Wide-area Damping Controller Research Articles

Dynamic Control Allocation for Damping of Inter-Area Oscillations

Use of actuator redundancy to achieve higher reliability is a widely accepted engineering design technique and is used in this study to build resiliency and ensure power system stability in the presence of high levels of renewables. This paper presents a new design method for fault-tolerant wide-area damping controllers (WADCs) using modal-based control allocation (MB-CA), which coordinates a set of actuators to contribute to damping of inter-area oscillations. In our proposed method, when an actuator fails or is unavailable (e.g., due to communication failure), the supervisory MB-CA distributes the control signals to the remaining healthy actuators based on effects on the modal system, desired control actions, and actuator constraints. Our proposed block offers the benefits of modular design where it is independent of the nominal WADC. The proposed method consists of mainly two design steps. The first step is to design a WADC based on a fault-free model using robust control methods. The second step is to design an MB-CA to manage actuator availability and constraints. To validate the feasibility and demonstrate the design principles, a set of comprehensive case studies are conducted on a modified 192-bus Western Electricity Coordinating Council system. Numerical results verify the effectiveness of the proposed approach in ensuring resiliency to different actuator failures and actuator availability.

A new scheme of WADC for damping inter-area oscillation based on CART technique and Thevenine impedance

In this paper, based on the CART technique and wide area measurement system (WAMS), a new scheme of wide area damping controller (WADC) is presented for inter-area oscillation in which each generator is equipped with an individual WADC which works based on the global inter-area signals. The proposed WADC scheme is an individual controller which uses angle and speed deviation of the center of inertia of the oscillating areas as global inter-area signals (GIS) (ΔωCOI, ΔδCOI). Each individual WADC consists of two CART1 and CART2 which perform as optimal gain estimators for estimating optimal gains K1 and K2 of the individual WADC of each generator. In fact, the proposed WADC scheme is an online and non-model based controller consisting of two CARTs which estimate optimal gains (K1, K2) from which inter-area control signal (ICS) is produced for direct presentation to AVR of generators. In this scheme, for selecting the most effective generators for participating in damping control, a combination index (CI) is presented which is maximized by binary genetic algorithm (BGA) for achieving most damping. The proposed CI index consists of generation pattern and Thevenin impedance of generators. For this purpose, for online estimation of Thevenin impedance of generators, an online approach is presented in which by using three consecutive measurements Thevenin impedance of generators are evaluated. The proposed CARTs are trained off line and then in the real time working mode of the proposed approach by using online GIS signals estimate optimal gains K1 and K2 from which individual control signal is deveopled. The proposed control scheme is demonstrated on IEEE 39-bus test system with promising damping effect for inter-area oscillation.

Design and Implementation of Delay-Dependent Wide-Area Damping Control for Stability Enhancement of Power Systems

In this paper, the hardware and software design and implementation are proposed for the wide-area damping control (WADC) strategies. First, the hardware-in-the-loop (HIL) real-time (RT) simulation system based on the RT-Lab is established as the closed-loop test platform for the WADC applied in multi-machine interconnected power system. The hardware, which contains the microcontroller, the peripheral analog to digital converter, and the digital to analog converter, are developed based on the AVR 32-bit development board. Three WADC algorithms, i.e., the phase-compensation, the delay-dependent state-feedback, and the dynamic output-feedback method, are introduced. Then, the software design of the above algorithms is proposed and the bilinear transform method is employed to get the discrete-time model of the controllers. The flowchart of each algorithm is designed for the implementation in the environment of hardware. The designed WADC is embedded in a real-time power system. Finally, case studies are carried out based on the HIL real-time simulation system. The proposed control concept and WADC design methods are validated by considering the big/small disturbance and the signal time-varying delay. The effectiveness of the proposed HIL closed-loop test system is also confirmed.

A Wide-Area Damping Controller Considering Network Input and Output Delays and Packet Drop

This paper presents the development of a novel synchrophasor measurement-based wide-area centralized damping controller to improve the stability of a power system in presence of time-varying delay and packet dropout in the communication network. Two different strategies have been adopted to deal with the input and the output delays. In the first strategy, the system output delay has been compensated by predicting the dynamics of the signals. In the second strategy, a wide-area controller, based on delay-range-dependent stability criteria, has been designed for the time-varying delays in the input signals. The network induced delays and the maximum amount of the consecutive packet dropout are assumed to be bounded. The controller parameters are optimally obtained using a trace minimization of certain matrix variables by formulating Linear Matrix Inequalities problem. The system has been identified by applying Prediction-Error-Minimization methodology, and proposing a new type of probing test input-signal. A new methodology has been proposed to obtain the feedback channel latency in real time. The proposed methodology has been simulated on New England 39-bus test system and also validated on a hardware testbed consisting of physical Phasor Measurement Units connected, in feedback loop, to a Real-Time Digital Simulator.

Event‐triggered communication in wide‐area damping control: a limited output feedback‐based approach

A conceptual design methodology is proposed for event-triggered based communication for wide-area damping controller in power systems. The event-triggering mechanism is adopted to reduce the communication burden between the origin of the remote signal and the wide-area damping controller (WADC) location. The remote signal is transmitted to the WADC only when an event-triggering condition based on a predefined system output, is satisfied. The triggering condition is derived from a stability criterion, and is monitored continuously by a separate event-monitoring unit located at the origin of the remote signal. The stability of the resulting closed-loop system is guaranteed via the input-to-state stability technique. The proposed event-triggered WADC is implemented on two typical test power systems – two area four machine and IEEE 39-bus 10-machine. The validation of proposed mechanism is carried out through non-linear simulation studies on MATLAB/Simulink platform. The numerical results show the efficacy of the controller in managing the communication channel usage without compromising the stated system stability objectives.

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.

Virtual Actuators for Wide-Area Damping Control of Power Systems

In this paper, a new approach to design fault-tolerant wide-area damping controllers (WADCs) is presented. Use of actuator redundancy to achieve higher reliability has always been an accepted engineering design technique and is used in this study to help ensure power system security. In our proposed method when an actuator fails or is unavailable (e.g., due to loss of communication), the supervisory controller redistributes the control signals to the remaining actuators. The WADC is initially designed to provide satisfactory damping. In the next step, virtual actuators (VAs) are designed to manage actuator failures without the need to redesign the nominal WADC. By inserting this reconfiguration block between the nominal WADC and the new actuator, there is no need to retune the WADC and the performance of the fault-free system can be recovered. Our proposed block is independent of the nominal WADC and does not need any information beyond that an actuator is unavailable. The approach is applied to Kundur's two-area system, and the 39-bus New England system. Numerical results show the effectiveness of the proposed method subjected to different failures.

Adaptive Delay Compensator for the Robust Wide-Area Damping Controller Design

This paper presents an adaptive delay compensator (ADC) on the basis of the latest development in wide-area measurement system (WAMS) to cater to varying latencies. The proposed compensator can effectively reciprocate the phase deviation resulting from varying delays to improve the performance of central wide-area damping controller (WADC). The greatest challenge to continuous delay compensation is the uncertainty regarding the inherent robustness of the central controller. The proposed technique provides an opportunity to epitomize the uncertainty retrieved from phase compensated delay. Next, taking the uncertainty into consideration, the mixed $H_{2}/H_{\infty}$ synthesis technique is adopted for the robust design of WADC. The comprehensive case studies are conducted including small signal analysis and nonlinear time domain simulation. Moreover, different delay variation scenarios are investigated and it is confirmed that the proposed scheme accomplishes the desired performance, both in terms of robustness and satisfactory damping action despite the presence of system nonlinearities and time varying delays.

Robust linear quadratic Gaussian‐based discrete mode wide area power system damping controller

In this study, linear quadratic Gaussian (LQG) control is used for designing a wide area damping controller (WADC) in power system. The designed continuous and discrete mode LQG-based WADC is robust enough to deal with the problem of imperfect communication medium. The imperfect communication medium includes process noise, measurement noise, packet drop-out and signal latency in the remote control signal. The appropriate control input and the controller location are selected using the modal residue method. The imperfections in the communication network are modelled using Pade approximations for time delay and by inserting Gaussian random noise. Using two typical test power systems, the performance of robust LQG-based WADC as a power system stability agent is assessed in the frequency domain and via time-domain simulation of the non-linear model on MATLAB/Simulink and DIgSILENT software platform. Finally, a real-time implementation of the designed WADC is demonstrated on the Opal RT-Lab real-time digital simulator.

Stability Analysis and Controller Design of a Wide-Area Time-Delay System Based on the Expectation Model Method

Stochastic time delay is a new challenge for communication networks in wide-area damping control (WADC) systems. Uncertainties introduced by stochastic time delays increase the difficulty of modeling, analyzing the stability, and designing the controller. In this paper, a new approach for stability analysis and controller design through expectation modeling is proposed to solve for the uncertainty in wide-area controlled power systems introduced by the effect of a stochastic time delay. In the proposed method, the expectation model that considers the detailed stochastic time delay distribution is derived to accurately model the effect of a communication network on the wide-area control performance. Through a matrix transformation of the expectation model, the eigenvalue of the WADC system that considers time delay can then be calculated; this eigenvalue can be used for analyzing the system stability. A novel expectation model-based controller design procedure is established, through which traditional methods can be applied in the controller design of a power system with a stochastic time delay. Finally, the effectiveness of the stability analysis and controller design methods are validated through simulations in a power system of four generators and two areas with an HVDC link, and a power system with eight generators and 36 buses.

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.

WAMS-Based SSR Damping Controller Design for FACTS Devices and Investigating Effects of Communication Delays

Recent technological progresses in the wide-area measurement systems (WAMS) are realizing the centralized controls as a breakthrough for improving the power systems stability. The most challenging deficiency against WAMS technology is related to communication delays. If this latency is neglected, it can deteriorate the damping performance of closed loop control or even degrade the system stability. This paper investigates a conventional Wide Area Damping Controller (WADC) for a static synchronous series compensator (SSSC) to damp out the Sub-Synchronous Resonance (SSR) and also investigation of the destructive effect of time delay in remote feedback signal. A new optimization algorithm called teaching-learning-based- optimization (TLBO) algorithm has been implemented to normalize and optimize the parameters of the global SSR damping controller. The IEEE Second Benchmark Model is considered as the system under study and all simulations are carried out in MATLAB/SIMULINK environment.

Robust wide‐area damping controller design for inter‐area oscillations with signals' delay

A new wide‐area damping control strategy is investigated for flexible AC transmission systems (FACTS) device using wide‐area measurement system (WAMS) signals. The purpose is to design a dynamic output wide‐area damping controller (WADC) for improving the stability of interconnected power systems. The time‐varying delay of wide‐area signal is incorporated into the design process, which can effectively reduce the delay effect on the damping performance. First, a discrete‐time plant model with time‐varying delay is established for power systems; then by using the proposed improved free‐weighting matrices (IFWMs) approach and a convex optimization algorithm, a new and less conservative delay‐dependent stability criterion, expressed in the terms of linear matrix inequalities (LMIs), is obtained without ignoring any useful terms on the difference of a Lyapunov function. Detailed case studies on a 4‐machine two‐area benchmark test system and 16‐machine five‐area NETS‐NYPS interconnected system show that the designed WADC can not only maintain effective damping performance under the condition of time‐varying delay but also get the maximum wide‐area time delay. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Using PMU signals from dominant paths in power system wide-area damping control

This article presents a comprehensive study of dominant inter-area oscillation path signals and their application for power system wide-area damping control (WADC). The analysis, carried out on both small and large study systems, focuses on the relationships that emerge from physical characteristics of inter-area oscillations, namely the modal observability of signals from dominant paths and their corresponding control loop system properties (i.e. stability and robustness). The aim is to be able to appropriately exploit the dominant path signals for the mitigation of inter-area oscillations. Guidelines and considerations are provided to facilitate the design of WADC using the proposed approach.

Design and implementation of a measurement-based adaptive wide-area damping controller considering time delays

Wide-area measurement systems enable the wide-area damping controller (WADC) to use remote signals to enhance the small signal stability of large scale interconnected power systems. System operating condition variations and signal transmission time delays are the major factors to worsen the damping effect and even deteriorate the system stability. This paper proposes a novel measurement-based adaptive wide-area damping control scheme using oscillation mode prediction and system identification techniques. These techniques adjust the parameters of WADC as well as the time delay compensation in an online environment. To achieve fast online implementation, an identified high order multi-input multi-output (MIMO) model is deformed into a low order single-input single-output (SISO) model according to the residue of MIMO model. The SISO model can accurately represent the power system dynamics in the form of a transfer function, capturing the dominant oscillatory behaviors in the frequency range of interest. Moreover, the WADC has been implemented on a hardware test-bed (HTB) by adding its output signal to the excitation system of a selected generator. The effectiveness of the proposed measurement-based adaptive WADC has been demonstrated in a two-area four-machine system on the HTB under various disturbance scenarios.

Stabilizing control of wide-area power system with signal transmission delay based on Hamiltonian functional method

The stability of wide-area power system with signal transmission delay is investigated in this paper. A non-linear time-delay Hamiltonian model of power system is constructed. Based on the proposed model, the Hamiltonian functional method is used to derive a delay-dependent steady stability criterion in term of matrix inequalities by constructing suitable Lyapunov–Krasovskii functional. Then the wide-area damping controller (WADC) for the power system is designed based on the delay-dependent sufficient conditions. The constant time-delay introduced by the transmission of the remote signals is investigated. The relationship between the parameters of WADC and the delay margin has been investigated. It is used to guide the design of WADC and achieve a trade-off between the damping performance and delay margin. Four-generator eleven-bus power system is used to illustrate delay effect on inter-area mode damping. The performance of the proposed controller is verified by the results of simulation in time-domain, and it is proved that the method proposed in this paper is effective.

Design of wide-area damping controllers using the block relative gain

A novel technique to determine the best pairing of inputs and outputs for the design of wide-area damping controllers (WADCs) is proposed. The method extends the conventional use of the relative gain array (RGA) for interacting control systems, to the block relative gain (BRG) to analyze interactions among multi-input multi-output (MIMO) controllers. First, geometric measures of controllability and observability are used to screen the most effective stabilizing signals for partially centralized control of large interconnected power systems. Then, the BRG analysis is used to quantify the potential for adverse interactions between a given set of controllers or subsystems. This gives candidate sets for supplementary controllers which are solved using linear matrix inequality (LMI) techniques and are evaluated in closed-loop mode to detect and quantify process interactions. In general, this approach also allows better coordination of control capabilities and the use of interaction measures to help in the choice of control location and structure. The effectiveness of the proposed control scheme on system behavior is tested on a realistic 5-area model of the Mexican interconnected power system.

Wide-Area Damping Controller for Power System Interarea Oscillations: A Networked Predictive Control Approach

Wide-area damping controller (WADC) requires communication networks to transmit remote signals. The usage of communication networks will introduce time delays into the control loop of the WADC. Ignoring this time delay would deteriorate the damping performance provided by the WADC or even cause the whole system instability. This paper employs networked predictive control (NPC) to design a WADC for the generator exciter to enhance the damping of interarea oscillations in a large-scale power system. The NPC incorporates with a generalized predictive control (GPC) to generate optimal control predictions, and a network delay compensator to detect and compensate both constant and random delays. Moreover, model identification is used to obtain an equivalent reduced-order model of the large-scale power system and deal with the model uncertainties and variation of operating conditions. Case studies are based on the New England 10-machine 39-bus system. Effectiveness of the proposed WADC is verified by simulation studies and compared with a conventional WADC and a GPC-based WADC without delay compensation.

Multi-objective attuned design of damping controllers using frequency-based functions in smart grids

Increasing expansion of power systems is accompanied by innovations in smart grid solutions to maintain system stability. This paper formulates the dual-dimensional supplementary damping controller (SDC) and accelerating power system stabilizer (PSS2B) design as a multi-objective optimization procedure including both performance and robustness criteria. In wide-area operation, PSS2B is used for damping low-frequency swings and maintaining the robustness of controller in a wide range of swing frequencies. A dual-dimensional controller model is employed for the SDC. The robustness requirement is procured by using the idea of pseudospectra to handle the changes of power system parameters and the time delay introduced by wide-area damping controller (WADC). The multi-objective optimization problem is solved using an improved non-dominated sorting genetic algorithm-II (INSGA-II) based on fuzzy decision making (FDM) method. Different simulations are carried out on a 4-machine 2-area test system in order to validate the effectiveness and robustness of the designed controllers.

A new wide area damping controller design method considering signal transmission delay to damp interarea oscillations in power system

Wide area damping controller (WADC) is usually utilized to damp interarea low frequency oscillation in power system. However, conventional WADC design method neglects the influence of signal transmission delay and damping performance of WADC designed by the conventional method may deteriorate or even has no effect when signal transmission delay is beyond delay margin, an index that denotes delay endurance degree of power system. Therefore, a new design method for WADC under the condition of expected damping factor and required signal transmission delay is presented in this work. An improved delay margin with less conservatism is derived by adopting a new Lyapunov-Krasovskii function and more compact bounding technique on the derivative of Lyapunov-Krasovskii functional. The improved delay margin, which constructs the correlation of damping factor and signal transmission delay, can be used to design WADC. WADC designed by the proposed method can ensure that power system satisfies expected damping factor when WADC input signal is delayed within delay margin. Satisfactory test results demonstrate the effectiveness of the proposed method.