Inter-area Oscillation Modes Research Articles

Designing of wide-area damping controller for stability improvement in a large-scale power system in presence of wind farms and SMES compensator

The main aim of this paper is the stability improvement of a large-scale power system including wind farms and SMES (Superconducting Magnetic Energy Storage) compensator. For this purpose, at first, the mathematical model of the whole system is extracted in order to accurately investigate the role of wind farms and SMES in the stability studies. The stability analysis is based on the design of damping controllers which is provided through the global signals dependent on the time delay and local signals without the time delay. In modeling of the time delay, damping factor of inter-area oscillation mode is used to obtain larger delay margin, and then, the Lyapunov-Krasovskii function and inequality integral are employed to evaluate the stability condition related to the time delay. The controllability/observability index is used to choose the best candidate signals in the input of WADC (Wide-Area Damping Controller) in order to enhance the residual value of the weakest critical mode identified by modal analysis. The simulation results are investigated through different scenarios of wind turbine and power system in non-linear time domain as well as frequency domain using eigenvalues analysis. The results verify the effectiveness of the proposed controller under various time delays.

Statistical inference of multivariable modal stability margins of time-delay perturbed power systems

This paper proposes a modal statistical inference algorithm to define multivariable operational stability limits of time-delay perturbed dynamic systems by employing remote sensor signals. Our proposal overcomes the drawbacks of linear independence and inter-area geometry of time-delays to analyze multiple-input, multiple-output dynamic systems. The manuscript contributes with: (a) the study of stability margins under distributed uncertainty and time-delays for large power systems, (b) the determination of stability conditions of inter-area oscillations through a new probabilistic modeling approach under the influence of intermissions, and (c) the usage of the proposed methodology to derive controlled stability limits and assess the modal resilience of perturbed power systems. Studies on the multi-scale signals sensitivity and multivariable polynomial intersection from empirical perspectives in modal stability analysis are also explored. Results on an IEEE 16-generator 68-bus system are presented to illustrate the effectiveness of the proposed algorithm. The estimation of multivariable operational stability limits and time-delays of inter-area oscillation modes are verified with the vector fitting procedure and first-order Padé approximation.

Ambient-Data-Driven Modal-Identification-Based Approach to Estimate the Inertia of an Interconnected Power System

A novel approach for estimating the inertia of an interconnected power system is presented using the identification of interarea oscillation modes (frequency, damping and mode shape) extracted from ambient data. The proposed method concentrates on estimating the values of the effective inertia of each area rather than the equivalent inertia of the entire system. Based on an equivalent two-machine system (ETmS) obtained by combining small signal stability analysis (SSSA) with the structure of the power grid, we derive a mathematical relationship between the effective inertia of each area and the interarea oscillation modes. Furthermore, the interarea oscillation modes can be extracted from ambient data, and the developed scheme enables an online estimation of the inertia only by using the outputs measured by PMUs. The performance of the proposed methodology is tested via numerical simulation cases and real data.

Optimal Oscillation Damping Controller Design for Large Scale Wind Integrated Power Grid

This article presents a reduced-order model-based optimal oscillation damping controller (OODC) design for doubly fed induction generator (DFIG) based wind turbines (WTs). The objective of OODC is to shift the critical interarea modes (IAMs) of the WT integrated power system to the desired location using optimal output feedback. Such a controller provides a supplementary control signal to the DFIG local controller to inject the modulated active and reactive power that provides damping support to the overall power system's local and IAMs of oscillation. In the design, first, a reduced-order model of the WT integrated power system that captures all the relevant system dynamics is designed. Then, a cost function-based optimization is formulated and solved to improve the damping of the critical modes. Simulation studies are conducted on a modified IEEE 68 bus system. The results of eigenvalue analysis show that the dominant and poorly damped IAMs are shifted toward the left half-plane thus enhancing the overall system stability margin. Also, nonlinear time-domain simulation is performed to show the effectiveness of the proposed OODC to effectively improve the damping of the IAMs of the system.

Dominant inter-area oscillation mode identification using local measurement and modal energy for large-scale power systems with high grid-tied VSCs penetration

Appropriate phasor measurement unit (PMU) signals must be selected to monitor electromechanical oscillations for large-scale renewable energy connected power system. Considering the response mechanism of the active and reactive power of grid-tied voltage source converters (VSCs) in the electromechanical time scale, a local measurement signal selection strategy for monitoring inter-area oscillations (0.1–0.7 Hz) based on the inherent electromechanical characteristics of the synchronous generators (SGs) is proposed. Moreover, optimized dynamic mode decomposition (OpDMD) algorithm is used to extract dominant modal parameters (e.g., oscillation frequency, damping ratio, and mode shape). First, from the perspective of frequency response characteristics, the dynamic interaction mechanism between grid-tied VSCs and the AC grid is revealed in the electromechanical time scale. Second, considering the intrinsic relationship between the inherent inertia constant of the SG and observability of response after a disturbance, a local measurement signal selection strategy for monitoring the inter-area electromechanical oscillation of power systems with high grid-tied VSCs penetration is proposed. On the basis of the selected local measurement signals, the OpDMD algorithm identifies dominant inter-area oscillation parameters. Results of the IEEE 16-generator 5-area system show that the proposed method can accurately extract electromechanical modal parameters from the limited PMU measurements, verifying the effectiveness of the local measurement signal selection strategy for inter-area oscillation monitoring of power systems with high grid-tied VSCs penetration.

PV Solar System Control as STATCOM (PV-STATCOM) for Power Oscillation Damping

This paper presents a novel control of photovoltaic (PV) solar system as a FACTS device STATCOM, termed PV-STATCOM, for power oscillation damping (POD) in transmission systems. In the proposed control, as soon as power oscillations due to a system disturbance are detected, the solar farm discontinues its real power generation function very briefly (few tens of seconds) and makes its entire inverter capacity available to operate as a STATCOM for POD. As soon as power oscillations are damped, the solar farm restores real power output to its pre-disturbance level in a ramped manner, while keeping the damping function activated. This results in much faster restoration than that specified in grid codes. During nighttime, the solar farm performs POD with its entire inverter capacity. It is shown from EMTDC/PSCAD simulations that the proposed control provides significant increase in power transfer capacity on a 24/7 basis in systems that exhibit both local inertial and interarea oscillatory modes. The proposed PV-STATCOM is about 50–100 times cheaper than an equivalent STATCOM for providing POD at the same location. This novel control can potentially bring large savings for transmission utilities and open up a new revenue making opportunity for solar farms for providing POD.

Wide-area measurement-based modal decoupling for power system oscillation damping

Inter-area oscillation modes usually fall within the same frequency range of 0.1–1.0Hz; thus, power oscillation damping (POD) control methods should avoid unnecessary excitation of weakly damped modes. This paper presents a decoupled control strategy to damp inter-area oscillations in the power grid. Pure oscillation mode signals are extracted from wide-area measurements and used as feedback input for POD actuators such as power system stabilizers or high-voltage direct current transmission. The decoupled control strategy is able to increase the damping of the concerned oscillation modes without deteriorating others. This proposed strategy could be implemented independently, or serve as a complement and work along with conventional POD controllers to damp concerned inter-area modes. The proposed method has been tested on a modified MinniWECC system. Extensive results indicate that inter-area oscillations can be successfully and precisely damped using the proposed decoupled strategy.

Cross-Gramian Model Reduction Approach for Tuning Power System Stabilizers in Large Power Networks

Poorly damped inter-area modes of oscillations represent a major concern to power system operation since they detain the power transfer capability of transmission networks. This situation becomes more stringent as the tie-lines are heavily stressed and/or large amounts of renewable energy resources are installed. To overcome this issue, a detailed mathematical model is proposed in this paper to reduce the linearized model of a large power system using the cross-Gramian technique. The presented approach divides the system into a study area which contains one generation unit with installed power system stabilizer (PSS) and an external one which comprises the rest of generation units in the system. Model order reduction is only applied to the external area with the objective of maintaining the characteristics of the original model. Meanwhile, the dynamics of the study area are preserved to provide the required damping through the designed PSS. In addition, an online tuning methodology is also presented to provide robust damping performance in response to changes in the system operating conditions. The deployed cross-Gramian model order reduction alleviates the computational burden and time associated with the online PSS tuning when original power system models are used. The effectiveness of the proposed approach is tested using the New-England 39-bus system in addition to another practical system which resembles the Northern Regional Power Grid India test system.

Integration of automatic voltage regulator and power system stabilizer: small-signal stability in DFIG-based wind farms

The increasing penetration of wind farms in the energy sector directly affects the dynamic behavior of the power system. The increasing use of wind energy in the power system worsens its stability and inherently influences the firmness of a small signal. To investigate these effects, one of the synchronous generators (SGs) of the grid is considered defective and is replaced by a doubly fed induction generator (DFIG)-based wind farm of the same rating. The small-signal stability of a power system is usually evaluated via eigenvalue analysis where local-area and inter-area oscillatory modes for the New England test system are identified. SG controls, such as automatic voltage regulator (AVR) and power system stabilizer (PSS), are added to attenuate the generated disturbances. In this study, the impact of wind energy on the small-signal stability of the power system is investigated. Different combinations of AVR and PSS types are considered to mitigate the undesirable alterations. A comparative study is performed based on numerical simulations to choose the best combination of AVR and PSS types. The obtained results prove that the proposed combination yields good results in terms of stability enhancement both under normal operating conditions and in DFIG-based wind farms.

Modeling and Simulation of a Synchronous Generator with Rotor Angle Stability and Solve Inter Area Mode of Oscillation in Power System using Power System Stabilizer(PSS)

Power System stabilizers are a form of supplementary control that is used to provide additional damping to the inter area mode oscillations or to stabilize a generator whose voltage regulator gain is such that it may result in negatively damped machine-to-system oscillations under certain conditions. It has seen observed that the damping of these small power oscillations can be improved by leading back appropriate stabilizing signals to the input of the gain’s exciter. Some input signals that have been considered in the research are slip speed, accelerating power, frequency. In this manuscript, we will use an establish approach to obtain a preliminary design for a power system stabilizer with slip speed as the feedback signal.

Studi Kestabilan Generator Sistem Sulselrabar

In the standard operating system, the input parameters such as changes in the mechanical torque of the turbine and changes in the field voltage of the amplifier from the exciter need to be considered. Some studies that can be done include the study of the dynamic stability of synchronous generators when dealing with small changes that occur using the eigenvalue approach which is the roots of the characteristic equations of the system state space equation. The eigenvalue can show information on system stability and is related to the response of time to changes in the system. The system used is in the Sulselrabar electrical system. From the simulation results show the characteristics of the system in terms of the frequency response and angle of the generator rotor. For the eigenvalue system value in the inter-area oscillation mode is -0.33293 + 4.0844i, for the oscillation mode it is -0.9043 + 7.9670i. While the generator frequency response, where oscillations occur before reaching steady state conditions. The biggest overshoot response occurs in Old Tello plants, with a maximum overshoot of 0.09124 pu and a minimum of -0.2227 pu. While the smallest overshoot response is found in the Bakaru hydroelectric power plant which is equal to 0.004681 maximum pu and -0.02563 minimum pu.

Small‐signal stability‐constrained optimal power flow analysis of multiterminal VSC‐HVDC systems with large‐scale wind farms

As a solution for the large‐scale wind power transmission in a power system model in East Japan, multiterminal VSC‐HVDC systems are proposed to be installed in the system model. To evaluate the effectiveness of the systems, small‐signal stability‐constrained optimal power flow (SSSC‐OPF) analysis in mixed AC/multiterminal VSC‐HVDC systems is developed. It is revealed by SSSC‐OPF analysis that the system reinforced only by an AC system is exposed to unstable operations. In contrast, mixed AC/multiterminal VSC‐HVDC systems do not suffer from such unstable system operations. On top of that, the differences in multiterminal VSC‐HVDC systems with different configurations are also discussed. Different annual fuel costs and wind power hosting capacity results are obtained due to AC transmission line capacities and interarea oscillation modes. The best multiterminal VSC‐HVDC system among all simulated multiterminal VSC‐HVDC systems is also concluded. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Applications of matrix perturbation theory to delayed cyber-physical power system

In this paper, the matrix perturbation theory is introduced to delayed cyber-physical power system (DCPPS) for analyzing the variations of eigenvalues and eigenvectors when small changes are imposed on system parameters and time delays. On one hand, a perturbation-based eigenvalue tracking method is presented to reliably track the targeted interarea oscillation modes so that wide-area damping controllers (WADCs) can be optimally designed to damp them. On the other hand, key factors affecting the accuracy of the solution operator discretization (SOD)-based eigenvalue computation methods for DCPPS are identified by matrix perturbation analysis, which provide a guidance for selecting suitable parameters to precondition the DCPPS. The study results on the 16-generator 68-bus test system validate the effectiveness of the two applications of matrix perturbation theory.

Generator Coherency and Network Partitioning for Dynamic Equivalencing Using Subtractive Clustering Algorithm

In this paper, a new method called subtractive clustering is presented to partition a power system into areas after a disturbance occurs. Subtractive clustering is basically used as a preprocessing step for other clustering methods to overcome their shortcomings, such as the need to predefine the number of areas and high dependency to random functions. However, due to the special characteristics of power systems, this method itself can be used to find areas. In subtractive method, the degree of coherency between all buses is used to form a density value for each bus. To calculate the degree of coherency between buses, the frequency components existing in the angular velocity variation of voltage phasors, in the range of interarea and local oscillation modes, are extracted. Then, the correlation between the real parts of these frequencies and the correlation between the imaginary parts are calculated individually. This means that the coherency between each pair of buses is assessed in two dimensions, which results in more efficient dynamic coherency identification. The capability of the proposed method is demonstrated for disturbances applied on the 16-machine, 68-bus system. It is observed that subtractive method is highly appropriate to find coherent areas for different disturbances.

Wide-Area Damping Controller Design Based on the Frequency Domain Self-Excitation Method

In this paper, a wide-area DC damping controller design method is proposed to damp the weak interarea oscillation modes. First, the low-order power system control model identification method is proposed based on the frequency domain self-excitation method to obtain the dominant modes and other related information. In what follows, the identified model is transformed into a low-order state space equation. By comparing the geometric metrics of different schemes, the various input signals and installation locations of the controller are selected. Furthermore, the damping controller parameter calculation is realized based on the self-excitation frequency domain identification method, which does not depend on the detailed model of the system. The design process is simple and it is easy to apply in the practical engineering of large-scale complex power grids. The applicability and effectiveness of the proposed controller design method are demonstrated through simulations of a two-area four-generator power system.

A Class of Switching Exploits Based on Inter-Area Oscillations

This work presents a new class of cyber-physical switching attacks that targets power transmission systems. The proposed approach relies on exciting inter-area oscillation modes in a coordinated manner to drive groups of system generators out of step. Our paradigm targets inter-area oscillations by switching a relatively small part (in the order of 2%) of the system load at a (low) frequency that resonates with one of the inter-area oscillation modes observed in the power system. The switching frequency of the targeted mode is chosen through measurement-based analysis of the frequency deviation at a select bus that is observable by the adversary. The inter-area switching attack is implemented as single-load switching and coordinated multi-load switching and is studied with a variety of switching signals. Numerical results show the potential and characteristics of the proposed switching exploitation when applied to the four-machine two-area power system and the Northeast Power Coordinating Council 68-bus system.

Robust and Coordinated Tuning of PSS and FACTS-PODs of Interconnected Systems Considering Signal Transmission Delay Using Ant Lion Optimizer

This paper presents an ant lion optimizer (ALO) that is used to solve the robust and coordinated tuning of power system stabilizers (PSS) and the power oscillation damping (POD) controller of flexible AC transmission system (FACTS) devices in the presence of remote signals in multimachine power systems. The remote signals are used for the damping of interarea oscillation modes and are modeled by Pade approximation. The static var compensator and thyristor-controlled series capacitor, two FACTS most deployed in practical applications, were considered in this study. The ALO algorithm mimics the hunting mechanism of ant lions in nature: where four steps of hunting prey such as entrapment of ants in traps, random walk of ants, elitism and catching preys/re-building traps are implemented. The two test systems which have been used for the application of the proposed methodology for tuning of PSS and FACTS-PODs are the New England–New York 16-generator 68-bus system, and the Brazilian equivalent system modeled with 24 synchronous machines and 107 buses. Results from these simulations demonstrate the applicability of the proposal in which the efficiency of ALO is highlighted as compared to other algorithms used for design of PSS and FACTS-PODs such as particle swarm optimization and sequential quadratic programming.

Impact of high-depth penetration of wind power on low-frequency oscillatory modes of interconnected power systems

This paper investigates impact of high-depth penetration of wind power, i.e., up to 30%, on low-frequency (0–2 Hz) oscillatory modes of interconnected power systems. The wind power is integrated as large Wind Power Plants (WPPs) based on Type-3 and Type-4 wind units represented by enhanced generic nonlinear and linearized models. The studies are based on eigen analysis of the 16-machine/68-bus NPCC equivalent system with multiple WPPs added to it. The case studies consider different ratios of Type-3/Type-4 WPPs to investigate impact of interaction between WPPs adopting different technologies on power system low-frequency dynamics. The studies reveal that WPPs can (i) noticeably impact the damping ratios of existing inter-area oscillatory modes at low-depth penetrations more than at high-depth ones, (ii) introduce new low-frequency oscillatory modes and (iii) cause instability by interacting with existing controllers in the system.

An LMI Approach with Pole Placement Objective for the Design of Robust SSSC Controller for Damping Inter-Area Mode Oscillation Considering Global Signal

This paper presents robust Static Synchronous Series Capacitor (SSSC) controller design using LMI approach with pole placement objective. The controller is designed for damping of inter-area mode oscillations in two area four machine test system considering a global signal. The control signals are obtained from wide area measurements (WAMs) system. Residue analysis is performed to decide best input signal to the controller. The mixed sensitivity approach in Linear Matrix Inequality (LMI) formulation is used to design thedamping controller. The uncertainty in load model composition results in the inaccurate estimation of the designed controller capability. So, different load model compositions including static and dynamic loads are considered here. Various contingency conditions are applied for testing the designed controller. The designed controller provides sufficient damping for such contingent conditions.

Cuckoo Search Optimization Algorithm for Designing of a Multimachine Power System Stabilizer

In this paper, new metaheuristic technique cuckoo search optimization (CSO) is explored for an optimal and robust power system stabilizer (PSS) designing for multimachine power systems and performance is evaluated by comparing with well-established techniques, i.e., genetic algorithm (GA), particle swarm optimization (PSO), and new harmony search optimization (HSO). An eigenvalue-based multiobjective function is implemented for simultaneous control of damping factor and damping ratio to damp out low-frequency local and interarea modes of oscillations. The PSS parameters are so intended that unstable and/or lightly damped mode eigenvalues are shifted to a specified D-shape zone in the left half of the s-plane. The selected metaheuristic techniques GA, PSO, HSO, and CSO are used to obtain PSS parameters for 10-machines, 39-bus New England Power System and the controllers designed are named as GAPSS, PSOPSS, HSOPSS, and CSOPSS, respectively. The performance of all designed PSSs controllers is evaluated by eigenvalues analysis, nonlinear simulations, and performance indices for various operating conditions under different scenarios of severe disturbances and their comparative analysis is observed. The robustness of all designed PSSs controllers is observed by testing them on unseen operating conditions and results are compared for the same. The performance of CSOPSS is found to be better than other controllers designed.