G. Huang

A Clustered Dynamic Model for a class of LInear Autonomous Systems Unsing Simple Enumerative Sorting

Simple, computationally efficient, enumerative techniques are introduced for establishing a clustered semidecoupled dynamic model for a class of autonomous linear systems exemplified by the electromechanical dynamics of the electric power system. Such a model consists of intercluster (usually slow) dynamics and intracluster dynamics (usually fast) which are respectively weakly coupled. The process starts by selecting the point in frequency where intracluster and intercluster dynamics tend to separate. The sorting technique then identifies the number of clusters, the width of separation in frequency, the specifics of the dynamic components and the coupling between them. No matrix manipulations like finding eigenvalues or inverses are required.

Paper: Control of reactive power and voltage in emergencies

A method is introduced which assures quite feasible computation of control actions to be taken to remedy voltage problems resulting in a section of a system because of a disturbance. The process is devised so as to conform to the natural structural features of the problem. A monitoring process is proposed. If a viability crisis is detected, first a cluster of interacting control tools are selected to match the cluster of violations. Then an effective viabilizing algorithm is carried out to restore viable voltage values in a manner least disruptive to the system. Note that the pinpointing of the cluster of violated and nonviolated network elements and the controls which are effective can in itself be very valuable information for the operator. The viabilizing algorithm only covers the affected clusters and it does not require on line system wide sensitivity computation. Consequently it is of small dimension and converges fast. Use of this approach should substantially improve both, cut and try approach by the operator on line and straightforward, computationally demanding computer implementations such as optimal load flow or linear programming approaches.

Stability Issues of Smart Grid Transmission Line Switching

This paper investigates the stability issues that might arise when incorporating transmission line switching into smart grid planning and operation. To demonstrate the feasibility of line switching, we use scenarios and dynamic simulations to demonstrate system security margin and online stability issues. Results show that proper line switching can resolve system emergency and boost system security margin, even though less transmission lines are used. Also it reveals that small signal instability can be triggered by line switching. It is necessary to apply sophisticated voltage controls and power system stabilizers (PSS) to avoid triggering rotor angle and voltage small signal instability for full benefits of line switching.

MERIT 2000-a new concept in power engineering education

This paper suggests an extensive use of simulation technology to enhance students understanding of the fundamentals, as well as practical solutions while making this approach quite effective in reducing overall classroom teaching time. This is achieved by efficiently presenting and explaining the analytical and practical aspects of related phenomena through simulation, as well as by redistributing some of the teaching to the laboratory environment. This approach will make sure that an additional time in the curriculum is made available for introduction of the new topics that will reflect the multidisciplinary issues created by the changing environment.

Restoration of the Large Electric Power System Using a Computer Generated Sequence of Target Systems

Abstract New techniques for restoration of a failed large power system are presented using decision and control approach (Zaborszky, 1980 b). The proposed method takes advantage of fast digital computing, reliable communications, data base structure, modern system theory to set up an expert computer-operator partnership. The computer establishes target systems for future time points for the most effective use of all equipment expected to be available. Effective computer operations are readily established for this task. Once the operator is presented with target systems which he knows to be viable he can very effectively pick action sequences to reach the target. In turn the computer again can check for consistency and arrange the precise time sequence of individual restoration steps. The result is the on line res t oration plan. During its entire preparation and execution the operator is monitoring the plan and the computer is monitoring its execution to guard against improper sequencing or time delays. Generation of the targets is the key feature of this approach. It is a large scale problem which must be done with high computational efficiency and with sufficient accuracy to make the proposed approach successful. Accordingly, the major part of the paper is devoted to the target generation problem.

New Results for Stability Monitoring of the Large Electric Power System the Phase Portrait of the Power System

Abstract Monitoring of the stability of power systems has never really become an on line tool even in the security, contingency sense, A three year research project sponsored by the US Department of Energy now is attempting to devise approaches which will remedy this situation and, potentially, even go beyond to monitor ongoing dynamic phenomena on line. Attainability of the latter goal is not assured but making on line dynamic security monitoring practically feasible would be an accomplishment of major importance. Also valuable theoretical insights are being developed in this project. This paper summarizes the approach used and presents new and quite complete results on the phase portrait of the power system, and the separatrix which defines the region of attraction around the stable equilibrium point, These results give very valuable insight into the structure of the phase portrait and will serve as the foundation for the techniques now under development for monitoring system stability on line.

Multi-intersected/recursive textured algorithms for large-scale convex optimization problems

In this paper, we extend our textured algorithm to multi-intersected textured models. We also describe the recursive textured decomposition process as a tree, in which we can obtain the overall solution by consolidating the end subsystem solutions. The proposed algorithms, their properties, and the theorems for exact convergence are then addressed. The worst-case time complexity of the algorithm with complete tree structure, in which parents in the same recursion level have the same number of children, is analyzed. Examples are given to demonstrate the use of the algorithms and the trade-off among the number of recursion levels, the number of sequential computing steps, and problem size reduction.

Computational algorithms for unstable and stable (load flow) equilibria of a power system

Fast parallel algorithms to compute unstable equilibria in the state space of a large electric power system are introduced and analyzed. The approach utilizes cluster separation. The algorithm proposed for finding stable equilibria is a novel and is much faster in parallel implementation than the sparse Newton-Raphson technique. The algorithm proposed for finding unstable equilibria is not only novel but is the only available algorithm for computing unstable equilibria. Necessary and sufficient conditions for stability and instability checking have been developed. These conditions give some indications how the (N-1) unstable equilibria can be located through cluster structures. Simulation results are also given to show the convergence of the algorithms. Time-complexity analysis of parallel implementation is described and shows the potential of the algorithms.<<ETX>>

A new packet-loss minimization routing algorithm for ATM high-speed data networks

An optimal routing algorithm to minimize packet loss in high-speed networks is proposed. In high-speed networks, such as ATM networks, packets could be lost while being routed to their destinations. Minimisation of packet loss probabilities becomes a major concern. The optimal routing problem (ORP) minimizing average network packet loss probabilities is more complicated since the ORP is a non-convex problem and the ordinary gradient projection algorithm can not be directly used to achieve optimal routing. To solve the packet loss ORP, we developed a HAD based two-stage algorithm, which can effectively avoid the traps of local minimum caused by the non-convexity of the problem and thus, can find the true optimal solution of the ORP with high computation speed.

Parallel optimal routing control by commodities for large data networks

In this paper, a new distributed algorithm is proposed to solve optimal routing problems (ORPs) for large data network with multicommodities. Contrast to the existing algorithms for general network topology, which have parallel time complexity of O(M/spl Phi//sup 2/) assuming that all the nodes of the network have a processor, our algorithm takes O(m/spl Phi//sup 2/) time units using the same number of processors if some mild network conditions are met. Here, /spl Phi/ is the diameter of the network; M is the number of commodities; m is a positive number usually much smaller than M. The exact value of m depends on the pattern of the OD pairs including the locations of origin nodes and destination nodes, and the flow demand of OD pairs. The implementation of the algorithm for a 200-node network is simulated using OPNET simulation tool and the results show that our algorithm is much faster than the general algorithms.<<ETX>>