Transient stability enhancement evaluation of cogeneration system by using FACTS elements

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.

With the development of science and technology, the cost of offshore wind power development and transmission has gradually decreased, making offshore wind power technology a research hotspot. The installed capacity has been increasing year by year. China has abundant offshore wind energy resources, which are much richer than those on land and are available for exploitation. Offshore wind speeds are stable and do not produce harmful substances. Therefore, studying the transient voltage stability of offshore wind power grid-connected systems to improve the utilization efficiency of offshore wind power and protect the ecological environment is critical. After large-scale wind power is connected to the grid, ensuring the stability of the system's transient voltage becomes crucial. This paper aims to deeply study the transient voltage stability of offshore wind farm grid-connected systems, providing theoretical support for the subsequent design and operation of offshore wind farms. A simulation model of a typical power system integrated with offshore wind farms was established using PSAT. Relevant transient voltage stability indices were calculated, and the impact of varying wind speeds on the transient voltage stability of the grid-connected system was investigated. Static Var Compensators (SVC) and Static Synchronous Compensators (STATCOM) were installed for comparative analysis. The results demonstrate that excessively low wind speeds degrade the system's transient stability, and the installation of SVC provides superior improvement in transient voltage stability compared to STATCOM.

Affected by the current limitation, grid-forming inverters (GFMs) will transition to a current source under grid faults, which makes the inverter-based microgrid lose the voltage support and then be switched to a current source interconnection microgrid (CSIM). It may deteriorate the system's transient synchronization stability (TSS). This issue has not been studied previously. To this end, this article proposes an analysis and enhancement method of TSS of CSIM. First, a large signal synchronization model of CSIM is derived, which takes into account the effect of the current limitation strategy of GFMs and the dynamic interactions between GFMs and grid-following inverters (GFLs). Second, by constructing the Lyapunov energy function, the criterion of TSS is obtained and the impacts of parameters on stability are investigated. Based on the stability criterion, the feasible region of current references of GFLs is clearly described. Therefore, a dynamic current control method of GFLs is proposed. It can well address the absence of equilibrium points (EPs) and strengthen the transient stability. Meanwhile, a novel antiwindup strategy of GFMs considering synchronization stability constraint is proposed, which can contribute to the fault recovery of GFMs. Finally, simulation and experimental results verify the effectiveness of the proposed methods.

New techniques and approaches are constantly being introduced to analyze and enhance the transient stability of renewable energy-source-dominated power systems. This review article extensively discusses recent papers that have proposed novel and innovative techniques for analyzing and enhancing the renewable source-dominated power system’s transient stability. The inherent low-inertia characteristics of renewable energy sources combined with fast-acting power electronic devices pose new challenges in power systems. Different stability concerns exist for grid-following and subsequent grid-forming converter/inverter connections to power grids; hence, distinct solutions for enhancing the transient stability have been devised for each. Moreover, the fundamental concepts and characteristics of converter/inverter topologies are briefly discussed in this study. Recent discussions and reviews of analysis and enhancement techniques in transient stability could lead to new ways to solve problems in power systems that rely primarily on renewable energy sources.

This paper proposes an adaptive sparse polynomial chaos expansion(PCE)-based method to quantify the impacts of uncertainties on critical clearing time (CCT) that is an important index in transient stability analysis. The proposed method can not only give fast and accurate estimations for the probabilistic characteristics (e.g., mean, variance, probability density function) of the probabilistic CCT (PCCT), but also provides crucial information about the sensitivity of random inputs with respect to the variance of PCCT. Utilizing the sensitivity information, mitigation measures can be developed for transient stability enhancement. Numerical studies on the WSCC 9-bus system demonstrate the high accuracy and efficiency of the proposed method compared to the Monte Carlo simulation method. The provided sensitivity information and the effectiveness of mitigation measures in transient stability enhancement are also verified.

This paper presents the results of transient stability improvement on a 2-generator 4-bus system. Supplemental control design of static VAr compensators (SVCs) and static synchronous compensators (STATCOMs) using H/sub /spl infin// optimal control is investigated. Most of the work on STATCOM used EMTP or EMTDC or hardware model to study its performance. In this research, a computer program is developed based on MATLAB using Simulink to carry out the simulation. For the sake of comparison of SVC and STATCOM, the same system, location and contingency are used. The dynamic responses of the synchronous machines subjected to a three-phase fault are given to demonstrate the effectiveness of the supplementary control of SVC and STATCOM. The results show that the proposed controller can provide better damping characteristics under all operating conditions.

Matlab SimPowerSystems is a modern design tool that allows scientists and engineers to rapidly and easily build models that simulate power systems. Not only can you draw the circuit topology rapidly, but your analysis of the circuit can include its interactions with mechanical, thermal, control, and other disciplines. The paper covers some case studies that provide detailed, realistic examples of how to use SimPowerSystems in power system analysis. The following types of studies is coverted on the paper:1. Thyristor‐Based Static Var Compensator: Study the steady‐state and dynamic performance of a static var compensator (SVC) on a transmission system.2. Transient Stability of a Power System with SVC and PSS: Study of the application of static var compensator (SVC) and power system stabilizers (PSS) to improve transient stability and power oscillation damping of the system.3. GTO‐Based STATCOM: Study the steady‐state and dynamic performance of a static synchronous compensator (STATCOM) on a transmission system.4. Control of load flow using UPFC: Study the steady‐state and dynamic performance of a unified power flow controller (UPFC).5. Chopper‐Fed DC Motor Drive: Study of a DC motor drive with armature voltage controlled by a GTO thyristor chopper.6. VSC‐Based HVDC Link: Modeling of a forced‐commutated Voltage‐Sourced Converter high‐voltage direct current (VSC‐HVDC) transmission link.7. Three‐Phase Network with Electrical Machines: Simulation of a three‐phase power system containing electrical machines and other three‐phase models.8. Variable‐Frequency Induction Motor Drive: Study of a PWM inverter‐driven variable‐frequency AC induction motor in variable‐voltage, variable‐speed operation.

This paper presents the electric power system analysis and design of an expanding steel cogeneration plant. The power system configuration and the equipment parameters of the cogeneration plant are well designed according to the power flow, short circuit, voltage fluctuation, harmonic flow and transient stability analyses. According to the power flow analysis, the site and capacity of shunt capacitor banks as well as the tap position of transformers are determined to maintain all the buses voltage at acceptable range and to keep the power factor above 0.95. Also, to comply with the restriction of circuit breaker capacity, the high impedance transformers are designed even if they consumed more reactive power from the system. In addition, the voltage fluctuation resulted from the dramatic reactive power variation of hot strip rolling mill can be greatly reduced if proper static var compensator (SVC) is installed. The significant voltage sag due to the starting of induction motor can be effectively improved by applying wye-delta transformer starter. Furthermore, the total voltage harmonic distortion (THD <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sub> ) and the total current demand distortion (TDD <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</sub> ) are both acceptable if the proper filters are installed. It is also found that the cogeneration system can keep stable operation in isochronous mode by applying the governor control action and the load shedding scheme after tie line tripping. It is concluded that the power system analyses is important for the steel plant with cogeneration unit to identify hidden problems and remedy strategy to ensure the system power quality and operation performance.

Problem statement: It is becoming increasingly important to fully utilize the existing transmission system assets due to environmental legislation, rights-of-way issues and costs of construction and deregulation policies that introduced in recent years. The Static Var Compensator (SVC) has been proposed for the better control power flow and dynamic performance. The exact long transmission line model consists of the resistance and reactance. Most of previous researches studies transient stability performance of the SVC in SMIB System with neglecting resistance of the line. Thus the fully capability of the SVC on transient stability improvement of power system may not be applied. The consideration of the resistance causes in the difficulty of deriving mathematical model. Approach: This study investigates the effect of the SVC on transient stability of the power system with consideration the exact long transmission line mode. The concept of two-port network is applied to simplify the mathematical model of the power system. The proposed method is tested on sample system and compared on various cases. Results: The first swing of rotor angle curve of the faulted system without resistance is obviously higher than that of with resistance whereas the second swing of the faulted system without resistance is slightly less than that of with resistance. The system with the SVC can improve transient stability of power system. Conclusion: It is found from this study that the SVC and resistance of the line can improve first swing of rotor angle. The resistance of the line provides the negative effect on second swing of rotor angle. The simulation results indicate that for practical long line, the resistance is very import parameters for evaluating transient stability of power system.

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.

To ensure the transient stability of power system connected to a wind farm, wind power plant must be able to supply reactive power at the point of the common coupling(PCC). The reactive power capability of each individual wind turbine may not sufficient to maintain stability. Also, there are large reactive power losses in connection cables between wind farm and PCC. The static synchronous compensator(STATCOM) is considered for transient stability enhancement, because it provides many advantages such as the fast response time and superior reactive power support capability. In this paper, the effectiveness of a STATCOM in enhancing transient stability of power system connected to a wind farm is presented. The results of dynamic simulations show that STATCOM installed at the PCC can enhance transient stability.

According to the grid codes, on wind farm for reactive power compensation and voltage stability requirements, this paper analyzes the extent of a static synchronous compensator (STATCOM) to voltage stability of doubly fed induction generator (DFIG) wind farm, compared to a static VAR compensator (SVC), and proposes a new scheme for coordinated control of reactive power between DFIG and STATCOM, to do this, DFIG stator, grid-side converter (GSC) and STATCOM supply reactive power to the grid coordinately, where the advantages and disadvantages of rotor-side converter (RSC) and GSC are taken into more consideration, and the reactive power control ability of DFIG is fully utilized. Based on test system, research results show that, STATCOM can provide more reactive power than SVC for voltage stability under the same capacity, especially during the serious voltage sag; The coordinated control scheme can not only improve the transient voltage stability, but also help reducing the capacity of STATCOM so that save the cost of investments in wind farms.

In a high percentage of new energy-islanded microgrids, the overall inertia of the system gradually decreases, and the transient stability requirements of the microgrid frequency and voltage become more and more demanding under low-inertia conditions. To improve the transient stability of low-inertia islanded microgrid frequencies and voltages, this paper proposes a transient stability enhancement strategy for islanded microgrids based on energy storage system (ESS)–virtual synchronous generator (VSG) control. Model predictive control (MPC) is added within the active control loop of the VSG to achieve dynamic correction of the active power reference value of the VSG; PI control link is added within the reactive control loop to achieve a fast dynamic response of the reactive power command value. The ESS achieves fast and accurate regulation of frequency and voltage according to the power reference value of the VSG active control loop and the power command value of the reactive control loop simultaneously. Considering the need to ensure the ability of VSG to operate stably during transients, a comprehensive current-limiting technique combining virtual impedance and phase limiting is used to limit the fault current of VSG and maintain its synchronization and stability. Finally, the simulation results verify the strategy’s effectiveness and the superiority of the transient stability enhancement effect.

The bifurcation study of power system voltage stability has an important role in understanding the voltage unstable process deeply. Bifurcation theory includes both static and dynamic bifurcation. Static bifurcation study is the primary task of bifurcation theory. The bifurcation study can analyze the impact of dynamic control performance on voltage stability especially for flexible AC system(FACTS) such as static synchronous compensator(STATCOM) and static var compensator (SVC). The reactive power compensation effect of STATCOM is better than SVC. In this paper, a kind of toolbox of MATLAB, PSAT, is used for the comparative static bifurcation analysis for power system with and without STATCOM, and the bifurcation value on the point is studied. The studied results show that STATCOM can add load limit and delay static bifurcation to improve voltage stability.

In present scenario power grid networks are intricately interconnected, and by the opening of the electrical power market, power networks have become more complex. Now the various aspects of safety, security, controllability, power quality, and stability are equally important. In this paper, our main focus will be on improving stability; transient stability. While improving transient stability conventional lead-lag Power System Stabilizer (PSS) provide low frequency oscillations. Main use of Static VAr Compensator (SVC) is to improve transient stability through voltage control. For simulation, 4 generator-6 bus multi machine power network is taken for the analysis of the proposed scheme and the results of two types of controllers, i.e. PSS and SVC are compared.