Supplementary Damping Controller Research Articles

Adaptive Supplementary Damping Control of VSC-HVDC for Interarea Oscillation Using GrHDP

Interarea oscillation is one of the main challenges for the secure and stable operation of a large-scale interconnected power system. To address this problem, this paper presents an adaptive supplementary damping controller (SDC) for voltage source converter based high voltage direct current (VSC-HVDC) by using the goal representation heuristic dynamic programming (GrHDP). Compared with conventional heuristic dynamic programming (HDP), GrHDP adds a new goal representation network to generate an adaptive reward signal to achieve better mapping relationship between the system states and the control action. To compensate phase shift between the output and input signals of a large-scale interconnected AC/DC power system, this paper proposes a parallel phase shift channel for the GrHDP. Moreover, the proposed GrHDP-SDC is a model-free control scheme, which does not need the mathematic model of the power system and has quick online learning ability to adapt to the variation of system operating conditions. Case studies are carried out on the 10-machine 39-bus system and 16-machine 68-bus system, respectively. Compared with the conventional lead-lag SDC (LL-SDC) and HDP-SDC, simulation results show that the proposed GrHDP-SDC can always provide satisfactory damping performance over a wide range of system operating conditions and disturbances.

Subsynchronous resonance and its mitigation for power system with unified power flow controller

Control strategy of unified power flow controller (UPFC) utilizing dq decoupling control is deduced in this paper, which can closely follow the control orders of the active and reactive power. The subsynchronous resonance (SSR) characteristics of a series compensated system equipped with UPFC are studied, and the results reveal that SSR characteristics of the system may vary significantly with UPFC in service or not. Consequently, supplementary subsynchronous damping controller (SSDC) for UPFC is proposed and investigated, and the effectiveness of the proposed SSDC is verified by damping torque analysis and time domain simulations.

Integration of DFIG-Based Wind Farms Into Series-Compensated Transmission Systems

Recent events have shown that doubly-fed induction generator (DFIG) wind turbines close to series capacitors are prone to subsynchronous oscillations (SSO). This paper analyzes these subsynchronous interactions (SSI) and a countermeasure to enable a reliable and secure integration of DFIG-based wind farms into series-compensated transmission systems. A case study based on a real power system is considered in this work. It has several transmission lines (many of them series compensated), various conventional and wind power plants, and a distributed load. This system allows to study the SSI among various wind farms and multiple subsynchronous modes, unlike previous studies which considered a single DFIG and one series-compensated line (i.e., one subsynchronous mode). An analytical investigation and development of fundamental concepts of the SSO are also discussed. A supplementary damping control (SDC) is designed to enhance the operating range and to damp the SSO of these series-compensated wind farms. A detailed analysis is carried out using eigenvalues and nonlinear time-domain simulations to evaluate the performance and robustness of the SDC. Besides the parameters usually studied, such as wind speed, series compensation level, control gains, the effects of conventional synchronous generation, type of load model, and system demand level on the SSI are also analyzed.

Alleviation of transient torsional torque stresses of turbine generator shaft segments using CBVLC supplementary controller

In this paper a bus voltage and line current (BVLC) supplementary subsynchronous damping controller (SSDC) is proposed to alleviate subsynchronous resonance (SSR) and damping power system oscillations in a power system. Both eigenvalue investigation and time-domain simulation results verify that the proposed method can damp torsional oscillations of the power system with SVS bus voltage and line current (BVLC) supplementary controller. The results demonstrate that the proposed controller has a successful performance in minimising the SSR. It is shown that the controller is able to stabilise all unstable modes. The study is performed on the system adapted from the IEEE first benchmark model. All the simulations are carried out in MATLAB/Simulink environment.

Supplementary damping controller design for SSSC to mitigate sub-synchronous resonance

This paper proposes to use gravitational search algorithm (GSA) to design a supplementary sub-synchronous damping controller for the static synchronous series compensator (SSSC) device to damp the torsional oscillations. The IEEE second benchmark model (SBM) which is a series compensated ac system is considered in this study for design and analysis purpose. The design problem is formulated as an optimization problem and GSA is employed to search for the optimal controller parameters. The dynamic performance of the system under study is evaluated at various levels of series compensation with different types of disturbances. Fast Fourier Transform (FFT) analysis and robustness analysis against operating point changes and system uncertainties are also investigated. For specific system studied in the paper, the superiority of the GSA optimization technique over genetic algorithm (GA) optimization technique is also shown by comparing the simulation results and various performance indexes.

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.

Trajectory-Based Supplementary Damping Control for Power System Electromechanical Oscillations

This paper considers a trajectory-based approach to determine control signals superimposed to those of existing controllers so as to enhance the damping of electromechanical oscillations. This approach is framed as a discrete-time, multi-step optimization problem which can be solved by model-based and/or by learning-based methods. This paper proposes to apply a model-free tree-based batch mode reinforcement learning (RL) algorithm to perform such a supplementary damping control based only on information collected from observed trajectories of the power system. This RL-based supplementary damping control scheme is first implemented on a single generator and then several possibilities are investigated for extending it to multiple generators. Simulations are carried out on a 16-generator medium-size power system model, where also possible benefits of combining this RL-based control with model predictive control (MPC) are assessed.

SSR Alleviation using BVLC Supplementary Controlled SVS of Series Compensated Power System

Abstract The sub synchronous resonance (SSR) is a substantial problem in power system having a steam turbine generator connected to a series compensated transmission system. Flexible AC transmission systems (FACTS) controllers are widely applied to mitigate SSR. In this paper, a bus voltage and line current (BVLC) supplementary subsynchronous damping controller (SSDC) is proposed to alleviate subsynchronous resonance (SSR) and damping power system oscillations in a power system. Both eigenvalue investigation and time-domain simulation results verify that the proposed method can damp torsional oscillations of the power system with SVS bus voltage and line current (BVLC) supplementary controller. The results demonstrate that the proposed controller has a successful performance in minimizing the SSR. It is shown that the controller is able to stabilize all unstable modes. The study is performed on the system adapted from the IEEE first benchmark model. All the simulations are carried out in MATLAB/SIMULINK environment.

Design of Wide-Area Power System Damping Controllers Resilient to Communication Failures

Recent research has demonstrated that wide-area signals obtained using synchronized phasor measurements could be more effective than local signals in damping inter-area oscillations in large interconnected systems. To transmit wide-area signals for use in controls, communication systems are required. Communication systems are vulnerable to disruptions as a result of which the reliability of the power system could be jeopardized. In order to counteract communication failures, resiliency could be built in either the communication system or the physical system. In this paper an approach is developed to build resiliency in grid controls in the physical system. The resiliency is achieved by robustly designing a novel redundant two-input single-output (TISO) supplementary damping controller (SDC) associated with a static VAr compensator (SVC) that utilizes both a wide-area signal and a local signal to guarantee that the system is stabilized if the wide-area signal is lost. Numerical tests on the IEEE 50-generator test system have demonstrated that the proposed SDC is effective in stabilizing the system and improving grid control resiliency in response to communication failures.

Simulation and study on mitigation measures of frequent subsynchronous oscillation with low amplitude at multi-power plants

Subsynchronous oscillation (SSO) with low amplitude that exceeds cumulative fatigue threshold of the generator shaft frequently could significantly reduce the shaft’s service life, which is a new SSO problem that emerges in recent years. According to the real recording oscillograph, the basic reason for frequently over-threshold SSO with low amplitude at multi-power plants was analyzed based on Hulunbuir League system. The sensitivities of the electrical damping to the main electrical parameters in the contributing loop of subsynchronous torsional interaction were calculated. Based on the sensitivities, a simulation method was presented, which was used to excite the same oscillation as the actual case by exerting disturbance on the firing angle. The limitation of wide-band and narrow-band supplementary subsynchronous damping controller (SSDC) for mitigating this kind of SSO was analyzed based on the electromagnetic transient simulation model of Hulunbuir League system. The difference of supplementary excitation damping controller (SEDC) and parallel-form FACTS connected to the generator terminal was compared from the aspects of response time and the ability of damping torque supplying. The analysis indicates that their response time is similar but FACTS has stronger ability of damping torque supplying than SEDC. Time-domain simulation method was used to compare the mitigation effects of SEDC, static var compensator (SVC) and static synchronous compensator (STATCOM). Considering the mitigation effect, the floor space limit of the power plant and so on, STATCOM was considered as the best mitigation measure. A control strategy of cascaded STATCOM for engineering application was presented and the capacity for SSO mitigation as well as output characteristics was analyzed. The analysis indicates that STATCOM using the proposed control strategy has better mitigation effect and output characteristics with smaller capacity.

Optimal Coordinated Design of Multiple Damping Controllers Based on PSS and UPFC Device to Improve Dynamic Stability in the Power System

Unified Power Flow Controller (UPFC) device is applied to control power flow in transmission lines. Supplementary damping controller can be installed on any control channel of the UPFC inputs to implement the task of Power Oscillation Damping (POD) controller. In this paper, we have presented the simultaneous coordinated design of the multiple damping controllers between Power System Stabilizer (PSS) and UPFC-based POD or between different multiple UPFC-based POD controllers without PSS in a single-machine infinite-bus power system in order to identify the design that provided the most effective damping performance. The parameters of the damping controllers are optimized utilizing a Chaotic Particle Swarm Optimization (CPSO) algorithm based on eigenvalue objective function. The simulation results show that the coordinated design of the multiple damping controllers has high ability in damping oscillations compared to the individual damping controllers. Furthermore, the coordinated design of UPFC-based POD controllers demonstrates the superiority over the coordinated design of PSS and UPFC-based POD controllers for enhancing greatly the stability of the power system.

An Eigenstructure-Based Performance Index and Its Application to Control Design for Damping Inter-Area Oscillations in Power Systems

An eigenstructure-based performance index is proposed in this paper to measure the dynamic performance of the system as well as control efforts. Calculation of this index is based on eigenstructure of the closed loop system and the design parameters; it does not rely on control structures. Therefore, this index can be applied for solving structurally constrained control problems. A tuning scheme based on this index is proposed for coordinating power system stabilizers (PSSs) and supplementary damping controllers (SDCs) for flexible AC transmission systems (FACTS) devices to damp inter-area oscillations of systems and to optimize their control efforts under multiple operating conditions. Both PSSs and SDCs utilize control structures as a low order single-input-single-output phase lead-lag compensator. Wide-area signals are employed to upgrade their effectiveness in damping inter-area oscillations. Time delays caused by usage of wide-area signals are also considered in the tuning scheme. Results of simulation on a four-machine two-area system and the New England and New York interconnected system show that the proposed index is effective in measuring dynamic performance of the system and the coordinatedly tuned PSSs and SDCs based on this index can robustly damp inter-area oscillations of systems with optimized control efforts.

Control of static synchronous compensator with supplementary damping enhancement for wind farm voltage regulation

This study presents a new control design approach for the wind farm voltage regulation using static synchronous compensator (STATCOM). A mode decoupling proportional plus integral (PI) controller, in which the control gains are synthesised by eigenstructure assignment (EA), is proposed for the STATCOM. EA is a state-space approach, which is used to improve system damping by eigenvalue assignment and alter system mode shape by eigenvector assignment. To embed the physical PI control loops in the state-space model, an equivalent transformation is proposed to map the feedback gain matrix to the PI controller. Owing to the presence of the physical PI control loops, the control signals would not mire into saturation when appropriate limiter according to the STATCOM capacity is placed in the control variables. To further alleviate the undesired oscillation mode excited by transient disturbance, a lead-lag-based supplementary damping controller (SDC) is adopted. Simulation comparisons are provided to show that the proposed technique can be an effective method for mitigating the voltage fluctuation in the wind farm because of the load changes and the wind gust.

DFIG rotor voltage control for system dynamic performance enhancement

This article develops a model of a doubly fed induction generator system including the detailed dynamics of the converter circuitry. The order of the converter controls in terms of providing damping to the system is identified through residue principles. Supplementary damping controller has been incorporated so as to compensate for the phase lag introduced by the rotor voltage input, which was observed to have the largest residue contribution at the lightly damped mode. The improvement in damping profile was verified by simulating the system for a number of disturbance conditions. While the power oscillation damping (POD) controller was observed to enhance the system damping generally, it was also able to ride through low voltage conditions arising out of severe fault conditions thus averting total system collapse.

Robust control methodology for the design of supplementary damping controllers for FACTS devices

In this paper, a new procedure to design Supplementary Damping Controllers (SDCs) for Flexible Alternating Current Transmission System (FACTS) devices is proposed. The control design problem is formulated as a search for a feasible controller subject to restrictions in the form of Linear Matrix Inequalities (LMIs). The main objective, from the application viewpoint, is the improvement of the damping ratios associated to inter-area oscillation modes. Unlike other types of formulations existing in the literature, this new formulation is capable of explicitly modeling the constraints on the controller bandwidth, which are crucial to avoid undesired amplification of high frequency noise signals coming into the controller input. To illustrate the efficiency of the proposed procedure, the design of an SDC for a Thyristor Controlled Series Capacitor (TCSC) placed in the New England/New York benchmark test system is carried out. The results show the designed controllers are able to provide adequate damping for the oscillations modes of interest for several different operating conditions.

Supplementary Damping Controller Design using Direct Heuristic Dynamic Programming in Complex Power Systems

In modern, large scale interconnected power grids, low-frequency oscillation is a key roadblock to improved power transmission capacity. Supplementary generator control, flexible AC transmission system (FACTS), and high voltage direct currents (HVDC) are engineered devices designed to damp such low frequency swings. In this paper a neural network-based approximate dynamic programming method, namely direct heuristic dynamic programming (direct HDP), is applied to power system stability enhancement. Direct HDP is a learning and approximation based approach to addressing nonlinear system control problems under uncertainty, and it is also a model-free design strategy. The action and critic networks of the direct HDP are implemented using multi-layer perceptrons; learning is carried out based on the interactions between the controller and the power system. For this design approach, real time system responses are provided through wide-area measurement system (WAMS). The controller learning objective is formulated as a reward function that reflects global characteristics of the power system under low frequency oscillation, as well as tight coupling effects among system components. Direct HDP control design is illustrated by case studies, which are also used to demonstrate the learning control performance. The proposed direct HDP learning control is also developed as a new solution to a large scale system coordination problem by using the China Southern Power Grid as a major test bed.

Expansion of System Operating Range by an Interpolated LPV FACTS Controller Using Multiple Lyapunov Functions

In this paper, a new gain-scheduling control design approach is applied to a supplementary damping controller (SDC) design for a FACTS device in the IEEE 50-machine system. The power system model with the FACTS device is linearized at different operating points to obtain an LPV open-loop model, whose state-space entries depend continuously on a time-varying parameter vector. A synthesis procedure for an improved LPV controller using multiple parameter-dependent Lyapunov functions and an interpolation scheme is presented and applied to the static VAr compensator (SVC) SDC design. Comparisons from simulation results are presented among the interpolated LPV controller designed using multiple parameter-dependent Lyapunov functions (MLPV SDC), the LPV controller designed using a single parameter-dependent Lyapunov function (SLPV SDC), and a conventional controller designed using the Root-locus method (RL SDC), which show that with an interpolated MLPV SDC for the SVC device, the system can achieve better robustness in an extended operating range

LPV Supplementary Damping Controller Design for a Thyristor Controlled Series Capacitor (TCSC) Device

In this paper, the Linear Parameter Varying (LPV) controller design technique is applied in the design of a supplementary damping controller (SDC) for a Thyristor Controlled Series Capacitor (TCSC). The power system model with TCSC devices is linearized at different operating points to obtain an LPV open loop model, whose state space entries depend continuously on a time varying parameter vector. Appropriate scheduling parameters are chosen and a suitable grid is formed in the entire parameter space. The locations of the TCSCs with their controllers are carefully chosen based on the analysis of mode shapes as well as the calculation of the modal controllability. An LPV damping controller for TCSC is then designed based on a single Lyapunov function under some realistic constraints. Comparisons from simulation results are presented between an LPV SDC and an H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">infin</sub> SDC, which show that the LPV SDC can guarantee robustness over a wider operating range as well as allow more flexibility in achieving specific performance objectives at each operating point

Robust Design of a Damping Controller for Static Var Compensators in Power Systems

This paper presents a systematic procedure for the synthesis of a supplementary damping controller (SDC) for static VAr compensators (SVC) in multimachine power systems. The robust performance in terms of the structured singular value (SSV or /spl mu/) is used as the measure of control performance. A wide range of operating conditions are used for testing. Simulation results on standard test systems show that the resulting SDC effectively enhances the damping of the interarea oscillations, providing robust stability and good performance characteristics both in frequency domain and in time domain.

Robust design of a damping controller for static VAr compensators in power systems

This paper presents a systematic procedure for the synthesis of a supplementary damping controller (SDC) for static VAr compensators (SVC) in multimachine power systems. The robust performance in terms of the structured singular value (SSV or /spl mu/) is used as the measure of control performance. A wide range of operating conditions are used for testing. Simulation results on standard test systems show that the resulting SDC effectively enhances the damping of the interarea oscillations, providing robust stability and good performance characteristics both in frequency domain and in time domain.