Power System Oscillation Modes Research Articles

Determination of dominant oscillation section in power system based on MSSA algorithm and dissipated energy

The identification of dominant oscillation paths is one of the key aspects in studying the stability of inter-area power grids. This paper proposes an improved multi-channel singular spectrum analysis (MSSA) algorithm combined with dissipative energy to identify dominant oscillation section in power systems. First, an improved MSSA method is introduced, which determines the order using the singular value energy spectrum and can effectively identify inter-area oscillation modes in power systems. Second, an energy function analysis method is proposed, which is well-suited for determining dominant oscillation section in power systems. This method is minimally affected by time-varying and nonlinear factors and allows for the visualization of generator states. Finally, the IEEE 68-bus system is used to construct an equivalent model, demonstrating the method's versatility. Simulation results validate the noise resistance, computational efficiency, and applicability to topology change scenarios of the proposed method. This method can accurately analyze inter-area oscillation modes and help to establish the dominant oscillation section.

Online Monitoring of Oscillation Modes for Small-Signal Security Assessment

This paper presents the main concepts of small-signal security assessment of power systems, focusing on the online monitoring of small-signal stability. In this work, a computational tool for online monitoring of oscillation modes (OLMO) in power systems is proposed. The objective of the methodology consists of determining small-signal stability margins, security levels, and corrective measures that can improve the damping factor of oscillation modes present in such systems. These corrective measures can be associated with possible redispatches of power plants. In this context, the Closest Security Boundary for Generation Redispatch using Eigenvalue Sensitivities, known as CSBGRES Method, could be applied to determine an optimized redispatch for the power plants of the system to ensure a desired minimum damping factor, previously chosen, for oscillation modes. The proposed tool can be applied for controlling power plant dispatches on Smart Grids, focusing on the damping factor of oscillation modes. A small test system is used to evaluate the proposed computational feature and the results were presented to demonstrate its importance to power system security. Results of the utilization of OLMO on the Brazilian Interconnected Power System (BIPS) are presented to prove the viability of using this method in large-scale power systems.

Improving power swing detection in the presence of doubly-fed induction generator wind farms based on setting adaptation

This article proposes a new approach to improve the security of transmission line protection by correctly detecting power swing when large-scale doubly-fed induction generator wind farms (DFIGWF) exist in the proximity of the relay. In the presence of large-scale DFIGWFs, following large disturbances, power swing may probably cause the distance protection to malfunction. This issue can also lead to widespread transmission line outage and cause instability in the power system. Therefore, a new approach is proposed to solve the challenge by adapting the power swing blocking (PSB) function in the distance protection relays and utilizing the dominant power system oscillation modes. Thus, related calculations are performed in a central module remotely connected to intelligent electronic devices (IEDs) for distance protection and stabilized against power swing. The calculation to adjust the PSB setting of the IEDs in the central module is based on the oscillation modes of the power system and the rate of change of impedance, which is influenced by the penetration rate of the DFIGWFs. Simulation studies have been done on two test systems and the results reveal that the proposed scheme significantly improves the security of distance protection against power swing under different DFIGWF intrusion conditions.

Impact analysis of COVID-19 pandemic on the electricity demand, frequency control and electromechanical oscillation modes of the Brazilian Interconnected Power System using low voltage WAMS data

COVID-19 pandemic presented unique features among the range of threats encountered over the last century. Its impact echoes throughout the world affecting societies and their patterns of behavior, hence affecting the usage of electricity and the operation of power systems. This paper provides an analysis of the impact of COVID-19 Pandemic on the electricity demand, frequency control and electromechanical oscillation modes of the Brazilian Interconnected Power System (BIPS), taking into account public data disclosed by the Brazilian Independent System Operator (BISO) and data acquired through the MedFasee Project, the Brazilian low voltage wide area monitoring system (WAMS) leaded by the Federal University of Santa Catarina. Main results indicate that the BISO has been successful on controlling the system frequency and the main electromechanical interarea modes, despite the occurrence of a significant demand reduction in the BIPS in a certain period of time due to the COVID-19 pandemic. The total time of operation in underfrequency or overfrequency registered during the months with most demand reduction is at most 20% lower than the maximum time registered in the other months studied. The damping of the modes observed in the months with demand reduction has not reached values lower than 10% and the frequencies of oscillation have varied in a range of 0.05Hz, in agreement to what has been observed in other months.

Evaluating generator damping for wind‐integrated power system in ambient conditions

This paper proposes a power system multimode generator energy loss factor (GELF) based on energy flow method under environmental excitation. This index can evaluate generator damping changes in different oscillation modes in power systems, timely discover the damping deterioration of the generator, and track the source of low-frequency oscillation. A signal expression method for electrical frequency domain under environmental excitation is derived. This method is combined with dissipated energy flow method to obtain a new type of GELF. In terms of signal processing, dynamic mode decomposition and Morlet wavelet filter extraction system mode components are used to improve computing accuracy. The proposed index enables online calculation with the support of phasor measurement unit and wide area measurement system. Simulation analysis is conducted in a standard 39 node system and wind-integrated power system. Test results show the effectiveness and generality of the proposed index and method.

Damping the electromechanical oscillation modes (EOMs) in DFIG-integrated power systems with sensitivity analysis and optimization to outputs of SGs

The electromechanical oscillation modes (EOMs) are the oscillations strongly related to the synchronous generators (SGs), which are dangerous to the security of the SGs and the stability of the power system. Integration of the doubly-fed induction generators (DFIGs) causes dynamic interaction among the SGs and the DFIGs, and adds the difficulty to damp the EOMs. This paper proposes a damping scheme to the EOMs based on the sensitivity analysis and the optimization model. The novelties include, 1) The sensitivities of the electromechanical loop participation ratios related to the EOMs are newly given by the sensitivities of the participation factors. 2) Since the participation factors are composed of the eigenvectors, by introducing the magnitude and phase angle constraints, the sensitivity model of the eigenvectors is improved to find the unique solution. 3) Since the bus powers changes the bus voltages and the eigenvalues, but are not shown in the state matrix, the sensitivities of the state matrix with respect to the power outputs of the SGs are derived with the help of the Jacobian matrix in power flow analysis. 4) Based on the sensitivities, an optimization model is proposed to coordinate the outputs of the SGs and damp the EOMs of the power systems. In the numerical analysis, the accuracy of the sensitivity models is verified by comparing with the result from continuous calculation. The optimization effect is verified by the time-domain analysis. It is found that the not only the active power but also the reactive power of the SGs are effective to damp the EOMs.

An Efficient Eigenvalue Tracking Method for Time-Delayed Power Systems Based on Continuation of Invariant Subspaces

Time delays are inevitable in the power systems with wide-area control signals, which may compromise the control pe-rformance and thus jeopardize the stability of the power systems. To analyze the impacts of system parameters on critical oscillation modes of a time-delayed power system (TDPS), a new method for eigenvalue trajectory tracking of TDPS is proposed in this paper based on the continuation theory of invariant subspaces. When small changes are imposed on system parameters, such as parameters of wide-area damping controllers (WADCs) and time delays, the invariant subspaces are continuously predicted and corrected, followed by the eigenvalues and eigenvectors. In the process, the predictor and corrector are computed by solving linear equations sparsely and in blocks, which is highly scalable and computationally efficient for large-scale power system applications. The 16-generator 68-bus test system and two real-world power grids in China are used to test and demonstrate the proposed method. The results show that the proposed method can accurately and efficiently track eigenvalue trajectories for TDPS, especially for large-scale power grids. In addition, the sensitivities of eigenvalues and eigenvectors with respect to WADCs' parameters and time delays are obtained as by-products of the approach.

A Method to Design Power System Stabilizers in a Multi-Machine Power System Based on Single-Machine Infinite-Bus System Model

This paper proposes a method to design power system stabilizers (PSSs) based on single-machine infinite-bus system models to mitigate the risk of low-frequency electro- mechanical power oscillations in an N-machine power system. First, models of N fabricated identical-machine power systems are established for the N-machine power system. Analysis in the paper indicates that the electromechanical oscillation mode of fabricated identical-machine power systems with the least damping is of less damping than the electromechanical oscillation modes of N-machine power system. Second, it is proved that models of fabricated identical-machine power systems are dynamically equivalent to the single-machine infinite-bus system models. Finally, it is suggested that the PSSs are designed using single-machine infinite-bus system models to enhance the least damped electromechanical oscillation mode of fabricated identical-machine power systems. This eventually improves the damping of electromechanical oscillation modes of N-machine power system, thus mitigating the risk of low-frequency electromechanical power oscillations. In the paper, the proposed method is demonstrated and evaluated by using three well-known example multi-machine power systems. Effectiveness of PSSs is confirmed by the results of modal computation and simulation.

DFIM versus synchronous machine for variable speed pumped storage hydropower plants: A comparative evaluation of technical performance

Abstract Nowadays, variable speed (VS) pumped storage technology has become a new trend, for providing better support to power systems towards de-carbonization. This study intends to conduct a comparative evaluation of technical performance of two types of pumped storage hydropower plant (PSHP): the state-of-the-art PSHP based on doubly fed induction machine (DFIM) known as VS and conventional PSHP based on synchronous machine (SM) known as fixed speed (FS). Aiming at this purpose, a case of 343 MW hydro pump-turbine (HPT) coupled to DFIM with 381 MVA in comparison to the SM with same capacity, i.e., 381 MVA, is applied as a study case. The detailed model (discrete mode) in MATLAB/SimPowerSystem™ is adopted to conduct simulations under diverse conditions. Simulations and evaluations are for both architectures under two operation modes (generating, motor), in terms of the following items: (1) frequency regulation, (2) transient stability assessment under fault ride-through condition, (3) harmonic distortion, (4) damping of different oscillation modes in power systems, (5) reactive power support considering actual limitations based on P-Q capability curves. The results show the performance differences between the two types of PSHP in diverse aspects for safe, stable and economical operation, as well as the performance in grid ancillary services.

Power System Oscillation Mode Prediction Based on the Lasso Method

This paper utilizes modern statistical and machine learning methodology to predict the oscillation mode of interest in complex power engineering systems. The damping ratio of the electromechanical oscillation mode is formulated as a function of the power of the generators and loads as well as bus voltage magnitudes in the entire power system. The celebrated Lasso algorithm is implemented to solve this high-dimension modeling problem. By the nature of the L 1 design, the Lasso algorithm can automatically render a sparse solution, and by eliminating redundant features, it provides desirable prediction power. The resultant model processes a simple structure, and it is easily interpretable. The precision of our sparse modeling framework is demonstrated in the context of an IEEE 50-Generator 145-Bus power network and an online learning framework for the power system oscillation mode prediction is also provided.

Improvement to observability measures of LFO modes in power systems with DFIGs

Observation of the low-frequency oscillation (LFO) modes in power systems is important to design the damping scheme. The state equations of the power system with the doubly-fed induction generators (DFIGs) are derived to find the LFO modes related to the synchronous generator (SGs) and the DFIGs. The definition of the observability measure is improved to consider the initial output and the attenuation speed of the modes. The sensitivities of the observability measures to the control parameters are derived. The numerical results from the small and large-disturbance validate the LFO modes caused by the DFIGs, and different observability measures are compared. Adjustment of the control parameters is chosen based on the sensitivity model to improve the observability and damping ratio of the LFO mode, and the stability of the wind power system.

Inter‐area low‐frequency power system oscillations caused by open‐loop modal resonance

This study examines a modal condition to cause inter-area, low-frequency, electromechanical power oscillations in an interconnected power system with two subsystems. The modal condition being examined is the closeness of two electromechanical oscillation modes from each subsystem on the complex plane, which is referred to as open-loop modal resonance. The analysis in this study indicates that under the condition of open-loop modal resonance, the electromechanical oscillation modes of the interconnected power system are located at approximately opposite positions on the complex plane with respect to the resonant electromechanical oscillation modes of the subsystems. Hence, when open-loop modal resonance occurs, one electromechanical oscillation mode of the interconnected power system must have reduced damping. In this study, the damping reduction in the inter-area, low-frequency power oscillations caused by open-loop modal resonance is demonstrated using example power systems. An incident of inter-area, low-frequency electromechanical power oscillations that occurred in an actual large-scale power system in China is examined. The examination results indicate that the poorly damped, inter-area, low-frequency power oscillation incident was caused by open-loop modal resonance.

A procedure to design wide-area damping controllers for power system oscillations considering promising input–output pairs

The expansion of the wide-area measurement system has provided some control strategies to improve the low-frequency oscillation modes in electric power systems. One of these strategies is to use remote signals for a wide-area damping controller (WADC) to enhance the small-signal stability of the power system. However, the expansion of the Electric Power System increased the generator number connected to the grid, and then some challenges to the WADC design surged such as which input–output pairs of the WADC should be designed to improve the closed loop system damping. Typically, the WADC is a centralized controller and may have many design elements. The interactions among the elements may compromise the central controller design and its purpose. This paper proposes a procedure based on genetic algorithms in order to design a robust central controller. This procedure automatically chooses the input–output pairs of the central controller that will contribute to damping the low-frequency oscillation modes. The design procedure considers topological changes and time delay variations. Small-signal analysis and time-domain nonlinear simulations are carried out in the multi-machine Australian Equivalent Power System, an IEEE benchmark model for small-signal stability analysis.

Evaluation of a Maximum Likelihood Estimator for the Identification of Power Systems Oscillation Modes

In this paper, a maximum likelihood (ML) estimator is applied for the estimation of power system oscillation modes. A regularization term is used in order to improve the estimation. An index is proposed to rank the modes and separate spurious from real modes. The ML estimator is compared with Prony method, and its advantages and limitations are discussed. Both methods are applied to synthetic systems and to real Phasor Measurement Unit (PMU) data acquired from the Brazilian Interconnected Power System (BIPS). The results show that the proposed maximum likelihood estimator is useful to complement and validate the results obtained by Prony analysis.

Prioritization of PMU Location and Signal Selection for Monitoring Critical Power System Oscillations

This paper proposes a method of selecting and/or locating phasor measurement unit (PMU) signals for monitoring critical oscillation modes in large power systems. A robust indicator, modal participation ratio, is introduced to identify critical PMU locations and signal channels, in order to monitor modes of interest to power system operators. This indicator is easy to compute in practice, and is theoretically rigorous based on linear control theory and spectral analysis. This indicator can suggest location and/or selection of PMUs in order to most effectively observe modes of interest to power system operators. The effectiveness and robustness of the algorithm is illustrated in both modified 68-bus system and 140-bus system.

Distributed Estimation of Power System Oscillation Modes Under Attacks on GPS Clocks

Phasor measurement units (PMUs) are playing an increasingly important role in wide-area monitoring and the control of power systems. PMUs allow synchronous real-time measurements of voltage, phase angle, and frequency from multiple remote locations in the grid, enabled by their ability to align to global positioning system (GPS) clocks. Given that this ability is vulnerable to GPS spoofing attacks, which have been confirmed easy to launch, in this paper, we propose a distributed real-time wide-area oscillation estimation approach that is robust to GPS spoofing on PMUs and their associated phasor data concentrators. The approach employs the idea of checking update consistency with histories and across distributed nodes and can tolerate up to one third of compromised nodes. It can be implemented in a completely decentralized architecture and in a completely asynchronous way. The effectiveness of the approach is confirmed by numerical simulations of the IEEE 68-bus power system models.

A method for the identification of low frequency oscillation modes in power systems subjected to noise

The high penetration of renewable energy sources and the consequent integration of such distributed energy generation systems into the grid have significantly increased the interaction between power sources, which can result in low frequency oscillations. Different control techniques are proposed in literature to suppress low frequency oscillations, but the first step to attenuate such oscillations is to characterize them in terms of their dominant modes. This paper combines different results from literature to propose a unified two-step methodology for the mode characterization of low frequency oscillations based on the signals acquired by wide area measurement systems. Since the measured signals typically contain noise, the first stage of the proposed method uses the basis pursuit denoising method combined with a Tunable Q-factor wavelet transform to increase the signal-to-noise ratio and improve the identification results. In a second stage, an improved version of the matrix pencil algorithm, as proposed in this paper, is used to identify the parameters of low frequency oscillation dominant modes. Both simulation and experimental results show that the proposed method has better characterization accuracy than traditional methods, especially when Gaussian noise is considered in the measurements. In addition, the processing time has proven to be reasonable for online identification and characterization of low frequency oscillations.

A VNS algorithm for the design of supplementary damping controllers for small-signal stability analysis

This paper presents a variable neighborhood search (VNS) optimization algorithm for the design of the parameters of supplementary damping controllers: power system stabilizers (PSS) and the interline power flow controller–power oscillation damping (IPFC–POD) set. The objective is to insert damping to local and inter-area oscillation modes in multimachine power systems. The electric power system dynamics is represented by the current sensitivity model. Simulations were carried out using three systems: a test system known as Two-Area Symmetrical and two real systems, the New England and the Reduced Southern Brazilian. The VNS method was compared with a multi-start algorithm in terms of performance, showing better convergence rates. The proposal was also able to obtain solutions with high damping levels, that showed to be robust when changes on the operating point of the power system were considered. Finally, it has been verified that the PSS controllers were effective for damping the local mode oscillations, while the IPFC–POD set operated mainly damping the inter-area modes.

On the impact index of synchronous generator displaced by DFIG on power system small-signal stability

As the maturity of wind power technology and the ageing and retirement of conventional synchronous generators, the displacement of synchronous generators by wind power generators would be a trend in the next few decades. The power system small-signal angular stability caused by the displacement is an urgent problem to be studied. The displacement of the SG by the DFIG includes withdrawing the dynamic interactions of the displaced SG and adding the dynamic interactions of the displacing DFIG. Based on this fact, a new index is proposed to predict the impact of the SG to be displaced by the DFIG on power system oscillation modes. The sensitivity index of the oscillation modes to the constant inertia of the displaced SGs, proposed in early literatures to estimate the dynamic impact of the SG being displaced by the DFIG, is also compared with the proposed index. The modified New England power system is adopted to show various results and conclusions. The proposed index can correctly identify the most dangerous and beneficial displacement to power system small-signal angular stability, and is very useful in practical applications.

Online monitoring of generator damping using dissipation energy flow computed from ambient data

Online monitoring of generator damping assists in identifying wrong parameters or detrimental changes in generator control systems that may reduce damping ratios of power system oscillation modes. An approach for generator damping estimation using ambient data during normal operation of power systems is proposed. The ambient phasor measurement data at generator terminal is collected and filtered, and then the dissipation energy flow (DEF) into the generator is computed. The rate of change of the DEF represents the rate of transient energy dissipation of the generator and is used to estimate the generator damping. Test results show the validity and possible applications of the approach. A more comprehensive online monitoring system of small-signal stability can be constructed using the approach together with system mode estimation methods.