M. Aldeen

Load-frequency control of interconnected power systems via constrained feedback control schemes

Abstract In this paper a method is presented for the derivation of output feedback and decentralized proportional-plus-integral (PI) controllers suitable for the load-frequency control of interconnected power systems. The controller design method is based on the solution of a standard state feedback optimal control problem, but with some constraints imposed on the structure of the feedback gain matrix. A two-area interconnected power system (TAIPS) is used as an example to illustrate the effectiveness of the proposed method. Simulation results show that the performances of the controllers obtained in this paper compare favourably with reported ones.

Computer-Aided Diagnosis of Melanoma Using Border- and Wavelet-Based Texture Analysis

This paper presents a novel computer-aided diagnosis system for melanoma. The novelty lies in the optimized selection and integration of features derived from textural, border-based, and geometrical properties of the melanoma lesion. The texture features are derived from using wavelet-decomposition, the border features are derived from constructing a boundary-series model of the lesion border and analyzing it in spatial and frequency domains, and the geometry features are derived from shape indexes. The optimized selection of features is achieved by using the gain-ratio method, which is shown to be computationally efficient for melanoma diagnosis application. Classification is done through the use of four classifiers; namely, support vector machine, random forest, logistic model tree, and hidden naive Bayes. The proposed diagnostic system is applied on a set of 289 dermoscopy images (114 malignant, 175 benign) partitioned into train, validation, and test image sets. The system achieves an accuracy of 91.26% and area under curve value of 0.937, when 23 features are used. Other important findings include 1) the clear advantage gained in complementing texture with border and geometry features, compared to using texture information only, and 2) higher contribution of texture features than border-based features in the optimized feature set.

On the stability of linear systems with delayed perturbations

This note presents sufficient conditions for delay-independent asymptotic stability for linear systems with delayed perturbations. These conditions are shown to be less restrictive than those reported in the literature. Numerical examples are given to illustrate the results. >

A memoryless state observer for discrete time-delay systems

This paper presents a reduced-order memoryless state observer with a /spl gamma/-stability margin (0</spl gamma/<1) for linear discrete-time systems with multiple delays in both the state and control vectors. The dynamics of the observer are derived from a set of unstable and/or poorly damped eigenvalues of the system. A simple and systematic design method is presented. A numerical example is given to illustrate the properties of the new observer and its design method.

Partial Feedback Linearizing Excitation Controller for Multimachine Power Systems to Improve Transient Stability

In this paper a new nonlinear excitation controller design to enhance transient stability of multimachine power systems is presented. Partial feedback linearization is first used to transform the nonlinear power system model into a partially linear system comprising a reduced-order linear part and a nonlinear dynamic autonomous part. Then a linear state feedback stabilizing controller is designed for the reduced-order linear part using optimal control theory to enhance the stability of the whole system. In this way, the performance of the stabilizing controller would be independent of the operating points of the power system and therefore is superior to those designed for completely linearized systems. It is shown that the controller design method ensures the stability of the nonlinear dynamic autonomous part. The design method is applicable to multimachine power systems but tested on a 3-machine 11-bus two-area test system. The performance of the proposed control scheme to large disturbances is evaluated, through computer simulation, and compared with a conventional power system stabilizer and an exact feedback linearizing controller.

A comment on "Decentralized stabilization of large scale interconnected systems with delays"

Hu claims new results in the above mentioned paper (ibid. vol.39, no.1, p.180-2 (1994)) regarding decentralized stabilization of large scale interconnected systems with delays. This note shows that the results presented in Theorems 1 and 2 and Corollaries 1 and 2 apply only to a very restrictive class of systems for which the number of inputs and outputs is equal to the number of states. An alternative stability condition is provided, which improves the existing one. >

Estimation of states, faults and unknown disturbances in non-linear systems

In this paper, we extend existing theory on non-linear unknown input observer design to a wider class of non-linear systems where the systems are subject to unknown input and output disturbances and experience faults. The approach used is to decouple the faults and unknown disturbances from the rest of the system through a series of transformations on state and output equations. Once total disturbance decoupling is achieved, an appropriate observer for the disturbance free part of the non-linear system is proposed and designed. The designed observer is, subsequently, used for estimation of unknown inputs, outputs, and fault signals. Two examples are given for illustration.

Robust Control for Power Sharing in Microgrids With Low-Inertia Wind and PV Generators

This paper presents a robust control design scheme for a multidistributed energy resource (DER) microgrid for power sharing in both interconnected and islanded modes. The scheme is proposed for micgrogrids consisting of photovoltaic (PV) units and wind turbine driven doubly fed induction generators (DFIGs). A battery is integrated with each of the wind and solar DER units. The control scheme has two levels: 1)one centralized multi-inputmulti-output robust controller for regulating the set reference active and reactive powers and 2)local real and reactive power droop controllers, one on each DER unit. The robust control scheme utilizes multivariable H∞ control to design controllers that are robust to the changes in the network and system nonlinearities. The effectiveness of the proposed controller is demonstrated through large-disturbance simulations, with complete nonlinear models, on a test microgrid. It is found that the power sharing controllers provide excellent performance against large disturbances and load variations during islanding transients and interconnected operation.

Stabilization of uncertain dynamic delay systems by memoryless feedback controllers

Methods are presented for the synthesis of simple centralized and decentralized memoryless feedback controllers that guarantee asymptotic stability of uncertain time-delay systems and uncertain interconnected time-delay systems, respectively. The methods allow the controllers to be synthesized using simple formulae. Numerical examples are given to illustrate the results.

On robustness and stabilization of linear systems with delayed nonlinear perturbations

In this paper, by employing a Razumikhin-type theorem, a robust stability criterion for a class of linear systems subject to delayed time-varying nonlinear perturbations is given. Then, stabilization of a class of linear systems subject to mismatched delayed time-varying nonlinear perturbations by linear controller is considered. For such systems, conditions which ensure closed-loop asymptotic stability are given. Numerical examples are given to illustrate the results.