Transient Stability Enhancement of Multimachine Power System Using Robust and Novel Controller Based CSC‐STATCOM

This paper proposes the control strategy of the shunt Flexible AC Transmission System (FACTS) devices to improve transient stability in multimachine power system. The multimachine power system has high nonlinear response after severe disturbance. The concept of Lyapunov energy function is applied to derive nonlinear control strategy and it was found that the time derivative of line voltage is not only can apply to control the shunt FACTS devices in multimachine system but also is locally measurable signal. The fuzzy logic control is also applied to overcome the uncertainty of various disturbances in multimachine power system. This paper presents the method of investigating the effect of the shunt FACTS devices on transient stability improvement. The proposed control strategy and the method of simulation are tested on the new England power system. It was found that the shunt FACTS devices based on the proposed nonlinear control strategy can improve transient stability of multimachine power system.

The role of shunt Flexible AC transmission System (FACTS) devices is to improve voltage profile. However, in the presence of Shunt FACTS Devices (SFDs), protection schemes may incorrectly operate as SFDs inject reactive power in the line. This study presents an Imaginary component of Virtual Fault Impedance (IVFI) based improved relaying for the transmission line in the presence of SFD which is immune to large variations in source impedance. During normal operation or during an external fault, the magnitude of IVFI is very large, on the other hand, during an internal fault, the magnitude of IVFI is either zero or very small. The proposed scheme can be used to detect the internal fault and to classify fault type and it is applicable to uncompensated transmission lines also. The EMTDC/PSCAD simulations are carried out to investigate the performance of the proposed scheme. The scheme is found to be selective, robust, and accurate for all possible faulty conditions, for different types of SFDs with different compensation levels and for high resistance faults.

Power system stability is a great concern in today's interconnected power system especially when the system is subjected to a fault. These faults occasionally lead to Low Frequency Oscillation (LFO). Therefore, Shunt Flexible AC Transmission System (FACTS) devices for example, SVC are employed to provide damping to attain system stability. The performance of SVC is totally dependent on proper tuning of its controller and usually heuristic optimization techniques are used to search the best controller parameters. In this paper, a popular metaheuristic optimization technique known as Firefly Algorithm (FA) is presented for optimal design of SVC controller in multi machine power system. In the simulation, the linearized model of power system and conventional lead-lag controller as SVC damping controller are used. The performance of obtained results using Firefly Algorithm (FA) is compared with the results obtained from Particle Swarm Optimization (PSO) Algorithm. The comparison of attained results show that FA can find more optimal parameter values of SVC damping controller and subsequently enhance power system stability.

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.

A new algorithm simulating the impacts of the VAR supporting devices such as the static var compensators (SVCs) and the synchronous condensers (SCs) under condition of symmetrical disturbances in multi-machine power system is mentioned. Some typical numerical examples are presented in this article.
 The comparisons of variation of the state parameters, such as the voltage, frequency, reactive power outputs and asynchronous torques…are simulated under condition of the action of the automatic voltage regulation systems of generators and of the VAR supporting devices.
 The transient energy margins are calculated and compared to assess the transient stability in multi-machine power system. Basing on this algorithm, the PC program uses the elements of the eigen-image matrix to bring the specific advantages for the simulation of the transient features of state variables.

Ensuring the transient stability of the power system networks is one of the prime challenges in the highly interconnected power systems. Though the low-frequency oscillations are not very harmful initially, failure to damping out may lead the system to go out of synchronism. The employment of flexible AC transmission systems (FACTS) devices may suppress these oscillations effectively in addition to the enhancement of power transfer capability. Among many FACTS devices, unified power flow controller (UPFC) is one of the most sophisticated ones. Tuning the parameters of power system stabilizer (PSS) coordinated with UPFC for a stable system is a multi-objective optimization problem. This paper aims to optimize the parameters of power system stabilizer (PSS) of power network incorporating UPFC using support vector regression (SVR) in real time to damp out the small signal oscillations hence to enhance the transient stability. System eigenvalues obtained from SVR tuned UPFC coordinated PSS and the fixed gain conventional PSS are compared to investigate the efficacy of the proposed technique for different loading conditions. Besides, time domain simulation comparison proves the superiority of the proposed technique over the conventional one. Furthermore, the statistical performance measures for training and testing datasets provide confidence on the developed SVR model.

Chapter 31 - Flexible AC transmission systems

Location and design of stabilizers in multimachine power systems

There has been significant strides to integrate renewable energy sources into our current power system. In this work, we focus on wind farm integration into a weak grid. To ensure that this proposed idea is suitable, we perform tests to ensure that the power system remains stable under some potential scenarios. To facilitate integration and suitable steady state conditions are maintained, the use of Flexible AC Transmission System (FACTS) devices are employed. In this work, we focus on the transient stability characteristic for power system stability. Specifically, we present how the use of Static Synchronous Compensators (STATCOM) in the first portion of this work, used alongside Static Synchronous Series Compensators (SSSC) to improve voltage stability, also improved transient stability of the wind dominated power system.

Growing number of wind turbines is changing electricity generation profile all over the world. This brings challenges for power system operation, which was designed and developed around conventional power plants with directly coupled synchronous generators. In result, safety and stability of the electrical network with high wind energy penetration might be compromised. For this reason transmission system operators (TSO) impose more stringent connection requirements on the wind power plant (WPP) owners. On the other hand flexible AC transmission systems (FACTS) devices offer enhancement of grid stability and can facilitate grid code compliance for WPP. In this paper state-of-the-art in FACTS for WPPs with AC connection is given. FACTS devices with their properties are described. HVDC, which in literature is also often recognized as FACTS device, is out of this paper scope. Academic and industrial research in FACTS applicability for WPPs is summarized. Examples of few existing FACTS applications for wind farms are given.

Power system stabilizers (PSS) are utilized to mitigate power system oscillations by excitation control. This paper proposes a PSS design based on a new population-based algorithm named Moth-flame optimization (MFO) algorithm in a multi-machine power system. A conventional speed-based lead-lag PSS is used for design purposes. The parameters of the sine-cosine algorithm based PSS are tuned using MFO to shift the weakly damped electromechanical mode eigenvalues towards the left half of S plane. Results so obtained has been extensively compared with those obtained by Bacteria Foraging (BF) and firefly algorithm (FA) which show the effectiveness of MFO in enhancing overall system stability over an extensive range of loading conditions and fault scenario.

Flexible AC Transmission Systems (FACTS) play a vital role in enhancing the stability, efficiency, and reliability of modern power systems. With the increasing complexity of power grids due to the integration of renewable energy sources, effective control of power flow, voltage regulation, and stability improvement are critical challenges. FACTS devices, such as Static Synchronous Compensator (STATCOM), Unified Power Flow Controller (UPFC), and Thyristor- Controlled Series Capacitor (TCSC), offer advanced solutions to mitigate these challenges by providing dynamic voltage control, reactive power compensation, and congestion management. This paper presents a comprehensive analysis of various FACTS devices, focusing on their control strategies, applications, and impact on improving power system performance. Simulation results demonstrate the effectiveness of FACTS devices in maintaining voltage stability, optimizing power flow, and minimizing transmission losses, ultimately contributing to a more efficient and resilient power grid.

High electricity growth in Nigeria coupled with an obsolete transmission network has necessitated novel approaches to power grid optimization. This paper compares the two technologies- Solar Photovoltaic (PV) system and Flexible AC Transmission System (FACTS) devices, in particular Static Synchronous Compensator (STATCOM), individually embedded to the 330 kV Nigeria 48-bus transmission grid in a simulation-based study. With the assistance of Power System Analysis Toolbox (PSAT) in MATLAB, this paper summarizes how these are the technologies that developed to increase Available Transfer Capability(ATC), gain better voltage stability and change power flow under normal as well as under Single Line Contingency. Five weak buses were used for the simulation featuring poor voltage performance and three deployment confirmations were studied (FACTS, PV, and the the base case without any enhancement). The results prove that solar PV and FACTS devices can independently be used to enhance the performance. ATC enhancement of FACTS deployment are almost 35.7% in ATC whereas solar PV gave an ATC enhancement of 29.6%. Voltage variation was decreased by 24.6% and 29.4% in the FACTS-only and PV-only case respectively, over the base case. These findings imply that FACTS has more transfer capacity, while PV systems have more voltage support. The results of this study offer valuable knowledge for power system planners and decision makers in developing countries where additional infrastructure development may not be feasible or immediate, but a need to reinforce the transmission network using flexible and low-cost solutions exists.

In electromechanical oscillation damping within power system, power system stabilizers (PSSs) are often deployed. However, a PSS is less effective in damping interarea oscillation and is limited by changes in network configuration due to weak tie-lines and load variations. Consequently, this paper presents a wide-area coordination approach that damps interarea oscillations using FACTS devices and phasor measurement units. We selected a static synchronous compensator (STATCOM) and static series synchronous compensator (SSSC) for realistic power system interarea oscillation damping. The performance of the coordinated FACTS installed in a power system depends on their suitable locations, sizes, tuned parameters, and remote input signal selection. Hence, we formulated a multiobjective problem to provide the STATCOM and SSSC's optimal solutions using multiobjective particle swarm optimization. In addition, we employed a participation factor to select suitable generator speed deviations as the wide area stabilizing signal. The proposed approach was tested on different configurations of the Kundur $2$-area $4$-machine test system within MATLAB and Psat environments. The outcome of the nonlinear simulation proved that the multimachine power system stability was enhanced.

This Voltage stability problems increasing day by day because of demand increase. It is very important to analyze the power system with respect to voltage stability. Location of FACTS devices is important for the enhancement of voltage stability. This paper investigates the voltage stability analysis of 14 bus systems by optimally locating Flexible AC Transmission System (FACTS) devices. Shunt and series FACTS controllers are introduced in the weakest bus and its effectiveness is assessed by comparing voltage profile and loading margins enhancement. It is shown that best location for static voltage stability margin is the “weakest bus” of the system. Continuation power flow (CPF) is done with PSAT (power system stability analysis Toolbox).