Subsynchronous Resonance and FACTS-Novel Control Strategy for Its Mitigation

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.

Sub-synchronous resonance (SSR) may result from the recent integration of wind power generating systems (WPGS) based on double-fed induction generators (DFIG) into weak grids using long transmission lines with series capacitor adjustment. The amount of series compensation used in the transmission line determines how much SSR affects the grid, which may lead to serious instability. Flexible alternating current transmission system (FACTS) devices, which aid in controlling and stabilizing grid oscillations, are a workable way to lessen the impacts of SSR. In order to analyze the efficacy of FACTS controllers in mitigating SSR, this work examines the modeling and control techniques of WPGS-DFIG employing Thyristor controlled series capacitor (TCSC), static Var compensator (SVC), and static synchronous compensator (STATCOM). Time-domain simulations on a modified IEEE First benchmark, with varying series compensation levels and grid fault circumstances, are used to verify the study's correctness and effectiveness. According to the simulation findings, the STATCOM controller mitigates SSR far more effectively than TCSC and SVC. The STATCOM controller optimizes the performance of the WPGS-DFIG system by increasing dynamic responsiveness and grid stability in SSR-prone conditions.

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.

The gate-controlled series capacitor (GCSC) was proposed initially for series compensation of transmission line to control power flow. Then, it was shown that, in some conditions, the GCSC could damp SSR even if no specific controller is used. In the present work, the GCSC was tested for mitigation of subsynchronous resonance (SSR) including a control loop. A detailed analysis of the use of the GCSC with turn-off angle control for SSR damping is presented. The power system used for the analysis of this phenomenon was the first IEEE benchmark. The actual possibility of eliminating SSR was verified by digital simulation using the ATP/EMTP (alternative transients program /electromagnetic transients program). As a result is it possible to say that GCSC is a powerful device for controlled series compensation both for power flow control and SSR damping

Comparison of BBO, WIPSO & PSO Techniques for the Optimal Placement of FACTS Devices to Enhance System Security

The Thyristor Controlled Series Compensator (TCSC) and Static Var Compensator (SVC) are variable impedance Flexible AC Transmission Systems (FACTS) Controllers. A combination of the TCSC and the SVC installation is proposed to acquire superior performance for the power system. The coordination between the two pieces of equipment is designed with the SVC treated as the supplement of the TCSC. When operation of the TCSC is constrained by the inherent limitation of equipment, such as due to the firing-angle limitation of the thyristors, the adjustable SVC can supply the auxiliary support to improve the overall performance. The voltage and angle stability margins can be greatly improved with the compatible control schemes of the TCSC and the SVC.

Flexible AC Transmission System (FACTS) controllers are advanced power electronic devices employed in electrical power systems to enhance system stability, reliability, and power transfer capabilities. These controllers enable dynamic and flexible control of various transmission parameters such as voltage, current, impedance, and phase angle, thereby improving the overall power system performance. FACTS devices are broadly classified into series, shunt, series- series, and series-shunt configurations, each designed to manage reactive power and regulate voltage either by injecting voltage in series or current in shunt with the transmission line. Well-known FACTS devices include Static Var Compensators (SVC), Static Synchronous Compensators (STATCOM), Thyristor Controlled Series Capacitors (TCSC), Static Synchronous Series Compensators (SSSC), and Unified Power Flow Controllers (UPFC), each serving specific roles in power flow control, voltage regulation, and transient stability enhancement. The integration of these controllers provides significant benefits such as increased transmission line capacity, improved voltage stability, minimized transmission losses, and damping of power system oscillations. They are capable of rapid response during transient disturbances, effectively mitigating voltage collapses and enhancing system resilience against faults and contingencies. FACTS controllers not only improve steady-state operational parameters but also address dynamic stability and transient conditions, enabling power systems to operate closer to their stability limits while maintaining security. Their deployment helps avoid costly infrastructural expansions by optimizing existing transmission assets, which is critical given environmental and economic constraints. Recent advances in semiconductor technologies and control algorithms have made FACTS devices more reliable, efficient, and adaptable to modern grids, including renewable integration and deregulated power markets. In summary, FACTS controllers play a vital role in modern power systems by providing flexible, efficient, and reliable solutions for power flow management, voltage control, and system stability enhancement, thereby supporting the evolving demands of today's complex electrical networks.

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.

Comparison of computational intelligence algorithms for loadability enhancement of restructured power system with FACTS devices

Series compensated power system may lead to a very unusual problem known as Subsynchronous Resonance (SSR). Flexible AC Transmission Systems (FACTS) controllers are widely applied to mitigate subsynchronous oscillations. The Static Synchronous Compensator (STATCOM) is a shunt device of the FACTS family using power electronics to control power flow and improve transient stability on power grids. With the advent of Wide Area Measurement (WAM) technology, it is possible to measure the states of a large interconnected power system with synchronized Phasor Measurement Units (PMU). In this paper the concept of using remote signals acquired through PMU has been proposed to damp SSR. An auxiliary subsynchronous damping controller (SSDC) for a STATCOM using the remote accelerating power of generator signal as the stabilizing signal has been designed to damp subsynchronous oscillations. This paper deals with a cascaded multilevel converter model, which is a 48-pulse (three levels) source converter. The voltage source converter described in this paper is a harmonic neutralized, 48-pulse GTO converter. The IEEE Second Benchmark (SBM) model is considered for the analysis and the complete digital simulation of the STATCOM within the power system is performed in the MATLAB/Simulink environment using the Power System Blockset (PSB).

Power Systems are playing a vital role in the energy development and energy transmission in a most efficient and useful ways. Need of power transmission requires huge series capacitors to bring in the stability of massive amount of electrical energy. However, there are practical scenarios where these series capacitors are not capable of being synchronous with the turbine generators and thus causing Subsynchronous resonance (SSR). Though we have Flexible AC transmission systems (FACTS), we still have no control on the SSR. Therefore, Mitigation of SSR as a focus on TCSC controlled power system had been introduced with constant and enhanced power control methodologies and developed. Still there is room for improvement and hence we have introduced a GCSC controlled power transmission system. This paper proposes an approach for Subsynchronous resonance mitigation in Single Machine Infinite Bus System (SMIB) System Using GCSC and TCSC with Conventional and Fuzzy Logic Controllers compared. We have adopted the First IEEE benchmark a so-called SMIB system and used MATLAB/SIMULINK to witness the controllability on SSR. To evaluate performance of both devices, we have taken three different ratings of GCSC. We have projected a detailed analysis of comparing TCSC designed with conventional methods are inadequate to control the dynamic torsional oscillations when compared to the proposed GCSC ratings. Results and analysis proves that our Proposed design of GCSC controlled power system has the better performance results with inclusion of Takagi Sugeno fuzzy logic controller over the proportional(P) controller with respective of all the proposed Ratings Considered in the design. We are able to damp the dynamic power Oscillations and SSR with this method.

Basic information is presented on SVC (static VAR compensator) interactions with series-compensated transmission lines. A potential exists for adverse interactions which are different from the type seen in AC systems without series compensation. Secure operation can be attained by minor modifications to the SVC control system, but specific studies are suggested, at least for each different SVC control type. Such studies will impose added difficulty in the process of specifying, bid evaluation, and commissioning of SVC equipment. Objectives of procedures to simplify this process are stated. >

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.

Electric arc furnace (EAF) is one of the largest loads in electric power systems. It is highly time varying and nonlinear. Its reactive power variations cause voltage fluctuations in nearby system which is known as flicker. On the other hand the nonlinear voltage-current characteristic causes strong voltage and current harmonics in EAF. To this end Flexible AC Transmission Systems (FACTS) technologies are used to mitigate the flicker and harmonics caused by EAF. The mostly used FACTS device in EAFss is Static VAr compensator (SVC) which can reduce the flicker and harmonics to some levels. Delays relevant to reactive power measurement and thyristor ignition reduce compensation capabilities of SVC. In order to prevent these delays, one can use faster compensation devices. Static Synchronous Compensator (STATCOM) may be considered as a high performance candidate for this purpose due to its fast and flexible response. In this article the performance of STATCOM is compared to SVC in EAFs plants. For this purpose the system is simulated with SVC and STATCOM in PSCAD/EMTDC using the practical EAF data records. Data records are the instantaneous EAF voltage and current recorded from EAFs in Mobarakeh steel company in Esfahan/Iran.

State estimation of power systems containing facts controllers