Subsynchronous Resonance Phenomenon Research Articles

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.

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.

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.

Adaptive Fuzzy Supplementary Controller for SSR Damping in a Series-Compensated DFIG-Based Wind Farm

Although using a series compensation technique in a long transmission line effectively increases the transmittable power; it may cause a sub-synchronous resonance (SSR) phenomenon. Gate-controlled series capacitor (GCSC) is an effective method for SSR damping by controlling the turn-off angle. In the previous studies, a constant supplementary damping controller (SDC) was used for controlling the turn-off angle, which can mitigate the SSR phenomenon. However, these methods can not capture the maximum transmittable power at different operating points. In this paper, a fuzzy logic controller (FLC) is proposed to compute the gain of SDC based on the wind speed and the error between the measured and reference line currents for transferring as much power as possible and damping the SSR phenomenon simultaneously. Using the MATLAB/SIMULINK program, the proposed method is tested at different operating points to validate its effectiveness and robustness. Compared to the traditional method (constant SDC), the maximum transmittable power, as well as SSR damping, is achieved in all studied cases by the proposed method (variable SDC).

Damping Subsynchronous Oscillations Using a High Voltage Direct Current-Based Multi-Modal Damping Controller

Conventional series capacitors in transmission lines are of paramount importance for enhancing power transfer capability. However, the major drawback of series capacitors is the induced subsynchronous resonance phenomenon in power systems. This phenomenon affects nearby turbogenerator shafts and severely limits their reliability. Also, the controls of High Voltage Direct Current links are considered as a potential source of subsynchronous oscillations. This paper investigates the performance of a multimodal damping controller to stabilize unstable torsional modes in combination with a Power System Stabilizer for inertial mode damping. This research uses time-domain simulation-based multimodal damping controller design methods, namely the test signal and phase correction methods. These two methods involve injecting a test signal at a frequency of interest into the rectifier current control loop and measuring its phase difference with the electromagnetic torque, thus providing corresponding compensators to minimize the resulting angle. This work uses Power System Computer-Aided Design for time-domain simulation and Fast Fourier Transforms Analysis to conduct the phase correction method and verify controller performance.

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.

Research about a fast identification method for intermittent single Sub-synchronous Resonance phenomenon in large scale doubly-fed wind farm

In this paper, a synchronous resonance (SSR) phenomenon caused by a large scale doubly-fed wind farm group after putting in series compensation device is analysed. By analysing the changing trends of the indicators during period of SSR phenomenon, 11 power quality indicators are chosen for calculated, then divided all the 11 indicators into 3 source data and 8 preliminary stage operational data by the observability of value. After divided the two kinds of data, a Pearson correlation coefficient between this two kind data was calculated to judge the relationship of them, and the characteristic indexes with stronger correlation during the resonance period were analysed. The maximum value of the above 8 characteristic indexes in the normal power generation process is used as the basic data for comparison, so as to realize the rapid and accurate judgement of the SSR moment. In the process of SSR judgement, the method has the characteristics of faster speed and simple determination, and it does not need to reform the existing power quality online monitoring device, and can realize real-time analysis and judgement of SSR phenomenon only by increasing extraction of the existing data function from the monitoring system. Finally, by testing data of two actual SSR events, the characteristic index determination method proposed in this paper is analysed and verified, and the feasibility of this method is proved.

Optimal design and application of fuzzy logic equipped control in STATCOM to abate SSR oscillations

SummaryThe phenomenon of subsynchronous resonance (SSR) is important to understand the operation and stability of the power system. The system becomes vulnerable to SSR oscillations due to series compensation that is unavoidable as it enhances transmission capability. So different alleviation measure is necessary, and this paper presents a novel control with the implementation of fuzzy logic control (FLC) and active disturbance rejection control (ADRC) for the abatement of SSR using a static synchronous compensator (STATCOM). This control can compensate for reactive power as well as alleviate SSR oscillations. Both the proposed controllers have the inherent capability to overcome the limitation of proportional and integral (PI) in a non‐linear framework. In the proposed control, the use of a phase‐locked loop is eliminated, thus providing a faster response. Thus, the proposed algorithm highly enhances the capability of STATCOM in controlling the level of series compensation, which results in a substantial reduction of the SSR oscillations. To validate the effectiveness of the proposed algorithm, an IEEE second benchmark model is simulated. Furthermore, the dynamics of SSR are put forth through various analyses, such as, eigenvalue analysis, frequency scan, fast Fourier analysis, and time‐domain analysis, which helps to better understand the problem of SSR.

ADRC-based control strategies to alleviate SSR using STATCOM

Increasing prominence of series compensation into the power system has evidently enhanced the rise of subsynchronous resonance (SSR). Alleviation of SSR with two novel control designs for static synchronous compensator (STATCOM) is proposed in this paper. Since it is quite challenging to optimize proportional and integral (PI) controllers in a nonlinear framework, hence a nonlinear active disturbance rejection controller (ADRC)-based strategies are proposed. First control design is template-based ADRC (TADRC), and the second control design is synchronous ADRC (SADRC). To validate the effectiveness of control schemes, an IEEE second benchmark model is used. Furthermore, different analyses are demonstrated to study the phenomenon of SSR. Firstly, the state space model-based design is provided for eigenvalue analysis. Fast Fourier transform (FFT) analysis is also carried out to show the dominant mode of oscillations along with the frequency scan at various levels of compensation. Finally, trends in generator speed and other parameters are shown in the time domain analysis of the system. The analyses and measures to alleviate the oscillations proposed in this paper are eminently cogent.

Understanding the Origin of SSR in Series-Compensated DFIG-Based Wind Farms: Analysis Techniques and Tuning

This paper is dedicated to presenting control-tuning methodologies for the rotor-side converter (RSC) and grid-side converter (GSC) of series-compensated DFIG-based wind farms (WF) and to determining the origin of subsynchronous resonance (SSR). Unlike conventional approaches to re-tuning controller gains to achieve desirable performance, these methodologies only consider the mathematical models of the states variables to be controlled. A PI cascade topology is used to control the RSC and GSC. An inner loop is required for current control and an outer loop for voltage control. Special consideration is taken for tuning the RSC because this converter is coupled with the mechanical variables as mechanical rotor speed of the DFIG. Compared with standard tuning, a better system behavior during a resonance condition is achieved with the proposed tuning methodology. Regarding the analysis of the SSR origin, the modal impedance (MI) technique is used as a tool to study SSR issues; its advantages compared to the driving point impedance technique are highlighted. In this context, the small-signal-stability (SSS) analysis is performed to evaluate the overall system. With the combination of MI and SSS, the phenomena of induction generator effect, torque interaction, and torque amplification are analyzed. As a result, the modes involved in the SSR phenomenon are identified and a discrimination procedure is described to determine the origin of the SSR.

A Recent Analytical Approach for Analysis of Sub-Synchronous Resonance in Doubly-Fed Induction Generator-Based Wind Farm

Sub-synchronous resonance (SSR) phenomenon occurs due to the interaction between wind turbine generators and series-compensated transmission lines. A doubly-fed induction generator (DFIG) is considered one of the most widely implemented generators in wind energy conversion systems. SSR analysis based on the eigenvalue method is the most important among the used methods. The accuracy of the eigenvalue method depends on the initial values of state variables. Previously, the initial values of the state variables were calculated based on the iterative approach which is suffering from convergence problem, lacking accuracy, and requiring a long computation time. Moreover, many steps and details haven’t been provided. Consequently, it is urgent to fill this gap and show how can implement the SSR analysis model in detail. In this paper, a new application of a recent analytical approach is proposed for SSR analysis. All information is provided, and the SSR analysis model of a DFIG-based series compensated wind farm is built step-by-step. In order to prove the effectiveness and accuracy of the proposed method, the eigenvalue analysis based on the proposed and iterative methods is compared with the time-domain simulation results at different wind speeds and variable compensation levels. The results prove that the eigenvalue analysis based on the proposed method is more precise, where it is consistent with the simulation results in all studied cases. MATLAB software is used to validate the results.

Analysis and Mitigation of Subsynchronous Resonance in Series-Compensated Grid-Connected System Controlled by a Virtual Synchronous Generator

Analogizing the subsynchronous resonance (SSR) phenomenon of the series-compensated grid-connected system based on synchronous generator, the virtual synchronous generator (VSG) also has the low-frequency oscillation problem owing to the impedance interaction between VSG and series-compensated network. Stability of the series-compensated grid-connected system controlled by VSG is analyzed by the impedance-based Nyquist stability criterion. Due to the inductive impedance of VSG, VSG is easy to couple with the series-compensated network in the low-frequency areas, which can lead to the SSR. With the increase of the series compensation level, the stability of VSG becomes worse and the induced oscillation frequency becomes higher. Therefore, a modulation signal feedforward active-damping control strategy with time-delay compensation is proposed to suppress this SSR, which directly feeds the active-damping control signal to the pulsewidth modulation modulator for reshaping the output impedance of VSG from the inductance to the resistance–inductance. Moreover, a value range of virtual resistance is given with considering the influence on the regular operation of VSG. Finally, the simulation and experimental results verify the correctness of the SSR analysis and the feasibility of the proposed active-damping control strategy.

Static Synchronous Series Compensator (SSSC) for Series Compensation of Transmission Line using Flying Capacitor Multilevel Inverter (FCMLI)

This paper deals with Five-Level Flying Capacitor Multilevel Inverter (FCMLI) based Static Synchronous Series Compensator (SSSC) as used for the series compensation of transmission line. Here, voltage is injected in series with the transmission line. It is preferred to other compensating devices because apart from controlling the active and reactive power flow, it helps to damp out unwanted oscillations, such as reducing the Sub-Synchronous Resonance (SSR), Ferro-resonance and thus helps in improving the Power Quality (PQ). Hence, FCMLI is used which helps to ameliorate the output waveform and reduces the auxiliary filtering requirements. Moreover, the control logic for the inverter that has been shown in such a way that voltage stress across each capacitor connected to DC-link voltage is equal. The control logic has been implemented in MATLAB/Simulink environment and the result is shown as there are no SSR phenomena and considerable less line loss.

Analysis and Mitigation of Subsynchronous Resonance in a Korean Power Network with the First TCSC Installation

This paper presents a detailed analysis results of the effect of a thyristor-controlled series capacitor (TCSC) on subsynchronous resonance (SSR), which was first applied to a Korean power system. First, the TCSC parameters were calculated, the structure of TCSC with synchronous voltage reversal (SVR) controller was presented, and the torsional characteristics of Hanul nuclear power generator rotor were studied to investigate the natural frequency and mode shape. The test signal method was used to determine the electrical damping in the frequency range of SSR operation through an electromagnetic transient analysis program in various system configurations. The SSR phenomenon was analyzed by comparing the electrical and mechanical damping of a conventional fixed series capacitor (FSC), and the case of a TCSC installed, and the effectiveness of the TCSC without any risk of SSR was demonstrated. As a result, when installing FSC, SSR occurred under sensitive operating conditions, but SSR was prevented in the case of TCSC compensation with SVR. The results obtained in this study can be effectively applied to the installation of TCSC in real power systems.

Analysis and mitigation of subsynchronous resonance based on integral control for DFIG‐based wind farm

Series capacitor compensation technology has been widely used in long-distance wind power transmission, which can improve the power transmission capacity and enhance the static stability of the power system. However, adding a series capacitor in the line may present a potential risk of subsynchronous resonance (SSR) to the system. This study focuses on the SSR caused by induction generator effect of the doubly-fed induction generator-based wind farms. The SSR phenomenon of wind power system is researched by the impedance analysis method. A mitigation strategy of adding a virtual inductance based on integral control is proposed for enhancing the system stability and alleviating the SSR. It has clear and intuitive physical concept, which is beneficial to system integration and provides a simpler and more economic method for mitigating SSR. Moreover, the principle and process of controller design are elaborated. Moreover, the time-domain simulation is carried out to prove the effectiveness of the proposed control strategy under different operating conditions considering various compensation levels and wind speeds. Finally, the suppression effects of the virtual inductance in rotor-side converter and grid-side converter are compared.

DAMPING SUB SYNCHRONOUS RESONANCE IN POWER SYSTEM USING TCSC & SVC

when the steam turbine-generator is connected with series of compensation along the transmission line, the sub synchronous resonance may happen. The Flexible Ac Transmission System (FACTS) controller of the devices wide use which has been used to reduce and suppress the phenomenon of sub-synchronous resonance the Thyristor Control Series Compensation (TCSC) and Static VAR Compensation (SVC) are the types of FACTS controller that has been used to put down the SSR and also for the purpose of provide a better and efficient solution to improve the transferred capacity system to connect the series compensation along the transmission line. Series capacitor work to increase the chance of creating sub synchronous resonance. Series capacitors also have an inclination to amplify the shaft stress during considerable network transien toccurrence, SSR phenomena happen which can cause damage of the shaft generator turbine. The first standard model of IEEE was adopted to study this phenomenon. This research deals the PID control of SVC( Static VAR Compensation) and TCSC (Thyristor Controlled Series Compensator) and excitation system controller for reducing SSR in power system. In this research, the method of Eigenvalue was used to analysis the sub-synchronous resonance phenomenon and the result was verified using DYMOLA simulation

Electric power frequency and nuclear safety - Subsynchronous resonance case study

Abstract The increase of the alternate current frequency results in increased rotational speed of the electrical motors and connected pumps. The consequence for the reactor coolant pumps is increased flow in primary coolant system. Increase of the current frequency can be initiated by the subsynchronous resonance phenomenon (SSR). This paper analyses the implications of the SSR and consequential increase of the frequency on the nuclear power plant safety. The Simulink MATLAB® model of the steam turbine and governor system and RELAP5 computer code of the pressurized water reactor are used in the analysis. The SSR results in fast increase of reactor coolant pumps speed and flow in the primary coolant system. The turbine trip value is reached in short time following SSR. The increase of flow of reactor coolant pumps results in increase of heat removal from reactor core. This results in positive reactivity insertion with reactor power increase of 0.5% before reactor trip is initiated by the turbine trip. The main parameters of the plant did not exceed the values of reactor trip set points. The pressure drop over reactor core is small discarding the possibility of core barrel lift.

An Improved Fast Detection Method on Subsynchronous Resonance in a Wind Power System With a Series Compensated Transmission Line

Subsynchronous resonance (SSR) occurs mainly in series compensated transmission line connected to the wind power system. This phenomenon (SSR) can lead to electrical instability and potential turbine generator shaft failure. Thus, the protection system is an essential part to avoid the harm of SSR. In this paper, an improved fast detection method is proposed to detect the SSR phenomenon in a very short time. It consists of two stages; first, the positive or negative half-cycle time of each cycle of voltage signal is detected based on four steps, namely, signal conversion, comparison, integrator, and sample and hold; second, the obtained time is compared with the damping and trip threshold values, and the best action is determined (addressing or trip) based on the value of half-cycle time. The effectiveness and superiority of the improved fast SSR detection method are validated at different compensation levels and compared with the traditional method and subsynchronous oscillation relay (SSO). The simulation results prove that the improved method is more efficient in all types of SSR phenomenon; induction generator effect (IGE), control interactions (CI), and torsional interaction (TI) at different compensation levels. In addition, a comparative study among these three types of SSR with the proposed method is carried out, and the obtained results show that the CI is a suitable type with the proposed method.

Analysis on SSR frequency components by studying two‐dimensional modulation of synchronous generator's flux linkage

As China's AC transmission system with series capacitor and HVDC transmission technology are widely used in long-distance and large-scale power transmission network, sub-synchronous resonance (SSR) problem becomes more prominent. This paper studied induction generator effect (IGE) and torsional interaction (TI) of synchronous generator by focusing on amplitude and frequency modulation of synchronous generator's flux linkage. IGE involves only electric system dynamics, which will only cause amplitude modulation of flux linkage, resulting in one or two frequency component added in stator current of non-salient pole synchronous generator (NPSG) or salient pole synchronous generator (SPSG) respectively. TI involves both electric and mechanical system dynamics, which will cause both amplitude and frequency modulation of flux linkage, resulting in multiple sub and super-synchronous frequency components added in stator current by means of Bessel function. This result will provide a new reference to understand the SSR phenomena containing multiple frequency components in practical power system. The IEEE first benchmark model is used to demonstrate the accuracy of the analysis results.

Analytic and Numerical Study of TCSC Devices: Unveiling the Crucial Role of Phase-Locked Loops

This paper proposes a hybrid dynamic model of thyristor controlled series compensators (TCSCs). The objective is to demonstrate, through advanced circuit theory tools and numerical simulations that some modeling aspects are not properly taken into account in the existing literature. In particular, we consider those related to the role of the TCSC impedance when the line current is polluted by harmonics and to the phase-locked loops (PLLs). Shooting methods and periodic small signal analyses are utilized to compute the impedance of the TCSC at sub-harmonics that are typical of the sub-synchronous resonance phenomenon. The case study focuses on the impact of sub-harmonics, on the behavior of the TCSC and on the synchronization of the firing angle through the PLL. Modeling recommendations are finally drawn based on the results presented in this paper.