A review of FACTS device implementation in power systems using optimization techniques

In electrical power systems, FACTS devices effectively control power flow and change bus voltages, leading to lower system losses and excellent system stability. The article discusses the research from the last decade that evaluated various methods for placing FACTS devices using the meta-heuristic approach to address the positioning of FACTS devices to maintain proper bus voltages and control line flow and improve the overall system efficiency. The need for more efficient electricity systems management has given rise to innovative technologies in power generation and transmission. The combined cycle power station is a good example of a new development in power generation and flexible AC transmission systems, generally known as FACTS, are controllers that improve transmission systems. Worldwide transmission systems are undergoing continuous changes and restructuring. They are becoming more heavily loaded and are being operated in ways not originally envisioned. Transmission systems must be


Introduction
In a power system network, the load increases daily, using the FACTS devices in a network that is very close to thermal capabilities, and improves system capacity and efficiency of the transmission line.They are utilized for the highest power flow to support the voltage increasing the transmission line capacity and stability margins [1].The author of [2] illustrates FACTS devices' effect on reactive and actual power flow using the tracing power flow approach.These power electronic-based devices may redistribute power in congested lines during high-load situations, controlling the active and reactive flow of power in the system.This increases system stability.For already-existing FACTS controllers in India, a survey on different types of FACTS controllers was conducted.TCSC is the first controller to be installed in India.By enhancing impedance and power quality, FACTS controllers provide voltage stability.The author discusses numerous FACTS controllers, their features, and cost comparisons of various controllers like.Series, Shunt, Series-Series, and Series-Shunt controllers are several FACTS controllers.The power transmission capacity of lines is increased via series controllers.
These FACTS devices must be built with great precision to produce good results due to the compensatory strategies and quick activity.
In recent years, the security of transport networks will become one of the major challenges of the future considering the economic and societal impacts of major incidents.The competitive aspect linked to deregulation as well as the difficulty of building new structures will lead operators to optimize infrastructure and architectural equipment, optimal management of energy transfers, effective real-time monitoring and control, etc.
The principal inspirations and novelties for this survey study are presented below: • The elements or limits that should be considered the best execution with respect to the accuracy of the solution, the speed of convergence and the effectiveness, with the most elevated achievement rate, while supporting the FACTS devices optimization issue are explored.To take care of the FACTS devices optimization issue, a synopsis of various enhancement strategies that have been broadly utilized, like classical optimization techniques, meta-heuristic methods, sensitive index methods and hybrid methods is viewed as in this work.• This concentrate additionally presents the benefits and drawbacks of numerous advancement procedures which have been utilized for solving FACTS device optimization issues.• Outline tables including the strategies applied, the test systems utilized, the types of FACTS devices examined and the helpful goals of each revised document.• A discussion is investigated toward the finish of this work about the qualities and shortcomings of numerous enhancement strategies that have been utilized for solving FACTS device optimization issues.
Nowadays, FACTS devices, based on power electronics, enable tighter continuous control of power flows with the following benefits: maintaining a voltage that is within acceptable ranges at load buses, controlling the flow of active and reactive electrical power in thermally constrained lines, improving safety measures, and operating electrical systems close to their capacity limits are some of the other improvements.Developing tools that enable us to successfully operate electrical networks, including the use of FACTS controllers, is crucial for all of these reasons.In addition, liberalization will impose defining a division of responsibilities as clearly as possible between the different actors who will use this same resource.To ensure or even improve this security, FACTS devices are based on power.Otherwise, it causes system insecurities that ultimately lead to system failure or a voltage drop [3].The study on FACTS controllers also reveals promising outcomes when using these tools to increase voltage stability in emergencies such as line outages, as mentioned by [4].There is a particular urge to use FACTS devices to discover solutions to all issues.Rapid industrialization and lifestyle expansion have increased reliance on the electrical power grid.A few uncertainties have emerged as a result of the rise in demand.Changed technologies are used for transmission setups that have been forced to operate outside the bounds of their sanity to overcome these uncertainties.By improving the power system's regulation, these restrictions can be minimized.
After adding FACTS devices, the transmission system would operate highly closely to its temperature and stability constraints.The AC power system has built-in power stability since the transmitting and receiving ends of the lines choose how much power flows between them.From eqn (1), consider voltages V 1 and V 2 at the sending and receiving limitations and θ 1 and θ 2 for the corresponding phase angles at the sending and receiving lines.We examine the power flow equation as follows: The main aim is to diminish the transmission power loss and to improve the bus voltage profile by acceptable coordination of the optimal control variables in the power transmission network.The real power loss mainly occurs due to highly resistive conductors and this leads to inefficient transportation of power from source to distribution side as shown in eqn (2) with equality constraints.Hence, it is highly essential to reduce real power loss in the networks.To maintain voltage stability, reactive power is an important parameter.Lack of adequate reactive power may lead to voltage collapse in the networks shown in eqn (3).So, there is a pressing need to adjust the voltage magnitudes in the network.Reactive power of generator inequality constraints is shown in eqn (4).The function's constraints can meet the real and reactive power limits.

Generator reactive power capability limit:
In a deregulated environment, the amount of power generated will depend on various factors, including the availability of fuel, the state of the environment, the state of the economy, and other considerations.At the same time, the load might also change because of the weather, the time of day, and expansion.A situation where the system's security might be questioned would result from the variance in the load and generation.For instance, if the stability or thermal limits of the power system are being approached, a sudden shift in the load or generation, no matter how slight, might result in power swings and cascaded tripping.
The constraints that have to be taken into consideration are the following: 1. Limitation of transient stability (2)

Enhancement of power quality
The power quality can be defined as the system where voltage remains pure sinusoidal continuously with constant magnitude, phase angle, and frequency.Some of the power quality requirements are as follows: 1.The voltage throughout the range must be constant 2. Maintain the frequency within the limits 3. Balancing the phase angle 4. Radio interference is not needed.
There are many causes of power quality problems.Some of them are discussed here.
1.A voltage sag occurs when the voltage drops below the nominal voltage level by less than 10% 2. Power supply interruption in a short-duration 3. A prolonged power outage lasting longer than 1 or 2 s 4. Raise voltage spikes from average to high voltages over a short period.A millisecondlong shift in frequency 5. Harmonic distortion occurs when the voltage and current waveforms are no longer sinusoidal.

Study of FACTS devices
Different industries are working together to get through the global warming challenge: people are paying more attention to renewable energy sources, smart grids are being developed, energy losses are being reduced, energy efficient methods are being explored, and distributed energy resources are being gradually integrated.FACTS devices are commonly employed for this purpose.The power factor becomes close to the accord if proper compensation techniques are applied, as shown in Fig. 1.The increased load could cause congestion and disrupt the electrical system's ability to regulate voltage, as shown in Table 1.If a sufficient supply of reactive power is not in the grid, it produces low voltage levels at the receiving end and, at worst, may even create blackouts, as shown in Table 2. FACTS devices are widely used to avoid this and ensure grid dependability.Hingorani and Gyugyi are attributed.Power electronic converter-based FACTS devices, as shown in Fig. 2 and contributions, as shown in Table 3, can be used in the transmission line, improving the transmission network's overall efficiency, as shown in Fig. 3.A group of FACTS devices whose application, performance, as shown in Table 4 installation, cost mva, and dynamic response of the system a shown in Fig. 4. Depending on the circumstances, loads may be resistive, capacitive, or inductive and conventional sources, as shown in Fig. 5.All of the variables that influence power losses in transmission systems, such as node voltages, voltage magnitudes, phase-angles, and line reactance can be controlled by precise FACTS devices in Table 5.
A power grid is a cumulative result of connecting many individual generators, consumers, and regulators.However, while the sources and control circuits are generally predetermined, as shown in Figs. 6 and 7, the loads are constantly shifting and typically unpredictable.When dealing with resistive loads, phase balancing is not critical.However, when operating with inductive or capacitive loads, the current and voltage are out of phase, resulting in a power factor that is less than unity.Improve compensation is necessary.

Series-connected controllers
These controllers are in charge of enhancing the capacity to transmit power.Reduce the sum line impedance from the transmitting end to the receiving end.In the end, series compensation works.Therefore, passing the damping can be used to lessen stability oscillations.One may manage the current flow direction a series controller uses.A variable might be the form of a series controller as variable power, reactor, or capacitor.It is an SSSC serial compensator with a voltage source that regulates the line's voltage drop and is transmittable power.It thus enhances the maximum power transmission they are lining up.The performance of the SSSC is examined by numerous places, such as the line's end, the line's center, etc., when the distance fault occurred relay.An inductive

Shunt-connected controllers
The transmission line's shunt controllers may be variable sources, variable impedances, or both.The system receives variable currents from the shunt controllers.
Reactive power changes depending on whether the current and voltage lines are in phase quadrature.These controllers with shunt connections can be positioned in the center of the transmission lines.One of the shunt controllers that control reactive power in lines is STATCOM.
A detailed analysis of STATCOM, deployed in a 5-bus power system, is provided.The shunt controller injects electricity into the transmission line after installing STATCOM to achieve the desired power flow via the lines of 0.43 P.U. and 0.154 P.U., respectively.The compensating approaches also demonstrate a lessening of the transmission cables' burden.A shunt compensator is further placed at bus 4 to enhance voltage control.All bus voltages are within the voltage limitations in these  shunt controller was taken and approached for the traditional cascade controller, consisting of an inner vector-current controller and several outside control loops.

Combined series-shunt controllers
Both series and shunt controllers are employed in the combination of series-shunt controllers.The series-shunt controller's fundamental working concept utilizes the shunt controller to manage voltage and the series controller to supply current to the lines.The actual power is exchanged between the controllers when assembled in the system.Real and reactive power is regulated using series-shunt controllers, which improve system performance.A type of series-shunt controller is the U.P.F.C.The power balance between the transmission system. 1) Real & reactive power monitoring.
2) Power loss and cost minimization.
3) Maximize the system loadability 4) Power transfer for heavy-loaded to light-loaded lines Integrating the shunt and series compensators allows for effective system parameter changes, such as the improvement of the power transfer capabilities.

Combined series-series controller
The formation of this combination occurs when two or more series controllers are joined.The primary function of a series controller is to compensate for reactive power imbalances across lines, but these controllers may also handle actual power differences by using power connections.This power transfer feature enables the controller to balance reactive and real power flow.An integrated series-series controller is the I.P.F.C.This converter, which regulates the flow of electricity in systems with many transmission lines, is one of the voltage source converters.They are typically positioned on hazardous transmission lines.

Analytical approach
Finding the best location for FACTS controllers in deregulated electric power systems is a primary goal addressed by many writers.S.T.A.T.C.O.M. and S.S.S.C. are ideally positioned to clear the congestion.The power system network utilizes several FACTS devices strategically to reduce the generation cost with the integration of wind power as renewable energy resources are added to the grid.Save costs using an ideal power flow program employing T.C.S.C. FACTS devices were also added where they belonged allocated T.C.S.C. and U.P.F.C. using a sensitivity-based method to increase system security.Similar to the optimal location of T.C.S.C. and S.S.S.C. was determined using a sensitivity factor based on line outage distribution to improve system security.For the U.P.F.C. and the T.C.S.C. ideal site respectively applied the sensitivity-based technique.The effectiveness of the FACTS device was also examined in contingency instances by both authors using T.C.S.C. to enhance the state of the power system network.Additionally, the power flow-based sensitivity factor was examined.

A survey on FACTS devices
Using the simulated-annealing technique and the IEEE 14-bus system, the author of this research established the ideal position for U.P.F.C.Using the differential evolution method, some of the authors have researched the best part and size for the T.C.S.C. and S.V.C. controllers to decrease line losses and increase voltage stability.L.O.S.F. is employed to find the line that will allow T.C.S.C. to be placed in the most advantageous location.Systems utilizing the IEEE 14-bus and 57-bus use this PSO approach.Locating S.T.A.T.C.O.M., a shunt controller, in the right place may make congestion issues worse artificially.If one line experiences a fault, I.P.F.C. is still relevant and will use other lines to supply electricity.The author determines where the I.P.F.C. controller should be placed to reduce congestion and describes how the S.T.A.T.C.O.M. controller in a P.V. solar farm works with power system stabilizers to reduce system oscillations.As a result, the system's transient and dynamic behavior is enhanced to reduce the cost of FACTS controller investment and power plant generation, and a GA-based strategy was explored.According to the authors, the multi-type FACTS controllers were positioned in the system optimally using the G.A. technique.The IEEE 30-bus system was used by the authors, and they explored how better congestion management may result from putting S.T.A.T.C.O.M. at an ideal position and lowering the system's running costs and decreasing production costs in the transmission system utilizing FACTS controllers, increasing the power system's capacity, and enabling yearly savings.Results show that S.V.C. and S.T.A.T.C.O.M. may reduce voltage failure and fall during emergencies and function as quick-response devices to maintain the power system's stability.Using FACTS devices, the D.E. algorithm suggested reducing the generator fuel cost.The controller U.P.F.C. is employed to manage congestion in a linked power system network by choosing the best position.FACTS are also utilized in A.C. transmission networks to increase stability and control the power delivered over the transmission line.The C.S.A. algorithm and two controllers, S.V.C. and T.C.S.C., are employed to regulate the dispatch of reactive power across the transmission line at the best possible efficiency.Following deregulation, the strain on transmission lines rose.FACTS devices are employed to lessen this stress on A.C. transmission lines.These gadgets decrease losses, generate costs, balance reactive demand and supply, and enhance voltage profiles.These advantages are achievable only when FACTS controllers are placed in the ideal location.

Congestion management using FACTS devices
The technological solution relies on the utilization of FACTS devices to regulate congestion FACTS controller, assist in managing the transmission line impedance, and the magnitude and angle of the bus voltage in increasing the flow of the line, as well as the system's reliability and security.Once these devices have been implemented, the transmission line loading limitations can be adjusted without infringing on any other requirements.The violation of transmission limit limits and the reduction of contracted power flow across transmission lines are caused by congestion.After deregulatory measures were taken, an increase in generator competition led to a rise in transmission line congestion, which caused difficulties for the system operator.The ideal placement and size of the FACTS controllers T.C.S.C. and S.S.S.C. are calculated by evaluating the magnitude and reactive power fluctuations in a congested environment.This helps ensure that the controllers are placed in the best possible locations.Under loading conditions, the ideal size and position of FACTS devices are determined by the magnitude of the voltage on the load buses and the needed reactive power of those buses.In an IEEE 14-bus system, T.C.S.C. and S.S.S.C. are utilized to determine the best position by analyzing the voltage magnitude and necessary reactive power of load buses.The ideal location of FACTS controllers is examined in a crowded environment.Congestion control is handled with the help of T.C.S.C.The U.P.F.C. is proposed to ease congestion while simultaneously reducing the cost of generating.
The supplier's objective is to supply its clients with reliable and uninterrupted access to the electrical grid at all times.For three-phase activities to be carried out, the steady supply must have a voltage waveform that is entirely sinusoidal and has a constant amplitude, frequency, and balance between the phase angles.On the other hand, a typical stable operation is not always achievable because of variations in the magnitude and angle of the voltage when a substantial reactive load is present in the circuit.Under certain circumstances, such as fault conditions or emergencies, a system may become unstable.Controlling the magnitude and angle of the voltage in diseases of the solid reactive load is made more accessible by developing semiconductor switch-based FACTS devices.Most of the time, S.T.A.T.C.O.M. is utilized for stability research.Controlling power flow over transmission lines is another function of the U.P.F.C., another device used for stability analysis that examines the ideal placement of the FACTS devices concerning enhancing the system's stability.

U.P.F.C
The U.P.F.C. is the most adaptable factor controller within the family of FACTS controllers Gyugyi proposed for controlling voltage and power flow in a particular conductor.One shunt device and one series device make up its two voltage supply devices (VSC).Furthermore, the two converters' D.C. capacitors are linked in parallel in Fig. 8.The dc voltage for both converters is provided by a common capacitor bank.In this process, the series converter exchanges both real and reactive power with the transmission line.The shunt-connected converter 1 is used mainly to supply the real-power demand of converter 2, which it derives from the transmission line itself.The shunt converter maintains the constant voltage of the dc bus.The reactive current can be achieved by the shunt converter performing the function of S.T.A.T.C.O.M. and injecting the reactive voltage into the line.The series device performs the function of S.S.S.C in Fig. 9.

TCSC
Thyristor controlled series capacitor (T.C.S.C.) offers practical ways to regulate and boost the power transfer level of a system by altering the apparent impedance of a particular transmission line in Fig. 10.To improve power system stability during emergencies, a T.C.SC.might be used in a planned manner.It is feasible to function steadily at 75 power levels, much more than the system's initial design intent, without affecting its stability.Additionally, T.C.S.C. is employed to lessen S.S.R. in Fig. 11 (sub-synchronous resonance) SVC A static V.A.R. generator is shown in Fig. 12 or absorbent material that is shuntconnected and whose output is modified to exchange capacitive or inductive current while maintaining or regulating particular power system characteristics (typically bus voltage)as shown in Fig. 13.

STATCOM
The ac system voltage of the static synchronous generator, as shown in Fig. 14, which is used as a shunt-connected static power unit compensator, controls the capacitive or inductive output current as shown in Fig. 15.

SSSC
A static synchronous generator in Fig. 16 that is run without the need for an external power source acts as a series compensator with an output voltage that is built into and controllable separately from the line current to speed or decelerates the overall reactive fall over the line and, as a result, dominating the transmitted electrical power in Fig. 17.The S.S.S.C. may include transiently rated energy storage or engrossing energy devices to increase temporary real power compensation, lengthen or lower the overall real (resistive) fall briefly over the line, and support the facility system's dynamic behavior.

Optimisation techniques
As a result of its effectiveness, FACTS devices may be used to address issues in the electrical grid.However, their high price and installation costs typically outweigh the savings on energy bills they produce.Because of this, a proper balance of devices is difficult.Many respected scientists and engineers have presented solutions to this problem over the past few decades.Optimization provides an unbiased evaluation of relevant elements.
Optimization methods come in two flavors: single-objective and multiobjective, each tailored to different goals.The benefits of using single objective approaches are that they are quick, cheap, and only produce one possible answer.However, a multiobjective optimization strategy considers several competing goals.It generates a collection of middle-ground options, or a pareto-optimal front of parallel solutions, that are more practical and feasible for use in challenging real-world scenarios.This review work motivates the researchers to do further research to improve the size and the location of the FACTS devices as in order to reduce the loss in power and maintain a voltage level.Figure 18 shows Clasification of optimal size and location.
Due to the growing renewable energy penetration, deploying FACTS devices with distributed energy has attracted more attention in recent years.The development decisions on series FACTS employing a deduced shifting factor model in a market environment with significant penetration of renewable energy sources were also identified using the stochastic mixed integer program bi-level model.
Additionally, because of its reduced model size, the proposed shift factor formulation is thought to perform better than a comparable Bq formulation in terms of computational speed.An essential setback for optimal power flow analysis is its restricted use in D.C. power flow.The co-optimization approach was alternatively reformed for transmission expansion planning with the T.C.S.C. site by two mixed integers linear programmed suggested to address the multi-optimization challenge more effectively.The best location for the generalized unified power flow controller (G.U.P.F.C.) and integrated power flow controller (I.P.F.C.) integrated with the wind farm and fuel cell was found using an improved squirrel search method.The model was influenced by the way flying squirrels move between trees in nature by gliding.
The various scenario-aware models that have been suggested perform well.When allocating S.V.C.s and T.C.S.C.s in a deregulated network, the accompanying uncertainty of wind power penetration is taken into account with dynamic line rating using a probabilistic approach.It was found that S.V.C. enhanced the maximum loadability limit of dynamic line rating more effectively than T.C.S.C. or other FACTS devices.
The correct placement and size of the FACTS devices are critical, especially from an economic standpoint.Additionally crucial to the technical advancement of the entire power system is the optimal functioning and control of these devices.As a result, research has focused on the best operating and controlling FACTS devices to enhance the power system's quality, dependability, and security.A nonlinear controller for a unified power quality conditioner (U.P.Q.C.) was designed using sliding mode control and instantaneous active and reactive power theories.It turned out to be more effective at compensating current and voltage distortion than the traditional proportionalintegral controller-the model with U.P.F.C. parameter settings.
Using a self-adaptive differential evolutionary algorithm, they consider transmission losses in U.P.F.C., coupling transformers, and failures of both converters.Utilizing the U.P.F.C. increased power flow while reducing line losses simultaneously.The first of its kind in Canada, the application of photovoltaic solar-based FACTS devices for stabilizing crucial induction motors.Such induction motor stabilization reduces disturbance in a power system.The new PV-STATCOM costs roughly 50 times less than a standard S.T.A.T.C.O.M. of comparable size.

Optimization programming techniques
The best location of FACTS devices is used to examine the various techniques, including linear and quadratic programming, nonlinear optimization programming, integer and mixed-integer optimization programming, and dynamic optimization programming.

Nonlinear optimization programming (N.L.P.)
The nonlinear optimization approach to evaluate controlling parameters suggests a nonlinear-interior-point-O.P.F.method for accessing the devices like G.U.P.F.C.

Integer and mixed integer optimization programming (I.P. & M.I.P.) techniques
In a power system transmission network, the integer and mixed-integer-optimization programme, the T.C.P.C.S.T., is used to control the actual power loss as well as generation limits and shifting phase angle constraints.

Dynamic programming (D.P.) techniques
The differential evolution (D.E.) method is employed to solve optimal power flow in power systems using the unified power flow controller (U.P.F.C.), an efficient and adaptable flexible A.C. transmission systems (FACTS) device, to reduce the generation cost and maintain the power flows within their security limitations.

Artificial intelligence (AI) techniques
The best placement of FACTS controllers is discussed in this part using a variety of artificial intelligence-based methodologies, including a genetic-algorithm (G.A.), artificialneural-network (ANN), Tabu-search-optimization (TSO), ant-colony-optimisation Fig. 21 Optimal location and sizing of FACTS devices to solve optimized techniques (A.C.O.) methodology, simulated annealing (S.A.) approach, particle-swarm -optimization (PSO) algorithm, and fuzzy logic-based approach.

Genetic algorithm (G.A.)
The ideal placement and U.P.F.C. parameter values are determined using G.A. and PSO to enhance the goal of strengthening power system security under single contingencies.Adopting a hybrid G.A. method for O.P.F. with FACTS devices is recommended.For the best placement of FACTS devices, multiobjective optimal power flow in GA regulates power flow through any transmission line.To enhance system capabilities, the perfect location to place phase shifters and the best quantity to use have been addressed using a genetic algorithm.A multiobjective evolutionary algorithm selects the location of FACTS devices for the power system security for enhancing power system load ability G.A. is used to locate upfc.A genetic algorithm determines the best placement of phase shifters in the network to reduce power flows, increase network load ability, and reduce production costs.

Evolution strategies (E.P.)
Evolutionary techniques suggest locating FACTS controllers in power systems in the best possible locations.Optimal allocation of FACTS devices using the evolutionary algorithm in reference enhances overall transfer capability.Some authors have proposed a hybrid-meta heuristic technique based on evolutionary computing and sequential quadratic programming for the best placement of FACTS devices like U.P.F.C. in the power system.The ideal location and FACTS device settings are determined while considering the power loss in transmission lines and voltage deviation buses.A multiobjective evolutionary method is applied.

Tabu search algorithm
The tabu-search algorithm is used to select the appropriate location for FACTS controllers in power systems.The ideal location of FACTS devices in the transmission network can be optimized with the help of a proposed hybrid-meta heuristic technique based on tabu search and nonlinear programming methods.

Simulated-annealing algorithm
Power loss minimization can be adopted with the help of simulated annealing and particle swarm optimization techniques.The location of FACTS devices can be dealt with with the help of tabu search and simulated annealing techniques are used.Suggests a hybrid-meta heuristic approach based on S.A. and PSO for loss minimization

Particle swarm-optimization (PSO) algorithms
The control parameters of FACTS devices can be investigated with the help of a particle swarm -optimization (PSO).The installation cost of T.C.S.C. and U.P.F.C. to find powersystem loadability can be calculated with the help of PSO techniques and the plan is to allocate FACTS based on anticipated security costs using a hybrid PSO.The best position for FACTS devices was determined using the PSO technique, considering installation costs and power system security.
Particle swarm optimization uses U.P.F.C. to find the line outage in the power system network suggesting optimal locations of multiple S.T.A.T.C.O.M. for improving voltage stability and loadability.

Fuzzy logic (F.L.) algorithms
Due to the increasing load on the existing power transmission lines, voltage stability and voltage collapse have become crucial challenges in the design and operation of power systems.Literature addresses these issues.Researchers have discussed a fuzzy logic-based strategy for the best positioning and scaling of FACTS controllers in power systems.➢ The main objective function of UPFC as shown in the above figure with references offers system stability, improved profile, relief from congestion problems and better safety of the electrical network ➢ The objective function of IPFC with references as shown in the above figure, it minimizes the cost of energy generation and reduces the power losses that occur in electrical networks by adjusting the parameters via compensation techniques.In addition to these, it can also enhance the voltage profile of the power system.➢ The objective function of SVC which consists of references as shown in the above figure can effectively monitor reactive power and is commonly employed for maintaining the voltage within prescribed limits and also for reducing frequency distortions.SVC can absorb as well as generate reactive power in its two different modes of operation.It can be used as a source of ideal reactive power when connected to the bus, and as variable admittance if connected to transmission lines.SVCs are also deployed to smooth flicker voltage in industries.They are widely used to ameliorate power losses, as well as to maintain reactive power, voltage levels and frequencies of the electrical networks at their desired levels.➢ The objective function of TCSC as shown in the above figure with references is based on series compensation techniques.TCSC can support inductive as well as capacitive compensation of the transmission lines.The power system becomes less prone to frequency disturbances and loadability enhancement is also facilitated by the use of TCSC.➢ The objective function of STATCOM references as shown in the above figure supply as well as consume the reactive power, to and from the electric circuit.It can successfully regulate the power factor and voltage of the power system.Additionally, it can be deployed to mitigate fluctuations in the system frequency, compensate for the reactive power when it changes rapidly, and also to maintain the voltage within prescribed safe limits.

Conclusions
This research provides a bibliographical survey of published work on the proper positioning and sizing of FACTS devices in power systems.To investigate the subject, researchers used a variety of heuristic optimization techniques.As essential guidelines for adequately positioning and sizing FACTS devices, the publication includes a thorough literature analysis and a list of published sources.System studies are very important for the implementation of FACTS controllers to determine the requirements for the relevant installation.Experienced network planning engineers have to evaluate the system including future developments.Right controllers of the right size at the right place have the right cost.The reliable operation of FACTS controllers requires regular maintenance in addition to using equipment of the highest quality standards.Maintenance requirements are minimal but important.According to the literature research, various FACTS devices, as seen in Fig. 2, may regulate a variety of power system characteristics.Additionally, numerous optimization methods are explored, and Table 3 provides an overview of their results.The types of FACTS controllers and their applications are discussed in this review study and are shown in Table 5. Twelve distinct types of controllers are investigated to assess the FACTS best position and use in the power system, and a total of 99 research publications are analyzed.Six of the total number of research publications are reviews, 14 are reviewed to describe the various types of FACTS controllers, and 16 are reviewed to control and optimize FACTS controllers.Thirty-six research articles are examined using the meta-heuristic and analytical methodology to determine the best locations for FACTS devices.The most suitable FACTS controller is to manage reactive and actual power with bus voltage using U.P.

Future outlook
The IEEE, the World Bank, and other organizations have published several papers indicating that there would be an increase in both the need for and production of energy in the future.Electric vehicles (E.V.) are anticipated to eventually replace traditional diesel and gasoline-powered automobiles.Numerous studies are being conducted to improve the interface between E.V. batteries and the power grid to facilitate quick battery charging and use batteries as energy sources during times of high demand.The future is predicted to see a growth in this tendency.Rooftop solar panel utilization is a different concept already gaining popularity; a sharp increase in its use is anticipated.Renewable energy generation is expected to increase significantly in the upcoming decades, and several forecasts have been produced to reduce global warming through zero carbon emissions.In this way, a paradigm change in the linkage of dispersed energy resources and renewable energy usage is foreshadowed.Because of their enhanced efficacy, versatility, and ability to act quickly in various situations, non-dominated sorting multiobjective optimization approaches and hybrid techniques are predicted to become increasingly prevalent in the future of optimization techniques.Regarding cutting-edge FACTS devices, due to their adaptability in automatically and selectively managing many power system characteristics, utilization of more general FACTS devices like U.P.F.C. and other variations is anticipated to increase in the future decades.
FACTS devices are necessary in the underground part of the coal mine power supply system for the reactive power compensation consumed by mining equipment.In China, research is actively being conducted on the development of an explosion-proof FACTS device in particular, it is necessary to note the patent for the construction of explosionproof STATCOM [Explosion-proof Statcom Reactive Compensation Device, URL: http:// www.lens.org], which can be placed in the underground part of a coal mine.Two generations of FACTS devices are considered, as a result, it was found that in coal mines it is advisable to use FACTS devices of the APF, PF, SVC and STATCOM types.FACTS devices of the D-FACTS and CPD types are very promising for use in coal mine conditions.The product line of the company FGI Science and Technology Co. (China) was analyzed.It was established that the volume of space occupied by STATCOM is in the range of 10 to 20 m 3 with rated unit power of 1 to 12 MVAr.Future developments will include the combination of existing devices, e.g.combining a STATCOM with a TSC (Thyristor Switched Capacitor) to extend the operational range.In addition, more sophisticated control systems will improve the operation of FACTS Controller.Improvements in semiconductor technology (e.g. higher current carrying capability, higher blocking voltages) could reduce the costs of FACTS Controllers and extend their operation ranges.Finally, developments in superconductor technology open the door to new Controllers like SCCL (Super Conducting Current Limiter) and SMES (Super Conducting Magnetic Energy Storage).There is a vision for a high voltage transmission system around the world to generate electrical energy economically and environmentally friendly and provide electrical energy where it's needed.FACTS are the key to make this vision live.

Fig. 1
Fig. 1 Objective functions of FACTS devices

Fig. 2
Fig. 2 Types of FACTS Controllers

Fig. 3
Fig. 3 Assessment of FACTS devices and their works Fig. 4 FACTS controllers applications in power systems

Fig. 5
Fig. 5 Diagram for conventional devices and FACTS devices

Fig. 6 Fig. 7
Fig. 6 Block diagram for power system without FACTS devices

Fig.Fig. 20 FACTS
Fig. Classification of optimal sizing and locations

Fig. 22 FACTS
Fig. 22 FACTS devices using in with optimization techniques F.C. and I.P.F.C.However, S.V.C. and S.T.A.T.C.O.M. are the most used tools for reactive power correction.The best controller for changing the transmission line's impedance is the T.C.S.C., while the S.S.S.C. controller offers active power regulation.Most researchers have employed modern metaheuristic optimization techniques to determine the best location and size for FACTS controllers.The optimal use of FACTS Controllers depends upon well-trained operators.Since most utility operators are unfamiliar with FACTS Controllers compared with for example switched reactors or capacitors), training on the operation of FACTS Controllers is therefore very important, which helps to learn what is important for the operators to know is are the appropriate settings of FACTS Controllers, especially the speed of response to changing phase angle and voltage conditions as well as operating modes.

Table 2
Compensation technique for finding objective functions

Table 3
FACTS devices controller's contribution to transmission lines T.C.S.C. 1. Controlling reactive power and true power in transmission line 2. Harmonics levels reducing U.P.F.C. 1. Voltage controls 2. Compensation for reactive power S.T.A.T.C.O.M. 1. Power flow control in sub-networks 2. Voltage profile maintenance I.P.F.C. 1. Power quality improvement 2. Voltage regulation S.V.C. 1. Power system stability enhancement 2. Damping power oscillations S.S.S.C.

Table 4
Comparison between different FACTS devices The specific constructional elements of U.P.F.C. are covered in how S.S.S.C. and S.T.A.T.C.O.M. were combined to create U.P.F.C.The author talked about U.P.F.C. and how it may improve power quality by managing both active and reactive power and the use of U.P.F.C. to regulate power flow in transmission lines by adjusting the impedance of the lines, the magnitude of the voltage, and the phase angle with wind energy generation.These two components are connected by a D.C. connection to provide a two-way power flow for the line's reactive and actual power adjustment.One G.U.P.F.C. device, two in series, and one in parallel with the line regulates the intelligent power system characteristics of the line, such as power flows, bus voltage, actual power, and reactive power.

Table 5
Survey on FACTS devices with optimization techniques