R.J. Betancourt

Analysis of inter-area oscillations in power systems using Adomian-Pade approximation method

A new methodology is proposed in this paper, it is based on Adomian-Pade method and it is used to characterize power system Oscillations. The differential equations of the system are solved using Adomian method and the oscillation characteristics are obtained by applying Pade approximation on this solution. The developed methodology is applied on a single machine — infinite bus system to identify oscillation modes. Results are compared against those obtained by commercial transient stability software.

Model-order reduction using truncated modal balanced realization

In this paper, a modal reduction approach based on the truncated balanced realization technique is proposed to compute reduced-order system models (ROMs). The method enables efficient computation of Gramian covariance matrices in terms of the system frequency response and can be used for control design. Methods for approximating the high-dimensional system dynamics with a low-dimensional model are examined and compared, and the prediction error of the ROMs is evaluated. The proposed technique is tested on a 46-machine dynamic equivalent of the Mexican interconnected system. The issues of accuracy, applicability, and computational effort are discussed.

Simplified Recursive Newton-type Algorithm for Instantaneous Modal Parameter Estimation of Sub-synchronous Oscillations

Abstract A method for instantaneous identification of parameters from sub-synchronous oscillations is proposed. The developed methodology uses an infinite impulse response band-pass filter bank to separate a generator unit multi-component speed signal into mono-components. A simplified recursive Newton-type algorithm is employed to estimate modal parameters from the separated mono-components, with special emphasis on damping estimation. Simulations with the IEEE second benchmark on sub-synchronous resonance as a test power system are used to assess the proposed method. Digital signal processor hardware is employed to validate the algorithm using actual signals.

Instantaneous modal estimation of sub-synchronous oscillations using Simplified Recursive Newton Type Algorithm

A method for instantaneous identification of parameters from sub-synchronous oscillations is proposed. The developed methodology uses an IIR band-pass filter bank to separate a generator speed signal into mono-component signals. A Simplified Recursive Newton Type Algorithm is employed to estimate modal parameters from the separated mono-component signals. Simulations with synthetic and test power system signals are used to assess the proposed method. The IEEE second benchmark on sub-synchronous resonance is used as a test power system.

Order Reduction of Power Systems by Modal Truncated Balanced Realization

Abstract In this paper, a general approach for constructing reduced-order models of power system models based on a truncated balanced realization (TBR) linear reduction procedure is described. The method enables efficient computation of Gramian covariance matrices in terms of the system frequency response, and it can be used for control design and sensitivity analysis. The method guarantees convergence of the controllability and observability Gramians and avoids the need for frequency sweep of the transfer function matrix. A key innovation for the TBR-based reduced-order models introduced in this paper is the use of modal information to approximate the controllability and observability Gramians. With this approach, the connection between the linear system modes and the Gramians is clarified, and the contribution of critical system motion modes to the collective dynamics is readily determined. Conditions for convergence of the model and approximation methods are then investigated, and the issues of accuracy, applicability, and computational effort are discussed. The technique is tested on two real-world test power systems.

Parameter identification of low frequency oscillations by Pade method

This paper proposes a novel methodology for characterization of nonlinear low frequency oscillations. Selecting a window of the speed machine signals, a polynomial in the z-domain of the samples is obtained, and then Pade approximation is used to obtain a rational equivalent of the polynomial. This equivalent has a direct relationship with a discrete transfer function which captures the dominant parameters embedded in the speed machine signals. The method is tested with corrupted noisy signals showing that it may be applied to real signals. The developed methodology is applicable to determine the oscillation parameters of speed signals of the 16-Machine 68-bus NPCC power system.

Fourier-based accurate reduced-order model for Linear power systems applications

A Fourier, series-based method for model reduction of large linear power system models is introduced. The method approximates the discrete-time system transfer function by a Fourier expansion and preserves the stability properties of the original system. An iterative procedure to determine both, the Fourier coefficients and the reduced-order model (ROM) is proposed. The developed model represents an alternative to model reduction of large-scale dynamical systems and is used to assess the effect of voltage control by means of static VAR compensators on system damping in a real-world power system.

Identification of costly contingencies by Transient Stability-constrained Optimal Power Flow

In this paper a security-cost relationship analysis from the perspective of Transient Stability Constraints Optimal Power Flow (TSCOPF) is presented. The main objective of this paper is to analyze the security-cost relationship under N-1 contingencies in the Electric Power System (EPS). The Center of Inertia (COI) concept of rotor angle generators is used to obtain a time-varying trajectory equivalent of each contingency. A severity index is proposed to evaluate the power system security. At the end of this paper, the generation cost related of each contingency is computed to identify the costly contingencies. The feasibility of the proposed analysis is demonstrated on the IEEE 30-bus test system.

Incorporation of hard excitation limits into power system normal form analysis

In this paper a theoretical framework for the incorporation of the effect of excitation limits on normal form analysis is presented. The limiter action is approximated by a smooth nonlinear type atan function which is incorporated in the power system dynamic model using singular perturbation theory. This generalized limiter model is employed to characterize the limits of a simple DC excitation system. Based upon this representation, a second order normal form model is developed and applied to evaluate the impact of excitation limiter on the nonlinear inter-area phenomena. Such a modeling capability offers improved understanding of nonlinear behavior, and should allow quantitative analysis of limit-induced oscillatory behavior. The proposed technique is tested on a two-area, four-machine system in which the effect of excitation limits is considered. Detailed numerical results are presented to verify the results.