Damping Of Inter-area Oscillations Research Articles

Fixed-order loop shaping robust controller design for parametric models to damp inter-area oscillations

The inter-area oscillations are common in power systems and can occur due to the changes in the load or generating power especially in long transmission lines. This paper presents the design of a robust fixed-order loop shaping controller to damp out the inter-area oscillations and to enhance the stability of the power system. The proposed loop shaping method is based on the shaping of the open-loop transfer function in the Nyquist diagram through minimizing the quadratic error between the actual and the desired open loop transfer functions in the frequency domain. The proposed method is robust with respect to multi-model uncertainty. Despite other robust controller design methods, the proposed approach deals with the entire system i.e. there is no need to reduce the system and still leads to a lower order controller. In addition, most of the robust methods are heavily dependent on selecting some weight filters which is not required in the proposed approach. This method is applied to the two-area four-machine system and 68 bus system and the effectiveness and robustness of the proposed method in damping inter-area oscillations are validated using case studies.

A Sliding Mode Based Damping Control of DFIG for Interarea Power Oscillations

This paper proposes a second-order sliding mode-based damping controller of DFIG for interarea oscillations. The proposed damping control strategy aims to utilize the reactive power modulation ability of DFIG to stabilize the power system in the event of oscillations caused by disturbances. First, the proposed controller is derived based on a two-area power system, and then it is extended to multiarea power systems. Compared with the conventional damping controller, the proposed one is insensitive to modeling uncertainties and parameter variations. Given the wide variation of operation points, the proposed sliding mode-based damping controller demonstrates a better robustness than the conventional damping controller. Simulation results on a two-area power system and a 10-machine 39-bus power system with DFIG-based wind farm integration show the improvement on system performance in interarea oscillation damping and demonstrate the robustness of the proposed control scheme in a wide operation region.

Inter-area Oscillation Damping using an STATCOM based Hybrid Shunt Compensation Scheme

FACTS devices are one of the latest technologies which have been used to improve power system dynamic and stability during recent years. However, widespread adoption of this technology has been hampered by high cost and reliability concerns. In this paper an economical phase imbalanced shunt reactive compensation concept has been introduced and its ability for power system dynamic enhancement and inter-area oscillation damping are investigated. A hybrid phase imbalanced scheme is a shunt capacitive compensation scheme, where two phases are compensated by fixed shunt capacitor (C) and the third phase is compensated by a Static Synchronous Compensator (STATCOM) in shunt with a fixed capacitor (CC). The power system dynamic stability enhancement would be achieved by adding a conventional Wide Area Damping Controller (WADC) to the main control loop of the single phase STATCOM. Two different control methodologies are proposed:<em> </em>a non-optimized conventional damping controller and a conventional damping controller with optomised parameters that are added to the main control loop of the unbalanced compensator in order to damp the inter area oscillations. The proposed arrangement would, certainly, be economically attractive when compared with a full three-phase STATCOM. The proposed scheme is prosperously applied in a 13-bus six-machine test system and various case studies are conducted to demonstrate its ability in damping inter-area oscillations and power system dynamic enhancement.

Optimum Damping of Inter-Area Oscillations Using a Wavelet Neural PI Network Controlled Static Synchronous Series Compensator

Optimum Damping of Inter-Area Oscillations Using a Wavelet Neural PI Network Controlled Static Synchronous Series Compensator

Fuzzy-PSS and fuzzy neural network non-linear PI controller-based SSSC for damping inter-area oscillations

In this paper, a new approach is recommended for damping out power system oscillations. In this approach, a new fuzzy neural proportional–integral (PI) controller (FNPIC) based static synchronous series compensator (SSSC) and a fuzzy-power system stabilizer (fuzzy-PSS) with a new structure are simultaneously employed. Adaptive learning rates based on the Lyapunov stability theory to enhance the convergence speed of the proposed controller are obtained. In the structure of fuzzy-PSS, a pattern search algorithm is used to adjust four gains. A two-area four-machine power system and a three-area, three-machine power system are employed to investigate the efficiency of the proposed method. Simulations results confirm the capabilities of proposed controller in suppressing the power system oscillations.

Effect of PODCs for DFIG Based Wind Farms in the Inter-area and Torsional Oscillation Damping

The damping contribution to inter-area and torsional oscillation modes of two power oscillation damping controllers (PODCs) in doubly-fed induction generators based wind farms is investigated in this paper. On one side, a no lead/lag compensation PODC is designed through eigenvalue analysis. On the other side, a PODC with lead/lag compensation is developed with the inclusion of an iterative process based on the bat optimization algorithm. Despite that both PODCs can effectively improve the damping of inter-area oscillations in this work, results from eigenvalue analysis and nonlinear time domain simulations of a sample multimachine power system reveal the relative negative impact that both of them may have on the shaft torsional oscillation mode damping.

Optimal design of convertible static compensator supplementary damping controller to avoid wide area uncontrolled islanding

This study presents a new design of a wide area damping controller for the convertible static compensator (CSC) to limit some major blackouts due to asynchronous oscillations. The adaptive neuro-fuzzy inference system (ANFIS) approach is adopted in the dual heuristic programming method to have an optimal response at different disturbances. The proposed ANFIS parameters are optimised by using the multi-swarm particle swarm optimisation method. The CSC dynamic performance in both of unified power flow controller and interline power flow controller configurations is investigated to increase the damping of inter-area oscillations and to prevent the uncontrolled network islanding. The Iranian power grid and New England power system are selected to install CSC and to apply the designed damping controller. It is shown that the considerable number of wide area blackouts could be avoided by CSC application equipped with the proposed damping controller. In other scenarios, which the controlled islanding is an unavoidable task, the boundaries of islands are determined adaptively considering the changes of generators coherency and the loadings of lines. Simulation results verify that the load shedding amounts are decreased and the stability margins of islands are increased. The uncontrolled islanding condition is also delayed significantly.

A Kalman Latency Compensation Strategy for Model Predictive Control to Damp Inter-Area Oscillations in Delayed Power Systems

Power systems control strategies that use global signals have shown better results than those based on local signals, but the remote signals are usually taken far away from the control center. Because of that, wide area power systems controlled using global signals are inherently delayed, and time delays jeopardize the stability of power systems. This paper presents a Kalman based time delay compensation strategy, which feed a Model Predictive Control (MPC) scheme to damp inter-area oscillations in power systems with latencies in their communications. A Kalman state estimator is employed to get the states. The proposal uses a dynamic reduced order model obtained using Hankel singular values. The methodology is promissory because it considers time delays in control schemes design processes, useful for either centralized or distributed wide area power system controllers based on widespread metering. This approach was validated for controlling inter-area oscillations in a test power system with two areas, 4 generators and a tie power line. Results suggest an enhancement of the power system dynamic performance upon the application of the method proposed.

A New Control Structure for Multiterminal DC Grids to Damp Interarea Oscillations

This paper analyzes the control structure of the multiterminal dc (MTDC) system to damp ac system interarea oscillations through active power modulation. A new control structure is presented that maximizes the relative controllability without the need for communication among the dc terminals. In point-to-point high-voltage dc (HVDC) transmission, the active power modulation of the two terminals occurs in opposite directions. In this case, the control direction is given and only needs to be phase compensated to align for maximal damping. In the case of MTDC systems, the control direction interrelates with the active power modulation share of the dc terminals and the relative controllability depends on this. The new control structure eliminates the need for communication between the dc terminals by performing dc voltage feedback loop shaping. This makes it possible to modulate the power in one terminal and let the other terminals react on the dc voltage change. Through loop shaping, where the feedback gain varies in the frequency plane compared to the regular droop design, the control direction is aligned with the direction of highest relative controllability. Loop shaping takes place without influencing the high frequency or steady-state gain. Simulations in the Nordic32 test system show the validity of the proposed controller and its structure.

A Study of Magnetic Amplifier-based Power Flow Controller for Power System Stability Improvement

This article presents a magnetic amplifier-based power flow controller as a new approach to control power flow based on a magnetically saturated reactor concept. The magnetic amplifier-based power flow controller uses the magnetic field as control medium to decrease the operating energy losses and increase system reliability. By providing continuous impedance, the magnetic amplifier-based power flow controller can suppress the inter-area oscillation and improve the system stability. A model of magnetic amplifier-based power flow controller is built and verified by lab experiments. A control strategy implementing the magnetic amplifier-based power flow controller is proposed to demonstrate the application of this new device to damp low-frequency oscillation in an interconnected power system. A comparative analysis of the controller's performance is carried out and incorporated with various input signals and multiple loading conditions. The simulations are conducted by power systems CAD (PSCAD, Manitoba Hydro International Ltd., Winnipeg, Canada). The results show the effectiveness of the controller in damping inter-area oscillations.

Wind power converters improving the power system stability

This study analyses the coordinated actions of modern wind power plants for improving the transient and small-signal stability in power systems. Supplementary controls on wind farms are considered, and specific modifications on the controllers are tailored to increase the grid-support services. The proposal is analysed and validated in a practical power system based on the Argentine electrical network. The wind farm supplementary controls use active and reactive power control loops as well as local and remote measurements. Local controls can rapidly respond decelerating the system frequency in the first instants of a fault, consequently reducing the transient angle separations and improving the first-swing stability. On the other hand, remote controls using global information are able to increase the damping of low-frequency inter-area oscillations. Structures combining centralised and decentralised control approaches will become more common in the near future. With this aim, the integration of fast local controls with remote controls is thoroughly studied using non-linear time-domain simulations and eigenvalue analyses. A robustness evaluation is also performed to validate the proposal over a wide range of operating conditions.

Decentralised wide‐area fractional order damping controller for a large‐scale power system

This study presents the design of wide-area fractional order damping controller for low frequency inter-area oscillations in Western Electricity Coordinating Council (WECC) system. The developed wide-area damping control scheme is implemented in a decentralised manner by examining the entire system through decentralised identification at the level of each generator bus and FACTS devices in large-scale system. The decentralised identification is done by applying n4sid (Subspace State Space System Identification) algorithm to the time-domain simulated response of WECC system. The main features of the proposed approach are: (a) measurement-based control which does not require complete model of WECC; (b) minimise the communicating signals required for damping controller and incorporate practical method of time-delay compensator (TDC) design to reduce the effect of time-varying delay. The performance of wide-area control (WAC) scheme is tested on the practical WECC system and verified by non-linear time-domain simulation. The proposed decentralised WAC scheme is compared with local and centralised control scheme, which enhances the damping of inter-area oscillation effectively compared to local control scheme and more reliable compared to centralised control scheme and its robustness is verified over a wide-range of operating conditions.

Optimum Damping of Inter-Area Oscillations Using a Wavelet Neural PI Network Controlled Static Synchronous Series Compensator

Optimum Damping of Inter-Area Oscillations Using a Wavelet Neural PI Network Controlled Static Synchronous Series Compensator

Adaptive inter-area oscillation damping controller for multi-machine power systems

The interconnection of multiple generation units in a power system can lead to inter-area oscillations that generally occur under critical operating conditions. To damp these oscillations, supplementary control can be provided by a wide area control (WAC) system using remote measurements from the power system. Wide area controllers designed with traditional approaches are non-adaptive and thus their control policy may not be optimal to nonlinear operation conditions and disturbances. In this paper, the concept of an artificial immune system (AIS) is applied in the development of an innate and adaptive controller to handle known, unknown and random disturbances in a power system. Furthermore, with synchronous generator coherency grouping, remote virtual generator measurements are used to generate supplementary control signals to a synchronous generator that is identified to have maximum controllability on a power system. Real-time simulation and frequency analysis results show the superior performance of AIS-based controller in damping inter-area oscillations for different power system conditions and disturbances.

A wide-area SVC controller design for inter-area oscillation damping in WECC based on a structured dynamic equivalent model

In our recent work [1], we constructed a reduced-order model of the Western Electricity Coordinating Council (WECC) power system using mathematically derived parameters from real Synchrophasor data. These parameters include inter and intra-area impedances, inertias, and damping factors for aggregate synchronous generators representing five geographical, and yet coherent, areas of WECC. In this paper, we use this reduced-order model as a tool to design a supplementary controller for a Static VAr Compensator (SVC), located at the terminal bus of one of the aggregate generators. Wide-area feedback consisting of phase angle and frequency measurements from Phasor Measurement Units (PMUs) in the other areas is used to design this controller. The objective is to damp the inter-machine oscillation modes of the reduced-order model, which in the full-order system corresponds to inter-area oscillations. The controller input is chosen via statistical variance analysis, and its parameters are tuned to improve the damping factors of the slow modes. The model is implemented in a real-time digital simulator, and validated using a wide range of disturbance scenarios. The closed-loop system is observed to be highly robust to all of these disturbances as well as the choice of operating points. Detailed experimental analyses of the capacity of the SVC to satisfy the damping specifications of supplementary control are also presented via multiple contingencies. The results are promising in aiding damping of inter-area modes in WECC, especially at a time of increasing penetration of wind and other renewable resources.

Damping interarea oscillations in power systems using finite time terminal sliding mode control of the unified power flow controller

This paper presents a new nonlinear controller for unified power flow controller (UPFC) based on the Lyapunov's finite time terminal sliding mode concept. Further instead of controlling the direct and quadrature-axis currents of the series voltage source converter (VSC), the instantaneous real-and reactive power components are used as control variables. This mode of control dispenses the unmodelled dynamics of the VSC phase-locked loop system and produces a robust control for the active-reactive power, and dc voltage excursions. Computer simulation results are obtained for a variety of operating conditions for 3-machine 6-bus power system using the finite time terminal sliding mode control and the results are compared with a standard input-output feedback linearisation approach to validate the superiority of the proposed controller.

Comparison and Performance Analysis of FACTs Controller in System Stability

In large inter connected power systems, inter-area oscillations are turned to be a severe problem. Hence inter-area oscillations cause severe problems like damage to generators, reduce the power transfer capability of transmission lines, increase wear and tear on network components, increase line losses etc. This paper is to maintain the stability of system by damping inter-area oscillations. Implementation of new equipment consists of high power electronics based technologies such as FACTs and proper controller design has become an essential to provide better damping performance than Power System Stabilizer (PSS). With development of Wide Area Measurement System (WAMS), remote signals have become as feedback signals to design Wide Area Damping Controller (WADC) for FACTs devices. In this work, POD is applied to both SVC and SSSC. Simulation studies are carried out in Power System Analysis Toolbox (PSAT) environment to evaluate the effectiveness of the FACTs controller in a large area power system. Results show that extensive analysis of FACTs controller for improving stability of system.

Design of a Fixed-Order Robust Controller to Damp Inter-Area Oscillations in Power Systems

This paper presents the design of a robust fixed-order H∞ controller to damp out the inter-area oscillations and to enhance the stability of the power system. The proposed H∞ approach is based on shaping the open-loop transfer function in the Nyquist diagram through minimizing the quadratic error between the actual and the desired open loop transfer functions in the frequency domain under linear constraints that guarantee robustness and stability. The proposed approach is robust with respect to multi-model uncertainty closed-loop sensitivity functions in the Nyquist diagram through the constraints on their infinity norm. The H∞ constraints are linearized with the help of a desired open-loop transfer function. The controller is designed using the convex optimization techniques in which the difference between the open-loop transfer function and the desired one is minimized. The two-area four-machine test system is selected to evaluate the performance of the designed controller under different load conditions as well as different levels of wind penetrations.

Comparative Research on the Influence of Signal Selection on Delay Margin in Interarea Oscillation Damping Control

Comparative Research on the Influence of Signal Selection on Delay Margin in Interarea Oscillation Damping Control

Coordinated design of PSS and TCSC to mitigate interarea oscillations

Abstract Thyristor controlled series compensator (TCSC) as a promising series flexible AC transmission system (FACTS) device is generally used for controlling the real power flow in transmission lines. It can increase the system stability as the complementary functionality by minimizing the power oscillations. The effectiveness of TCSC in its primary and supplementary applications depends on the selection of its optimal location and defining a proper input signal. In this paper, a new method based on the active power sensitivity approach is applied to find the optimal location of TCSC. In addition, Hankel singular values (HSVs) and right half plane-zeros (RHP-zeros) analyses have been proposed to find the most appropriate stabilizing input signal for the supplementary functionality of TCSC to damp out the interarea modes of oscillation. Finally, the optimal design of power oscillation damper (POD) and simultaneous coordinated design of power system stabilizer (PSS) and POD are implemented separately in a large-scale power system. The tuning problem of POD-TCSC parameters as well as the coordinated POD-TCSC & PSS are converted to a multi-objective optimization problem and solved using particle swarm optimization (PSO) algorithm. The performance of the proposed method has been validated through eigenvalue analysis and nonlinear time domain simulation in a 16-machine 68-bus test system. The simulation results show a satisfactory robust performance with an excellent capability in damping of local and interarea power oscillations.