Analysis of SSR Mitigation Using Gate Controlled Series Capacitors

The subsynchronous resonance (SSR) phenomenon may occur when a steam turbine-generator is connected to a long transmission line with series compensation. The main purpose of this works is to verify the capability of the gate controlled series capacitor (GCSC) to mitigate SSR. For this study the GCSC was tested in conjunction with the first IEEE benchmark system. The actual possibility of controlling SSR was verified by digital simulation using the ATP/EMTP (alternative transients program/electromagnetic transients program). As a result it was shown that GCSC is a powerful device for controlled series compensation both for power flow control and SSR damping. It was shown also that in some case the GCSC can damp SSR even without a specific control. GCSC can also damp electromechanical power oscillations as shown in some simulations

This paper investigates the sub-synchronous resonance (SSR) phenomenon in a series compensated doubly-fed induction generator (DFIG) based wind farms. A detailed linear state space model of a fixed-series compensated DFIG wind farm is presented for different operating point conditions. The model of the system includes a wind turbine aerodynamics, a 6 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> order induction generator, a 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> order two-mass shaft system, a 4 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> order series compensated transmission line, an 8 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> order rotor and generator side converter controllers, and 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> order DC link model. The 22 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> order system is modeled in Matlab/Simulink, and modal analysis is performed on the modeled DFIG wind farm, and eigenvalues of the system are calculated. The eigenvalue analysis and time-domain simulation results show that SSR can potentially occur in the fixed-series compensated DFIG-based wind farm even at realistic levels of series compensation. The fixed-series capacitor is replaced with a gate-controlled series capacitor (GCSC), which is a series flexible ac transmission system (FACTS) device composed of a pair of gate-commutated switches in parallel with a capacitor that enables one to control impedance and power flow of transmission lines, for series compensation and SSR damping. The root-locus analysis is employed to design a SSR damping controller (SSRDC) for the GCSC. It is shown than a well-designed SSRDC for the GCSC can alleviate the SSR in DFIG-based wind farms. The IEEE first benchmark model adapted with a DFIG-based wind farm is employed as a case study.

Objective: The phenomenon of Sub Synchronous Resonance (SSR) on series-compensated long transmission line with steam turbine generator results into adverse oscillations. Therefore, occurrence of SSR should be reduced to the lowest possible level. Method/Analysis: In this paper, the use of STATCOM and subsynchronous damping controller (SSDC) is proposed to alleviate SSR. The rotor speed deviation of generator is being captured and given to the STATCOM. The IEEE second benchmark model (IEEE SBM) on SSR is adopted to analyze and validate the proposed controller. For this, the controller is applied on STATCOM, which in turn is regulating the line. Findings: SSR generates due to the presence of frequency other than the nominal frequency in the system. By calculating frequency response and FFT analysis, the resonant frequency present in the system, is calculated. Then conventional STATCOM is applied, which shows that STATCOM with no auxiliary control is not capable of damping the SSR oscillations. But with auxiliary SSDC on same STATCOM, effectively mitigate the SSR. Novelty/Improvement: The SSR alleviation is done by conducting transient simulations using MATLAB environment on detailed three-phase model, which is non-linear in nature. Fast Fourier Transform (FFT) analysis is also performed to demonstrate the capability of proposed controller.

This study addresses Load frequency control (LFC) of an unequal multi source three area interconnected power system using damping controller based gate controlled series capacitor (GCSC) in all areas, to provide robust damping, low frequency oscillations and reduce tie line power error. A new controller, fractional order integral derivative with filter (FOIDN) cascaded with tilted-integral-derivative ( $\text{FOIDN}+\text{TID}$ ) controller used for modeling the GCSC. The dynamic responses of the system are compared with and without considering damping controller based GCSC. Simulation results showed that the proposed $\text{FOIDN}+\text{TID}$ based GCSC controller is capable to achieve better system dynamic performance in comparison to the other coordinated controllers based like GCSC. Also the system eigen value and damping ratio are obtained and compared with and without GCSC.

The subsynchronous resonance (SSR) is an important problem in the power system, and especially the series compensated transmission lines may cause SSR in the turbine generators, such that it leads to the electrical instability at subsynchronous frequencies and potential turbine-generator shaft failures. Taking the Vietnamese Vungang thermal plants as an example, a shaft failure of Vungang I thermal power unit has occurred on November 24, 2015, due to SSR. The main cause for this failure is a resonance caused by the series capacitors on the 500 kV grid. This paper analyzes the SSR based on the location of shaft cracks and turbine generator mode shape for Vungang I and II thermal power plants. On the basis of that, it develops a novel control strategy for each Flexible AC Transmission system (FACTS) device as the thyristor controlled series compensator (TCSC), static VAR compensator (SVC), and static synchronous compensator (STATCOM). Then they are comparable to one another in order to choose a feasible solution for mitigating the SSR. The effectiveness of the proposed control strategy is verified via time domain simulation of the Vietnamese 500/220 kV transmission system using EMTP-RV and PSS/E programs. The obtained results show that the proposed strategy for SVC can be applied to immediately solve the difficulties encountering in the Vietnamese power system.

Series compensation of transmission line increases its power transfer capability, however leads to serious destructive phenomenon known as Sub-Synchronous Resonance (SSR). Several SSR mitigation techniques in wind power plant (WPP) are found in literature however, very little information is available on mitigation of SSR in a series compensated type 3 WPP using STATCOM. This paper reports the performance of remote power signal based STATCOM SSRDC for mitigation of SSR due to induction generator effect (IGE) in series compensated type 3 WPP. A first bench mark (FBM) model is adopted with type 3 WPP for SSR studies. A STATCOM with SSRDC is employed at PCC. It is shown that STATCOM with damping controller is capable of mitigating SSR even at higher rating of WPP and higher series compensation level. Electromagnetic transient simulations using MATLAB/Simulink have been carried out to analyze the performance of STATCOM with and without SSRDC for mitigation of SSR in series compensated type 3 WPP.

Summary form only given. This paper presents a computational approach for an offline measurement based design of an optimal damping controller using adaptive critics for a new type of FACTS device - the gate controlled series capacitor (GCSC). Remote measurements are provided to the controller to damp out system modes. The optimal controller is developed based on the heuristic dynamic programming (HDP) approach. Three multi-layer perceptron (MLP) neural networks are used in the design - the identifier/model network to identify the dynamics of the power system; the critic network to evaluate the performance of the damping controller; and the controller network to provide optimal damping. This measurement based technique provides an alternative to the classical linear model based optimal control design. The eigenvalue analysis of the closed loop system is performed with time domain responses using the Prony method. Analysis of the simulation results show potential of the HDP based optimal damping controller on a GCSC for enhancing the stability of the power system.

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.

This paper presents a theoretical consideration on the possibility of subsynchronous resonance (SSR) in longitudinal power systems. Shunt capacitors are used for reactive power compensation in our country, but series capacitors are not used in general. The possibility of SSR is therefore small. However, if power transmission increases, and accordingly, if shunt compensation increases in amount, there is no guarantee that SSR will never occur. First, we investigate network impedance viewed from a generator. Its resonance frequencies become lower with increasing transmission power. One of them gets subsynchronous if the power exceeds a certain value. In this area, there is some possibility of SSR, which is confirmed with the damping property of the generator. The admittance matrix of the load buses is singular at the resonance frequencies. Their number is equal to the dimension of the matrix. The frequencies are common to all generators but not limited to one particular generator. One of them becomes equal to 60 Hz as we increase transmission power. We regard this power as a limit for SSR. However, steady-state stability limit is lower than this limit, and steady operation is not possible at the limit. Therefore, it is impossible to enter the area of SSR. Thus, we conclude that SSR does not occur in shunt compensated systems. However, this property is easily lost if some series compensation is introduced. © 1999 Scripta Technica, Electr Eng Jpn, 130(3): 30–38, 2000

The potential of Fully Rated Converter-based wind turbines (FRC-WTs) on the mitigation of subsynchronous resonances (SSR) in the power system having series-compensated transmission line. IEEE First Benchmark Model (FBM) was featured with Aggregated FRC-WTs to perform the studies. The potential occurrence and mitigation of the SSR in steam turbine were investigated. The Linear Quadratic Regulator (LQR) was used to damp SSR oscillations occurred at steam turbines. MATLAB code was used to perform Eigenvalue analysis and digital time-domain simulations were used to test the control strategy.

The paper reports investigation on different parameters of an 11-kV line that affect the lightning impulse failure of a distribution transformer in Pakistan. The equivalent model of the transmission system was developed in ATPDRAW, and the simulations have been carried out in Alternative Transients Program — Electromagnetic Transients Program (ATP-EMTP). The results of the study are used to enhance our understanding about the factors that contribute to distribution transformers' insulation failure which enables us to provide better protection for the distribution transformer and primary distribution (11-kV) lines in Pakistan.

This paper evaluates the impact of dynamic loads (induction motors) on the damping of Subsynchronous Resonance (SSR) based on load location and aggregate load inertia for the IEEE 68 bus network simulated in DIgSILENT. The severity of SSR oscillations is shown to increase in the presence of Subsynchronous Resonance Load Interactions (SSRLI), whereby dynamic loads may contribute towards negative damping under certain network topologies. This change in severity is investigated for each load location by replacing the static (constant impedance) load model, traditionally used in SSR studies, with a 50% static and 50% dynamic load model. The paper shows that the torsional damping and thus the severity of SSR is sensitive to the location and aggregate inertia of the dynamic load. These results establish the sensitivity of torsional damping to dynamic load location, size and aggregate inertia. In the absence of accurate knowledge of load composition, 50% static and 50% dynamic load composition can be used as a recommendation for the modelling of load during EMT studies of SSR, to avoid conservative results and over/under design of protection or mitigation strategies.

Series compensations have been widely used in modern power systems to extend the power transfer capacity. Since more and more renewable power generation systems are installed in power systems, the grid-connected inverters (GCIs) used by the renewable power generations may interfere with series-compensated power lines, which introduce subsynchronous resonance (SSR) causing power system failure that has been observed in real cases. The phase-locked loop (PLL) of the GCI's control system is the main factor that can cause the SSR in the series-compensated power grid. To mitigate the impact of the PLL and obtain the stable operation of the power system, a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis voltage feedback method has been proposed in literature to damp the harmonic oscillations in the weak power grid where, however, the series compensation is not considered. Because the real <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis voltage cannot be obtained, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis voltage output from the PLL is used as the feedback variable in literature. However, due to the dynamic response of the PLL, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis voltage output from the PLL is different from the real <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis voltage, and the direct use of it for the damping of the SSR in the power grid with series compensations is invalid, which is investigated in this article. Besides, an observed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis voltage feedback method is proposed in this article to damp the SSR in the series-compensated power grid with GCIs being connected. By putting an observer in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis voltage feedback path, the real <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis voltage can be estimated and applied to damp the SSR. Simulation and experimental results have been provided to verify the effectiveness of the proposed observed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis voltage feedback method in the damping of the SSR.

Electrical systems are subjected to constraints more severe continuation with overvoltage's which can be due to lightning and switching strikes. Under the influence of the intense corona effect which accompanies of atmospheric overvoltage, these overvoltages undergo deformations at the same time as an attenuation of their amplitude, this phenomenon of distortion, which is superimposed on the distortion by skin effect, is due to the dissipation of energy by injection of space charges around the conductor, this process with place as soon as the instantaneous voltage exceeds the threshold voltage of the corona effect conductors. In this paper, an analogical model of the corona effect has been implemented in the Alternative Transients Program/ Electromagnetic Transients Program (ATP/EMTP). This model was incorporated into a transmission lines, the line is divided on a number of the short sections. This study is to have the attenuation and the distortion of the overvoltage waves due to the corona effect on this transmission line.

Flexible AC Transmission System devices are reactive power compensation devices employed to suppress the sub synchronous resonance (SSR) in the systems. The main important issue in the transmission lines of power system is SSR and it occurs during the condition, when series compensator is employed to improve the reactive power. It occurs at sub synchronous frequencies due to Electrical instability occurs as the result of shaft failures. Different FACTS devices such as the Static Synchronous Reactor (SSR), Static Synchronous Series Compensator (SSSC), Static Synchronous Compensator, Thyristor Controlled Series Compensator (TCSC), and Unified Power Flow Controller (UPFC) are analysed and reviewed in terms of SSR mitigation to develop a new strategy to mitigate SSR in the system. The new Multilevel inverter-based control strategy will be designed and developed based on the review and analysis using MATLAB Simulink to mitigate the SSR.