Analysis Of Subsynchronous Oscillation Research Articles

Analysis of Subsynchronous Oscillation Caused by Multiple VSCs With Different Dynamics Under Strong Grid Connections

It is known that multiple voltage source converters (VSCs) with similar dynamics may induce subsynchronous oscillations (SSOs), particularly under weak grid connections. This study investigated the small-signal stability of multiple VSCs with different dynamics, utilizing both the model with default parameters and the model that accounts for deviations in VSC dynamics. The results indicates that the DC voltage control loops of the VSCs may cause growing SSOs even under strong grid connections. The direction and amplitude of the deviations are affected by the differences between the actual and default parameters. The impact of deviations is the largest when all the parameters are larger or smaller than the default parameters. However, the impact is reduced when some of the parameters are larger and others are smaller than the default parameters. On this basis, two reduced-order stability analysis methods were proposed to quickly and accurately assess the SSO risk in the power system. A sample power system with multiple VSCs is used to demonstrate and evaluate the conclusions and proposed methods.

Characteristics Analysis of Sub-Synchronous Oscillation Caused by DFIG Wind Farm Integrated Into MMC-HVDC System

Characteristics Analysis of Sub-Synchronous Oscillation Caused by DFIG Wind Farm Integrated Into MMC-HVDC System

Subsynchronous oscillation analysis method based on broad learning system

This paper presents a method to analyze the Sub Synchronous Oscillation (SSO) problem based on broad learning system (BLS), which can quickly analyze the risk of SSO in a system and take measures. The simulation system is constructed by the eigenvalue analysis method to obtain training data, that solves the problem which is difficult to obtain actual data in SSO problem and makes the model more accurate and the conclusion more convincing. Subsequently, BLS is applied for feature extraction and the prediction model is constructed, the model can show the deep relationship between the oscillation source and topology of the system as well as various operating data, which is difficult to be expressed by formula. The system was tested and validated in the 41-bus system. The feature importance analysis method which comes from eXtreme Gradient Boosting (XGboost) algorithm is proposed and combined with the BLS prediction model, which can analyze the influence of each variable on the prediction results in different series compensation levels, and is validated in the 41-bus system, that makes the results of prediction more interpretable. Finally, the results of simulation show that the model can predict data with high accuracy and give adjustment plans for effective control of the system to avoid the risk of SSO.

Medium-frequency and sub-synchronous oscillation analysis of direct-drive wind farms connected to the parallel-compensated AC grid

Medium-frequency and sub-synchronous oscillation analysis of direct-drive wind farms connected to the parallel-compensated AC grid

Analysis of Sub-Synchronous Oscillation of Virtual Synchronous Generator and Research on Suppression Strategy in Weak Grid

Analysis of Sub-Synchronous Oscillation of Virtual Synchronous Generator and Research on Suppression Strategy in Weak Grid

Impact of Fixed/Variable Speed Hydro, Wind, and Photovoltaic on Sub-Synchronous Torsional Oscillation—A Review

Series compensation is a cost-efficient way to enhance the system reliability and the power transfer capabilities of long transmission lines. As a result of series compensation, the sub-synchronous oscillation (SSO) causes a severe risk of torsional interactions (TI). Therefore, SSO becomes a serious risk factor in grid-integrated renewable energy systems. Numerous researchers have evaluated SSO instances in several types of asynchronous generators in power systems. In this paper, the categorization and the overview of the SSO phenomena have been vital for the different mechanisms, sophisticated systems, analytical techniques, and multiple reviews that have been propagated. This study provides SSO analysis for various types of renewable energy power plants. Finally, while dealing with conventional and new power systems, this study summarizes recent SSO-damping and alleviation techniques for practical perception and future perspectives.

Medium-Frequency and Sub-Synchronous Oscillation Analysis of Direct-Drive Wind Farms Connected to the Parallel Compensated Ac Grid

Medium-Frequency and Sub-Synchronous Oscillation Analysis of Direct-Drive Wind Farms Connected to the Parallel Compensated Ac Grid

Analytical model building for Type-3 wind farm subsynchronous oscillation analysis

Many real-world scenarios confirmed insights developed based on the dq-frame nonlinear analytical model for doubly-fed induction generator (DFIG)-based type-3 wind subsynchronous resonance (SSR) study by the authors in 2010. A few real-world observations do not align with the simulation results from that model. In real-world scenarios, when a type-3 wind farm is radially connected to a series compensated line, even at a low compensation level, SSR occurs. This phenomenon has not been replicated by the nonlinear analytical model. In this paper, we revisited the analytical model by including phase-locked-loop (PLL). A modular modeling approach is presented in this paper. The inputs and outputs of each subsystem and the interconnections among subsystems are identified first. The overall system is then developed with all blocks integrated. The analytical model is capable of dealing with various transmission topologies, providing both large-signal time-domain simulation results and small-signal analysis. The new analytical model can successfully replicate the aforementioned phenomena and provide insights of type-3 wind SSR phenomena. The accompanying software package will be posted in the public domain.

Analysis of SSO in DFIG grid with series compensation

Doubly fed induction generator (DFIG) has become the most widely used type of wind power generation due to its superior technical performance. Series compensation technology is widely used in large-scale and long-distance wind power transmission system because of its high cost performance and significant improvement of transmission capacity. However, it may cause subsynchronous oscillation (SSO). This paper first introduces the definition and harm of subsynchronous oscillation, and then analyzes the advantages and disadvantages of series compensation technology, as well as the mechanism and suppression measures of subsynchronous oscillation of DFIG connected system through series compensation. Through modeling and simulation analysis, the suppression effect of additional subsynchronous damping controller (SSDC) on subsynchronous oscillation of DFIG control system is verified.

Analysis of Subsynchronous Oscillation of Direct Drive PMSG Based Wind Farm Under Low Operating Condition

Aiming at the sub-synchronous oscillation (SSO) problem that direct-drive permanent magnetic synchronous generator (PMSG) based wind farm under low operating conditions connects to the grid, based on the idea of graphical block modeing, the wind turbine generation (WTG), collector circuit and grid are regarded as discrete components. On the basis of establishing detailed models of each component, two linearized models of direct-drive PMSG based wind farm under different collector circuit topological structure is constructed. Wind farm impedance model is constructed based on state space equation of linearized model. The influences of current inner loop control parameters, grid strength, operating conditions on SSO characteristics are analysed. The difference between the two models in the study of SSO is compared. Finally, a time-domain simulation model of direct drive PMSG based wind farm connected to grid is built in EMTDC/PSCAD and the validity of the theoretical analysis is verified.

An equivalent model for sub-synchronous oscillation analysis in direct-drive wind farms with VSC-HVDC systems

Field experiences have shown that sub-synchronous oscillation (SSO) can occur in direct-drive wind farms with VSC-HVDC systems. Due to the complexity of the detailed wind farm model, a dynamic equivalent model, with a reasonable order reduction of the detailed model and still reflecting inside-wind-farm and wind-farm-grid SSO characteristics is essential. In this paper, based on the principle that similar matrices have identical eigenvalues, the SSO analysis of an N-machine wind farm with VSC-HVDC system is conducted by simplifying it into two single-machine systems. The modeling method of the two single-machine systems is presented. Four case studies are presented to verify the effectiveness of the proposed model when compared with the detailed model in various scenarios. The proposed model is also benchmarked with the output multiplication-based equivalent model (OMM). Comparison results show that although the system order is reduced significantly, the proposed simplified equivalent model can still reflect inside-wind-farm and wind-farm-grid SSO modes in various scenarios. Meanwhile, the rationality of the OMM in terms of the wind-farm-grid SSO analysis is verified theoretically.

Subsynchronous Oscillation and Advanced Analysis: A Review

Subsynchronous oscillation (SSO) is classified as subsynchronous resonance, torsional interaction, or control interaction, depending on which devices or controllers are involved. Researchers have conducted numerous studies and developed methodologies on how to analyze SSO cases in different types of power systems. For these diverse mechanisms, complicated systems, and analytical methods, the overall summary and categorization of the SSO phenomena have been crucial, and numerous reviews have been published to this end. However, with the emerging inverter-based and power-electronics-based devices, in addition to the high computational capability, more advanced analytical methods have recently been researched, and more general, up-to-date literature surveys are thus needed. This study reviews the various SSO types depending on the interaction mechanisms, before investigating a number of representative SSO events in terms of the devices. Following this, the study evaluates the existing cutting-edge methods for SSO analysis and compares them to ascertain the appropriate method for specific SSO types. The review provides distinct practical considerations for the analysis to simplify the entire procedure. Ultimately, this paper presents a summary of modern SSO-damping and mitigation methods for pragmatic insight and future perspectives for a reader when dealing with old and the latest power systems.

Subsynchronous Oscillation Analysis of Grid-Connected Converter Based on MIMO Transfer Functions

Subsynchronous oscillations (SSOs) induced by the interaction between wind farms based on direct-drive permanent magnet synchronous generators (D-PMSGs) and weak grids have attracted extensive attention. To better understand this SSO phenomenon, this paper derives multi-input multi-output (MIMO) transfer functions between the references of the current controller and the current of a grid-connected converter in the d-q frame, where the dynamic of PLL is considered. The dynamic of PLL lead to positive feedback in the MIMO transfer function, which impairs the stability of the overall system and induces the SSO phenomenon. Using the classical root locus method, the influence of correlated control parameters and different operation conditions on the system stability is substantially analysed. It is found that heavy load, low short circuit ratio (SCR) will intensify the SSO instability of system. Nonlinear electromagnetic transient simulations of a D-PMSG-based weak-grid-connected wind-farm system using PSCAD/EMTDC software effectively verify the correctness of the model proposed in the SSO analysis.

Frequency‐coupled impedance model based subsynchronous oscillation analysis for direct‐drive wind turbines connected to a weak AC power system

Recently, the emerging subsynchronous oscillation (SSO) issue caused by interactions between power electronic converters and weak grids has provoked serious stability concerns. Impedance modelling based method has been widely used to analyse the emerging SSO phenomenon. In this paper, a frequency coupled impedance model (FCIM) is proposed to analyse this interaction. The FCIMs at multiple frequencies are measured and then the transfer function model is identified. The modelling method is then applied to type-4 wind turbine based farms connected to a weak AC grid. The aggregated impedance of the whole system is obtained by combining the FCIMs of all components in the power system. The system stability is then investigated by varying the online number of wind turbines. Time-domain simulations using PSCAD/EMTDC are carried out to verify the proposed methods of impedance modelling and stability analysis.

SSO analysis and SSDC parameter optimisation based on the wind farm connected to HVDC transmission system

The interaction between renewable energy generation and high-voltage direct current (HVDC) transmission system becomes an essential cause of the subsynchronous oscillation (SSO) problem. In this study, the permanent magnet synchronous generator-based wind farm connected to HVDC transmission system is studied. The susceptivity analysis is carried out to find the main influence factors of the SSO problem. Besides, a parameter design method for subsynchronous damping controller is proposed. The configuration and the performance indicator are discussed, and then the optimisation algorithm is developed based on hybrid genetic algorithm and electromagnetic transient simulation. Finally, the proposed design method is validated by simulation in PSCAD/EMTDC.

Mitigation of subsynchronous oscillation in a VSC-HVDC connected offshore wind farm integrated to grid

This paper focuses on analyzing and mitigating subsynchronous oscillations (SSO) in a doubly-fed induction generator (DFIG)-based offshore wind farm when connected to power grid through voltage source converter based HVDC (VSC-HVDC). Two dominant kinds of oscillation modes are found by modal analysis. One is subsynchronous shaft torsional oscillation (SSTO). However, only a little information exists in published literature regarding SSTO of an offshore wind farm. The other one, which in this paper is named as subsynchronous equipment interaction (SSEI), is due to the interaction between the converter controller of VSC-HVDC and that of wind farm. Research about SSEI is rare and lacks comprehensiveness. For further analysis and mitigation of SSO, participation factor (PF) analysis is conducted in this paper to find variables strongly correlated with SSTO and SSEI. Major contributions of this paper are (1) qualitative principle analysis of these two modes, (2) investigation of the influence of strongly-correlated variables on the oscillation characteristics of each mode and (3) application of damping controllers to comprehensively mitigate SSTO and SSEI.

REVIEW ON SUB-SYNCHRONOUS OSCILLATIONS IN WIND FARMS: ANALYSIS METHOD, STUDY SYSTEM, AND DAMPING CONTROL

More and more attention on wind farm sub-synchronous oscillation (SSO) has been paid as many SSO incidents in wind farms have occurred. This paper presents an overview of recent SSO issues in wind farm from the perspective of control, including the analysis methods, the study system, and the SSO mitigation by damping control. Three major analysis methods, as well as different study systems for wind farm SSO study, are comprehensively reviewed. The adaptability and complexity of the methods and study systems are analysed, and an overall survey of recent SSO analysis is given. Among the wind farm SSO mitigation methods, the sub-synchronous damping controller (SSDC) is one of the most commonly used methods in practice. Its configuration and signal selection are introduced in this paper.

An Online Measurement Approach of Generators’ Torsional Mechanical Damping Coefficients for Subsynchronous Oscillation Analysis

The series compensation capacitor and HVDC are widely used in Chinese power grids to increase the transmission capability of long distance lines, which might cause subsynchronous oscillation (SSO) between the turbine generators and power systems. The torsional mechanical damping coefficient of a turbine generator reflects the inherent damping level of the shaft and, thus, is a critical factor in SSO analysis. However, the torsional mechanical damping coefficient under practical operating conditions is difficult to obtain from the design parameters. In this paper, a novel approach is developed for online torsional mechanical damping coefficient measurements. The torsional interaction mechanism of identical parallel connected turbine generators is investigated, and then the characteristics of in-phase mode (IPM) and anti-phase mode (APM) are described. From this analysis, an active stimulating method for APM is presented, and a practical scheme for online torsional mechanical damping coefficient measurement is designed. This approach takes advantage of the APM features and decouples the generators from the grid. Moreover, the proposed approach has been implemented in the Yimin power plant in Inner Mongolia to realize online measurement of the torsional mechanical damping coefficient. Field test results are presented to demonstrate the effectiveness of the proposed approach.

Analysis of Sub-Synchronous Oscillation (SSO) Caused by HVDC Transmission System

Sub-synchronous oscillation (SSO) caused by highly non-linear HVDC devices can lead to shaft failure and electrical instability of a turbo-generator at oscillation frequency lower than power grid frequency. With increasing HVDC installed in power systems, analysis of SSO becomes a great concern of electrical engineers. In this paper, the reason and process of the SSO are presented by analyzing equations of the mass-springs model. Research methods of SSO are reviewed in HVDC system. And advantages of digital time-domain simulation are demonstrated through combining with algorithm of Prony.

Damping Analysis of Subsynchronous Oscillation Caused by HVDC

High Voltage Direct Current transmission (HVDC) will cause torsional interaction under certain conditions. Among a variety of factors, improper rectifier control has fateful effect. In the paper, the test signal method which is the time-domain form of the complex torque coefficient approach (CTC approach) is studied. Its application conditions in multi-machine systems are summarized. Using the test signal method, impacts of DC power, DC voltage, rectifier controller parameters and generator output on electrical damping characteristics in the Suizhong system are studied based on time-domain simulation model.