Power System Low Frequency Oscillation Research Articles

Mayfly Optimization Algorithm Applied to the Design of PSS and SSSC-POD Controllers for Damping Low-Frequency Oscillations in Power Systems

In this paper, it is proposed to apply the mayfly optimization algorithm (MOA) to perform the coordinated and simultaneous tuning of the parameters of supplementary damping controllers, i.e., power system stabilizer (PSS) and power oscillation damping (POD), that actuate together with the automatic voltage regulators of the synchronous generators and the static synchronous series compensator (SSSC), respectively, for damping low-frequency oscillations in power systems. The performance of the MOA is compared with the performances of the genetic algorithm (GA) and particle swarm optimization (PSO) algorithm for solving this problem. The dynamics of the power system is represented using the current sensitivity model, and, because of that, a current injections model is proposed for the SSSC, which uses proportional-integral (PI) controllers and the residues of the current injections at the buses, obtained from the Newton–Raphson method. Tests were carried out using the New England system and the two-area symmetrical system. Both static and dynamic analyses of the operation of the SSSC were performed. To validate the proposed optimization techniques, two sets of tests were conducted: first, with the purpose of verifying the performance of the most effective algorithm for tuning the parameters of PSSs, PI, and POD controllers, and second, with the purpose of performing studies focused on small-signal stability. The results have validated the current injections model for the SSSC, as well as have indicated the superior performance of the MOA for solving the problem, accrediting it as a powerful tool for small-signal stability studies in power systems.

Design and Optimization of Fractional Order PID Controller to Enhance Energy Storage System Contribution for Damping Low-Frequency Oscillation in Power Systems Integrated with High Penetration of Renewable Sources

This paper proposes adding a controller to the energy storage system (ESS) to enhance their contribution for damping low-frequency oscillation (LFO) in power systems integrated with high penetration of different types of renewable energy sources (RES). For instance, wind turbines and photovoltaic (PV) solar systems. This work proposes superconducting magnetic energy storage (SMES) as an ESS. The proportional–integral–derivative (PID) and fractional-order PID (FOPID) are suggested as supporter controllers with SMES. The PID and FOPID controller’s optimal values will be obtained using particle swarm optimization (PSO) is used as the optimization method. Both local area and inter-area oscillation is considered in this work as a LFO. To investigate the impact of adding the SMES with the proposed controller, a multimachine power system with different integration scenarios and cases is carried out with a PV system and wind turbine. The system responses are presented and discussed to show the superiority of the proposed controller both in the time domain and by eigenvalues analysis.

A Hybrid Technique for Analysis of Low-Frequency Oscillation in Power System

Estimating the low-frequency oscillation in an interconnected power system is the most important requirement to keep the power system in a stable operating condition. This research work deals with a hybrid robust and accurate approach using a combination of Estimation of signal parameters via rotational invariant techniques (ESPRIT) and Prony algorithm to extract the low-frequency oscillatory modes present in the power system. The observation inspires the hybrid method that the true modes of the signal are present in any signal processing technique (for example, Prony algorithm) along with other fictitious modes regardless of the order of the power system. Moreover, this research obtained true modes by calculating Euclidean distance and applying the threshold value concept. The proposed technique is tested with different noise conditions and varying sampling rates of Phasor Measurement Unit (PMU) to check the proposed hybrid technique’s robustness compared to Prony and the multiple ESPRIT method. Finally, the proposed method is applied to the real signal obtained from the Western Electricity Coordinating Council (WECC) network, and it estimates accurate and precise parameters compared to other methods. The accuracy for estimation of frequency and attenuation factor is calculated for the three-mode synthetic signal at a noise level of 10dB by the hybrid algorithm, multiple ESPRIT, and Prony algorithm, which shows that hybrid algorithm has minimum percentage error. Thus, the proposed hybrid algorithm accurately estimates the parameters of low-frequency oscillation as compared to other existing methods without involving any fictitious modes.

The Delay-Dependent DOFC for Damping Inter-Area Low-Frequency Oscillations in an Interconnected Power System Considering Packet Loss of Wide-Area Signals

In this paper, the inter-area low-frequency oscillations are restrained in the interconnected power system by making use of the delay-dependent wide-area dynamic output feedback controller (DOFC). Modal analysis is adopted to obtain the modes of inter-area oscillation to be controlled and the Schur truncation model reduction technique is represented to reduce the order of the power system. The augmented closed-loop system model, where the transmission delay and packet loss of wide-area signals are considered, is established. The sufficient conditions of exponentially mean-square stable are obtained according to Lyapunov’s stability theory. Finally, case studies are carried out on a two-area four-machine power system, where our proposed controller, a conventional controller, and the wide-area damping controller in the existing references are installed, respectively. The simulation results under different external disturbances, packet loss rates, and delays are presented to show the effectiveness and advantages of our proposed controller.

Online DMDc Based Model Identification Approach for Transient Stability Enhancement Using Wide Area Measurements

This letter proposes an online control strategy to enhance the overall damping of low-frequency power system oscillations of large inter-connected electrical networks. To achieve this objective, the proposed approach employs wide area measured signals to estimate an accurate online model of power system dynamics using the dynamic mode decomposition with control (DMDc) method. The DMDc technique applies singular value decomposition (SVD) to the collected data matrices such that an accurate low-order approximation of system dynamics is obtained. The estimated model is thereafter utilized in designing the wide area damping controller (WADC) using discrete linear quadratic regulator (DLQR). Furthermore, kalman filtering is deployed to update the states of the designed controller and to remove the noise that is contained in the measured signals. The effectiveness of the proposed method is tested on the 10 machines, 39-bus New England test system.

Damping of Low-Frequency Oscillations in Power Systems by Large-Scale PV Farms: A Comprehensive Review of Control Methods

Global warming and the desire to increase the use of clean energy have led to increasing the installation and operation of renewable energy power plants (REPPs), especially large-scale photovoltaic (PV) farms (LPFs). Given that the LPFs are added to power system or replace conventional power plants, they must be able to perform the basic tasks of synchronous generators (SGs). One of these tasks is the ability to mitigate the low-frequency oscillation (LFO) risk. Also, one of the LPFs problems is reducing the power system inertia and increasing the risk of LFOs. Therefore, these types of power plants must damp the LFOs through a power oscillation damping controller (PODC), similar to the performance of power system stabilizers (PSSs) in the SGs. This paper represents an overview of the different PODCs and control methods for LFOs damping by LPF. It seems that it can be a driver for future studies. Different studies show that the application of PODCs for LPFs can play an effective role to damp the LFOs and increase the power system stability.

Impact of Virtual Synchronous Machines on Low-Frequency Oscillations in Power Systems

The low-frequency oscillations (LFOs) inherent in power systems will be impacted by the increasing penetration of renewable energy sources (RESs). This paper investigates the impact of virtual synchronous machine (VSM) based RESs on the LFOs in power systems. A detailed two-machine test-bed has been developed to analyze the LFOs which exists when VSMs replace synchronous generators. The characteristics of the LFO modes, and the dominant states have been comprehensively analyzed. Furthermore, this study analyzes the LFO modes which exists in an all-VSM grid. The role of the power system stabilizers in the all-VSM grid has been comprehensively evaluated. The IEEE benchmark two-area four-machine system has been employed to corroborate the results of the small-signal analysis, and observe the transient performance. The analysis in this paper have been performed in MATLAB/SIMULINK environment.

Comparison of Different Methods for Identification of Dominant Oscillation Mode

Abstract This paper introduces and compares the various techniques for identification and analysis of low frequency oscillations in a power system. Inter-area electromechanical oscillations are the focus of this paper. After multiresolution decomposition of characteristic signals, physical characteristics of system oscillations in signal components are identified and presented using the Fourier transform, Prony’s method, Matrix Pencil Analysis Method, S-transform, Global Wavelet Spectrum and Hilbert Huang transform (Hilbert Marginal Spectrum) in time-frequency domain representation. The analyses were performed on real frequency signals obtained from FNET/GridEye system during the earthquake that triggered the shutdown of the North Anna Nuclear Generating Station in the east coast of the United States. In addition, according to the obtained results the proposed methods have proven to be reliable for identification of the model parameters of low-frequency oscillation in power systems. The relevant analyses are carried out in MATLAB coding environment.

A Robust Direct Parameter Identification of Exponentially Damped Low-Frequency Oscillation in Power Systems

Low-frequency oscillations in power systems can be modeled as an exponentially damped sinusoid (EDS) signal. Its frequency, damping factor, and amplitude are identified by the robust algorithm proposed in this paper. Under the condition of no noise, the exponentially convergent property of the proposed identification is proved by the use of time scale change, variable transformation, slow integral manifold, averaging method, and Lyapunov stability theorem in sequence. Under the condition of bounded additive noise, the antinoise performance of the identification of each parameter is investigated by the perturbed system theorem and error synthesis principle. The robustness of the proposed method is embodied in the following aspects: the exponential convergence for EDS signal with a wide range of frequency, especially with a rather low frequency; the boundary values of identification errors resulting from high-frequency sinusoidal noise of both frequency and damping factor can be adjusted by tuning the design parameters; and the different effects of the four design parameters on tracking performance and antinoise performance of each parameter identification. Simulation results demonstrate the performance of the algorithm and validate the conclusions.

Optimal Supplementary Controller Design for IPFC to Damp Low-Frequency Oscillations in Power Systems

Abstract: In this paper, the use of interline power flowcontroller (IPFC) on damping low –frequency oscillations(LFOs) are discussed and a new genetic algorithm(GA)-basedmultistage fuzzy (MSF) DC-Voltage regulator is proposed forIPFC to dampen low- frequency oscillations in (Double line)power system. The suggested control strategy isestimated under various operating conditions, and then it iscompared with conventional controllers to determine itseffectiveness. Time-simulation studies proved the robustperformance of the proposed regulator.Index Terms: Flexible AC transmission systems (FACTS),IPFC, low-frequency oscillation (LFO), genetic algorithm(GA)-based multistage fuzzy (MSF) DC-voltage regulator

Equipment-Level Locating of Low Frequency Oscillating Source in Power System With DFIG Integration Based on Dynamic Energy Flow

In view of the complex correlation between Doubly Fed Induction Generator (DFIG) internal components and control links which makes it difficult to locate the oscillating source in the equipment level, a DFIG equipment-level oscillating source locating method based on dynamic energy flow is proposed. Firstly, the energy correlation topology network of DFIG internal components and control links is constructed. On this basis, the analytical expressions of dynamic energy flows of DFIG internal components and control links are derived. And then, through Partial Directional Coherence (PDC) analysis, the values of causality between dynamic energy flows of DFIG internal components and control links are calculated, and the diagram of DFIG internal oscillation transmission causality is depicted. Thus according to the distribution pattern of causality values in the causality diagram, the oscillation transmission route is identified and the oscillating source is located. Finally, simulation tests in Real Time Digital Simulator (RTDS) of IEEE 10-machine 39-bus system verify that, the proposed method can quantitatively describe the intensity of interaction between dynamic energy flows of DFIG internal components and accurately identify the oscillation transmission route and the oscillating source in the equipment level. The proposed method can accurately track the original control link/physical component that causes the system to oscillate. Therefore, this paper will facilitate research on DFIG parameter tuning and oscillation suppression measures for low-frequency oscillation in power system.

Optimal robust disturbance observer based sliding mode controller using multi-objective grasshopper optimization algorithm to enhance power system stability

Power system stabilizer (PSS) has operated as an auxiliary controller for the synchronous generator excitation system to suppress the power system low frequency oscillations. This paper aims to design an optimal robust disturbance observer based sliding mode controller (RDO-SMC) acting as PSS to enhance the power system dynamic stability through the nonlinear control of excitation system. Indeed, the sliding disturbance observer has expeditiously estimated the accumulated consequence of unknown nonlinearities, parameter uncertainties, non-ideal dynamic models and exterior time-varying interferences in support of sliding mode controller. The sliding surface trajectory has been mathematically derived using Lyapunov theory. RDO-SMC has investigated the low frequency suppression of both the terminal voltage and angular speed. Due to multi-objective nature of the designed control problem, multi-objective grasshopper optimization algorithm (MOGOA) has been implemented to optimally tune the parameters of RDO-SMC and other understudy controllers. To verify and validate the performance of proposed controller, the analyses have been performed in single-machine infinite-bus and multi-machine power systems under different disturbance conditions. At last, the comprehensive simulation results have certainly confirmed the dynamic capability of the optimal RPO-SMC.

Low-Frequency Oscillation in Power System

Low-frequency oscillation can collapse the stability of the power system, which is considered to be one of the most significant challenges to a power system engineer. In earlier decades modal analysis was carried out for identifying lowfrequency oscillation modes, which have various drawbacks. In the present era, with the application of the Phasor measurement unit & various signal processing techniques, identification of lowfrequency oscillation is being carried out with accuracy to an extent. This paper provides a survey of recent research and development in the field of identification of low-frequency oscillation by different signal processing techniques. It is expected that this literature survey will provide researchers with some future direction in finding relevant references and developing suitable techniques for low-frequency oscillation detection in the interconnected power system.

Application of Prony Algorithm Based on EEMD for Identifying PSS Parameters

Some problems may caused by controller poor optimal control performance because of PSS parameters are hard for debugging, this paper proposes EEMD (Ensemble Empirical Mode Decomposition) and Prony algorithm combined online identification method for power system low-frequency oscillation. Firstly the EEMD is used to deal with the unstable signal and select the IMF (Intrinsic Mode Function). Secondly the model parameters of low-frequency oscillation in power systems are obtained by analyzing the IMF with Prony algorithm. Finally the PSS parameters have calculated through the residue method base on oscillation system dominant mode. Simulative results of case study show that it is better to identify the dominant mode of the signal. The proposed method has a certain reference value for engineering application.

Mode-based damping torque analysis method in power system low-frequency oscillations

The mode-based damping torque analysis (M-DTA) method for studying the effect of an external controller on power system low-frequency oscillations is proposed in this paper. Firstly, based on the interconnection model between the system and the controller in the frequency domain, the oscillation loop corresponding to the electromechanical oscillation mode is built, and the mode-based damping torque of the controller can be calculated. Then, the application of the M-DTA method in the power system is illustrated. The derivation shows that in the single-machine infinite-bus power system, the M-DTA method is completely equivalent to the classical damping torque analysis (C-DTA) method. In the multi-machine power system, the mode-based damping torque reflects the effect of the controller on the oscillation mode directly, overcoming the shortcomings of the C-DTA method in which there is no direct correspondence between damping torque and the oscillation mode. By deriving the relationship with the residue index, the M-DTA method shows higher accuracy than the residue method in applications such as controller parameter adjustment. Finally, two example power systems are presented to demonstrate the application of the proposed M-DTA method.

Assessment and Damping of Low Frequency Oscillations in Hybrid Power System Due to Random Renewable Penetrations by Optimal FACTS Controllers

This paper presents a detail investigation on low frequency oscillations of a variable solar and wind penetrated power system. An optimized UPFC controller is proposed for damping low frequency oscillations to enhance small signal stability of such a power system. The modulation index of series converter and phase angle of shunt converters are controlled simultaneously in proposed UPFC controller there by incorporating the advantage of SSSC and STATCOM. The squirrel search algorithm (SSA) is proposed for tuning controller gains. The proposed UPFC controller has been compared with SSSC and STATCOM controllers to damp oscillations. Random variation of SPV, wind energy and their integration with varying synchronous generations has been considered in this work. It has been observed that increasing solar, variable wind and their interaction with variable synchronous power generation put more detrimental effect on low frequency power system oscillations. The detail time domain simulation and system eigen values predicted that proposed controller is able to damp these oscillations much efficiently for enhancing stability of such a critical power system.

Influence of Rotor Damping Structures on Damping Torque Coefficient of Turbo-Generator During Low-Frequency Oscillation Caused by Large Disturbance

The damping structures of turbo-generators, such as rotor damping bars, core, and slot wedges, can provide positive damping effect for the low-frequency oscillation of power system. However, the magnetic saturation, distortion, and skin effect of generators make nonlinear damping effects during the low-frequency oscillation caused by large disturbance. In order to quantitatively describe the damping effect of the three damping structures, the damping torque coefficient (DTC) during the low-frequency oscillation is calculated by coupling time-stepping finite element method with the polynomial approximation method. The DTCs of turbo-generator with different rotor damping structures are obtained by comparing the individual and combined effect of the three damping components. Since there are several material options for the rotor slot wedges and damping bars, the influence of these materials on DTC is studied. A rotor damping structure that can not only improve the symmetry of rotor damping structure, but also enhance the DTC of turbo-generator is proposed. The results provide theoretical basis for power system stability enhancement by improving the rotor damping structures of turbo-generator.

Reduced-Order Dynamic Model of Modular Multilevel Converter in Long Time Scale and Its Application in Power System Low-Frequency Oscillation Analysis

A reduced-order dynamic phasor model of modular multilevel converter (MMC) in long time scale, which is applied for power system low-frequency oscillation analysis, is investigated. A tenth-order dynamic phasor model is derived in consideration of the internal circulation current dynamic of MMC. The model is verified via electromagnetic transient simulation. Then, an application of the singular perturbation method to MMC model reduction is presented. Separation of eigenvalues is used as a characterization of time scales and small time constant states is eliminated in the full-order model of MMC. MMC high-voltage direct current (HVdc) models with various orders are embedded into the four-machine two-area system to compare the low-frequency oscillation analysis results. The frequency domain analysis and time domain simulations show that the second-order model has satisfactory performance in describing the low-frequency characteristics of MMC. Moreover, the influence of MMC-HVdc transmission power and outer loop controller parameters on low-frequency oscillation is investigated using the second-order model. The effectiveness of reduced-order model in supplementary controller parameter design is also validated by comparing the difference in the response of various-order models to supplementary frequency-based control.

Integrations of Neural Networks and Transient Energy Functions for Designing Supplementary Damping Control of UPFC

This article presents an integrated scheme for supplementary damping control of unified power flow controllers (UPFCs) in order to mitigate low-frequency oscillations in power systems. The entire control system consists of the primary control and the supplementary control. In the primary control, the passivity-based control is considered in the current control loop of two converters for achieving more prompt and accurate dynamical responses. In the supplementary control, the transient energy function (TEF) approach will be explored first for designing the damping control of UPFCs. This control action can be considered as an extension of droop control used in the synchronous generator. In order to further cope with unmodeled dynamics of power systems and provide the online dynamic adaptation ability, neural networks approximated control actions are designated for online weight adjustments of the TEF-based supplementary control. Numerical simulations on three benchmark systems have been performed to validate the proposed control method for providing the extra damping and suppressing power swings even under severe operating conditions.

Damping of low-frequency oscillation in power systems using hybrid renewable energy power plants

Global warming, increase in environmental pollution, and high cost of electrical power generation using fossil fuels are considered the most important reasons for the application of renewable energy power plants (REPPs) around the world. In recent years, a new generation of REPPs called hybrid renewable energy power plants (HREPPs) has been implemented in order to have higher efficiency and reliability than conventional REPPs such as wind power plants and photovoltaic power plants. The HREPPs include two or more renewable energy generation units such as wind turbine generation units, and PV generation units. In case of high penetration of these types of power plants, the most common tasks of synchronous generators should be supported by them. One of these tasks is the ability to reduce the low-frequency oscillation (LFO) risk through power oscillation damper such as the power system stabilizers of synchronous generators. In this paper, a novel method is proposed for LFO damping by HREPPs, which is based on the design of an optimal power oscillation damper (OPOD) implemented in the generic HREPP controller model. The structure of the proposed OPOD is a 2nd-order single-input lead-lag controller, and its performance is investigated in a modified two-area test system. The simulation results show the proper performance of the HREPP for LFO damping using the proposed OPOD in the various loading levels and different short circuit ratio values.