Mitigation of voltage sags in distribution line system using static VAR compensator and static synchronous compensator

Now-a-days renewable energy sources are playing a vital role in global energy systems. Wind energy conversion method is cheaper compared to other conversions such as solar and tidal etc. There are many power quality issues in wind farms such as voltage sag, swell and harmonics arise due to grid, nonlinear load and three phase faults. These voltage fluctuations can be eliminated with the help of advanced reactive power compensation devices such as SVC (Static Var Compensator), STATCOM (Static Synchronous Compensator) and DVR (Dynamic Voltage Restorer). To reduce such power quality issues, it is essential to design, model and analyse the FACTS (Flexible AC Transmission line) device. In this project, STATCOM is used as a compensating device. STATCOM is a static synchronous generator operated as a parallel connection static reactive compensator. It is capable of generating or absorbing real and reactive power. Also, the compensator performance is analysed with the help of Proportional Resonant (PR) controller device. The STATCOM is connected parallel with the transmission line. When fault occurs, it will inject or absorb the reactive power to the line through the transformer according to the voltage requirement. The whole system is simulated through MATLAB/SIMULINK application. The simulation gives the effective influence of STATCOM on the improvement of voltage profile as well as reduction of Harmonics in grid connected Wind Energy Conversion System.

The rapid expansion of offshore wind energy and its integration into weak power grids have introduced significant challenges to system stability, particularly under fault conditions that cause voltage sags. Ensuring adequate Low Voltage Ride Through has become essential for maintaining grid reliability and preventing large-scale disconnections of wind farms.To address voltage sags caused by short-circuit faults during the grid integration of large-capacity offshore wind farms via weak networks, this paper establishes a simulation model of a permanent magnet synchronous generator (PMSG)-based offshore wind farm in the PSAT platform. Taking the Critical Clearing Time (CCT) as the core evaluation index, the Low Voltage Ride-Through (LVRT) capability is systematically assessed. By simulating short-circuit disturbances, the transient voltage response at the point of common coupling is analyzed, followed by a comparative evaluation of the voltage support effects of three dynamic reactive power compensation devices: Static Var Compensator (SVC), Static Synchronous Compensator (STATCOM), and Unified Power Flow Controller (UPFC). Results indicate that the rational configuration of dynamic reactive power compensation effectively mitigates voltage drops, significantly extends the CCT, and enhances transient stability margins. The distinct response characteristics and support efficacies of different devices are clarified, providing a theoretical foundation for optimizing LVRT strategies and selecting compensation equipment in offshore wind integration.

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.

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 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.

The Electronic based FACTS controllers are static equipment. Its principle purpose is to control AC transmission. The parameters of FACTS are enhancement of controllability, ability of power transfer, control of line impedance, load angle and the magnitude of bus voltage. A unified power controller is to be a static device and this system device should have quick reactive transmission. This paper focuses on the issues like voltage sag and swell of power quality. HPFC is used to moderate the voltage variation and improve power quality and also used tocouple the phase controllable bridges to produce current which is injected into a transmission line by using series of transformers. The UPFC is a combination of a static synchronous compensator (STATCOM) and a static synchronous series compensator (SSSC)which is coupled with common DC link. The HPFC eliminates the common dc link between the shunt and series converters and alsoit performs in transmission line to exchange real power between converters at the 3 rd harmonic frequency. The HPFC employs. Several 1-phase converters like D-FACTS concepts as the seriescompensator .These concepts reduce the rating of the components and offer a high reliability. Since the HPFC can immediately control the active and reactive power flow and the voltage magnitude, it implies a great potential for power oscillation damping. The case study contains a HPFC located in an exceedingly single-machine infinite bus power grid with 2 parallel transmission lines that simulated in MATLAB/Simulink. Keywords— Power Quality, voltage Sag and voltage Swell, Unified Power Flow Controller, Hybrid Power Flow Controller.

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.

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.

Voltage sag in a power system is an unavoidable power quality issue, and it is also an urgent concern of sensitive industrial users. To ensure the power quality demand and economical operation of the power system, voltage sag management has always drawn great attention from researchers around the world. The latest research that realizes the power quality conditioning has used dynamic voltage restorers (DVRs), static VAR compensator (SVCs), adaptive neuro-fuzzy inference systems (ANFISs), and fuzzy logic controllers based on DVR to mitigate voltage sag. These devices, methods, and control strategies that have been recently used for voltage sag mitigation have some limitations, including high cost, increased complexity, and lower performance. This article proposes a novel, efficient, reliable, and cost-effective voltage sag mitigation scheme based on a modular multilevel converter (MMC) that ensures effective power delivery at nominal power under transient voltage conditions. The proposed method, the MMC, compensates for the energy loss caused by voltage sags using its internal energy storage of the submodules, and ensures reliable power delivery to the load distribution system. Furthermore, control strategies are developed for the MMC to control DC voltage, AC voltage, active power, and circulating current. Detailed system mathematical models of controllers are developed in the dual synchronous reference frame (DSRF). Validation of the results of back-to-back MMC for dynamic load distribution system is analyzed which proves the effectiveness of the proposed scheme for voltage sag mitigation.

This paper deals with the design and implementation of cascaded H-bridge multilevel voltage source converter-based static synchronous compensator (STATCOM) for simultaneous active and reactive power compensation, voltage stability and damping of power oscillations. The main objective is to provide active power support and maintain the voltage stability by compensating the reactive power in the power system. In this paper, the multi pulse inverter-based STATCOM has been replaced by multilevel inverter-based STATCOM to overcome the drawbacks of the former. Cascaded H-bridge (CHB) MLI for implementation of STATCOM has been used as CHB MLI is considered the best for STATCOM applications due to its modular structure and requirement of lesser number of components. MLI-based STATCOM is used to provide simultaneous reactive power and active power compensation established by using super-capacitor. The super-capacitors are connected with each DC link capacitor of CHB MLI by using the DC-DC buck boost converter. The STATCOM is also used to provide voltage stability during the power quality problems such as voltage sag and voltage swell, it is established by injecting or absorbing reactive power. The STATCOM is also used for damping the power oscillations by controlled injection of reactive power hence enhancing transient stability. Nine-level cascaded H-bridge MLI-based STATCOM is designed for simultaneous reactive power and active power compensation, voltage stability and damping the power oscillations. Exhaustive simulations have been carried out using MATLAB/Simulink and SimPowerSystems software. The simulation results are presented to prove the effectiveness of MLI-based STATCOM for simultaneous active and reactive power compensation, voltage stability and damping of power oscillation.

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.

Voltage dip is a power quality problem that occurs the most frequently in the Provincial Electricity Authority (PEA) power system and impacts the industry's sensitive load. This paper presents a photovoltaic (PV) farm converter control as a static synchronous compensator (STATCOM), supplying dynamic reactive power for voltage dip mitigation and the industry's failure load reduction near the PV farm. The PV farm's power system and the industry connect with the 22 kV distribution system of Bang Phra khru substation (BPH) in Phra Nakhon Si Ayutthaya Province. A case study simulated on the DIgSILENT PowerFactory software and converter control as STATCOM operated in two modes: full STATCOM mode and partial STATCOM mode is presented. The distribution system data has been collected from the Geographic Information System (GIS). The voltage dip event data, caused by a single line to ground fault on other feeder and affected sensitive load, received from disturbance analyzer. The results of both STATCOM modes demonstrated an increased voltage value in the standard range of PEA. The partial STATCOM mode showed the voltage value better than the full STATCOM mode. As a result, PEA should improve the grid code determined the PV farm installed near the industry's sensitive load had to support dynamic power.

Voltage sag is considered to be the most serious problem of power quality. It is caused by faults in the power system or by the starting of large induction motors. Voltage sag causes about 80% of the power quality problems in power systems. One of the main reasons for voltage sag is short circuit fault, which can be compensated for by a distribution static compensator (DSTATCOM) as an efficient and economical flexible AC transmission system (FACTS) device. In this paper, compensation of this voltage sag using DSTATCOM is reviewed, in which a sliding mode control (SMC) technique is employed. The results of this control system are compared with a P+Resonant control system. It will be shown that this control system is able to compensate the voltage sag over a broader range compared to other common control systems. Simulation results are obtained using PSCAD/EMTDC software and compared to that of a similar method.

The surge in demand for electricity has driven the power system to operate at a lower efficiency level. With the many actions taken to improve the electric grid, voltage unbalance and line overload have become challenging problems to address. Voltage control can be determined in generation, transfer, and electricity usage. When the power system is under stress, reactive current unbalance significantly contributes to voltage instability. To maximize the efficiency of a power system, flexible transmission systems system (FACTS) devices must be used most effectively and feasible. FACTS devices like Static VAR Compensators (SVCs) and Static Synchronous Compensators (STATCOMs) can reduce instability in heavily burdened lines, resulting in lower system losses and more excellent network reliability. In this paper, FACTS controllers such as SVC and STATCOM are incorporated in the Kurdistan power system simulated by using PSAT software based on MATLAB for the improvement of voltage profile, minimization of the system losses, and cost of the system. Also, the graphical comparisons of the results are presented to investigate the effectiveness of the proposed methods.

Voltage sags and interruption are one of most important of power quality problems. They can influence performance of equipment such as induction motors. They are generally caused by short circuit faults in transmission and distribution systems which propagate in entire of power systems. When their appear at a motor terminal, its effects are the speed and the torque will decrease to a level lower than values of the normal and even the motor become stall if magnitude of the voltage sags and duration exceed certain limit. The voltage can return to nominal voltage after end of the voltage sag and interruption. The motor will experience re-acceleration to normal condition is accompanied by large inrush current. A study on induction motors was carried out to confirm these effects. Single-phase and three-phase of small induction motors were used for investigating the effects caused by symmetrical voltage sags and interruption through experimental and simulation.