Low Frequency Electromechanical Oscillations Research Articles

Robust control of static Var compensator-based power oscillation dampers using polynomial control in power systems

A static Var compensator (SVC) installed in a power transmission network can be effectively exploited to enhance the damping of low frequency electromechanical oscillations. The application of robust control theory offers more reliable and robust damping controller to achieve desired damping level considering variations in the operating conditions of power system. This paper presents a new approach to design a robust proportional-integral (PI) controller for stabilizing power system oscillations. The variability in operating conditions is captured using an interval polynomial and then, Kharitonov’s theorem is used to design the desired damping controller. The proposed method is based on plotting the stability boundary locus in the ( kp-ki) plane and then computing the stabilizing values of the parameters of a PI controller. Besides stabilization, computation of stabilizing PI controllers that achieve user specified gain margin (Gm), phase margin (Pm) and bandwidth is studied simultaneously. This novel method enables designers to make the convenient trade-off between stability and performance by choosing the proper margins and bandwidth specifications. In addition, the most appropriate stabilizing input signal is selected using Hankel singular value (HSV) and right half plane-zeros (RHP-zeros) for the SVC-based supplementary damping controller. The effectiveness and robustness of the proposed controller are demonstrated using eigenvalue analysis and time-domain simulation for a 16 machine 68-bus test system. The simulations and analysis are implemented in matrix laboratory environment and power system analysis toolbox.

Power System Stability Improvement through the Coordination of TCPS-based Damping Controller and Power System Stabilizer

To guarantee the secure and reliable operations of power systems through the rapid damping of low-frequency electromechanical oscillations (LFEOs) is the ultimate objective of this s ...

Measurement-Based Hybrid Approach for Ringdown Analysis of Power Systems

System identification methods have been widely used for the study of low frequency electromechanical oscillations and the development of low order dynamic models. This paper introduces a hybrid frequency/time-domain approach to estimate the dominant modes contained in ringdown responses of power systems. Practical issues and solutions encountered in the application of the hybrid method are discussed. The performance of the proposed technique is evaluated by applying the Monte Carlo method to synthetic signals and simulated responses from a large-scale power system, as well as to measurements recorded in a microgrid laboratory test facility. Results in all cases proved to be very accurate, verifying the robustness of the proposed method.

Coordinated tuning of the parameters of PI, PSS and POD controllers using a Specialized Chu–Beasley's Genetic Algorithm

This paper presents a Specialized Chu–Beasley's Genetic Algorithm (SCBGA) to perform coordinated tuning of the parameters of proportional-integral and supplementary damping controllers (power system stabilizers and interline power flow controller-power oscillation damping) in multi-machine electric power systems. The objective is to insert additional damping to low frequency electromechanical oscillations. The current sensitivity model was used to represent the system, therefore all of its devices and components were modeled by current injection. A novel current injection model for the interline power flow controller is presented and a static analysis is considered to validate it. The New England test system – consisting of 10 generators, 39 buses, and 46 transmission lines, divided into two areas with both local and inter-area oscillation modes – was used for the simulations. The SCBGA was compared to other five algorithms: a Random Search, a Local Search, a Simulated Annealing, a Genetic Algorithm, and a Particle Swarm Optimization method, in terms of performance for the tuning of the parameters of the controllers. The results demonstrated that the SCBGA was more efficient than these other techniques. In addition, the obtained solutions proved to be robust when variation of the loads was considered.

A Modified RLS Algorithm for Online Estimation of Low-Frequency Oscillations in Power Systems

A number of methods have been proposed and implemented to improve system damping against low-frequency electromechanical oscillations in the power system. Among these, flexible ac transmission systems (FACTS) can be used to provide power oscillation damping (POD) function to the power system. The design of the POD algorithms in these devices requires estimation of the power oscillation frequency components and this is mostly achieved through the use of various filter combinations. However, these filter-based solutions are characterized by low bandwidth to extract the required signal components accurately, and this limits the dynamic performance of the FACTS controllers. Moreover, the filters are designed for specific frequencies, and a change in the system would reduce the performance of the methods. Thus, there is a need for a better estimation algorithm with fast and selective estimation of the required signal that is robust against system parameter uncertainties. In this paper, this is achieved by the use of a recursive least square algorithm that uses variable forgetting factor and a frequency adaptation mechanism. The investigated method has fast estimation in transient conditions without compromising its selectivity in steady state. The effectiveness of the proposed method is proven through simulation as well as experimental verification.

A Non-Stationary Analysis of Low-Frequency Electromechanical Oscillations Based on a Refined Margenau-Hill Distribution

This paper focuses on the use of quadratic time-frequency distributions (QTFDs) to characterize the temporal variation of low-frequency electromechanical oscillations (LFEOs) using ringdown data. A refined Margenau-Hill distribution (MHD) and a procedure to extract the instantaneous frequencies and damping factors as well as initial phase angles of system low-frequency modes when the analyzed signal is multi-component are proposed. The refinement process enjoys a fast-converging iterative algorithm and without loss of generality it can be applied to other QTFDs for using in other applications. A non-stationary synthetic signal as well as simulated ringdown data of a 5-area, 16-machine power system and real measured data of Western Systems Coordinating Council (WSCC) system are used to demonstrate the efficiency of the proposed method in the presence of measurement noise.

BBO algorithm-based tuning of PID controller for speed control of synchronous machine

A biogeography-based optimization (BBO) algorithm was used for tuning the parameters of a proportional integral derivative (PID) controller-based power system stabilizer (PSS). The proposed method minimizes the low frequency electromechanical oscillations (0.1–2.5 Hz) and enhances the stability of the power system by optimally tuning the PID parameters. This was achieved by minimizing the objective function of the integral square error for various disturbances. The performance of the BBO algorithm was tested on a single machine infinite bus system for a different range of operating conditions and the results were compared with particle swam optimization, adaptation law, and conventional PSS. The result analysis concluded that the BBO algorithm damps out the low frequency oscillations in the rotor of the synchronous machine effectively when compared to other methods. The algorithms were simulated with MATLAB/Simulink. The results from the simulation showed that the proposed controller yields a fast convergence rate and better dynamic performance.

Lead Lag Controller of TCSC Optimized by Bees Algorithm for Damping Low Frequency Oscillation Enhancement in SMIB

Power system is often vulnerable to low frequency electromechanical oscillations due to the interconnected configuration. A common lead-lag controller is used for one of the FACTS devices known as Thyristor Controlled Series Compensator (TCSC) as supplementary controller for damping purpose in order to improve transient stability and power oscillation damping of the system. As Bees Algorithm (BA) optimized the parameters of the TCSC lead-lag controller, thus its named is TCSC-BALL. In this study, the optimization problem is formulated as a constrained optimization with the main objective is to move the system eigenvalues to the left as far as possible in order to improve the system stability. Then, the system is simulated in MATLAB by using The Phillips-Heffron model for single machine infinite bus (SMIB) with responses of increases in mechanical power at t=1 second. The performance is observed in terms of electromechanical eigenvalues position on s-plane and damping responses of low-frequency oscillations where the system implemented with the TCSC-BALL controller given better results as compared to the system without and with the inclusion of conventional Power System Stabilizer (CPSS).

Estimation of Electromechanical Oscillations From Phasor Measurements Using Second-Order Generalized Integrator

On-line estimation of low-frequency electromechanical oscillations in an interconnected power system has attracted much attention as this provides vital information about the stability condition of the power system. In this paper, a measurement-based method for the estimation of the frequency, magnitude, and damping of an oscillation is proposed. The method can be applied to the phasor measurement data to extract further information about the power system. The proposed method is derived by applying modifications to the existing concept of second-order generalized integrator and adaptive notch filter. This paper details the mathematical derivation and stability properties of the proposed method and presents the simulation results to confirm the analytical derivations and the desirable performance of the proposed method.

Wavelets as a tool for power system dynamic events analysis – State-of-the-art and future applications

Power system is constantly exposed to disturbances of varying intensity and cascading propagation of disturbance that can lead to partial or total power system blackout. Some of the consequences are network topology changes, outage of generator units or occurrence of low-frequency electromechanical oscillations (LFEO). One of the techniques for signal analysis and processing used in the past 20 years for power system disturbance analysis, and helped in better understanding of power system dynamic, is Wavelet Transform (WT). This work reviews WT applications for power system dynamic behavior analysis. With research made on vast literature it can be concluded that WT technique has different applications in disturbances identification and localization, LFEO identification and analysis, and assessment of active power imbalance.

Power System Oscillations Damping by Robust Decentralized DFIG Wind Turbines

This paper proposes a new robust decentralized power oscillation dampers (POD) design of doubly-fed induction generator (DFIG) wind turbine for damping of low frequency electromechanical oscillations in an interconnected power system. The POD structure is based on the practical 2 nd -order lead/lag compensator with single input. Without exact mathematical model, the inverse output multiplicative perturbation is applied to represent system uncertainties such as system parameters variation, various loading conditions etc. The parameters optimization of decentralized PODs is carried out so that the stabilizing performance and robust stability margin against system uncertainties are guaranteed. The improved firefly algorithm is applied to tune the optimal POD parameters automatically. Simulation study in two-area four-machine interconnected system shows that the proposed robust POD is much superior to the conventional POD in terms of stabilizing effect and robustness.

Power Systems Oscillations Damping with Regard the Finite Speed of Propagation the Electromechanical Waves

Damping of the power system electromechanical oscillations with magnitude-phase excitation controller (MPH-EC), which is responsive to the deviations of the magnitude and phase of the terminal voltage phasor, and taking into account the finite speed of propagation the electromechanical waves, caused perturbation the power balance are considered in this paper. The structure of an integrated excitation control system of synchronous machines (IECS SM) using a remote phasor measurement units (PMU’s) to identify the cross-sections (tie lines) of electromechanical oscillations and putting into operation the function of power system stabilizer, installed on the revealed cross-sections of electromechanical oscillations has been proposed. A significant advantage of the proposed method and technology of damping the low-frequency electromechanical oscillations in the power system is its selectivity in relation to the main modes, with the lowest damping ratio, making the greatest contribution to the development of the power system instability, due to the action of the optimal number of MPH-EC located taking into account the given grid topology.

An Adaptive Power Oscillation Damping Controller by STATCOM With Energy Storage

This paper deals with the design of an adaptive power oscillation damping (POD) controller for a static synchronous compensator (STATCOM) equipped with energy storage. This is achieved using a signal estimation technique based on a modified recursive least square (RLS) algorithm, which allows a fast, selective, and adaptive estimation of the low-frequency electromechanical oscillations from locally measured signals during power system disturbances. The proposed method is effective in increasing the damping of the system at the frequencies of interest, also in the case of system parameter uncertainties and at various connection points of the compensator. First, the analysis of the impact of active and reactive power injection into the power system will be carried out using a simple two-machine system model. A control strategy that optimizes active and reactive power injection at various connection points of the STATCOM will be derived using the simplified model. Small-signal analysis of the dynamic performance of the proposed control strategy will be carried out. The effectiveness of the proposed control method to provide power oscillation damping irrespective of the connection point of the device and in the presence of system parameter uncertainties will be verified through simulation and experimental results.

Damping of Low Frequency Electro-Mechanical Oscillations Using UPFC Based on Cuckoo Optimization Algorithm

In this study alinearized Heffron-Phillipsmodel of a single machine power system installed with a unified power flow controller (UPFC) has been presented. The selection of the output feedback parameters for the UPFC controllers is converted to an optimization problem which is solved by cuckoo optimization algorithm (COA).COA, as a new evolutionary optimization algorithm, is used in multiple applications. This optimization algorithm has a strong ability to find the most optimistic results for dynamic stability improvement. The effectiveness of the proposed controller for damping low frequency oscillations is tested and results compared with imperialist competitive algorithm (ICA).The controllers are tested to variations in system loading. There sulks analysis reveals that COA minimized cost function and improved dynamic stability, better than ICA. In addition, the potential and superiority of the proposed method over the ICA is demonstrated. The simulation results analysis shows that the designed COA based output feedback UPFC damping controller has an excellent capability in damping low frequency oscillations and enhance rapidly and greatly the dynamic stability of the power systems.

Generator Coherency Using the Wavelet Phase Difference Approach

In this paper, the wavelet phase difference (WPD) approach is applied for the identification of power system areas with coherent generator groups. This approach allows observation, at different frequency bands, of movement of low frequency electromechanical oscillations (LFEO), identified at different parts of the power system and the identification of the inter-area components that move or do not move together. An illustration of the applied approach was performed on the New England (NE) 39-bus test system. The interesting results of WPD application are also presented in a real wide-area measurement data from European interconnected power system. By using the discrete wavelet transform (DWT) and Hilbert-Huang transform (HHT), the validation of results from WPD approach is also given.

Applications of wavelets and neural networks for classification of power system dynamics events

This paper investigates the possibility of classifying power system dynamics events using discrete wavelet transform (DWT) and a neural network (NN) by analyzing one variable at a single network bus. Following a disturbance in the power system, it will propagate through the system in the form of low-frequency electromechanical oscillations (LFEOs) in a frequency range of up to 5 Hz. DWT allows the identification of components of the LFEO, their frequencies, and magnitudes. After determining the energy components' share of the analyzed signal using DWT and Parseval's theorem, the input data for the classification process using a NN are obtained. A total of 5 classes of disturbances, 3 different wavelet functions, and 2 different variables are tested. Simulation results show that the proposed approach can classify different power disturbance types efficiently, regardless of the choice of variable or wavelet function.

Use of ANFIS Control Approach for SSSC based Damping Controllers Applied in a Two-area Power System

In an interconnected power system, low frequency electromechanical oscillations are initiated by normal smallchanges in system loads, and they become much worse following a large disturbance. Flexible AC TransmissionSystem (FACTS) devices are widely recognized as powerful controllers for damping power system oscillations. Thestandard FACTS controllers are linear controllers which may not guarantee acceptable performance or stability in theevent of a major disturbance. To overcome the drawbacks of conventional controllers, ANFIS (Adaptive Neuro-FuzzyInference System) control scheme has been developed in this paper, and it has been applied for the externalcoordinated control of series connected FACTS controllers known as Static Synchronous Series Compensators(SSSCs) employed in a two-area power system. In neuro-fuzzy control method, the simplicity of fuzzy systems andthe ability of training in neural networks have been combined. The training data set the parameters of membershipfunctions in fuzzy controller. This ANFIS can track the given input-output data in order to conform to the desiredcontroller. Simulation studies carried out in MATLAB/SIMULINK environment demonstrate that the proposed ANFISbased SSSC controller shows the improved damping performance as compared to conventional SSSC baseddamping controllers under different operating conditions.

Low Frequency Oscillations Damping by UPFC with a Multi Stage Fuzzy and Supplementary Controllers

Low frequency electromechanical oscillations are inevitable characteristics of power system which affect the transmission line transfer capability and the system stability. In this work, a new POD controller with DC-voltage regulator based on genetic algorithm is proposed for the UPFC for damping low frequency oscillations. The construction and implementation of this controller is fairly easy, which can be useful in real world power system. The effectiveness of the proposed controller has been tested on a SMIB power system in comparison with conventional UPFC controllers, GAMSF DC-voltage regulator and PSOMSF DC-voltage regulator under different operating conditions.

Modeling and unified tuning of distributed power flow controller for damping of power system oscillations

A new control scheme to improve the stability of a system by optimal design of distributed power flow controller (DPFC) based stabilizer is presented in this paper. The paper demonstrates the basic module, steady state operation, mathematical analysis, and current injection modeling of the DPFC. The purpose of the work reported in this paper is to design an oscillation damping controller for DPFC to damp low frequency electromechanical oscillations. The optimal design problem is formulated as an optimization problem, and particle swarm optimization (PSO) is employed to search for the damping controller parameters. Results demonstrate that DPFC with the proposed model can more effectively improve the dynamic stability and enhance the transient stability of power system compared to the genetic algorithm based damping controllers. The r and λ are relative magnitude and phase angle of DPFC controller. Moreover, the results show that the λ based controller is superior to the r based controller.

Hybrid Approach for Power System Operational Planning With Smart Grid and Small-Signal Stability Enhancement Considerations

Operational planning of power systems, especially in terms of overall reliability and security, is a key issue in the smart grid development. Hence, it is necessary to develop new strategies to cope with increasing uncertainties arising from the fast changing ways power systems are being operated. This paper presents a comprehensive approach to determine an optimal transmission network expansion plan considering the enhancement of small-signal stability through wide-scale deployment of the existing and planned transmission system assets. The dynamic model of the transmission network operational planning (TNOP) is solved based on a combination of the Mean-Variance Mapping Optimization (MVMO), and the classic dynamic programming method embedded with a heuristic procedure. Besides, a probabilistic eigenanalysis-based recursive method is proposed to determine the optimal control strategies that are highly relevant to the enhancement of the system small-signal stability performance throughout the planning horizon. Numerical results demonstrate the viewpoint and the effectiveness of the proposed approach in providing optimal strategies of minimum cost while avoiding the instability risk associated to poorly damped low-frequency electromechanical oscillations.