Subsynchronous Resonance Modes Research Articles

Battery energy storage-based system damping controller for alleviating sub-synchronous oscillations in a DFIG-based wind power plant

This paper presents the issue of the Sub-synchronous resonance (SSR) phenomenon in a series compensated DFIG-based wind power plant and its alleviation using a Battery Energy Storage-based Damping Controller (BESSDCL). A supplementary damping signal is developed considering the angular speed deviation and is incorporated into the BESS control system. Wide-area Measurement System data is used to determine the angular speed deviation. A linearized system model is developed to perform eigenvalue analysis, and to detect and examine unstable SSR modes. The variation of wind speed and three-phase fault are also taken into consideration to validate the robustness of the controller. To further verify the efficacy of the proposed damping controller, time-domain simulations are performed using MATLAB/Simulink. The application of the proposed BESSDCL stabilizes all the unstable system modes effectively at wind speeds of 7 m/s, 9 m/s, and 11 m/s, and at 40%, 50%, and 60% series compensation levels, as well three-phase fault conditions.

A preordainment approach for design of auxiliary damping controller and SSSC tuning to enhance SSR mode stability in DFIG based windfarm

ABSTRACT Sub-synchronous resonance (SSR) is a growing concern in wind turbine generators-based series capacitive compensated networks at low wind speed and peak compensation levels. It is feasible to increase the stability of SSR mode caused by a transmission line’s passive series compensation by providing active compensation using a flexible ac transmission system controller cooperating with an auxiliary damping controller. This paper presents preordainment and enhancement of SSR mode in DFIG-based series capacitive compensated line by incorporating an additional damping controller into the static synchronous series compensator (SSSC). The auxiliary damping controller modulates the reactive voltage injected by SSSC into the transmission line by considering the appropriate input control signal, reflecting the SSR instability, and giving the maximum damping to the SSR mode. The optimal input control signal is determined via residue analysis, and the design procedure of the auxiliary damping controller is presented using root locus plots. The root locus plots offer a visual representation of the loci for each mode and preordain eigenvalues for new stability, which aids in the design of the auxiliary damping controller. This feature allows to predetermine the SSR mode eigenvalue while before connecting it with SSSC. Accordingly, it provides a controlled dampening to SSR mode such that the desired damping ratio for SSR mode can be achieved without influencing the stability of other modes. The impact of the designed auxiliary damping controller is examined at high compensation levels and low wind speed. The eigenvalue analysis results show that the preordained eigenvalues found using root locus plots are correct and the proposed approach predominantly enhances the stability of SSR mode. The fast Fourier transform (FFT) analysis and transient simulations are used to show the detuning and dampening of SSR mode. The proposed work is executed using MATLAB/Simulink.

Application of Hankel Dynamic Mode Decomposition for Wide Area Monitoring of Subsynchronous Resonance

In recent years, subsynchronous resonance (SSR) has frequently occurred in DFIG-connected series-compensated systems. For the analysis and prevention, it is of great importance to achieve wide area monitoring of the incident. This paper presents a Hankel dynamic mode decomposition (DMD) method to identify SSR parameters using synchrophasor data. The basic idea is to employ the DMD technique to explore the subspace of Hankel matrices constructed by synchrophasors. It is analytically demonstrated that the subspace of these Hankel matrices is a combination of fundamental and SSR modes. Therefore, the SSR parameters can be calculated once the modal parameter is extracted. Compared with the existing method, the presented work has better dynamic performances as it requires much less data. Thus, it is more suitable for practical cases in which the SSR characteristics are time-varying. The effectiveness and superiority of the proposed method have been verified by both simulations and field data.

Mitigating Subsynchronous Resonance Using Synchrophasor Data Based Control of Wind Farms

Series compensation is used to improve power system transmission capacity. Subsynchronous resonance (SSR) associated with such a system is a challenging issue. Today, with increasing integration of wind farm (WF) to power network, the stability of the system gets deteriorated due to variation in wind speed at the WFs. The reaction between the SSR modes and the doubly fed induction generator converters is known as subsynchronous control interaction (SSCI), due to which, it becomes more challenging to achieve power system stability. To overcome these issues, in this paper, a synchrophasor data-based control (SDC) technique is proposed. The proposed controller diminishes induction generator effect, torsional interaction, and the SSCI effect on the series compensated network, integrating multiple WFs. The SDC provides an auxiliary SSR damping control (SSRDC) with thyristor controlled series compensation (TCSC). This SSRDC uses synchrophasor data from WF connected point of common couplings (PCCs) inside the grid to improve the SSR oscillation damping. The proposed method maintains reference voltage angle of the PCCs by controlling equivalent impedance of the grid. The impedance provides significant damping for SSR along with the TCSC control. The proposed SDC is tested for modified 39-bus New England system with WFs and is found to be effective. Comparison of this method with conventional local control demonstrates its superior performance.

Characteristic Analysis of Subsynchronous Resonance in Practical Wind Farms Connected to Series-Compensated Transmissions

The emerging subsynchronous resonance (SSR) caused by the interaction of wind turbine generators (WTGs) with series compensation has aroused great concerns. For this particular issue, this paper is aimed to fill the gap between theoretical studies and actual observations. By analyzing the field data of 58 SSR events captured in a practical wind power system and examining the observed dynamics with previous theoretical results, the mechanism and characteristics of SSR are revealed in a more explicit and substantial way. The necessary conditions and dominant influential factors are identified and the underlying reasons are discovered. Theoretically derived as well as practically measured impedance models have demonstrated that the converter control of doubly fed induction generator (DFIG) produces negative resistance at the slip frequency and thus causes unstable SSR; while permanent magnet synchronous generators and self-excited induction generators are just passively engaged in those SSR incidents. The distribution of the oscillation frequency has also been examined with field measurements. It is discovered that WTGs at different locations participate into the same SSR mode and their frequencies are not fixed but keep changing with the time, the variation of grid topology, and the number of online generators.

Subsynchronous Resonance Monitoring Using Ambient High Speed Sensor Data

This paper proposes a framework for online monitoring of subsynchronous oscillations using ambient sensor data from high speed sampling devices such as digital fault recorders (DFRs). Ambient data is continuously available in the form of routine system responses to random load fluctuations. This paper shows the usefulness of ambient data for tracking the frequency, damping ratio and mode shape of torsional modes related to subsynchronous resonance (SSR). Frequency domain decomposition (FDD) and recursive least square (RLS) algorithms are tested for ambient monitoring of SSR modes. IEEE second SSR benchmark model is used as the study system. Nonlinear and linearized equations of this system are analyzed for testing the performance of measurement based methods and to compare their results with respective linearized system modes. It is shown that both electrical and mechanical signals can be used for the SSR monitoring while the torsional modes are more observable in mechanical signals such as generator speeds. In addition to estimating the frequency and damping ratio, torsional mode shapes can be identified by implementing FDD as a multi-dimensional method on the speeds of the masses of the turbine shaft. The algorithms are tested on an archived real system data set from a DFR.

SSR Damping Controller Design and Optimal Placement in Rotor-Side and Grid-Side Converters of Series-Compensated DFIG-Based Wind Farm

This paper deals with subsynchronous resonance (SSR) phenomena in a capacitive series-compensated DFIG-based wind farm. Using both modal analysis and time-domain simulation, it is shown that the DFIG wind farm is potentially unstable due to the SSR mode. In order to damp the SSR, the rotor-side converter (RSC) and grid-side converter (GSC) controllers of the DFIG are utilized. The objective is to design a simple proportional SSR damping controller (SSRDC) by properly choosing an optimum input control signal (ICS) to the SSRDC block, so that the SSR mode becomes stable without decreasing or destabilizing the other system modes. Moreover, an optimum point within the RSC and GSC controllers to insert the SSRDC is identified. Three different signals are tested as potential ICSs including rotor speed, line real power, and voltage across the series capacitor, and an optimum ICS is identified using residue-based analysis and root-locus method. Moreover, two methods are discussed in order to estimate the optimum ICS, without measuring it directly. The studied power system is a $\mathbf{100\;{\rm MW}}$ DFIG-based wind farm connected to a series-compensated line whose parameters are taken from the IEEE first benchmark model (FBM) for computer simulation of the SSR. MATLAB/Simulink is used as a tool for modeling and designing the SSRDC, and power system computer aided design/electromagnetic transients including dc (PSCAD/EMTDC) is used to perform time-domain simulation for design process validation.

Modeling and Control of Gate-Controlled Series Capacitor Interfaced With a DFIG-Based Wind Farm

This paper presents application and control of the gate-controlled series capacitor (GCSC) for series compensation and subsynchronous resonance (SSR) damping in doubly-fed induction generator (DFIG)-based wind farms. The GCSC is a new series FACTS device composed of a fixed capacitor in parallel with a pair of antiparallel gate-commuted switches. The study considers a DFIG-based wind farm, which is connected to a series-compensated transmission line whose parameters are derived from the IEEE first benchmark model for computer simulation of the SSR. The small-signal stability analysis of the system is presented, and the eigenvalues of the system are obtained. Using both modal analysis and time-domain simulation, it is shown that the system is potentially unstable due to the SSR mode. Therefore, the wind farm is equipped with a GCSC to solve the instability of the wind farm resulting from the SSR mode, and an SSR damping controller (SSRDC) is designed for this device using residue-based analysis and root locus diagrams. Using residue-based analysis, the optimal input control signal to the SSRDC is identified, which can damp the SSR mode without destabilizing other modes, and using root-locus analysis, the required gain for the SSRDC is determined. MATLAB/Simulink is used as a tool for modeling, design, and time-domain simulations.

Analysis of sub‐synchronous resonance in doubly‐fed induction generator‐based wind farms interfaced with gate – controlled series capacitor

This paper first presents a step-by-step tutorial on modal analysis of a doubly-fed induction generator (DFIG)-based series compensated wind farm. The model of the system includes a wind turbine aerodynamics, a sixth-order order induction generator, a second-order two-mass shaft system, a fourth-order order series compensated transmission line, an eighth-order rotor-side converter (RSC) and grid-side converter (GSC) controllers, and a first-order DC-link model. Then, using modal analysis and time-domain simulations, it is shown that a fixed-series compensated DFIG is highly unstable due to the sub-synchronous resonance (SSR) mode. In order to damp the SSR mode, the wind farm is interfaced with the gate-controlled series capacitor (GCSC) - which is a new series flexible AC transmission system (FACTS) device. A SSR damping controller (SSRDC) is designed for the GCSC using residue-based analysis and root locus diagrams, and an effective input control signal (ICS) to the SSRDC is identified in order to simultaneously increase damping of both the SSR and super-synchronous (SupSR) modes. The IEEE first benchmark model on SSR is adapted with an integrated DFIG-based wind farm to perform studies. Matlab/Simulink is used as a tool for designing process, and PSCAD/EMTDC is used for time-domain simulations.

Modal Analysis of Induction Generator Based Wind Farm Connected to Series-compensated Transmission Line and Line Commutated Converter High-Voltage DC Transmission Line

This article presents a comprehensive analysis of the potential of sub-synchronous resonance in induction generator based wind farms connected to a line commutated converter based high-voltage DC transmission line. Since series-compensated lines are also known to cause sub-synchronous resonance in induction generator based (Type 1) wind farms, this study also considers a series-compensated line in parallel with the high-voltage DC line for the investigation of sub-synchronous resonance potential. The CIGRE benchmark high-voltage DC system and the IEEE first benchmark system are considered as the study system components. A linearized state-space model of the study system is developed for eigenvalue analysis followed by participation factor analysis. A sensitivity study of the sub-synchronous resonance modes with respect to variation in different model parameters, such as rectifier firing angle, DC line power flow, and series compensation level, is also reported. It is found that the high-voltage DC rectifier station current regulator does not interact with any of the sub-synchronous modes of the wind farm. However, in the event that the high-voltage DC line is blocked during a contingency, the wind farm will operate radially with the series-compensated line and may experience sub-synchronous resonance oscillation due to the induction generator effect.

Modal Analysis of a DFIG-Based Wind Farm Interfaced With a Series Compensated Network

Interests of subsynchronous resonance (SSR) in series compensated electric networks with wind power penetration have arisen recently. To better understand the nature of such systems, modal analysis of a doubly-fed induction generator (DFIG)-based wind energy system interconnected with a series compensated electric network is conducted in this paper. The system model is built in Matlab/Simulink. The major contributions of the paper include: 1) identification of the four system modes (SSR, supersynchronous, electromechanical, and shaft modes) of a DFIG-based wind farm interfaced with a series compensated network, 2) investigation of the impacts of various parameters and operating conditions on those modes, and 3) prediction of the dynamic performance of the system using modal analysis and confirmation of such prediction via time-domain simulation results.

Hybrid series compensation scheme capable of damping subsynchronous resonance

The study presents a hybrid series capacitive compensation scheme which is capable of damping subsynchronous resonance (SSR). The hybrid scheme is a combination of a single-phase thyristor-controlled series capacitor (TCSC) and a fixed series capacitor in series in one phase of the compensated transmission line and fixed capacitors on the other two phases. The hybrid scheme creates a phase imbalance during system disturbances. The phase imbalance causes a suppression of the energy exchanged between the electrical and mechanical sides of the turbine-generator and, therefore results in reduction of the growing torsional stresses at SSR mode. The validity and effectiveness of the proposed scheme have been demonstrated on the IEEE first and second benchmark models through time-domain simulations using the EMTP-RV.

DAMPING OF SUBSYNCHRONOUS RESONANCE OSCILLATIONS USING THE VOLTAGE MAGNITUDE AND PHASE ANGLE CONTROL OF STATIC PHASE SHIFTER

The voltage magnitude and phase Angle control of static phase shifter (VMPA–SPS) to damp the subsynchronous resonance(SSR) oscillations is investigated. A linear mathematical model of seriescompensated transmission line power system with static phase shifter is developed .The input control signals to the simulated power system is the phase angle and voltage magnitude deviations of static phase shifter. A controllability measure based on singular value decomposition (SVD) is used to identify the effectiveness of each control input signal on the electromechanical modes. A state feedback supplementary controller based on the linear quadratic regulator principle with a full rank observer is used to modulate the voltage magnitude and phase angle deviations of SPS to stabilize the SSR modes under different operating conditions and compensation levels of the compensated transmission line. To validate the effectiveness of the proposed supplementary controller , the studied power system is subjected to different disturbances. The digital simulation results prove the powerful of the proposed static phase shifter supplementary controller in terms of the fast damping of the SSR oscillations with less overshoot/undershoot.

Series compensation of radial power system by a combination of SSSC and dielectric capacitors

This paper shows that the addition of dielectric capacitors lowers the cost of series compensation by static synchronous series compensator (SSSC). Normally the capacitor resonates with the line inductance and the L-C electrical resonance can interact with the torsional resonances of the multiple-inertia elastic shaft of steam turbine-generators to give rise to subsynchronous resonance (SSR) instability. The SSSC has two functions: (1) to provide some series capacitive reactance compensation; (2) to damp out incipient unstable SSR modes. Digital simulation using HYPERSIM shows that for an overall degree of capacitive compensation of 0.7 pu, the SSSC component is only about 1/3 of the capacitive Mvar. Based on the transient stability limit, the transmissibility of the line is increased by a factor of 2.23.

Suppression of torsional oscillations using thyristor‐controlled conductance in parallel to series‐capacitor segment

AbstractThis paper presents the analyzed results of a study on the application ofthyristor‐controlled conductance in parallel to one series‐capacitor segment for suppressing sub synchronous resonance (SSR) that occurs in a series‐compensated power system. The IEEE Second Benchmark Model, systems, which has one turbine‐generator set, is taken as a standard model for this study. In order to stabilize all SSR modes in the studied system, a unified approach based on modal control theory is proposed to design a damping controller which is a dynamic output feedback compensator using shaft speed deviation of the studied generator as a feedback signal. To demonstrate the effectiveness of the proposed control scheme, frequency‐domain approach based on eigenvalue analyses and time‐domain approach based on non‐linear model simulations are performed. The simulated results show that the proposed SSR damping scheme can effectively suppress torsional oscillations of the studied system.

Computing the damping of subsynchronous oscillations due to a thyristor controlled series capacitor

We extend eigenvalue analysis of subsynchronous resonance (SSR) to include thyristor switchings. The eigenvalue computation takes account of the time variations and nonlinearities of both the thyristor switchings and the generator. An example is presented using the IEEE first benchmark SSR model. The paper contributes an accurate method to compute the damping of the SSR modes with a TCSC.

Damping of subsynchronous oscillations using adaptive controllers tuned by artificial neural networks

Artificial neural networks (ANNs) are utilised to adapt the controller gains of two widely used control schemes i.e. static VAr compensators (SVC) and excitation controllers (EC), for the damping of subsynchronous resonance (SSR) on a power system. To have good damping characteristics of SSR modes over a wide range of operating conditions, the parameters of the adaptive controllers are adapted based on generator loading conditions. Multilayer feedforward artificial neural networks (ANNs) are developed to serve for the purpose of controller parameter adaptation. The inputs to the ANN include the real power output P and reactive power output Q which characterise generator loading conditions. The outputs from the ANN are the desired controller gains. Time domain simulations are also performed on the IEEE first benchmark model to demonstrate the effectiveness of the proposed adaptive control schemes.

Damping subsynchronous resonance using superconducting magnetic energy storage unit

A novel damping scheme using superconducting magnetic energy storage (SMES) unit is proposed in this paper to damp subsynchronous resonance (SSR) of the IEEE Second Benchmark Model, system-1 which is a widely employed standard model for computer simulation of power system SSR. The studied system contains a turbine-generator set connected to an infinite bus through two parallel transmission lines, one of which is series-capacitor compensated. In order to stabilize all SSR modes, simultaneous active and reactive power modulation and a proportional-integral-derivative (PID) damping controller designed by modal control theory are proposed for the SMES unit. A frequency domain approach based on eigenvalue analysis and time-domain approach based on nonlinear model simulations are performed to validate the effectiveness of the damping method. It can be concluded from the simulation results that the proposed damping scheme can effectively suppress SSR of the studied system. >

Suppression of common torsional mode interactions using shunt reactor controllers

The paper presents the results of a study on the utilization of shunt reactors for the damping of common torsional mode interactions of a power system containing series-capacitor compensation. The IEEE Second Benchmark Model, system-2, which has two sets of nonidentical turbine-generators connected to an infinite bus via a common series-capacitor compensated transmission line, is employed to investigate the possible unstable subsynchronous resonance (SSR) modal interactions which can be suppressed by using reactive power compensation. A set of shunt reactors are proposed and connected to the studied system and a unified approach based on modal control theory is employed to design shunt reactor controllers in order that all SSR modes in the system can be stabilized. For clearly demonstrating the effectiveness of the proposed scheme, SSR mode eigenvalues under different loading conditions and sensitivity analysis of shunt reactor controllers' parameters are performed. Dynamic responses of the nonlinear system simulation under a torque disturbance on a generator shaft and a severe three-phase short-circuit fault at an infinite bus are also carried out. >

Torsional oscillations of series capacitor compensated AC/DC systems

Torsional oscillations in an AC/DC power system that result from series-capacitor compensation and HVDC converter controllers are investigated. A feasible approach for damping the torsional modes by coordinating the controllers of a static VAr compensator (SVC) unit with the supplemental subsynchronous damping control (SSDC) of the HVDC rectifier is presented. An eigenvalue method is used for the studies, and the analytical results are verified by detailed digital computer simulation, using the BPA's Electromagnetic Transients Program (EMTP). The studies show that in a series-capacitor-compensated AC/DC system, the SSDC can be used to damp the subsynchronous resonance (SSR) modes only over a limited range of operating conditions. The coordinated SVC-SSDC approach provides adequate damping for all the SSR modes under all operating conditions, particularly at high series-compensation levels.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>