Harry C. S. Rughooputh

Elitist multiobjective evolutionary algorithm for environmental/economic dispatch

The environmental/economic dispatch problem is a multiobjective nonlinear optimization problem with constraints. Until recently, this problem has been addressed by considering economic and emission objectives separately or as a weighted sum of both objectives. Multiobjective evolutionary algorithms can find multiple Pareto-optimal solutions in one single run and this ability makes them attractive for solving problems with multiple and conflicting objectives. We use an elitist multiobjective evolutionary algorithm based on the nondominated sorting genetic algorithm-II (NSGA-II) for solving the environmental/economic dispatch problem. Elitism ensures that the population best solution does not deteriorate in the next generations. Simulation results are presented for a sample power system.

Evolutionary multi-objective environmental/economic dispatch: stochastic versus deterministic approaches

Due to the environmental concerns that arise from the emissions produced by fossil-fueled electric power plants, the classical economic dispatch, which operates electric power systems so as to minimize only the total fuel cost, can no longer be considered alone. Thus, by environmental dispatch, emissions can be reduced by dispatch of power generation to minimize emissions. The environmental/economic dispatch problem has been most commonly solved using a deterministic approach. However, power generated, system loads, fuel cost and emission coefficients are subjected to inaccuracies and uncertainties in real-world situations. In this paper, the problem is tackled using both deterministic and stochastic approaches of different complexities. The Nondominated Sorting Genetic Algorithm – II (NSGA-II), an elitist multi-objective evolutionary algorithm capable of finding multiple Pareto-optimal solutions with good diversity in one single run is used for solving the environmental/economic dispatch problem. Simulation results are presented for the standard IEEE 30-bus system.

Performance improvement of spread spectrum spatial-domain watermarking scheme through diversity and attack characterisation

We present a spatial-domain-watermarking scheme for data hiding and copyright protection of still images using the attack characterisation approach. A small number of bits are embedded onto an image in the spatial domain using a method similar to the direct sequence spread spectrum. Perceptual analysis is used to guarantee the imperceptibility of the watermark and proper scaling of the raw mask values maximises the robustness of the watermark, while keeping it imperceptible to the human senses. We add two types of watermarks: reference and robust. The reference watermark is used to assess the way, in which the marked signal has been modified, so that the robust watermark can be optimally extracted. The watermarking system requires two keys; one for generating the pseudo-noise sequence for spread spectrum modulation and another for embedding the two watermarks in a checkerboard arrangement, where the use of the key introduces spatial uncertainty about the location of the watermark bits. This approach has been implemented for a spatial diversity of 64 and 256. Simulation results reveal the effectiveness of the new approach.

Digital chaotic coding and modulation in CDMA

Conventional CDMA system uses PN sequences to spread user information. The number of shift registers used to generate them limit the lengths of these sequences. Good correlation properties can be achieved by Walsh codes and time-shifted version of PN sequences. The ability to predict future sequence is nevertheless possible, though difficult. Transmission therefore is not completely secured. Several other codes (Gold codes, Kasami etc) perform equally well as PN sequences, however it has been reported that these do not improve the security aspect of the system. Hence there is a need for a highly secure code that can be regenerated at the receiver and that can mimic PN sequences for spreading. In this paper, chaotic codes are investigated and their performance compared with the conventional PN sequences in an AWGN and Raleigh fading channel. The other type of spreading code which is the Walsh code uses its orthogonal property for user separation in the channel. This paper also investigates the behaviour of chaotic code in a multi-user situation. The auto and cross correlation properties of the spreading codes are also investigated. Chaotic codes are dependent on initial conditions and are continuous in nature. The undeterministic property of its amplitude from past sequences yields better security. Common modulation techniques (BPSK, QPSK) require higher SNRs to give similar performance in a multi-user environment. The use of QAM in order to improve BER whilst simultaneously inheriting secure property of chaotic codes is also investigated.

Stochastic Evolutionary Multiobjective Environmental/Economic Dispatch

Power system operation is subject to many uncertainties since acquired data are subject to inaccuracies due to inaccuracies in the process of measuring and forecasting of input data and changes of unit performance during the period between measuring and operation. In the environmental/economic dispatch problem, both fuel cost and emission are to be simultaneously minimized. In this paper, in order to obtain a solution closer to real-world situations, a constrained Monte Carlo sampling scheme is considered with stochastic decision variables, power system loads and objective functions whereby NSGA-II is used for solving the resulting stochastic environmental/economic dispatch problem. Simulation results presented for the standard IEEE 30-bus system show that the optimized system is reliable if stochastic variables are correlated.

A fuzzy logic controlled genetic algorithm for optimal electrical distribution network reconfiguration

Electrical distribution network reconfiguration is a complex optimization process aimed at finding a radial operating structure that minimizes the system power loss while satisfying operating constraints. This paper presents the application of a fuzzy controlled real coded genetic algorithm to solve the reconfiguration problem. Two controllers are used to adaptively adjust the crossover and mutation probabilities based on the fitness function. Simulation results are presented for the proposed method which is compared to a genetic algorithm with fixed crossover and mutation probabilities.

Solving the multiobjective environmental/economic dispatch problem with prohibited operating zones using NSGA-II

A thermal or hydro generating unit may have prohibited operating zones due to physical limitations of power plant components caused, for example, by vibrations in a shaft bearing which are amplified in a certain operating region. In this case, the unit can only operate above or below the prohibited operating zone. The effect of prohibited operating zones on the multiobjective environmental/economic dispatch problem is investigated in this paper. The IEEE 30-bus system with transmission losses has been considered with prohibited operating zones and simulation performed using the elitist Nondominated Sorting Genetic Algorithm (NSGA-II) for two constraint handling methods, namely penalty parameterless and decoder-based approaches. Simulation results show that both methods can equally handle this particular scenario in the environmental/economic dispatch problem. Different number of prohibited operating zones was considered for the six generators in the system yielding discontinuous and non-convex non-dominated fronts.

Optimal network reconfiguration of electrical distribution systems

Distribution systems are critical links between the utility and customer, in which sectionalizing switches are utilized for both protection and configuration management. Usually, distribution systems are designed to be most efficient at peak load demand. Obviously, the network can be made more efficient by reconfiguring it according to the variation in load demand. This paper surveys the methods that have been proposed to solve the network reconfiguration problem and presents an integration of two algorithms: a network-topology-based three-phase distribution power flow algorithm and an algorithm for determining power loss of a radial configuration for a power distribution network. Simulation results of the proposed method on a 22 kV Bramsthan section of the CEB network of Mauritius are presented.

Effect of channel coding on the performance of spatial watermarking for copyright protection

We present a spatial-domain-watermarking scheme for data hiding and copyright protection of still images using the attack characterization approach and demonstrate the effect that the application of channel coding has on the watermark detection performance. The scheme uses techniques such as direct sequence spread spectrum modulation, perceptual analysis and diversity to maximize the robustness of the watermark while keeping it imperceptible. Furthermore, Bose-Chaudhuri-Hocquenghem (BCH) block codes and turbo codes are used to provide error protection against attacks in the watermark channel. Simulation results are provided to demonstrate the improved performance when the proposed approach is implemented with and without channel coding. The superiority of turbo codes against BCH block codes is demonstrated and some constraints involving the application of these codes to watermarking are also discussed.

Neural network decoding of turbo codes

Berrou et al. (1993) presented a new class of codes (turbo codes) whose performances in terms of bit error rate (BER) are very close to Shannons limit. Very low BER of 10/sup -5/ at E/sub b//N/sub o/ ratio of 0.7 dB has been achieved using iterative decoding of turbo codes. However, the decoding scheme is characterized by complex receiver structures, high computational costs, and long iterative procedures. In this paper, we describe a neural network decoder for turbo codes. Simulation results reveal that this novel decoder has a performance very close to the maximum a posteriori decoder.