Allahyar Montazeri

Design and comparison of LQG/LTR and H∞ controllers for a VSTOL flight control system

In this paper two robust controllers for a multivariable vertical short take-off and landing (VSTOL) aircraft system are designed and compared. The aim of these controllers is to achieve robust stability margins and good performance in step response of the system. LQG/LTR method is a systematic design approach based on shaping and recovering open-loop singular values while mixed-sensitivity H-infinity method is established by defining appropriate weighting functions to achieve good performance and robustness. Comparison of the two controllers show that LQG method requires rate feedback to increase damping of closed-loop system, while H-infinity controller by only proper choose the weighting functions, meets the same performance for step response. Output robustness of both controllers is good but H-infinity controller has poor input stability margin. The net controller order of H-infinity is higher than the LQG/LTR method and the control effort of them is in the acceptable range. (c) 2006 The Franklin Institute. Published by Elsevier Ltd. All rights reserved.

A new adaptive recursive RLS-based fast-array IIR filter for active noise and vibration control systems

Infinite impulse response filters have not been used extensively in active noise and vibration control applications. The problems are mainly due to the multimodal error surface and instability of adaptive IIR filters used in such applications. Considering these, in this paper a new adaptive recursive RLS-based fast-array IIR filter for active noise and vibration control applications is proposed. At first an RLS-based adaptive IIR filter with computational complexity of order O(n^2) is derived, and a sufficient condition for its stability is proposed by applying passivity theorem on the equivalent feedback representation of this adaptive algorithm. In the second step, to reduce the computational complexity of the algorithm to the order of O(n) as well as to improve its numerical stability, a fast array implementation of this adaptive IIR filter is derived. This is accomplished by extending the existing results of fast-array implementation of adaptive FIR filters to adaptive IIR filters. Comparison of the performance of the fast-array algorithm with that of Eriksons FuLMS and SHARF algorithms confirms that the proposed algorithm has faster convergence rate and ability to reach a lower minimum mean square error which is of great importance in active noise and vibration control applications.

The use of ‘particle swarm’ to optimize the control system in a PZT laminated plate

In many active noise and vibration control systems it is desired to reduce the vibration and also the noise emitted by flexible structures. With this objective the task of the controller is to control the maximum number of modes allowed by the control systems limitations. Some of the key parameters in the control system design for this purpose are the location, number and size of actuators and sensors on a flexible structure. In this paper a simply-supported thin plate with laminated piezoelectric sensors and actuators is studied for noise and vibration attenuation. For this purpose, a performance index based on Hankel singular values of the system is selected. The resulting nonlinear optimization problem is solved using a new particle swarm optimization (PSO) algorithm. The results are compared with a genetic algorithm and verified with a simple state-feedback controller.

Nonlinear Model Predictive Control of Chemical Processes with a Wiener Identification Approach

Some chemical plants such as pH neutralization process have highly nonlinear behavior. Such processes demand a powerful Wiener identification approach based on neural networks for identification of the nonlinear part. In this paper, the pH neutralization process is identified with NN-based Wiener identification method and two linear and nonlinear model predictive controllers with the ability of rejecting slowly varying unmeasured disturbances are applied. Simulation results show that the obtained Wiener model has good capability to predict the step response of the process. Parameters of both linear and nonlinear model predictive controllers are tuned and the best obtained results are compared. For this purpose, different operating points are selected to have a wide range of operation for the nonlinear process. Simulation results show that the nonlinear controller has better performance without any overshoot in comparison with linear MPC and also less steady-state error in tracking the set-points.

Optimal placement of loudspeakers and microphones in an enclosure using genetic algorithm

In this paper genetic algorithm has been used for optimal placement of loudspeakers and microphones in an experimental enclosure for active noise control system. A control system with two secondary loudspeakers and four error microphones is used to reduce the potential energy generated by primary source in a frequency range of 50 Hz to 300 Hz. By choosing the average of potential energy in this frequency range as a performance index, genetic algorithm is used to find the global minimum of this function. This performance index is a function of the locations of microphones and loudspeakers, hence a configuration of them corresponds to a value for this performance index. In this genetic algorithm a multivariable binary coding scheme along with a random initial population are used. Computation of the potential energy, and also the acoustical pressure pattern in a specified level shows that the locations obtained by genetic algorithm are very effective in the results.

A Computationally Efficient Adaptive IIR Solution to Active Noise and Vibration Control Systems

In spite of special advantages of IIR filters in active noise and vibration control (ANVC) applications, the multimodal error surface and instability problem of adaptive IIR filters has prevented its extensive use. To alleviate these problems, in this paper, a new RLS-based fast array adaptive IIR filters in ANVC applications is proposed. The algorithm is developed with slow adaptation assumption and by transforming the active noise and vibration control problem to an output-error identification problem. By derivation of the fast-array equivalent form both computational complexity and numerical stability of the proposed algorithm are improved. The geometrical illustration of the algorithm, in a simple case, is also given to unify and complete its mathematical formulation. In spite of low computational complexity of the order , simulation results confirm high convergence speed of the proposed algorithm and also its ability to reach the lower minimum mean square error in comparison with commonly used adaptive IIR algorithms in ANVC systems.

Design and Analysis of Robust Minimax LQG Controller for an Experimental Beam Considering Spill-Over Effect

In this brief the design and analysis of an optimal robust minimax linear quadratic Gaussian (LQG) control of vibration of a flexible beam is studied. The analysis is performed by transforming the minimax LQG control design problem to its equivalent mixed sensitivity design problem. The first six modes of the beam in the frequency range of 0-700 Hz are selected for control purpose. Among these modes, three modes in the frequency range of 100-400 Hz are used for control, while the other three modes are left as the uncertainty of modeling. Both the model and the uncertainty are measured based on experimental data. The nominal model is identified from frequency response data and the uncertainty is presented by frequency weighted multiplicative modeling method. For the augmented plant consisting of the nominal model and its accompanied uncertainty, a minimax LQG controller is designed. Analysis and tradeoff between robust stability and robust performance is shown by selecting two different choices of uncertainty modeling. Simulation results used to show how the uncertainty weights can be tuned so that the proposed robust controller increase the damping of the system in its resonance frequencies and maintain the robust stability of the feedback system at the same time.

Modal analysis for global control of broadband noise in a rectangular enclosure

Modal analysis for examination of the possibility of the global reduction of broadband noise in a rectangular enclosure has been studied in this paper. By developing a modal model of the acoustic environment of the enclosure the shape modes and their frequencies are obtained and on suitable bandwidth for the controller design is calculated. In order to simplify the analysis the noise sources are assumed localized and internal in one corner of the kiosk. The analysis results show that due to the existence of some degenerate modes in this application, the control action is complicated. Simulation results demonstrate how positions and number of loudspeakers and microphones will change the performance of the controller and its corresponding control effort. Based on these results and analysis a reasonable size for the controller and proper locations for sensors and actuators are proposed. Simulation results also confirm the effectiveness of the proposed system in reduction of the acoustic potential energy in the kiosk.

Modeling and Eigenfrequency Analysis of Sound-Structure Interaction in a Rectangular Enclosure with Finite Element Method

Vibration of structures due to external sound is one of the main causes of interior noise in cavities like automobile, aircraft, and rotorcraft, which disturb the comfort of passengers. Accurate modelling of such phenomena is required in eigenfrequency analysis and in designing an active noise control system to reduce the interior noise. In this paper, the effect of periodic noise travelling into a rectangular enclosure is investigated with finite element method (FEM) using COMSOL Multiphysics software. The periodic acoustic wave is generated by a point source outside the enclosure and propagated through the enclosure wall and excites an aluminium flexible panel clamped onto the enclosure. The behaviour of the transmission of sound into the cavity is investigated by computing the modal characteristics and the natural frequencies of the cavity. The simulation results are compared with previous analytical and experimental works for validation and an acceptable match between them were obtained.

A Novel Technique for Design and Stability Analysis of Adaptive IIR Filters in ANVC Aplications

The use of IIR filters instead of FIR filters in active noise and vibration control applications has some special advantages. However, multimodal error surface and instability problem of adaptive IIR filters has prevented its extensive use like FIR filters, and hence invokes more research on these subjects. In this paper, a new approach to design and stability analysis of adaptive IIR filters in active noise and vibration control applications, is proposed. The approach is based on transforming the ANVC problem to an output-error identification problem and the conditions for stability are derived using Popov hyperstabilty theory. The performance of the algorithm is compared to that of the Erriksons FuLMS and SHARF algorithms, and it is shown that the proposed algorithm has a faster convergence rate and the ability to converge to global optimum of filter weights.