UPFC-unified power flow controller: theory, modeling, and applications

To improve the efficiency of existing transmission lines, Smart Power Flow controlled (SPFC) is presented based on Flexible AC transmission (FACTS). By Injecting controllable voltage in series to transmission lines, reactive and active power can be controlled. SPFC helps the transmission lines to obtain their maximum power capacity by avoiding the redundant reactive power which overloads the transmission line. This paper investigates three different modes of SPFC using a 48-pulse controller i.e., static synchronous series compensator (SSSC), unified power flow controller (UPFC), and static synchronous compensator (STATCOM). STATCOM, SSSC, and UPFC are designed to stabilize voltage and provide compensation to reactive power of the power grid system, by using a 48-pulse converter. Using 48-pulse STATCOM reduces harmonics and gives the maximum power at 90 degrees of injected voltage in SSSC. The overall SPFC has been investigated and simulated in MATLAB/SIMULINK environment.

Improvement of synchronizing power and damping power by means of SSSC and STATCOM: A comparative study

Today, there is a large increase in the demand for electricity. The transmission and distribution networks, however, cannot fulfill unbound demands due to the scarcity of resources. Power lines have losses which make the situation more unfavorable for maximum power transfer. Implementing a flexible AC transmission system (FACTS) is one of the best ways to reduce line losses. This paper proposes a FACTS-based method for minimizing the fault current in the system. Switchgear and protection equipment also perform better when this is done. Moreover, due to the reduced fault current of the switched system, a larger amount of power can be transmitted. Static synchronous series compensator (SSSC), static synchronous compensator (STATCOM), and unified power flow controller (UPFC) are evaluated in this case. With STATCOM and UPFC, fault currents are significantly reduced. Furthermore, STATCOM and UPFC can also reduce the fault currents in the power system in addition to voltage regulation and power flow control. A MATLAB/Simulink model is used to evaluate the model’s feasibility.

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.

This paper addresses two issues: enhancement of fault recovery and controller design accounting for filter dynamics. Performance of the unified power flow controller (UPFC) is improved by a proposed modification of the UPFC into a double static synchronous series compensator (SSSC) in order to double its capability in fault recovery mode. A battery is required as an energy source in the DC link of the double SSSC during the recovery. The battery will be charged during normal operation of the UPFC. The size of the battery for the SSSC has been investigated. It was found that the double SSSC in fault recovery mode has almost twice the performance of the UPFC and the size of battery for the UPFC is reasonable for grid scale use. One of the important parts of the UPFC is the filter at the output of the inverter. The function of the UPFC filter is to attenuate the harmonics generated by the inverter. In this paper, a harmonic trap filter, together with a low-pass filter, are applied to the UPFC and investigated. Single-phase models are used to design cut-off frequencies whilst the d-q model is included in the UPFC controller design. It was found that if the filter dynamics are neglected in the control design, as is often seen in simulation studies, then the controller's response will be different. The test system used in this work is a one-machine, infinite bus bar system. All of the simulations were implemented using the Electromagnetic Transients Program (EMTP) which is a powerful simulation tool for power system simulation. In additional, the Matlab and Simulink programming environment were used to provide transfer function simulation for the controller design. The simulation results from both programs are compared.

This paper addresses two issues in operation of a unified power flow controller (UPFC), enhancement of fault recovery and controller design accounting for filter dynamics. Performance of a UPFC is improved by a temporary modification of the UPFC into double static synchronous series compensator (SSSC) in order to double its capability in fault recovery mode. A battery is required as an energy source in the DC link of the double SSSC. The size of the battery for the SSSC has been be investigated. It was found that the double SSSC in fault recovery mode has almost twice the performance of the UPFC and the size of battery for the UPFC is reasonable for grid scale use. With the double SSSC in fault recovery mode, a combination control mode is suggested for the UPFC. One of the important parts of the UPFC is the filter at the output of the inverter. The function of the UPFC filter is to attenuate the harmonics generated by the inverter. In this paper a harmonic trap filter together with a low-pass filter are applied to the UPFC and investigated. Single-phase models are used to design cut-off frequencies whilst the d-q model is included in the UPFC controller design. It was found that if the filter dynamics are neglected in the control design, then the controllers response will be different. The test system used is a one-machine, two transmissions lines and an infinite busbar. All of the simulations were implemented using the EMTP. Additionally Matlab and Simulink programming environment were used to provide transfer function simulation for the controller design. The simulation results from both programs are compared.

7 - Modern flexible AC transmission system (FACTS) devices

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 static synchronous series compensator (SSSC) has the ability to emulate a reactance in series with the connected transmission line. A static synchronous compensator (STATCOM) is able to provide the reactive power to an electricity network. When fed with some supplementary signals from the connected power system, both SSSC and STATCOM are able to participate in the power system inter-area oscillation damping by changing the compensated reactance or the provided reactive power. This paper analyses the influence of SSSC and STATCOM on power system small signal stability. The damping controller schemes for SSSC and STATCOM are presented and discussed. The IEEE 39-bus New England system model as the test system is built in DIgSIELNT PowerFactory, in which the damping control strategies for both SSSC and STATCOM are validated by time domain simulations and modal analysis. Furthermore, comparison studies show that the SSSC is a better solution in term of equipment capabilities and costs.

The Flexible alternating current transmission systems (FACTS) is considered one of the most developed technologies applied for enhancing the performance of system due to their ability of adjusting different parameters in the transmission systems such as the buses voltage, the transmission line impedance, the active and reactive powers flow in transmission lines. The static synchronous series compensator (SSSC) is an effective member of the FACTS which is connected in series with the transmission lines and it consists of a solid-state voltage source inverter coupled with a transformer which aims to control and secure the operation of the power system. The main function of SSSC is inserting a controllable voltage in series with the transmission line to control the active and reactive powers flow in transmission lines. Solving the optimal reactive power dispatch (ORPD) problem is nonlinear, non-convex and it becomes a complex problem with integration of the SSSC. The contributions of article include, 1) an efficient and reliable optimization algorithm is developed to solve the ORPD problem and identify the optimal location and ratings of the SSSC, 2) The proposed algorithm is based on modifying the salp swarm algorithm (SSSA) using Levy Flight Distribution and spiral movement of particles to enhance the searching capabilities of the SSA, 3) an efficient model of SSSC based on power injection approach is used for representation the SSSC in ORPD. The ORPD is solved with and without the SSSC controller to minimize power losses and voltage deviations as well as improve the voltage stability. The proposed algorithm for ORPD is tested on the standards IEEE 30-bus and 57-bus systems. The simulation results demonstrate that MSSA is more effective and superior for solving the ORPD compared with some other reported meta-heuristic techniques. Moreover, the system performance is enhanced considerably with optimal inclusion the SSSC.

Flexible AC Transmission System devices are reactive power compensation devices employed to suppress the sub synchronous resonance (SSR) in the systems. The main important issue in the transmission lines of power system is SSR and it occurs during the condition, when series compensator is employed to improve the reactive power. It occurs at sub synchronous frequencies due to Electrical instability occurs as the result of shaft failures. Different FACTS devices such as the Static Synchronous Reactor (SSR), Static Synchronous Series Compensator (SSSC), Static Synchronous Compensator, Thyristor Controlled Series Compensator (TCSC), and Unified Power Flow Controller (UPFC) are analysed and reviewed in terms of SSR mitigation to develop a new strategy to mitigate SSR in the system. The new Multilevel inverter-based control strategy will be designed and developed based on the review and analysis using MATLAB Simulink to mitigate the SSR.

The necessity to deliver cost effective energy in the power market has become a major concern in this emerging technology era. Therefore, establishing a desired power condition at the given points are best achieved using power controllers such as the well known High Voltage Direct Current (HVDC) and Flexible Alternating Current Transmission System (FACTS) devices. High Voltage Direct Current (HVDC) is used to transmit large amounts of power over long distances. The factors to be considered are Cost, Technical Performance and Reliability. A Flexible Alternating Current Transmission System (FACTS) is a system composed of static equipment used for the AC transmission of electrical energy. It is meant to enhance controllability and increase power transfer capability of the network. It is generally a power electronics-based system. A Unified Power Flow Controller (or UPFC) is a FACTS device for providing fast-acting reactive power compensation on high-voltage electricity transmission networks. The UPFC is a versatile controller which can be used to control active and reactive power flows in a transmission line. The focus of this paper is to identify the improved Power Transmission Capability through control scheme and comprehensive analysis for a Unified Power Flow Controller (UPFC) on the basis of theory, computer simulation. The conventional control scheme cannot attenuate the power fluctuation, and so the time constant of damping is independent of active- and reactive-power feedback gains integrated in its control circuit. The model was analyzed for different types of faults at different locations, keeping the location of UPFC fixed at the receiving end of the line, With the addition of UPFC, the magnitude of fault current and oscillations of excitation voltage reduces. Series and Shunt parts of UPFC provide series and shunt injected voltage at certain different angles.

This paper presents a new methodology of incorporating power flow controllers, specifically flexible AC transmission systems (FACTS), into distributed DC optimal power flow (DCOPF). The distributed DCOPF problems are then solved by the alternating direction method of multipliers (ADMM). Efficient modeling of the power flow control capabilities of prominent FACTS devices, such as the unified power flow controller (UPFC) and the static synchronous series compensator (SSSC), enables the seamless integration of FACTS into the ADMM-based distributed DCOPF, thus allowing FACTS operation to be co-optimized with generator dispatch under a distributed control paradigm for the power system. The proposed ADMM-based distributed DCOPF problem with FACTS devices are studied through simulations on a 6-bus system and a modified IEEE 118-bus system to verify its convergence to the optimal generator dispatch.

The utilization of renewable energy sources for energy transition is gaining significant popularity due to pollution control and other environmental benefits. To move toward green energy generation, the integration of renewable energy sources with the existing conventional grid plays a key role. The performance of a modern interconnected power system, particularly with a high penetration of renewable energy sources, is significantly impacted by power system oscillations. Flexible Alternating Current Transmission System (FACTS) devices are recommended to improve control framework performance, and the power system stabilizer is the customary controller for damping such oscillations. FACTS offer a powerful strategy as they can control transport voltage, transmission line impedance, and power flows. This paper presents an efficient control scheme that combines four FACTS controllers: the static VAR compensator for controlling reactive power in control frameworks, the unified power flow controller for managing active and reactive power flows on transmission lines, the static synchronous compensator for maintaining system voltage stability, and the static synchronous series compensator for controlling transmission line impedance. To address the challenges posed by the variability of renewable energy sources such as wind and solar, the ant colony optimization algorithm is employed to optimally tune the controllers’ parameters. By generating controlled voltage and interfacing with the transmission line, these controllers enhance system stability, even under fluctuating renewable energy inputs. The IEEE 30-Bus system was used for simulation and control design, demonstrating the effectiveness of this approach in damping inter-area oscillations and improving the stability and resilience of a renewable-energy-integrated power system.

Most of the pollution issues created in power system is due to the power quality problems like faults, harmonics etc. In this paper a grid connected fixed speed wind turbine induction generator subjected to asymmetric fault gets attenuated by unified power flow controller (UPFC) as it compensates the positive and negative sequence voltages thereby reducing the torque oscillations and improving the life time of the drain. It is the combination of static compensator (STATCOM) and static synchronous series compensator (SSSC). The control theory is based on vector control- dq(direct quadrature axis) reference frame fed PI, hysteresis control and fuzzy logic control using DSOGI-PLL(Dual second order generalized integrator- Phase locked loop). The proposed system is implemented using MATLAB / SIMULINK platform with and without Unified power flow controller. The effect of UPFC for fixed speed windturbine under faults is analysed using the above three controllers and its performance is evaluated.