Inter-area Modes Research Articles

Identification of coherent trajectories by modal characteristics and hierarchical agglomerative clustering

This paper introduces a novel method to identify coherent generators using the inter-area modal characteristics of power systems. The key idea is to extract the inter-area modes from the simulated data and then to apply a clustering strategy. Thus, the proposed method consists of extracting the phase of the oscillatory modes via a modal identification technique and applying a hierarchical agglomerative clustering technique together with the Elbow's method to gather the phases of each mode, enabling to provide coherent trajectories of generators. The proposed method uses a Taylor-Fourier filtering strategy to remove noises and nonlinearity in the time evolution of coherent generators. Simulated signals with noise added are used for assessing the proposition. Results corroborate the proposed strategy for identifying coherent trajectories in large-scale power systems.

Security region-based small signal stability analysis of power systems with FSIG based wind farm

Based on the Security Region approach, the impact of fixed-speed induction generator based wind farm on the small signal stability of power systems is analyzed. Firstly, the key factors of wind farm on the small signal stability of power systems are analyzed and the parameter space for small signal stability region is formed. Secondly, the small signal stability region of power systems with wind power is established. Thirdly, the corresponding relation between the boundary of SSSR and the dominant oscillation mode is further studied. Results show that the integration of fixed-speed induction generator based wind farm will cause the low frequency oscillation stability of the power system deteriorate. When the output of wind power is high, the oscillation stability of the power system is mainly concerned with the inter-area oscillation mode caused by the integration of the wind farm. Both the active power output and the capacity of reactive power compensation of the wind farm have a significant influence on the SSSR. To improve the oscillation stability of power systems with wind power, it is suggested to reasonably set the reactive power compensation capacity for the wind farm through SSSR.

Optimal Placement and Tuning Approach for Design of Power System Stabilizers and Wide Area Damping Controllers Considering Transport Delay

Abstract In this paper, a novel optimal placement and parameter tuning approach for Power System Stabilizer (PSS) is proposed to damp both local and inter-area modes in mesh like power system. The design target is two-level PSS consisting of ΔP type local PSS and Δθ type Wide Area Damping Controller (WADC). For the PSS placement, modeshape with eigenvector sensitivity and coherency analysis are used to determine the appropriate placement of both local PSS and WADC. For the PSS parameter tuning, metaheuristics based approach via Mean Variance Mapping Optimization (MVMO) is employed in order to consider the time domain analysis. The proposed objective function designs at first the local PSS only to improve damping coefficient and damping ratio of eigenvalue. After that, it designs the WADC overlapping with already designed local PSS by time domain analysis, taking into account the transport delay in the remote signal between Phasor Measurement Unit (PMU) and PSS. The proposed method is applied in IEEE New England 39-Bus (NE 39-bus) system model. Then, modeshape and coherent grouping analysis give us understandable system aspect, the local PSS and the WADC optimized by using MVMO considering the transport delay improve both local and inter-area modes whereas a method ignoring the transport delay make system poorly damped.

Effects of Data Size on Stochastic Subspace Identification Method for Power System Electromechanical Modes

Power system electromechanical mode identification is important in mitigating poorly damped oscillations. Stochastic subspace identification (SSI) is a data driven technique used for power system modeling and analysis. The data sensitivity of SSI method and its effects on power system electromechanical mode identification is studied in this paper. The different data sizes are analyzed for effectiveness in identifying electromechanical modes present in a multi-area power system under a system disturbance. IEEE68 bus New England-New York benchmark test power system has been simulated on a real-time digital simulator for this study to generate the data needed. The oscillation frequencies including the inter-area and intra-area modes in the range from 0.3-2.0 Hz are investigated. The results prove that the data size effects the identification of electromechanical modes present.

Mitigation of Low Frequency Oscillations by Optimal Allocation of Power System Stabilizers: Case Study on MEPE Test System

The increases in power network and weak tie-line have led power system oscillation problems. To improve the oscillatory stability, installing the power system stabilizer (PSS) with optimal allocation is considered due to excessive cost. This paper recommends the suitable PSS locations by using eigenvalue analysis and participation factor to enhance the system oscillation damping. The effects of installed PSSs in damping local and inter-area modes of oscillations are confirmed through time domain simulation results. The effectiveness of proposed approach is tested and validated on MEPE test system. Robustness of stabilizers against dynamic response of generator speed deviation, rotor angle deviation, and response of mechanical power are observed to access the performances of PSSs.

A Robust Decentralized Wide Area Damping Controller for Wind Generators and FACTS Controllers Considering Load Model Uncertainties

This paper presents a systematic procedure to design a decentralized wide area damping controller for the wind farms and flexible ac transmission system (FACTS) controllers in a smart grid considering uncertainties in the load parameters. The effect of uncertainties in load parameters on damping of inter-area modes of oscillations is investigated through the probability collocation method. A robust $\boldsymbol {H_{\infty }}$ output feedback controller is then designed for the uncertain fuzzy system by satisfying linear matrix inequalities, which are obtained from the original bilinear matrix inequalities derived from the Lyapunov-based stability criterion. The input and output signals for the proposed controller are selected based on a joint observability/controllability index. The input signals are wide area signals obtained from the phasor measurement units and the output signals are fed to wind farm generators and the FACTS controllers. The input signal delay compensation is addressed in this paper. The performance of the controller has been tested on New England 39 bus system developed on real time digital simulator and on a practical large Indian power system under various operating scenarios and faults. Its effectiveness is also compared with a conventional power system stabilizer, local damping controllers, and an existing robust centralized wide area controller designed based on mixed $\boldsymbol {H_{2}} / \boldsymbol {H_{\infty }}$ output feedback synthesis.

Non-smooth Optimization Based WADC Tuning in Large Delayed Cyber-Physical Power System by Interarea Mode Tracking and Gradient Sampling

This paper presents a nonsmooth optimization-based method to optimally tune wide-area damping controllers in large delayed cyber-physical power system (DCPPS). The objective is to maximize the damping ratios of the weakly damped interarea oscillation modes under multiple operating conditions. An eigenvalue-perturbation and receding-tracking method is then proposed to reliably trace the targeted interarea oscillation modes during the optimization process. The Broyden–Fletcher–Goldfarb–Shanno method combined with the gradient sampling technique is employed to efficiently solve the presented nonsmooth, nonconvex, and nonlinear eigenvalue optimization-based problem. The effectiveness of the proposed method is validated by the significantly improved damping of the interarea oscillation modes in the two-area four-machine test system and a real-life large DCPPS.

Modal Analysis and Stability Enhancement of 150 kV Sulselrabar Electrical System u sing PSS and RFB based on Cuckoo Search Algorithm

Small signal stability is one of the factor to assesst the reliability of a power system. Small signal stability is related to the ability of a power system to maintain synchronization after being exposed by small disturbance. In Indonesia, the reliability of power system is one of the important aspect that has to be achieved. However, very scant attention has been paid on studied small signal stability performance on Indonesia electricity. Hence, this paper studied the small signal stability analysis and its enhancement. 150 kV Sulselrabar interconnected power system is used as test system. To enhance the performance of the system designing coordinated controller of power system stabilizer (PSS) and redox flow batteries (RFB) using cuckoo search algorithm (CSA) is conducted. Eigenvalue, damping ratio, participation factor analysis, and time domain simulation is performed to assess the small signal stability performance and the successfulness of the CSA to optimize the PSS and RFB parameter. From the cases studies, it is found that 150 kV Sulselrabar has 12 local mode and 4 inter-area mode. Furthermore, the coordinated controller between PSS and RFB based on CSA could enhance the small signal stability performance of 150 kV Sulselrabar interconnected system indicated by higher damping, smallest overshoot and fastest settling time.

Design of A Hvdc-Based Controller for Load Change Compensation and Stabilization of Inter-Area Oscillations

As an interconnected power system via a High-Voltage Direct Current (HVDC) link is subjected to a rapid load change with the frequency of inter-area oscillation mode, system frequency and tie line power may be severely disturbed and oscillate. To compensate for the rapid load change and stabilize both frequency and tie line power oscillations due to the inter-area mode, the dynamic power flow control via a HVDC link can be exploited. To implement this concept, a new design method of HVDC-based controller is proposed. To grasp a physical characteristic of the inter-area oscillation frequency, the technique of overlapping decompositions is employed to achieve the subsystem embedded with the inter-area mode. Consequently, the second-order lead/lag controller of HVDC link can be designed in this subsystem. To acquire the desired overshoot of frequency oscillations, the parameters of the controller are automatically optimized by the Tabu Search (TS) algorithm. The effectiveness of the designed controller is investigated in a three-area longitudinal interconnected power system which represents the interconnection between the south of Thailand and Malaysia power systems.

A novel 2-stage WAPSS design method to improve inter-area mode damping in power systems

A novel 2-stage WAPSS design method to improve inter-area mode damping in power systems

Damping Inter-Area Oscillations With Large-Scale PV Plant by Modified Multiple-Model Adaptive Control Strategy

Studies suggest that inter-area low-frequency oscillations can be damped with supplementary damping control of large-scale photovoltaic (PV) plants. Multiple-model adaptive control (MMAC) is applied as the damping strategy to deal with uncertain variations of the postdisturbance operating conditions. To reduce the scales of the model bank and the damper bank, K-means clustering algorithm is used taking inter-area modes as features for operating condition clustering, and a common damper is designed for each cluster. Based on the deviation between the output dynamic responses of the actual system and models, Bayesian approach is employed to calculate the probability of each model representing the actual system in real time, followed by updating weights of each damper's output. The weighted average of the individual damper's outputs is attached to the reactive power control of the PV plant. A new continuous form of probability calculation with an inertial link is proposed to smooth weight fluctuation caused by discrete calculation in conventional MMAC and ease stress of power regulation of the PV plant. The nonlinear simulation results demonstrate that the proposed control strategy is able to sufficiently damp the inter-area modes of interest in unexpected operating conditions without any prior knowledge about the postdisturbance state.

Wide-area Power System Damping Control Coordination Based on Particle Swarm Optimization with Time Delay Considered

To ensure satisfactory dynamic performance of controllers in time-delayed power systems, a WAMS-based control strategy is investigated in the presence of output feedback delay. An integrated approach based on Pade approximation and particle swarm optimization (PSO) is employed for parameter configuration of PSS. The coordination configuration scheme of power system controllers is achieved by a series of stability constraints at the aim of maximizing the minimum damping ratio of inter-area mode of power system. The validity of this derived PSS is verified on a prototype power system. The findings demonstrate that the proposed approach for control design could damp the inter-area oscillation and enhance the small-signal stability.

Effect analysis of generator governor system and its frequency mode on inter-area oscillations in power systems

The governor system of a synchronous generator not only can influence the damping characteristics of inter-area oscillations but also introduces a special ultra-low frequency mode into the power system. This mode, called frequency mode, has a lower frequency than that of inter-area modes and would appear when the governor system regulates the rotor speed. In this paper, the influence of governor system on the damping characteristics of inter-area oscillations is investigated by using the torque analysis theory. Then the feature of the frequency mode and its influence on inter-area oscillations are analyzed by using a 4-machine 2-area benchmark system. The analysis results show that the frequency mode is a control mode of the governor system and its damping ratio is mainly influenced by the parameters of the proportional-integral-derivative (PID) controller used for the governor system. When the governor system makes the damping ratio of an inter-area mode negative and the dead band is taken into account, the inter-area oscillation will gradually become an equal amplitude oscillation in case the damping of the frequency mode is relatively strong, while the inter-area oscillation will appear like a beat frequency oscillation in case the damping of the frequency mode is relatively weak. Finally, simulation results of a practical large-scale interconnected power system validate the effectiveness of the above analysis results.

Two‐level coordinated controllers for robust inter‐area oscillation damping considering impact of local latency

Local latency adversely affects the stabilising performance of damping controllers especially in the two-level control scheme. By considering both wide area and local latencies, this study presents the two-level coordinated control which consists of wide area centralised and local controls of power oscillation damper (POD) and power system stabiliser (PSS) for robust power oscillation damping. The PODs are equipped with the doubly fed induction generator (DFIG) wind turbine, the solar photovoltaic generator (SPV), and the static VAR compensator (SVC). The centralised PODs of DFIG, SPV, SVC, and the centralised PSSs act as the primary damping controllers. When the communication failure occurs, the local PODs of such devices and the local PSSs are activated and used as the backup damping controllers. To achieve the damping performance and robustness, the parameters of centralised and local controllers are individually optimised based on the worst scenarios determined by the lowest damping ratio of target inter-area oscillation modes. Study results in New England and New York IEEE 68-bus system demonstrate that the proposed two-level coordinated controllers are superior to the conventional two-level controllers in terms of damping performance and robustness against various operating conditions.

Flywheel Energy Storage Model, Control and Location for Improving Stability: The Chilean Case

A flywheel energy storage (FES) plant model based on permanent magnet machines is proposed for electro-mechanical analysis. The model considers parallel arrays of FES units and describes the dynamics of flywheel motion, dc-link capacitor, and controllers. Both unit and plant-level controllers are considered. A 50-MW FES plant model is tested in the Northern Chile Interconnected System (NCIS) when connected to the Argentinian Interconnected System (AIS). The FES plant provides transient support for primary frequency regulation and its impact on stability is studied using small-signal analysis and time domain simulations. To identify the best location to install the FES plant, eigenvalue sensitivity for the interarea mode is analyzed. The results are validated for different operation scenarios of wind and solar power. By installing the FES plant in the NCIS best location, the damping ratio of the interarea mode is increased from 0.53% to 13.1%. Moreover, the power transfer from the NCIS to the AIS can be augmented from 90 to 180 MW while still keeping the damping ratio above 9%. These findings are promising and may lead to useful planning criteria for energy storage deployment.

Impact of Multi-terminal HVDC Grids on Enhancing Dynamic Power Transfer Capability

This paper proposes the exploitation of multiterminal HVDC grids to improve transfer capability in power systems. Multiterminal HVDC systems based on voltage source converters (VSC-MTDC) have been recognized as a promising alternative for the wind power integration. Under low wind scenarios, these grids originally dedicated for wind power transmission can be exploited as an additional interarea transmission path, providing extra dynamic security. The paper focuses on small-signal stability assessment, especially in poor damped oscillations associated with interarea modes. Simulations performed through a generic computational framework have shown that the high level of flexibility and controllability provided by voltage source converters can considerably improve the transfer capacity, while preserving adequate dynamic performance.

Use of Polytopic Convexity in Developing an Adaptive Interarea Oscillation Damping Scheme

An adaptive control scheme based on the convexity property of polytopes for damping interarea oscillations is developed here. A polytopic control guarantees requisite damping when the current operating point lies inside it. Multiple polytopes increase the robustness of the control provided the polytope inside which the operating point lies after a disturbance is correctly identified. In this paper, the identification of the correct polytope is performed using Kalman-filters and the mean-chi square variable. A 29-machine 127-bus model of the Western Electricity Coordinating Council (WECC) system is used as the test system for this analysis. The simulation results demonstrate that the proposed adaptive control is able to provide adequate damping to the interarea modes of oscillation under changing operating conditions without any prior knowledge of the postdisturbance operating state. It is also found to be more robust than some of the modern controllers proposed previously.

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.

Adaptive wide‐area power oscillation damper design for photovoltaic plant considering delay compensation

With the increasing amount of grid-connected photovoltaic (PV) plants in a power system, the volatility and uncertainty of power generated from PV plants may adversely impact on the power system stability, for example increasing the risk of interarea oscillation. To solve the problem, this study proposes an adaptive wide-area power oscillation damper (WPOD) based on goal representation heuristic dynamic programming (GrHDP) algorithm for PV plant to enhance damping of the concerned interarea mode. By using GrHDP, the adaptive WPOD (A-WPOD) does not need the model of the power system and has adaptivity to different operating conditions. Moreover, an adaptive delay compensator is also employed for the proposed A-WPOD to compensate the communication delay existing in the wide-area signal. Case study is carried out on a 16-machine 68-bus system with a large-scale PV plant. Simulation results show that the A-WPOD can provide satisfactory damping performance and compensate the communication delay over a wide range of operating conditions.

Fuzzy Type-2 Controller Design for Small-Signal Stability Considering Time Latencies and Uncertainties in PMU Measurements

Wide-area damping controllers are generally provided in a large network to prevent small-signal oscillations. These controllers utilize remote measurements provided by synchrophasors. However, these communicated measurements are delayed and uncertain. Type-2 fuzzy provides higher order approximation of uncertainty and is able to provide solutions for real-world problems in more a reliable manner. Therefore, in this paper, a wide-area damping controller based on interval type-2 fuzzy system is designed. Proposed controllers not only consider time latencies of communicated signals but also eliminate various measurement uncertainties and noise by modeling foot of uncertainty (FOU). First, eigenvalue analysis of the system is performed to identify interarea modes responsible for small-signal instability. To nullify this instability, a control scheme is proposed. In proposed control scheme, participation factors are utilized to select suitable controller location. However, feedback signals are chosen through controllability indexes. Later, type-1 and type-2 controllers are designed by changing membership functions. Performance of type-2 controllers is checked for different FOUs. Furthermore, type-1 and type-2 controllers are compared, in terms of settling time, peak overshoot, and damping factor. Effectiveness of proposed control scheme and controllers are successfully tested on two-area four-machine and five-area sixteen-machine systems.