A Multi-Model Approach to Design a Robust Fixed-Order Controller to Improve Power System Stability

The rapid increase in power system grid has resulted in additional challenges to reliable power transfer between interconnected systems of a large power network. Large-scale penetration of intermittent renewable energy increases uncertainty and variability in power systems operation. For secure operation of power systems under conditions of variability, it is imperative that power system damping controllers are robust. Electromechanical oscillations in the range of 0.2 Hz to 1 Hz are categorized as inter-area modes. These modes arise due primarily to the weak interconnections characterized by long transmission lines between different operating areas of an interconnected power system. One of the main challenges to secure operation of interconnected power systems is the damping of these inter-area modes. This dissertation introduces two multi-model approaches (loop shaping and H∞) to designing a fixed-order robust supplementary damping controller to damp inter-area oscillations. The designed fixed-order supplementary damping controller adjusts the voltage reference set point of the Static Var Compensator (SVC). The two main objectives of the controller design are damping low-frequency oscillations and enhancing power system stability. The proposed approaches are based on the shaping of the open-loop transfer function in the Nyquist diagram through minimizing the quadratic error between the actual and the desired open-loop transfer functions in the frequency domain. The H∞ constraints are linearized with the help of a desired open-loop transfer function. This condition can be achieved by using convex optimization methods. Convexity of the problem formulation ensures global optimality. One of the advantages of the proposed approach is the consideration of multi-model uncertainty. Also, in contrast to the methods that have been studied in literature, the proposed approach deals with full-order model (i.e., model reduction is not required) with lower controller order. In addition, most of the current robust methods are heavily dependent on selecting some weighting filters: such filters are not required in the loop-shaping approach. The proposed approaches are compared with different existing techniques in order to design a robust controller based on H∞ and H2 under pole placement. With large-scale power systems, it is difficult to handle large number of states to obtain the system model. Thus, it becomes necessary to use only input/output data measured from the system, and this data can be utilized to construct the mathematical model of the plant. In this research, the mentioned approaches are offered in order to design a robust controller based only on data by using system identification techniques. The mentioned techniques are applied to the two-area four-machines system and 68 bus system. The effectiveness and robustness of the proposed method in damping inter-area oscillations are validated using case studies

Synchronization of spatiotemporal semiconductor lasers and its application in color image encryption

Optical chaos is a topic of current research characterized by high-dimensional nonlinearity which is attributed to the delay-induced dynamics, high bandwidth and easy modular implementation of optical feedback. In light of these facts, which adds enough confusion and diffusion properties for secure communications, we explore the synchronization phenomena in spatiotemporal semiconductor laser systems. The novel system is used in a two-phase colored image encryption process. The high-dimensional chaotic attractor generated by the system produces a completely randomized chaotic time series, which is ideal in the secure encoding of messages. The scheme thus illustrated is a two-phase encryption method, which provides sufficiently high confusion and diffusion properties of chaotic cryptosystem employed with unique data sets of processed chaotic sequences. In this novel method of cryptography, the chaotic phase masks are represented as images using the chaotic sequences as the elements of the image. The scheme drastically permutes the positions of the picture elements. The next additional layer of security further alters the statistical information of the original image to a great extent along the three-color planes. The intermediate results during encryption demonstrate the infeasibility for an unauthorized user to decipher the cipher image. Exhaustive statistical tests conducted validate that the scheme is robust against noise and resistant to common attacks due to the double shield of encryption and the infinite dimensionality of the relevant system of partial differential equations.Comment: 20 pages, 11 figures; Article in press, Optics Communications (2011

A general scheme for information interception in the ping pong protocol

The existence of an undetectable eavesdropping of dense coded information has been already demonstrated by Pavi\v{c}i\'c for the quantum direct communication based on the ping-pong paradigm. However, a) the explicit scheme of the circuit is only given and no design rules are provided, b) the existence of losses is implicitly assumed, c) the attack has been formulated against qubit based protocol only and it is not clear whether it can be adapted to higher dimensional systems. These deficiencies are removed in the presented contribution. A new generic eavesdropping scheme built on a firm theoretical background is proposed. In contrast to the previous approach, it does not refer to the properties of the vacuum state, so it is fully consistent with the absence of losses assumption. Moreover, the scheme applies to the communication paradigm based on signal particles of any dimensionality. It is also shown that some well known attacks are special cases of the proposed scheme.Comment: 10 pages, 4 figure