Joe H. Chow

An Analysis of Interarea Dynamics of Multi-Machine Systems

The slow coherency concept is introduced and an algorithm is developed for grouping machines having identical slow motions into areas. The singular perturbation method is used to separate the slow variables which are the area center of inertia variables and the fast variables which describe the intermachine oscillations within the areas. The areas obtained by this method are independent of fault locations. Three types of simulation approximations illustrated on a nonlinear 48 machine system indicate the validity of this algorithm.

A Sparsity-Based Technique for Identifying Slow-Coherent Areas in Large Power Systems

A sparsity-based technique is developed for the identification of coherent areas in large power systems. The technique, based on the slow-coherency approach, is novel in that it introduces small machines at the load buses to retain the system sparseness. Then the computation of the slow eigenbasis for the identification of slow-coherent groups of machines is performed by the Lanczos algorithm which is an efficient eigenfunction computation method for large, sparse, symmetric but unstructured matrices. The technique also groups the load buses into coherent areas, information that is useful for network reduction. Two large scale models of portions of the U.S. power system are used as illustrations. The computation time required is of the order of magnitude of that required for a few load flow solutions.

HVDC-AC Harmonic Interaction Part II -AC System Harmonic Model with Comparison of Calculated and Measured Data

This paper is Part II of a two part series. The two papers will report part of the research project RP-1138 sponsored by EPRI and BPA on HVDC-AC System Interaction from AC Harmonics. The two papers describe the harmonic impedance measurement of Bonneville Power Administrations (BPA) system as seen from the Celilo HVDC substation, the development of analytical techniques to calculate the harmonic impedance of the system, and comparison of the calculated and measured results.

Multi-Stage Rescheduling of Generation, Load Shedding and Short-Term Transmission Capacity for Emergency State Control

A multi-stage formulation of the problem of scheduling generation, load shedding and short term transmission capacity for the alleviation of a viability emergency is presented. The formulation includes generation rate of change constraints, a linear network solution, and a model of the short term thermal overload capacity of transmission lines. The concept of rotating transmission line overloads for emergency state control is developed. The ideas are illustrated by a numerical example.

Torsional Model Identification for Turbine-Generators

A method for identifying the parameters of a turbine-generator torsional model from measured data is presented. The method is based on the use of trajectory sensitivities and least squares to compute changes in model parameters. This method is illustrated by identifying the shaft stiffness and inertia constants of a torsional model from data collected by a Torsional Vibration Monitor.

Multivariable feedwater control design for a steam generator

A multivariable feedwater control design for drum water-level regulation in a heat-recovery steam generator is presented. The control design is based on a projective output feedback scheme and is used to coordinate the tandem-connected feedwater valves of a low-pressure and a high-pressure drum. One of the design objectives is to minimize the blowdown from the drums during start-ups. Results demonstrating the control performance and the improvement over a traditional single-loop feedwater control design are shown.<<ETX>>

Coherency Based Decomposition and Aggregation

Abstract Relationship between coherency, area decomposition and aggregation is investigated for a class of models of electromechanical networks, including power system models. It is established that coherency conditions and a physically meaningful area-aggregate, reproducing a prescribed set of system modes, depend on external connections only. Coherency with respect to a set of slowest modes (“slow coherency”) and an earlier developed grouping algorithm are used to identify weakly coupled areas, as demonstrated on a 48-machine model of the Northeast United States power system

Direct Power System Transient Stability Analysis with Detailed Machine Models

Abstract Most of the investigations into direct methods for power system stability analysis have been limited to lower order simplified models as Lyapunov functions are readily constructed for conservative systems. This paper presents recent results on extending direct methods to more realistic multi-machine models. The results are based on the general concept of constant total system energy. It can be shown that the post-disturbance Newton’s second law equation for each rotating machine multiplied by its transient speed, and integrated over time, results in energy terms that added with kinetic energy terms must equal an arbitrary constant when evaluated along a trajectory that satisfies the post-disturbance equations. This constant energy or Hamiltonian formulation is then used in conjunction with the potential energy boundary surface method to estimate power system stability. The method is illustrated on a simple system with a high order machine model and associated voltage control.

Simulation Testing Of Rate Allocation Control To Relieve Transmission Overloads During Emergencies

Rate allocation control is a feedback algorithm for dynamic rescheduling of power flows to alleviate transmission link overloads. For computation speed, the control algorithm uses simplifying approximations including linearization. To investigate the potential of rate allocation control as a tool for on-line emergency control, it is tested with a simulation program with detailed modeling of prime mover dynamics, nonlinear load flow, and conventional governors and voltage regulators. The test case is a realistic emergency scenario developed from a well-known power system upset. Two of the simulations are presented to demonstrate several features of the rate allocation control.

Simultaneous Generation of Sensitivity Functions using only One Sensitivity Model

Abstract Sensitivity functions are used in many model parameter identification methods and adaptive control algorithms. Since one sensitivity model has to be used for each parameter, the computation requirement is large when many parameters have to be identified or adapted. This paper proposes a method to reduce the computation requirement by using one sensitivity model suitable for the generation of sensitivity functions for all parameters. Instead of using modal transformations and eigenvector sensitivities as previously proposed, this paper uses an input-output transfer function approach. Several sufficient conditions in terms of controllability are given for the implementation of the method.