors of the multi-exciter/structure system, an H-infinity robust controller is designed to decouple the coupling between structure and exciters based on the identified system model. A MIMO vibration control system combined with a flexible plate and three electromagnetic exciters is adopted to demonstrate the proposed method, both numerical simulation and model experiments showing that the output force of each exciter can trace its target force accurately within the requested frequency band.

H∞-Optimal Control for Robust Financial Asset and Input Purchasing Decisions

This analysis formulates an approach for converting minimax LQ (linear-quadratic) tracking problems into LQ regulator designs, and develops a Matlab application program to calculate an H-infinity robust control for discrete-time systems with perfect state measurements. It uses simulations to explore examples in financial asset decisions and utility input purchasing, in order to demonstrate the method. The user is allowed to choose the parameters, and the program computes the generalized Riccati Equation conditions for the existence of a saddle-point solution. Given that it exists, the program computes a minimax solution to the linear quadratic (LQ) soft-constrained game with constant coefficients for a general scalar model, and also to a class of matrix systems. The user can set the bound to achieve disturbance attenuation.

A Robust H-infinity Control Approach of Uncertain Tractor Trailer System

This paper proposes a robust H-infinity control strategy for a differential drive Tractor with a single Trailer unit. This articulated vehicle being a complicated non holonomic system, the number of control inputs is less compared to the number of generalized coordinates. A linearized nominal model for this system is obtained by combining the kinematics and dynamics. A robust H-infinity output feedback control is designed using mu synthesis for the nominal plant when subjected to model uncertainties in unstructured form and output disturbances. Analysis on the robust uncertain closed-loop system is performed in both time and frequency domains. The simulation results indicating satisfactory stability and performance are presented. The step response and reference tracking are also found to be satisfactory.