Subsynchronous Resonance Research Articles

LQR control strategy for virtual synchronous generator adapted to stiff grid

Virtual synchronous generators (VSG) exhibit good small-signal stability in low short-circuit ratio (SCR) grids. However, the small-signal stability of the grid decreases as its SCRs increase, and there is even a risk of sub-synchronous resonance (SSR). The VSG sequence impedance model considering the frequency coupling effect is developed. The reasons for SSR caused by VSG integration into a stiff grids are analyzed using the sequence impedance analysis method and the Nyquist criterion. To enhance the grid-connected stability of VSG under stiff grids conditions, a linear quadratic regulator (LQR) control strategy with full-state feedback was proposed. The control strategy of LQR can effectively improve the phase margin of VSG output impedance in the low-frequency region, and it also exhibits strong robustness to variations in grid short-circuit ratios. It can also significantly improve the stability margin of the grid-tied system consisting of VSG and stiff grid, and effectively suppress the occurrence of SSR. Finally, the effectiveness and reliability of LQR control strategy are verified by OPAL-RT experimental platform.

Simulation Modeling of Subsynchronous Resonance of an Autonomous Power District with a Gas Turbine Unit

Simulation Modeling of Subsynchronous Resonance of an Autonomous Power District with a Gas Turbine Unit

Sub-synchronous oscillation suppression strategy for virtual synchronous generators based on dual-loop sliding mode control

The virtual synchronous generator (VSG) has synchronous voltage source characteristics that can effectively improve the stability of high-penetration renewable energy power systems. However, the output impedance of VSG using traditional voltage–current inner-loop control has lower damping in the sub-synchronous frequency range. Therefore, when the VSG is connected to a grid with series compensation for long-distance transmission of renewable energy, in the sub-synchronous frequency range, there is a potential interaction between the inductive output impedance of VSG and the capacitive impedance of the line, leading to the occurrence of sub-synchronous resonance (SSR). To address this challenge, the stability of a series-compensated grid-connected system employing voltage–current inner-loop control was analyzed using VSG sequence impedance modeling. A dual-loop sliding mode control strategy (SMC-DL) was proposed to suppress SSR occurrence. This control strategy can significantly enhance the damping of VSG’s output impedance in the sub-synchronous frequency range, and effectively suppress SSR. Compared to traditional control strategies, this control strategy does not require the addition of virtual impedance, avoids voltage offset issues, adapts to grids with different series compensation levels. Finally, the effectiveness of this approach was verified through simulations and experiments.

Advancing Distance Relaying Reliability: S Transform Solution for Renewable Energy-Infused Smart Grid

Distance relaying is a crucial component in safeguarding transmission lines globally. However, the presence of Sub-Synchronous Resonance (SSR) introduces challenges, as oscillations in voltage and current magnitudes adversely affect the performance of conventional distance relays. Detecting faults accurately during these oscillations poses a significant challenge for traditional relaying mechanisms. This paper addresses the issue of SSR-induced maloperations in distance relays, particularly in the context of the increasing penetration of renewable energy resources in smart grids. The integration of wind power into the grid generates sub-synchronous oscillations, leading to protection issues. In response, a novel solution leveraging the S transform, a modern signal processing technique, is proposed to enhance the robustness of distance relaying under such challenging conditions. The developed algorithm is implemented in MATLAB and rigorously tested on the First Benchmark Model of sub-synchronous resonance. Simulation of the model is conducted in the PSCAD simulation software, and the results are thoroughly validated in MATLAB. The study demonstrates the efficacy of the S transform-based approach in accurately identifying faults and mitigating maloperations caused by SSR, thereby improving the reliability of distance relaying in smart grids with high renewable energy integration.

The Analysis of Sub-Synchronous Resonance in a Wind Farm for a Doubly-Fed Induction Generator Using Modern Analytical Method

The occurrence of Sub-Synchronous Resonance (SSR) phenomena can be attributed to the interaction that takes place between wind turbine generators and series-compensated transmission lines. The Doubly-Fed Induction Generator (DFIG) is widely recognized as a prevalent generator form employed in wind energy conversion systems. The present paper commences with an extensive exposition on modal analysis techniques employed in a series of compensated wind farms featuring Doubly Fed Induction Generators (DFIGs). The system model encompasses various components, including the aerodynamics of a wind turbine, an induction generator characterized by a sixth-order model, a second-order two-mass shaft system, a series compensated transmission line described by a fourth-order model, controllers for the Rotor-Side Converter (RSC) and the Grid-Side Converter (GSC) represented by an eighth-order model, and a first-order DC-link model. The technique of eigenvalue-based SSR analysis is extensively utilized in various academic and research domains. The eigenvalue technique depends on the initial conditions of state variables to yield an accurate outcome. The non-iterative approach, previously employed for the computation of initial values of the state variables, has exhibited issues with convergence, lack of accuracy, and excessive computational time. The comparative study evaluates the time-domain simulation outcomes under different wind speeds and compensation levels, along side the eigenvalue analysis conducted using both the suggested and non-iterative methods. This comparative analysis is conducted to illustrate the proposed approach efficacy and precision. The results indicate that the eigenvalue analysis conducted using the proposed technique exhibits more accuracy, as it aligns with the findings of the simulations across all of the investigated instances. The process of validation is executed with the MATLAB program. Within the context of the investigation, it has been found that increasing compensation levels while simultaneously decreasing wind speed leads to system instability. Therefore, modifying the compensation level by the current wind speed is advisable.

Effective numerical simulations of synchronous generator system

Synchronous generator system is a complicated dynamic system for energy transmission, which plays an important role in modern industrial production. In this article, we propose some predictor-corrector methods and structure-preserving methods for a generator system based on the first benchmark model of subsynchronous resonance, among which the structure-preserving methods preserve a Dirac structure associated with the so-called port-Hamiltonian descriptor systems. To illustrate this, the simplified generator system in the form of index-1 differential-algebraic equations has been derived. Our analyses provide the global error estimates for a special class of structure-preserving methods called Gauss methods, which guarantee their superior performance over the PSCAD/EMTDC and the predictor-corrector methods in terms of computational stability. Numerical simulations are implemented to verify the effectiveness and advantages of our methods.

Sub-synchronous resonance in grid-forming PMSGs connected to series-compensated networks

Sub-synchronous resonance in grid-forming PMSGs connected to series-compensated networks

Damping Subsynchronous Resonance Oscillations Using A Dynamic Switched Filter-Compensator Scheme

The paper presents a new effective method to damp subsynchronous resonance (SSR) – shaft torsional oscillations for large synchronous generators. This is achieved by using a dynamic power filter and static compensator (DFC) scheme. The proposed scheme with a switched series capacitor compensation and a modulated Tuned-Arm-Filter can be used to damp SSR oscillation modes using a novel Tri-loop Error-driven dynamic controller.

Black Widow Optimization Algorithm-Based Sub Synchronous Resonance Investigation with Series Compensation

The integration of wind farms into the transmission network has raised various concerns and objections. To address these challenges, the deployment of series compensators has gained significance as an effective method for enhancing the power transmission capacity of existing lines, particularly for the integration of large-scale wind farms. However, the use of series reactive compensation lines can lead to a phenomenon known as sub-synchronous resonance (SSR) in turbo generators. This SSR can cause electrical instability at sub-synchronous frequencies and potential damage to the turbine’s generator shaft, particularly during periods of peak production. As a result, the assessment of SSR through comprehensive surveys is crucial for wind power engineers to make informed decisions and ensure the safety of turbines. This study explores the potential of SSR through the utilization of the black widow optimization technique. The analysis takes into account variables such as variations in the speed of the wind, compensation spectrum, and wind velocity and examines the eigenvalue and involvement components under various operating situations. To validate our findings, electromagnetic transient simulations are conducted using the PSCAD/EMTDC software, employing the initial IEEE reference systems. This research contributes to a deeper understanding of SSR and its implications for wind energy systems.

Unstable Subsynchronous Interaction Induced by Blocking Filters in a Wind-Thermal Combined Power System

Blocking filters (BFs) are applied to reduce the risk of shaft related subsynchronous resonance (SSR) in thermal power plants connected to series compensated transmission lines. However, when doubly-fed induction generator (DFIG)-based wind farms are connected in parallel with the existing thermal power plants, the same BFs may cause unstable subsynchronous interaction (SSI) with the DFIGs. This paper investigates the potential risk of this new type of SSI caused by BFs, which are originally designed to reduce the SSR risk. First, a representative system model of thermal power units with BFs and DFIGs integrated into grid is established. Then, impedance-based analyses and time-domain simulations are carried out to analyze the mechanism and characteristics of the SSI. The results indicate that the interaction between BFs and DFIGs may induce unstable oscillation in the system. In particular cases where series compensation in the transmission line is bypassed, the risk of SSI instability still exists. With series compensation operating normally, the interaction among BFs, DFIGs, and series compensated lines becomes even more complex. The paper also investigates the effects of system parameters such as the number of online DFIGs, wind speed, and series compensation level on the SSI characteristics.

Analysis of Subsynchronous Resonance via Torsional Interactions in Electromechanical Systems through Different Fault Points

Analysis of Subsynchronous Resonance via Torsional Interactions in Electromechanical Systems through Different Fault Points

FUZZY LOGIC CONTROLLED STATCOM WITH A SERIES COMPENSATED TRANSMISSION LINE ANALYSIS

The integration of wind farms with transmission networks exhibits several problems. The sub-synchronous resonance (SSR) plays a vital role in those issues, and it must be reduced. Two effective flexible ac transmission system (FACTS) based voltage control devices, namely static synchronous series compensator (SSSC) and static compensator (STATCOM) are proposed in this paper to mitigate the SSR. Detailed eigenvalue analysis was conducted to prove the successful mitigation of SSR by two controllers in a series of compensated wind farms. To find the dominant control scheme, the eigenvalues of the proposed controllers are compared with PSCAD/EMTDC simulations. Finally, a comparison study is carried out between the two proposed SSR controllers.Further, the fuzzy logic control based on STATCOM and SSSC is also developed to enhance the stability margin of the wind turbine. The results have been validated with the IEEE 1st SSR benchmark system. From the results, it is proven that Fuzzy Logic Controller (FLC) based SSSC exhibits better performance than STATCOM.

Proposed sub‐synchronous resonance damping controller for large‐scale wind farms

AbstractThis paper deals with the mitigation of sub‐synchronous resonance (SSR) in doubly‐fed induction generator (DFIG)‐based wind farms using a sub‐synchronous resonance damping controller (SSRDC). The performance of the SSRDC depends on its input control signal and the location of its output control signals. Hence, this paper presents an algorithm to select the best location for applying the SSRDC. The DFIG parameters are used as the inputs of this algorithm. Also, the participation factors analysis is employed as this algorithm's main core. The output of this algorithm determines that the control signal of SSRDC can be applied either in the grid‐side converter (GSC) and/or in the rotor‐side converter (RSC). The best input location in the GSC is the DC‐link voltage and the best input location in the RSC is the q‐component of the rotor voltage. The accuracy of this algorithm was evaluated by investigating the effect of various input signal locations on the SSR using the eigenvalue analysis. This analysis indicated that the dc‐link voltage and the q‐components of the rotor voltage are the most effective signals on the sub‐synchronous oscillatory modes. Moreover, this paper introduces a new SSRDC using these two signals. The performance of this controller is validated through the eigenvalue analysis and a time domain simulation.

The Impact of Phase-Locked Loop (PLL) Architecture on Sub-Synchronous Control Interactions (SSCI) for Direct-Driven Permanent Magnet Synchronous Generator (PMSG)-Based Type 4 Wind Farms

Electric vehicles (EVs) are a promising solution to reduce carbon dioxide (CO2) emissions, but this reduction depends on the fraction of renewable sources used to generate electricity. Wind energy is thus a vital candidate and has experienced a remarkable surge recently, establishing itself as a leading renewable power source worldwide. The research on Direct-Driven Permanent Magnet Synchronous Generator (PMSG)-based type 4 wind farms has indicated that the Phase-locked Loop (PLL) bandwidth significantly impacts Sub-Synchronous Resonance (SSR). However, the influence of PLL architecture on SSR remains unexplored and warrants investigation. Therefore, this paper investigates PLL architectural variations in PLL Loop Filter (LF) to understand their impact on SSR in type 4 wind farms. Specifically, an in-depth analysis of the Notch Filter (NF)-based enhanced PLL is conducted using eigenvalue analysis of the admittance model of a PMSG-based type 4 wind farm. The findings demonstrate that the NF-based enhanced PLL exhibits superior performance and improved passivity in the sub-synchronous frequency range, limiting the risk of SSR below 20 Hz. Additionally, Nyquist plots are employed to assess the impact on system stability resulting in increased stability margins. In the future, it is recommended to further investigate and optimize the PLL to mitigate SSR in wind farms.

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.

Damping sub-synchronous resonance in DFIG wind farms: An innovative controller utilizing wide-area measurement systems

The use of series shunt compensators along with wind energy in power systems has increased significantly. One of the main disadvantages of wind energy and series compensation is the phenomenon of sub-synchronous amplification. In this paper, a control method with fuzzy system based on wide area measurement systems (WAMS) and considering time delay in order to increase the damping of sub-synchronous oscillations in compensated networks with capacitive compensators and wind turbines. The DFIG type is provided in the GSC converter’s voltage control loop for the system’s stable operation. The simulation results using MATLAB/Simulink software on Modified IEEE First Bench Mark test networks show the effectiveness of the proposed method in damping sub-synchronous oscillations in power systems compensated with series capacitors.

Gate‐controlled series capacitor: A new methodology for mitigating sub‐synchronous resonance in a series‐compensated DFIG‐based wind farm

AbstractSeries‐compensated transmission lines can lead to a sub‐synchronous resonance (SSR) phenomenon at high compensation levels, where the system lacks stability. Gate‐controlled series capacitor (GCSC) is widely used to damp the SSR. Here, an effective and new methodology for damping the SSR is presented. The proposed method aims to alleviate the SSR phenomenon based on estimating both the frequency and the maximum value of the voltage magnitude signal rather than using the Proportional Integral controller. The appropriate turn‐off angle corresponding to the maximum value of the voltage magnitude signal is applied to the GCSC on the condition that the estimated frequency of the voltage magnitude signal is within the range of the SSR frequency. If the estimated frequency of the voltage magnitude signal is out of the range of the SSR frequency, the steady‐state turn‐off angle (1130) is applied to the GCSC. The capability of the proposed method for damping the SSR under various compensation levels, various wind speeds, and sub‐synchronous control interaction (SSCI) is validated by time‐domain simulation and eigenvalue analysis. Compared to the presented latest method for SSR damping using GCSC, all the obtained results demonstrate that the oscillations converge faster when the proposed method is activated.

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.

A d-axis current error compensation method based on coupling mechanism for Grid-Connected inverters under weak grid

Three-phase grid-connected inverters (GCI) are widely used in wind farms as they serve as the interface between the renewable energy system and the grid. However, the sub-synchronous resonance (SSR) issues have been observed between GCI and weak grid, which seriously threatens the stable operation of grid-connected system. In this paper, the coupling mechanism between the GCI and the weak grid is analyzed from the perspective of power angle relationship. Revealing that there is a small signal coupling between d-axis current and power angle due to the grid impedance introduced by weak grid, which further destabilizes the studied system through PLL feedforward paths. It provides an explanation for the limitations of short circuit ratio (SCR) and phase-locked loop (PLL) bandwidth. Then, a d-axis current error compensation method employed in current control is proposed to damp SSR. The method introduces an extra parallel branch to compensate the PLL feedforward effect and increases the qd-axis impedance amplitude of GCI to decrease the coupling degree between the GCI and weak grid simultaneously. By employing the proposed compensation method, the SSR issues of the GCI under weak grid can be effectively solved under grid impedance fluctuations and high PLL bandwidth. Finally, the experimental results verify the correctness of the theoretical analysis and the effectiveness of the proposed compensation method.© 2017 Elsevier Inc. All rights reserved.

Impedance-frequency characteristic analysis of bypass damping filter in suppressing AC–DC system’s subsynchronous resonance

Recently, subsynchronous resonance (SSR) in HVDC transmission is considered to be related to electronic converter equipment and complex control systems. Aiming at the subsynchronous resonance problem caused by frequent topology changes of AC–DC systems, this paper firstly proposes an impedance-frequency characteristic analysis method based on Thevenin Equivalent and Fast Fourier Transform (FFT) algorithm. This method is used to analyze the impedance frequency characteristics of AC–DC systems after the bypass damping filter (BDF) is configured. Firstly, based on the IEEE first benchmark model, the mechanism of BDF in suppressing subsynchronous resonance is explained by quantitative analysis, and the BDF parameter setting method is proposed. Then, the time domain simulation model of a single-machine HVDC system with BDF is established in PSCAD/EMTDC. Finally, according to Thevenin’s theorem, the equivalent structure of each subsystem is simplified, and the FFT algorithm is used to solve the harmonic equivalent impedance of each subsystem. After BDF is configured, the mechanical resonance frequency ”transfers” from 16Hz to 10Hz, and the minimum electrical damping changes from -0.9637 to -0.4581. The results show that the BDF configuration can change the impedance-frequency characteristics of the system, thereby improving the electrical damping in the torsional vibration mode in a targeted manner, and has a certain effect on suppressing the subsynchronous resonance of AC–DC systems.