Fixed-speed wind-generator and wind-park modeling for transient stability studies

Increasing levels of wind-turbine generation in modern power systems is initiating a need for accurate wind-generation transient stability models. Because many wind generators are often grouped together in wind parks, equivalence modeling of several wind generators is especially critical. In this paper, a reduced-order dynamic fixed-speed wind-generator model appropriate for transient stability simulation is presented. The model is derived using a model reduction technique of a high-order finite-element model. Then, an equivalencing approach is presented that demonstrates how several wind generators in a wind park can be combined into a single reduced-order model. Simulation cases are presented to demonstrate several unique properties of a power system containing wind generators. The results in this paper focus on horizontal-axis turbines using an induction machine directly connected to the grid as the generator.     

Use of ARMA block processing for estimating stationary low-frequency electromechanical modes of power systems

Accurate knowledge of low-frequency electromechanical modes in power systems gives vital information about the stability of the system. Current techniques for estimating electromechanical modes are computationally intensive and rely on complex system models. This research complements model-based approaches and uses measurement-based techniques. This paper discusses the development of an autoregressive moving average (ARMA) block-processing technique to estimate these low-frequency electromechanical modes from measured ambient power system data without requiring a disturbance. This technique is applied to simulated data containing a stationary low-frequency mode generated from a 19-machine test model. The frequency and damping factor of the estimated modes are compared with the actual modes for various block sizes. This technique is also applied to 35-min blocks of actual ambient power system data before and after a disturbance and compared to results from Prony analysis on the ringdown from the disturbance.     

Identifying linear reduced-order models for systems with arbitraryinitial conditions using Prony signal analysis

A method of identifying reduced-order linear models for systems operating in the neighborhood of an equilibrium point is presented. The method is based on Prony signal analysis, which has recently received considerable attention in the study of power system electromechanical oscillations. Prior to the application of the input test signal, the system can be in a transient state. The system input test signal is piecewise continuous and allows several Prony analyses to be performed during a transient, with each analysis conducted between input discontinuities. Results of these Prony analyses can be combined in various ways to obtain system eigenvalues, transfer-function residues, and initial condition residues. Two examples are given to illustrate the use of the method     

Estimating damping effectiveness of BPA's thyristor controlledseries capacitor by applying time and frequency domain methods tomeasured response

Recently, a 500 kV thyristor controlled series capacitor (TCSC) was installed in the Bonneville Power Administration system in the Northwestern United States. Extensive field testing has included modulation experiments to determine the effect of the TCSC on low-frequency oscillations. This paper discusses modulation procedures, analysis methods, and results for estimating the damping effectiveness of the TCSC. Modulation methods include driving the TCSC with step and random noise, and analysis techniques include time (Prony analysis) and frequency-domain identification. Results indicate that: (1) the TCSC can have significant impact on system dynamics; and (2) under a very small feedback gain, the TCSC provides measurable added damping     

Transfer function identification in power system applications

The authors present an introduction to concepts and applications of transfer function identification in power systems. They begin with a brief introduction to transfer function identification methods using least-squares approaches and then discuss applications which include static VAR compensators, model validation applications, and software validation. A comparison is also made between eigenvalues obtained from transfer function identification and small signal analysis. Methods for testing the validity of identified transfer functions are also discussed     

A performance limit for a finite-settling-time system using alook-ahead control

A performance limit is presented for a system designed to have finite-settling-time while using look-ahead control, under the design requirement that sampled output track both step inputs and ramp inputs with zero error in finite time. This performance limit clarifies the relationship between the least amount of overshoot attainable, the settling-time, the look-ahead horizon, and the time delay of the plant. The optimum design of a preview-controlled finite-settling-time system is discussed     

Impacts of the distributed utility on transmission system stability

The distributed (or dispersed) utility concept is rapidly becoming a reality in some service areas. In this framework, modular generation and storage assets along with selected demand-side management programs are used in place of the more traditional infrastructure upgrades to ensure reliable service to a group of utility customers. From among the many technical challenges associated with the proliferation of distributed resources, this paper deals with the impacts of distributed architectures upon the bulk transmission system. Bulk transmission system transient and small-signal stability are addressed through the use of extensive case studies. Planning tools and methods are discussed, and some general conclusions related to stability issues are drawn     

Identifying a hydraulic-turbine model from measured field data

An approach is proposed for identifying hydraulic-turbine model parameters from measured response data. The frequency response from the turbine-gate position to the machine power is measured at given steady-state operating conditions, and a structured model is fitted to the response. The fitting process is based on a nonlinear optimization method that provides numerical robustness. This approach allows one to fine tune and validate existing models or to identify a model without initial theoretical analysis. Theoretical development of the approach is discussed and results are presented for a 115-MVA unit at the Mt. Elbert pumped-storage powerplant operated by the Bureau of Reclamation     

An application of Prony methods in PSS design for multimachinesystems

A method for obtaining transfer functions for power system stabilizer (PSS) design is presented. It results in an accurate reduced-order model of a generator connected to a large system. The method is based on Prony signal analysis and incorporates both local and interarea electromechanical oscillatory modes. Two PSS units are designed using the proposed method along with root-locus and sequential decentralized control techniques. The design procedure and results are illustrated using computer simulation of a 27 bus system with 16 generators. The test system was developed to exhibit interarea modes that are comparable to the western North American power system. This provides a new perspective on damping interarea oscillatory modes using PSS units