Wide-area Damping Controller Design Research Articles

Improving the time delay in the design of the damping controller with the aim of improving the stability of the power system in the presence of high penetration of renewable energy sources

Due to the high penetration of renewable energy sources (RES) such as wind units in power systems, the need to check the stability of transmission networks has been given more attention than before. Therefore, in this paper, due to the importance of the topic, the wide area damping controller (WADC) has been used for the battery energy storage system (BESS) connected to the photovoltaic unit and the permanent magnet synchronous generator (PMSG) in the dc link. The WADC design is based on free weight matrices (FWM), which can solve a set of constraints based on the linear matrix inequality (LMI) based on the delay-dependent feedback control theory. The working method is that the constraints related to LMI are considered in such a way that it has the ability to tolerate the maximum amount of time delay. FWM has been used to communicate between LMI constraints and the maximum value of the time delay margin. FWM matrices are also based on an iterative algorithm based on linearization of the conical complement, which tries to search for the most optimal value for the control parameters. To implement the simulation results in MATLAB software, an improved power system of 16 machines has been used, the results of which are clearly analyzed and show the superiority of the proposed method compared to other mentioned methods.

Interacting Multiple Model Strategy Based Adaptive Wide-Area Damping Controller Design for Wind Farm Embedded Power System

The intermittent nature of Wind Turbine Systems (WTSs) can severely affect the Low-Frequency Oscillations (LFOs) in the power system. Hence, a Wide-Area Damping Controller (WADC) is designed in this paper to provide adequate damping to critical LFO modes. This WADC utilizes a modal-based prescribed degree approach, ensuring the specified shift of concerned modes from their existing position. However, the design of WADC at a fixed operating point and time delay in feedback signals does not provide robust performance as these uncertainties may vary for different time intervals. Specifically, time-varying delays should be tackled appropriately, or the system's damping performance will be severely hampered. Keeping this in view, an Interacting Multiple Model (IMM) infrastructure is employed to provide robust damping performance for such uncertainties. The IMM strategy utilizes the deviation of output error between actual and probable plants, through which weights are assigned to corresponding probable WADCs via the Bayesian framework. The simulations are performed on the nonlinear 4-machine, 11-bus system and the complex 16-machine, 68-bus system using MATLAB/Simulink platform. The results demonstrate that the proposed IMM-based WADC furnishes adequate damping to critical LFO modes for operating point and time delay uncertainties.

Large-Scale Solar PV Converter based Robust Wide-Area Damping Controller for Critical Low Frequency Oscillations in Power Systems

Integration of large-scale renewable energy sources in legacy power system has negative impact on inertia and low-frequency oscillations (LFOs). Critical LFO modes are the primary concern in system stability as they limit the power transfer capability in inter-region tie-lines. Therefore, to provide adequate damping to critical LFO modes, a robust wide-area damping controller (WADC) design is required. In this paper, time delayed feedback control (TDFC) based WADC design is carried out with large-scale solar photovoltaic (SPV). In the design process, geometric technique is used to determine the appropriate wide-area signals. Time delays and noises in feedback signals as well as different operating scenarios have severe implications on the damping performance of WADC. Hence, considering these uncertainties, the proposed WADC parameters are tuned by modified particle swarm optimization (PSO) algorithm. The performance of proposed WADC is demonstrated on SPV-integrated IEEE 4-machine 11-bus and 16-machine 68-bus systems. Critical modes of the system are damped by more than 10 % damping ratio in both cases. Furthermore, nonlinear dynamic simulations demonstrate that the proposed WADC provides robust performance over wide operating scenarios. Finally, practical efficacy of the proposed method is established by experimental validation through real-time simulation using OPAL-RT.

A UPFC‐based robust damping controller for optimal use of renewable energy sources in modern renewable integrated power systems

This paper proposes coordinated design of wide-area damping controller (WADC) in the presence of renewable energy resources in a large-scale power system. To tackle with constant and time-varying delays in wide-area system, a robust criterion based on H∞ has been used for the coordinated WADC design. By using an auxiliary function in Lyapunov function, conservatism of linear inequality matrix (LMI) is reduced, such that larger delay margin and larger feasibility region is obtained in the presence of delays. The wind farms here are composed of doubly-fed induction generator (DFIG) and squirrel-cage induction generator (SCIG), which are connected to common bus of photovoltaic (PV) system by using unified power flow controller (UPFC). Then, the renewable energy units are integrated with 10 and 16-machine power systems. Afterwards, by identifying oscillating modes, the coordinated design of WADC is carried out for rotor-side-converter (RSC) in DFIG, DC/AC converter in the PV units, shunt converter (SHC) in UPFC, and power system stabilizer (PSS). Different scenarios of power system operating conditions are considered to evaluate performance of the proposed approach. The simulations in power system analysis toolbox (PSAT) and programming in MATLAB demonstrate effectiveness of the conducted method.

Design of a Reduced-Order WADC for Wind Turbine System-Integrated Power System

The impact of wind turbine system (WTS) on power system stability is elaborately addressed in the literature. However, low-frequency oscillations, especially inter-area oscillations (IAOs) can be adversely affected due to their intermittent nature. This article proposes a wide-area damping controller (WADC) for WTS-integrated power system to damp IAOs effectively. The feedback signals (linear combination of the system states) are directly measurable from phasor measurement units. Therefore a reduced-order estimator is proposed instead of a full-order estimator to design the WADC. Furthermore, to select appropriate feedback signals for WADC design, combined geometric measure and modal decomposition techniques are utilized. The overall procedure to design the reduced-order WADC includes feedback signal selection, state feedback formulation using modal transformation approach, and reduced-order estimator design using loop transfer recovery procedure. Moreover, the WADC parameters are selected considering operating point uncertainties and variable time delays in feedback signals. Performance of the proposed WADC is validated on WTS-integrated 16-machine, 68-bus system. The simulation results show that the proposed WADC gives robust performance over broad operating scenarios.

Delay dependent wide area damping controller design for a linear parameter varying (LPV) power system model considering actuator saturation and changing environmental condition

Delay dependent wide area damping controller design for a linear parameter varying (LPV) power system model considering actuator saturation and changing environmental condition

A Modal Transformation Approach to Design Reduced Order Functional Observer-Based WADC for Low-Frequency Oscillations

Low-frequency oscillations (LFOs) are one of the major concerns in modern power system; hence, these should be appropriately treated in order to achieve reliable operation. In this regard, we propose a novel wide-area damping controller (WADC) to dampen LFO modes effectively. The proposed WADC utilized thyristor controlled series compensator (TCSC) based flexible ac transmission system (FACTS) device through which supplementary input is provided. The selection of modal feedback signals for WADC design is carried out using coordinated modal transformation and linear quadratic regulator (LQR) approach. However, these signals are not accessible directly through the phasor measurement devices (PMDs). Hence, this paper utilizes a reduced-order functional observer to estimate the feedback signals using PMD data. The estimated feedback signals are further modulated by simple gains to improve the damping of critical LFO modes. The proposed methodology is validated on benchmark 4-machine 11-bus system and a more practical 25-machine, 105-bus system representing the complex Eastern Regional Grid (ERG) of India. The results obtained on these nonlinear systems show a significant improvement in damping of the critical LFOs leaving the other modes almost unaffected.

Data-driven model-free adaptive damping control with unknown control direction for wind farms

The wide-area damping control (WADC) designed by conventional model-based methods faces the challenge from the strong nonlinearity, time-varying structure, and disturbances from complex operating conditions of the interconnected multi-machine power systems. In this paper, as one of the data-driven methods, the model-free adaptive control (MFAC), which employs the pseudo-partial derivative (PPD) to linearize the nonlinear power system dynamically, is adopted to design WADC for its advantages of the low cost, simple structure & low calculation burden, and the analyzable stability. However, when applied to the WADC design, the prototype MFAC is infeasible due to the assumed known control direction, the non-zero steady-state controller output, and unconsidered disturbances. To solve these problems, a novel data-driven adaptive WADC, consisting of control direction correction, PPD updating, one-step-ahead weighted predictive control, is proposed, moreover, the stability of the closed-loop system considering disturbances is thoroughly analyzed. Finally, case studies with various disturbances are conducted to validate the proposed control strategy.

Wide-area damping control using signal restoration under communication uncertainties

Abstract In large-scale power systems, the wide-area damping controller (WADC) using remote input signals is an effective device that can be applied to deal with poor inter-area oscillation damping. However, its control effect will be degraded by communication uncertainties such as variable time delays in both input and output sides of WADC, partial and complete communication failures. This paper focuses on a new WADC design by regarding communication uncertainties. Such uncertainties are mathematically formulated and analyzed in order to signify its impact on the oscillatory stability. The signal restoration of input and output pairs of WADC is proposed to alleviate an adverse effect of communication uncertainties. Simulation study in an IEEE 50-machine 145-bus test system elucidates that the proposed WADC is superior to that of the conventional WADC without considering communication uncertainties in both performance and robustness.

Measurement‐based wide‐area damping of inter‐area oscillations based on MIMO identification

Interconnected power grid exhibits oscillatory response after a disturbance in the system. One such type of oscillation, the inter-area oscillation has the oscillation frequency in the range of 0.1–1 Hz. The damping of inter-area oscillations is difficult with local controllers, but it can be achieved using a wide area damping controller (WADC). For effective control, the input to the WADC should be the most observable signal, and the WADC output should be sent to the most controllable generator. This study presents a measurement-based novel algorithm for multi-input-multi-output (MIMO) transfer function identification of the power system to estimate such oscillation frequencies. The wide-area control loop is estimated using the MIMO transfer function, and the WADC design is a combination of the discrete linear quadratic regulator and Kalman filtering for the damping of inter-area oscillations. Since the MIMO identification is performed using the actual measurements, the proposed method can accurately monitor changes in the power grid, whereas the conventional methods are derived from small-signal analysis of a linearized model that does not consider changing operating conditions. The overall algorithm is implemented and validated on a RTDS/RSCAD® and MATLAB® real-time co-simulation platform using two-area and IEEE 39-bus power system models.

Unified Residue Method for Design of Compact Wide-area Damping Controller Based on Power System Stabilizer

A wide-area damping controller (WADC) is effective in damping inter-area low-frequency oscillation (LFO), if the time delay in a wide-area control loop can be properly handled. In order to simplify the WADC design and enlarge the delay adaptation range, the classic power system stabilizer (PSS) is adopted, and a new unified residue (UR) method is proposed for compact WADC design. The strategy of control loop selection is also improved by modifying the relative residue index based on a few dominant oscillation modes. The designed PSS-based compact WADC is as simple as classic PSS with no more than two lead-lag phase compensation units. Case studies are carried out on an IEEE 16-machine 68-bus power system. Simulation results demonstrate that the control loop selection before the WADC design is necessary and that the proposed selection strategy can easily pick out the suitable candidate control loops. In addition, it is feasible for the UR method to design WADCs with different time delays in the selected control loops. All the designed WADCs are effective in damping inter-area LFO and robust to time delay variations under operation conditions. Comparisons among five design methods for PSS-based WADC show that the proposed UR method is superior in delay adaptation, the conciseness of WADC structure and computation speed of parameters.

Practical supplementary controller design for the bi‐layer WAC architecture through structurally constrained H 2 norm optimisation

The objective of this paper is to suggest a suitable design procedure that may be useful for the practical realisation of the bi-layer wide area control (WAC) architecture. The bi-layer WAC architecture indicates the deployment a communication-free supplementary WAC loop in parallel to the conventional WAC loop. The bi-layer WAC system was found to have the potential to counterbalance the communication-related problems that arise in the conventional WAC loop. However, until now, no specific work has been reported in literature for the practical design of the supplementary wide area damping controller (WADC). It is essential to design the supplementary WADC in a way so that it can be practically implemented without the support of any communication network. The particular problem is resolved here by defining a suitable structure of the feedback gain matrix in the supplementary WAC loop. A novel structurally constrained norm optimisation technique is developed to design the particular feedback gain matrix with the proper structure. Here, the structurally constrained norm optimisation is performed for an output feedback loop instead of a state feedback loop. The usefulness of the supplementary WADC design produced is thoroughly verified through real-time (RT) experimentations.

Eigen-Analysis Considering Time-Delay and Data-Loss of WAMS and ITS Application to WADC Design Based on Damping Torque Analysis

Data-loss from wide-area measurement systems (WAMS) is a stochastic event and eigenvalues of power systems containing data-loss cannot be calculated directly. This paper proposes a unified model of WAMS data containing time-delay and data-loss according to its mathematical expectation. Based on Pade approximation, the model is incorporated into a system linearized model with WAMS. Thus, an eigen-analysis can be conducted to analyze the impacts of data corruption and to calculate the system stability time-delay margin. Then, the unified model is applied to damping torque analysis (DTA) to derive the damping torque index (DTI) with WAMS. The DTI can be used to select feedback signals and conduct the parameter design of a wide-area damping controller (WADC). Finally, the 2-area 4-machine (2A4M) Kundur system and Eastern China power grid (ECPG) are simulated to validate the feasibility of the model and its application. The results demonstrate the impacts of data corruption on system dynamic performance and the ability of the method to improve the small-signal stability of interconnected power grids.

Adaptive latency compensator considering packet drop and packet disorder for wide area damping control design

Network based wide-area controls will form an important part of smart grid implementation to improve power system stability. The performance of such control systems can seriously deteriorate under various network uncertainties such as time-varying delays, packet loss, and packet disorder. To address these issues, an Adaptive Time Delay Compensation (ATDC) scheme has been suggested to design wide area damping controller for a Flexible AC Transmission System (FACTS). The proposed TDC scheme is based on a direct phase advancement methodology that requires the signal modal information such as amplitude, frequency, and damping. This information has been utilized to compensate the latency by predicting the future trajectories of oscillatory response. An Adaptive Extended Kalman Filter (AEKF) is employed to estimate the low-frequency oscillatory modes with missing measurement data. To compensate the error due to packet disorder, a new methodology of packet-reordering, has been proposed. Further, the Wide-Area Damping Controller (WADC) is designed addressing the issue of sampled data control. The performance of the proposed scheme has been validated on the 16-machine, 68-bus power system.

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

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

Additive Model Decision Tree-Based Adaptive Wide-Area Damping Controller Design

An adaptive wide-area damping controller (WADC) scheme based on gain scheduling (GS) technique and decision tree (DT) approach is presented. For the predefined operating scenarios, several robust controllers are designed, so that each controller performs well within a certain range of load/generation variation and contingencies. Considering the best acting controller in each operating condition as the target of classification, several DTs are trained using stage-wise additive modeling by multiclass exponential loss function (SAMME). The weighted combination of DTs is referred to as additive model DT (AMDT) that is used to interpolate the controller coefficients from phasor measurement unit (PMU) signals. Afterward, the combined controller is applied to damp the interarea oscillations. Case studies on the IEEE 39-bus 10-machine and 68-bus 16-machine test systems demonstrate the effectiveness of the proposed controller in a wide range of operating conditions as well as its robustness in the presence of uncertainty in the predicted scenarios.

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.

Hybrid Transient Energy Function-Based Real-Time Optimal Wide-Area Damping Controller

This paper presents a real-time wide-area damping controller design based on a hybrid intelligent and direct method to improve the power system transient stability. The algorithm applied as a nonlinear optimal wide-area damping controller monitors the oscillations in the system and optimally augments the local excitation system of the synchronous generators. First, energy functions and Prony analysis techniques are used to identify these local or interarea oscillations and develop stability or damping performance index at a given time. Second, artificial neural networks are deployed to learn the dynamics of the system and energy functions based on supervised learning to construct an optimal control design. Then, using online reinforcement learning the quadratic objective function based on the stability index is estimated and optimized forward-in-time. Results on the IEEE 68-bus in Power System Toolbox and HYPERSIM real-time simulator show better transient and damping response when compared to conventional schemes and local power system stabilizers.

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.