Inter-area Oscillation Modes Research Articles

Tuning of Power System Stabilizer (Unitrol D) in Benghazi North Power Plant

The use of power system stabilizers (PSSs) to damp power system swing mode of oscillations is of practical important. The authors purpose is to retune the power system stabilizer (PSS1A) parameters in Unitrol D produced by ABB– was installed in 1995 in Benghazi North Power Plants (BNPPs) at General Electricity Company of Libya (GECOL). Power systems are steadily growing with larger capacity, so the optimal values of the power system stabilizer (PSS1A) parameters should be retuned. A particle swarm optimization technique (PSO) is used to determine the parameters of the PSS off-line. The objective is to damp the local and inter-area modes of oscillations that occur following power system disturbances. The retuned power system stabilizer (PSS1A) can cope with large disturbance at different operating points and has an enhanced power system stability, The MATLAB package with SIMULINK is used for the design and simulations.

New algorithm for mode shape estimation based on ambient signals considering model order selection

Using time-synchronized phasor measurements, a new signal processing approach for estimating the electromechanical mode shape properties from ambient signals is proposed. In this method, Bayesian information criterion and the ARMA(2n,2n – 1) modeling procedure are first used to automatically select the optimal model order, and the auto regressive moving averaging models are built based on ambient data, then the low-frequency oscillation modal frequency and damping ratio are identified. Next, Prony models of ambient signals are presented, and the mode shape information of multiple dominant interarea oscillation modes are simultaneously estimated. The advantages of the new ARMA-P method are demonstrated by its applications in both a simulation system and measured data from China Southern Power Grid.

Input/ouput signal selection for wide-area supplementary damping controllers based on probabilistic eigenanalysis

Abstract This paper explores the design of wide-area supplementary damping controllers (WASDCs) with the aim of minimizing the risk of occurrence of poorly damped inter-area oscillations. The selection of proper input and output signals for the WASDC is tackled through probabilistic indexes of geometric observability and controllability that are derived from Monte Carlo-based probabilistic eigenanalysis. A case study on the New York-New England interconnected test system, which exhibits multiple inter-area oscillatory modes, demonstrates the viewpoint and effectiveness of the proposal in providing satisfactory overall system damping performance over a large number of operating conditions.

Application of genetic algorithm in optimization of unified power flow controller parameters and its location in the power system network

This work demonstrates the application of Genetic Algorithm (GA) technique for the simultaneous stabilization of power systems using a Unified Power Flow Controller (UPFC). The GA is applied to find the optimal location of the UPFC and to tune its control parameters under different operating conditions. The problem is formulated as a multiobjective optimization problem which aims at maximizing the damping ratio of the electromechanical modes using different lines fitted with the UPFC. The approach is successfully tested on the 16-machine 68-bus New England–New York interconnected system and on the Iraqi National Super Grid System (INSGS) to validate its effectiveness in the damping of local and inter-area modes of oscillations. In addition, the proposed approach demonstrated better performance when compared to a fuzzy-based UPFC damping controller.

Robust Wide-Area TS Fuzzy Output Feedback Controller for Enhancement of Stability in Multimachine Power System

This paper presents a systematic procedure for designing a wide-area centralized Takagi-Sugeno fuzzy controller to improve the angular stability of a multimachine power system. The proposed fuzzy controller is robust and designed by satisfying certain linear matrix inequality conditions, to stabilize the system at multiple operating points. The bilinear matrix inequality problem, encountered in Lyapunov-based stability criterion, has been converted into a convex optimization problem to eliminate iterative solution. The input-output control signals are selected in the proposed control scheme by defining joint model controllability and observability index applying geometric approach. The proposed wide-area control scheme employs a global signal from the centralized controller to damp out the interarea mode of oscillations, apart from the local controllers, which are assumed to be present to damp out the local mode of oscillations. The proposed control scheme has been implemented on three test systems. The effectiveness of the proposed control scheme has been compared with a robust wide area control scheme based on mixed H2/H∞ output feedback synthesis and with a conventional power system stabilizer control scheme.

Wide-Area Robust Coordination Approach of HVDC and FACTS Controllers for Damping Multiple Interarea Oscillations

A robust coordination approach for the controller design of multiple high-voltage direct-current (HVDC) and flexible ac transmission systems (FACTS) wide-area controls (WACs) is presented in this paper and has the aim of stabilizing multiple interarea oscillation modes in large-scale power systems. The suitable wide-area control signals, which are given to HVDC and FACTS wide-area controllers, respectively, are chosen from a large number of candidate items. Then, a sequential robust design approach is planned for the wide-area controller coordination of HVDC and FACTS devices. This approach is based on the robust control theory and is formulated as a standard problem of multiobjective mixed H2/H∞ output-feedback control with regional pole placement constraints. The linear matrix inequality (LMI) theory is applied to solve such a robust control problem. A case study on the 16-machine 5-area system, which is modified with one HVDC interconnected transmission, one shunt-FACTS device (SVC), and one series-FACTS device (TCSC), is performed to validate the robust performance in terms of multiple oscillations damping under various operating conditions.

Controlling PMSG-based wind generation by a locally available signal to damp power system inter-area oscillations

SUMMARY The work reported in this paper adds damping to the inter-area mode of oscillation in a power system with relatively high penetration of wind power, by modulating active power output of the permanent magnet synchronous generator wind turbines (PMSG-WTs) using local information. The dc-link voltage of the voltage source converter is used as a local signal for controller input. This input signal is processed through phase compensator blocks, and the output of the controller is used to vary the active power reference signal of the machine side converter controller. The results are compared to the cases of the same supplementary controller loop with a global signal as its input, added to the both PMSG-WTs and doubly fed induction generator wind turbines. An optimization-based approach is proposed to adjust and coordinate various control loops of the grid-connected PMSG-WTs. The performance of the supplementary damping control loop is evaluated, employing modal analysis and time domain simulations of a power system test case. Copyright © 2012 John Wiley & Sons, Ltd.

A Stepwise Regression Method for Estimating Dominant Electromechanical Modes

Prony analysis has been applied to estimate inter-area oscillation modes using phasor measurement unit (PMU) measurements. To suppress noise and signal offset effects, a high-order Prony model usually is used to over-fit the data. As such, some trivial modes are intentionally added to improve the estimation accuracy of the dominant modes. Therefore, to reduce the rate of false alarms, it is important to distinguish between the dominant modes that reflect the dynamic features of a power system and the trivial modes that are artificially introduced to improve the estimation accuracy. In this paper, a stepwise-regression method is applied to automatically identify the dominant modes from Prony analysis. A Monte Carlo method is applied to evaluate the performance of the proposed method using data obtained from simulations. Field-measured PMU data are used to verify the applicability of the proposed method. A comparison of results obtained using the proposed approach with results from a traditional energy-sorting method shows the improved performance of the proposed method.

Techniques for the Analysis and Optimization of Electromechanical Stability towards Local and Inter-Area Oscillation Modes

This paper investigates the problem of electromechanical stability related to the dynamic interaction between the turbine-alternators and the network. In particular, this paper refers to a software package, named ALICE and developed by CESI and Terna in MATLAB®, which makes available within an unique environment features for linearized analysis of electromechanical cycle and multivariable optimization of power system stabilizers. By using of ALICE, it is possible to make stability analysis of the linearized system, both in local and inter-area frequency interval, and, above all, to take out, thanks to different automatic optimization techniques, the most appropriate calibration of the gains of additional stabilizing feedbacks in order to achieve an adequate damping of electromechanical oscillations.

Power system damping using GA based fuzzy controlled TCSC device

In introduction, this paper investigates the application of TCSC hybrid controller for improving damping inter-area modes of oscillations. The proposed controller comprised fuzzy logic proportional and derivative controller with the conventional proportional and integral controller (FUZZY PD + PI) turn by genetic algorithm techniques. Approaching the proposed control scheme implements the characteristics of the GA’s global optimization to optimize the FPID control parameters, KP, KI and K to obtain the best control effect by minimizing the integral time square error online. The performance of the proposed hybrid control in increasing the damping of local and inter-area modes of oscillation is demonstrated in a two area four machine 11-bus systems and a practical reduce system of south Malaysian power network called TNB 25-bus system. Results shows that this type of hybrid control is proved to be more robust and effective in damping electromechanical oscillations of the power systems in comparison with the conventional PID regulators used for TCSC control. The GA optimization technique is also found to be effective and efficient in tuning the FPID parameters. Key words: TCSC, power system oscillations, fuzzy logic control, GA and PID.

Comparative performance evaluation of SMES–SMES, TCPS–SMES and SSSC–SMES controllers in automatic generation control for a two-area hydro–hydro system

This paper presents the automatic generation control (AGC) of an interconnected two-area multiple-unit hydro–hydro system. As an interconnected power system is subjected to load disturbances with changing frequency in the vicinity of the inter-area oscillation mode, system frequency may be severely disturbed and oscillating. To compensate for such load disturbances and stabilize the area frequency oscillations, the dynamic power flow control of static synchronous series compensator (SSSC) or Thyristor Controlled Phase Shifters (TCPS) in coordination with superconducting magnetic energy storage (SMES) are proposed. SMES–SMES coordination is also studied for the same. The effectiveness of proposed frequency controllers are guaranteed by analyzing the transient performance of the system with varying load patterns, different system parameters and in the event of temporary/permanent tie-line outage. Gains of the integral controllers and parameters of SSSC, TCPS and SMES are optimized with an improved version of particle swarm optimization, called as craziness-based particle swarm optimization (CRPSO) developed by the authors. The performance of CRPSO is compared to that of real coded genetic algorithm (RGA) to establish its optimization superiority.

Targeted approach to apply masking signal-based empirical mode decomposition for mode identification from dynamic power system wide area measurement signal data

This study proposes an improved masking signal approach for the effective handling of the mode mixing problem associated with closely spaced mode frequency components of power system signals while applying empirical mode decomposition (EMD). The effectiveness of the proposed technique is shown with the help of synthetic as well as real-timesignals. A multifrequency synthetic signal with frequencies in the range of inter-area oscillation modes of a typical power system is analysed to identify a dominant modal frequency component with the existing and the proposed technique as well. Different modal frequencies are extracted from the wide area measurement signals (WAMS) recorded in the Eastern Interconnect Phasor Project on 20th July 2005. The modal frequency extracted is compared with the extracted frequency using the masking signal approach adopted in the standard EMD technique. Further, the WAMS data recorded on Northern grid of the Indian Power System have also been analysed. The data obtained from four recently installed PMUs after an incident of loss of generation of 2000 MW, which occurred at Rihand Super Thermal Power Station on 1st June 2010, have been analysed in this study. The magnitude and frequency variations of various signals extracted are compared using the Hilbert spectrum.

Multi-machine power system stabilizer adjustment using Simulated Annealing

In this paper, the authors are willing to find the optimal and robust design for power system stabilizers (PSSs) in a multi-machine power system. In this regard a new Meta heuristic method as Simulated Annealing (SA) is used. The PSS parameters are computed to assure maximum damping performance under different scenarios. A multi machine electric power system is used to illustrative the performance of proposed method. The efficacy of this technique in damping local and inter-area modes of oscillations in multimachine power systems is confirmed through nonlinear simulation results. Simulation results are carried out by numerical simulations on MATLAB software. Keywords: Multi Machine, Power System Stabilizer, Low Frequency Oscillations, Simulated Annealing

Mode shape estimation and mode checking for IAO using correlation analysis technique

This paper presents a novel algorithm for rapid estimating mode shape and checking the corresponding mode for inter-area oscillation (IAO) using correlation analysis (CA). It firstly extracts the weak damping components strongly associated with the objective IAO mode from the tie-line active power signals came from wide area measurement system (WAMS), through a low-pass or band-pass filter which is designed by the priori knowledge of modal frequency obtained from off-line calculation. Then their self-correlation and cross-correlation coefficients resulted from the CA technique are used to determine the IAO mode shape for tie-line power deviation or equivalent speed deviation, which is always able to correspond to an IAO mode. Finally, the results are checked with their corresponding items in the modal form (MF) obtained by off-line calculation and on-line correction in order to confirm the dominant IAO mode and its mode shape at current state. Two pairs of stationary and non-stationary synthetic signals are utilized to verify the applicability of CA. The case studies have been carried out on a 4-area and 9-bus system and a planning case in East China Power Grid (ECPG). The results show that the proposed algorithm is efficient and effective, and also indicate its potential practicability for WAMS of bulk power system.

Optimal location and signal selection of UPFC device for damping oscillation

Unified power flow controller (UPFC) is used for controlling the real and reactive power in transmission line and bus voltage simultaneously and independently. An additional task of UPFC is to increase transmission capacity as result of power oscillation damping. The effectiveness of this controller depends on its optimal location and proper signal selection in the power system network. A residue factor has been proposed to find the optimal location of the UPFC controllers and eigenvalue analyses are used to assess the most appropriate input signals (stabilizing signal) for supplementary damping control of UPFC to damp out the inter-area mode of oscillations. The proposed residue factor is based on the relative participation of the parameters of UPFC controller to the critical mode. A simple approach of computing the residue factor has been proposed, which combines the linearized differential algebraic equation model of the power system and the UPFC output equations. While for signal selection a right-half plane zeros (RHP zeros) and Hankel singular value (HSV) is used as tools to select the most receptive signal to a mode of the inter-area oscillation. The placements of UPFC controllers have been obtained for the base case and for the dynamic critical contingences. The effectiveness of the proposed method of placement and selection of signals are demonstrated on practical network of TNB 25 bus system of south Malaysian network and New England 39 bus system.

ROBUST DESIGN OF POWER SYSTEM STABILIZERS USING AN OPTIMAL ALGORITHM

A robust design of power system stabilizers using an optimal algorithm for multi-machine power systems is presented in this paper. Based on the proposed method the widely applied conventional power system stabilizers (CPSS) in a multi-machine system is designed in two stages. In the first stage, the time constants of CPSSs are tuned using the physical concept based phase compensation technique based on the frequency response of the GEP(s). In the second stage, the gains of the CPSSs are simultaneously tuned by converting it to an optimization problem which is solved simultaneously by solving a special form of robust pole assignment problem using a constrained optimal algorithm. The effectiveness of the proposed two-stage method in damping local and inter-area modes of oscillations over wide range operating conditions for a four-machine power system is confirmed through eigenvalue analysis and time domain simulation results.

Dynamical Behavior Comparison Between Variable Speed and Synchronous Machines With PSS

The dynamic performances of variable speed and fixed speed units are compared in the case of 2 × 320 MW pumped storage power plant. The case study of the pumped storage power plant with standard synchronous machine with PSS is presented and, then, the corresponding variable speed system is designed for this case. Unsteady numerical simulations of both architectures enable to demonstrate that the variable speed architecture improves the power system stability characteristics for both the local and the inter-area modes of oscillation. Moreover, the damping of active power oscillations originated by the part load operation of the pump-turbine in generating mode is investigated as well.

Damping inter-area modes of oscillation using an adaptive fuzzy power system stabilizer

This paper introduces an indirect adaptive fuzzy controller as a power system stabilizer used to damp inter-area modes of oscillation following disturbances in power systems. Compared to the IEEE standard multi-band power system stabilizer (MB-PSS), indirect adaptive fuzzy-based stabilizers are more efficient because they can cope with oscillations at different operating points. A nominal model of the power system is identified on-line using a variable structure identifier. A feedback linearization-based control law is implemented using the identified model. The gains of the controller are tuned via a particle swarm optimization routine to ensure system stability and minimum sum of the squares of the speed deviations. A bench-mark problem of a 4-machine 2-area power system is used to demonstrate the performance of the proposed controller and to show its superiority over other conventional stabilizers used in the literature.

Oscillation Damping Enhancement via Coordinated Design of PSS and FACTS-Based Stabilizers in a Multi-Machine Power System Using PSO

This paper investigates the enhancement of power system stability via coordinated design of Power System Stabilizers (PSSs), Thyristor Controlled Series Capacitor (TCSC)-based stabilizer, and Static Var Compensator (SVC)-based stabilizer in a multi-machine power system. The design problem of the proposed stabilizers is formulated as an optimization problem. Using the developed linearized power system model, the particle swarm optimization (PSO) algorithm is employed to search for optimal stabilizer settings that maximize the minimum damping ratio of all system oscillating modes. The proposed stabilizers are evaluated on a two-area weakly-connected multi-machine power system with unstable interarea oscillation mode. The nonlinear simulation results and eigenvalue analysis show the effectiveness of the proposed coordinated stabilizers in damping low frequency power system oscillations and enhancing the system stability.

GPS synchronized phasor measurement units-based wide area robust PSS parameters optimization

This paper proposes an optimization method of wide area robust power system stabilizer (PSS) using global positioning system (GPS) synchronized phasor measurement units (PMUs). Assuming multiple PMUs are located in an interconnected power system, the steady-state phasor data are obtained by applying the small load perturbation. Based on the phasor data, the coupled vibration model (CVM) included with the PSS can be established and applied to estimate the dominant inter-area oscillation modes. In the robust PSS (RPSS) optimization, unstructured system uncertainties such as various generating and loading conditions, variation of system parameters etc. are represented by the inverse additive perturbation and included in the CVM. To enhance the system robust stability margin, the optimization of PSS parameters is carried out in the CVM. The genetic algorithm (GA) is applied to solve the problem and achieve the PSS parameters automatically. Simulation studies in the IEEJ Western Japan 10-machine power system confirm that the robustness of the proposed PSS is much superior to that of the compared PSS against various operating conditions and fault locations. Copyright © 2010 John Wiley & Sons, Ltd.