Electromechanical Oscillation Modes Research Articles

97/02867 EMTP models for simulation of shunt reactor switching transients

This paper presents a novel Fuzzy Gravitational Search Algorithm (FGSA) for optimal design of multimachine power system stabilizers (PSSs). The FGSA technique is characterized as simple, robust and capable to solve difficult combinatorial optimization problems. For achieving optimal tuning of PSS parameters, the problem is formulated as an optimization problem with the time domain-based objective function over a wide range of operating conditions and is solved by the proposed FGSA technique. The performance of the proposed FGSA based-PSS design is validated for two multimachine systems: a 3-machine 9-bus system and a 10-machine 39-bus. The effectiveness and robustness of proposed method is demonstrated using many performance indices. The results prove that the proposed FGSA assures a well damping to the electromechanical modes of oscillations for a wide range of system operation conditions. The superiority of the proposed method is proved compared to different optimization methods.

EFFICIENT INCREMENTAL FUZZY LOGIC CONTROLLER FOR POWER SYSTEM STABILIZATION

The paper presents an efficient and simple fuzzy logic power system stabilizer (FLPSS) for damping electromechanical modes of oscillations and enhancing power system synchronous stability. The essential feature of the proposed controller is that the pole placement approach is used to assign the open-loop poles at certain specified locations at nominal operating point. Then the fuzzy logic controller is employed to excite the synchronous machine excitation system by an incremental signal for enhancing the power system stability over a wide range of operating condition and exciter gain. The input signals to the FLPSS is the speed deviation and speed deviation change. The simulation results using the proposed controller are carried out on an synchronous machine connected to infinite bus through transmission line.Moreover,a comparison between the conventional fixed-gain PI controller and the proposed FLPSS is presented. The results validate the effectiveness of the proposed FLPSS in terms of less overshoot/undershoot and enhancing the power system stability over a wide range variation of generator loading conditions and a variety of exciter gain.

A novel fuzzy state feedback controller for power system stabilization

A novel fuzzy logic controller (FLC) is developed for damping electromechanical modes of oscillations and enhancing power system synchronous stability. The proposed controller is based on state feedback control system. The input signals to the controller are the weighted sum of the mechanical states and the electrical states weighted sum, while its output signal is added to the conventional fixed-gain PI controller output signal to give the excitation control signal. The simulation results using the proposed controller are carried out on an synchronous machine infinite bus system. Moreover, a comparison between the conventional fixed-gain PI controller and the proposed FLC is presented. The results validate the effectiveness of the proposed FLC in terms of less overshoot/undershoot and enhancing the power system stability over a wide range variation of operating conditions.

An adaptive fuzzy logic power system stabilizer

The paper presents an adaptive fuzzy logic power system stabilizer (PSS) design for damping oscillatory electromechanical modes of oscillations and enhancing the first-swing synchronous stability margins. The novel design utilizes a multivariable damping signal vector consisting of machine speed deviation, rate of speed deviation, and voltage deviation. The design is based on a multizonal PID structure and fuzzy logic variable-gain scheduling to optimize the damping action. The fuzzy logic PSS is proposed for use in parallel with the conventional analog type PSS with added simple switching criteria. The two PSS blocks can be allowed independent, sequential, and/or combined operation with different effective stabilizing weighting. The paper investigates an individual conventional PSS, a rule based fuzzy PSS, and hybrid operation. The parallel operation of a conventional PSS and a fuzzy logic one provides optimal sharing of the damping action under small- as well as large-scale generation-load mismatch or variations in external network topology due to fault or switching conditions.

Damping of inter-area and local modes by use of controllable components

This paper deals with damping of inter-area and local electromechanical oscillation modes using controllable series capacitor (CSC) and controllable shunt capacitor (SVC). The impacts of SVC and CSC on the structure of the system closed loop matrix are investigated. By analyzing the sensitivities of the system inter-area and local modes to the control action of the controllable devices, some general conclusions concerning the damping of inter-area and local modes are made. A numerical example is provided to support the analytical findings. This paper provides an insight and understanding in the basic characteristics of damping effects of the studied devices. The insight is obtained by the study of a simple power system which exhibits both inter-area and local power swings. The understandings and findings could form the basis in analysis of realistic and more complex systems. >

A neuro-fuzzy hybrid power system stabilizer

Abstract The paper presents a novel neuro-fuzzy hybrid power system stabilizer (PSS) design for damping electromechanical modes of oscillation and enhancing power system synchronous stability. The hydrid PSS comprises a front-end conventional analog PSS design, an artificial neural network (ANN) based stabilizer, and a fuzzy logic post-processor gain scheduler. The stabilizing action is controlled by the post-processor gain scheduler based on an optimized fuzzy logic excursion based criterion J0. The two PSS stabilizers, conventional and neural network, have their damping action scaled online by the magnitude of J0 and its rate of change dJ0. The ANN feedforward two-layer based PSS design is the curve fitted nonlinear mapping between the damping vector signals and the desired optimized PSS output and is trained using the benchmark analog PSS conventional design. The fuzzy logic gain scheduling post-processor ensures adequate damping for large excursions, fault conditions, and load rejections. The parallel operation of a conventional PSS and a neural network PSS provides optimal sharing of the damping action under small as well as large-scale generation-load mismatch or variations in external network topology due to fault or switching conditions.

Synchronous generator stabilizer design through incomplete state feedback

It is well known that there is more flexibility offered by state feedback in multivariable systems beyond closed-loap eigenvalue assignment. However, it is difficult to use only measurable state variables in single-input control systems to assign some closed-loop system poles and also achieve some kind of optimality, for example, the sum of squared errors under a step-input is minimized. An algorithm is developed in this paper to solve this problem, this algorithm is applied to the synchronous generator stabilizer design problem to present a new method. In this new stabilizer design method, only measurable state variables are used to relocate a pair of conjugate system poles corresponding to the electro-mechanical oscillation mode in the power system; and to minimize, subject to physical limits, the sum of squared machine speed-diversions under a step disturbance.

Synchronizing and damping torque coefficients and power system steady-state stability as affected by static VAr compensators

The utilization of static VAr compensators (SVC) for supplying reactive power at certain points of an electric power system is an efficient way for fast control of transient and steady-state voltage changes following short-circuits, load rejection, opening of severely loaded transmission circuits, etc. Other SVC applications include the increase of power transmission capacity through interconnections between areas of a power system and the damping enhancement of local or inter-area electromechanical oscillation modes. This paper fundamentally deals with these last two issues by analyzing the results of synchronizing and damping torque coefficient calculations for a generation station connected radially to a much larger power system. The results presented pertain to a double-circuit, 800 km, 500 kV transmission system during a one-circuit out contingency.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A procedure for oscillatory parameter identification

A procedure is proposed where a power system is excited with a low-level pseudo-random probing signal and the frequency, damping, magnitude, and shape of oscillatory modes are identified using spectral density estimation and frequency-domain transfer function identification. Attention is focussed on identifying system modes in the presence of noise. Two example cases are studied: identification of electromechanical oscillation modes in a 16-machine power system; and turbine-generator shaft modes of a 3-machine power plant feeding a series-compensated 500-kV network.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Power system stabilizer design based on the pole assignment technique for SIMO systems

A new power system stabilizer (PSS) design method for single-machine infinite-bus systems is developed. This design method not only assigns the poles corresponding to the electro-mechanical oscillation modes in the system, but also locates other system poles in suitable places in the s-plane. The design procedure is used first to translate a PSS design problem to an equivalent constant output feedback controller design problem for a single-input multi-output (SIMO) system. Then, a new algorithm developed in this paper is applied to design a constant output feedback controller to achieve the desired closed-loop system pole locations. Finally, the controller gains are transferred back to the parameters in the PSS. The extension of the method to multi-machine power systems is also illustrated.

Application of regression analysis in novel power system stabilizer design

The paper presents the methodology for designing knowledge based power system stabilizers (PSSs). The proposed methodology relies on extensive nonlinear digital or analog simulation to detect correlation patterns between input damping states and the PSS output signal. Use of linear and nonlinear least square regression analysis results in a linear and nonlinear state feedback structure that is easier to implement and effective in damping either local or interarea electromechanical modes of oscillation. The PSS design technique is a two-step process: firstly, to identify the most effective damping signals for feedback via fast Fourier spectra analysis and SISO transfer function identification, secondly, to search for the most effective linear/nonlinear regression law that ensures the damping effectiveness. The regression law is based on an ideal PSS analog ‘model’ with excellent damping performance with the objective of emulating, or duplicating, such performance over a given time period (3–5s). PSS designs are compared using a specified state variation weighting function J with the objectives of minimizing the machine speed and acceleration power, as well as the active and reactive power deviations. This is done iteratively for each design simulation run and the best regression law is adopted.

An application of Prony methods in PSS design for multimachine systems

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. >

An Adaptive Power System Stabilizer

This paper presents an adaptive power system stabilizer utilizing the eigenvalue control strategy. The control algorithm is based on the identification of decoupled subsystem model parameters in real-time from local measurements only. The concept of decentralized stabilization of power system electromechanical oscillatory modes is discussed and control procedure for local electromechanical eigenvalue assignment is developed. The robustness and efficiency of the proposed adaptive controller to enhance overall system stability are illustrated on several examples, including the three-machine, 45 order power system model.

Digital controller design for enhancing steady-state stability of interconnected power systems

This paper presents a microprocessor based digital controller design for static phase-shifters used with other stability enhancement tools to damp inter-area electromechanical modes of oscillations and stabilize AC interties. The digital controller's robustness under different contingency conditions such as system parameter changes, disturbances, control loop and sensor failures are assessed.

A Novel Excitation Control Design for Multimachine Power Systems

This paper presents a generalized excitation control design that ensures not only a desired damping of the critical electro-mechanical modes of oscillation but also the zeroing of the terminal voltage error independent of terminal voltage excursions. The excitation system consists of a compensation transfer function utilizing the machine speed or terminal frequency and/or electrical power. A comparison of the proposed design with a conventional excitation system control indicated its effectiveness in enhancing small scale as well as large scale system stability.

A Novel Excitation Control Design for Multimachine Power Systems

This paper presents a generalized excitation control design that ensures not only a desired damping of the critical electromechanical modes of oscillation but also the zeroing of the terminal voltage error independent of terminal voltage excursions. The excitation system consists of a compensation transfer function utilizing the machine speed or terminal frequency and/or electrical power. A comparison of the proposed design with a conventional excitation system control indicated its effectiveness in enhancing small scale as well as large scale system stability.

Control Design of an Active and Reactive Power HVDC Modulation System with Kaman Filtering

This paper discusses results of an EPRI contract on control design for an ac/dc transmission system to increase power transfers limited by dynamic stability. The control is acbieved by modulating the rectifier dc current or power and the inverter dc voltage. Coordinated active and reactive power modulation is accomplished by Linear Quadratic (LQ) control design. Improved performance is realized by utilizing reactive power coupling between dc and ac networks to modulate dc and ac active power. For the demonstration system, power modulation with coordinated voltage modulation is shown to be about ten times more effective than power modulation alone. Control interactions between electromechanical modes of oscillation are eliminated by Kalman filtering. Filtering permits excellent control performance with a minimum of system measurements. Modern control technology is applied within realistic system constraints, such as measurements.

Control Design of an Active and Reactive Power HVDC Modulation System with Kalman Filtering

This paper discusses results of an EPRI contract on control design for an ac/dc transmission system to increase power transfers limited by dynamic stability. The control is acbieved by modulating the rectifier dc current or power and the inverter dc voltage. Coordinated active and reactive power modulation is accomplished by Linear Quadratic (LQ) control design. Improved performance is realized by utilizing reactive power coupling between dc and ac networks to modulate dc and ac active power. For the demonstration system, power modulation with coordinated voltage modulation is shown to be about ten times more effective than power modulation alone. Control interactions between electromechanical modes of oscillation are eliminated by Kalman filtering. Filtering permits excellent control performance with a minimum of system measurements. Modern control technology is applied within realistic system constraints, such as measurements.