Series Flexible AC Transmission System Research Articles

Modeling of active and reactive power steady state load in optimal reactive power planning

With the flow of time, the load patterns in electricity markets are changing rapidly in world-wide. The power engineers are becoming more vigilant to provide an uninterrupted power supply at any loading conditions. This article proposes a unique planning strategy of reactive power (VAr) considering static load model in power transmission systems. The active and/ or reactive power oriented exponential load model for static load is considered during the study of load flow solution. The power losses from load flow solution is measured and minimized through the proper placement of compensation devices. Series and shunt type FACTS (flexible ac transmission system) devices are used in order to compensate the flow of reactive power. Also, the separate and collective effects of active and reactive power exponents on load flow study are included during total operating cost (TOC) calculation of the system. The TOC is formulated empirically by adding different cost components such as cost owing to real power loss, VAr generation cost component, compensation device cost components and line charging cost. To validate the impetus of the proposed model, IEEE 14, IEEE 39 and IEEE 118 bus transmission systems are considered in this research work.

Linear modelling of series FACTS devices in power system operation models

This paper presents injection-shift-factor-based linear modelling for various types of series flexible ac transmission system (FACTS) devices within the DC power flow framework. The presented models allow FACTS devices to be properly integrated in current operation and planning software tools, which is key to harnessing the power flow capabilities provided by FACTS technology. Although recent literature has attempted to develop linear models for FACTS devices, the existing models do not accurately reflect the actual operating range for many FACTS devices. Compared to the existing models, the modelling approach presented here reflects the principle of operation of each type of series FACTS device in adjusting transmission line reactance. Through mathematical derivation, linear constraints for FACTS operation are formulated, which are used to formulate power system operation models. The formulated problems are then analysed through simulation studies on various test systems. The results highlight the significant computational efficiency improvements provided by linear FACTS modelling in DC-based operation models.

A Hybrid SATS Algorithm Based Optimal Power Flow for Security Enhancement Using SSSC

Security and performance of the power system is the prime concern in its planning and operation. It is essential to devise proper measures for maintenance and improvement of security in the power system. Static synchronous series compensator (SSSC) is a type of series flexible AC transmission system device. The present research proposes a hybrid simulated annealing and Tabu search (Hybrid SATS) algorithm with SSSC to solve security constrained optimal power flow problems. The primary objective of the research work is to enhance the security of the power system and minimise the generator fuel cost. Contingency ranking is used to select line outages. The line flow limit violations in various single line outages are relieved effectively by Hybrid SATS with SSSC method, which keeps power flows within their security limits. Simulation studies are carried out on standard IEEE 30 bus to identify effectiveness of the proposed hybrid method and the obtained outcomes are put in comparison to SA with SSSC and TS with SSSC methods.

Wavelet transform-based protection of transmission line incorporating SSSC with energy storage device

Series compensation is generally used with long transmission lines to increase power transfer through the line and to enhance system stability. In the case of voltage source converter-based series flexible AC transmission system (FACTS) controller, an energy storage device can be incorporated at the DC bus which further improves control of real and reactive power flow. However, four-quadrant operation of FACTS controllers with energy storage device poses new challenges for the operation, control and protection of power system. Most commonly used protection scheme for long transmission lines, the distance relay, may not be reliable in case of lines compensated with series FACTS controllers. This paper proposes a new wavelet transform-based relay logic for fast and reliable detection, and classification of faults in a hybrid series-compensated long transmission line incorporating a passive series capacitor and static synchronous series compensator with energy storage device (SSSC-ES). The proposed relay logic is also able to accurately estimate the location of fault, and a wavelet transform-based boundary condition is used to discriminate between internal and external faults. It is shown through various simulation case studies that the four-quadrant operation of SSSC and fault resistance have negligible impact on the performance of the wavelet transform-based relay.

On design of a robust decentralized controller for an interconnected multi-area power system with FACTS devices

In this article, a robust active disturbance rejection control (ADRC) is proposed for load frequency control (LFC) of an interconnected multi-area power system. Two widely employed test systems, namely, two-areas and four-areas hydro-thermal power utilities are concerned to validate the efficacy of the suggested method. To enhance the performance of the system, series flexible ac transmission system (FACTS) like thyristor controlled series compensator (TCSC) and thyristor controlled phase shifter (TCPS) are considered. The simulation results indicated that the system performance is improved with the inclusion of FACTS devices. The adjustable parameters of the proposed FACTS controllers are optimized using particle swarm optimization (PSO) algorithm employing an Integral of Time multiplied Absolute Error (ITAE) criterion. The investigations showed that the proposed controller provides better dynamic performance than others from the point of view of settling time, peak over/undershoot. Finally, the sensitivity analysis of the system is inspected by varying the system parameters and operating load conditions from their pre-specified values. It is observed that the suggested controller based optimization algorithm is robust and performs satisfactorily with the variations in operating load conditions, system parameters and load patterns.

Optimization of Series Compensation in Transmission Networks Using Artificial Neural Networks

To respond to the ever-increasing power demand of load centers, power is transmitted at extrahigh voltages. However, an increase in power transfer level should be supported by an enhanced level of security. Flexible AC Transmission System (FACTS) devices present an economical and efficient alternative to consider for achieving higher power transfer level with enhanced security instead of introducing new transmission facilities, to maintain a large stability margin of power in transmission line. This project aims to optimize the level of series compensation in transmission networks using Artificial Neural Network (ANN). Series compensation enables higher level of power to be transferred by reducing (reactive) losses. Among the series FACTS controllers, Thyristor Controlled Series Compensator (TCSC) has been chosen to be optimized on an SMIB system. Lead-Lag (LL) based TCSC remain the controller of choice due to the favorable performance to cost ratio. Nevertheless, modeling the highly non-linear power system with a linear controller, limits the system’s performance during adversities. ANN being non-linear per se and possessing high generalization capabilities, offers more versatility in modeling the power system. Indeed, an ANN based TCSC was designed and the performance during contingencies was compared to that of the LL based TCSC. As expected, the ANN based TCSC demonstrated a damping capability twice as fast and offering the SMIB system with a higher robustness as well as better resistance to fault condition. To increase the accuracy and reliability of the proposed controller, the investigation can be performed on a multi-machine system with different loading conditions as well as determining the optimal location of the TCSC module.

OPTIMAL POWER FLOW WITH TCSC DEVICE USING CUCKOO OPTIMIZATION ALGORITHM

Optimal Power Flow (OPF) problem is an optimization tool through which secure and economic operating conditions of power system is obtained. In recent years, Flexible AC Transmission System (FACTS) devices, have led to the development of controllers that provide controllability and flexibility for power transmission. Series FACTS devices such as Thyristor controlled series compensators (TCSC), with its ability to directly control the power flow can be very effective to power system security. Thus, integration TCSC in the OPF is one of important current problems and is a suitable method for better utilization of the existing system. This paper is applied Cuckoo Optimization Algorithm (COA) for the solution of the OPF problem of power system equipped with TCSC. The proposed approach has been examined and tested on the IEEE 30-bus system. The results presented in this paper demonstrate the potential of COA algorithm and show its effectiveness for solving the OPF problem with TCSC devices over the other evolutionary optimization techniques.

Transfer Capability Improvement Through Market-Based Operation of Series FACTS Devices

Traditionally, electric system operators have dispatched generation to minimize total production costs, ignoring the flexibility of the transmission system. Implementation of smart-grid systems could allow operators to co-optimize flexible transmission alongside generation dispatch; the technologies that would enable such co-optimization are still regulated as part of the monopoly transmission system. One particular flexible transmission asset is variable impedance flexible AC transmission system (FACTS). This paper 1) points out the positive externality problem existing in a recent market design proposal with active transmission participation, and 2) proposes a sensitivity-based method to estimate the marginal market value of FACTS adjustments to overcome this positive externality problem. The marginal value would suggest efficient impedance adjustments to the operator and provide the right financial incentives for the FACTS owners to operate their assets in a socially optimal way. Revenue adequacy is demonstrated under specific conditions and more broadly investigated through simulation studies. An analytical example on a two-bus system as well as a numerical study on the IEEE 118-bus system are presented. The results suggest that inclusion of a price signal for FACTS devices would lead to significant social welfare improvements in competitive power markets.

Neoteric HANFISC–SSSC based on MOPSO technique aimed at oscillation suppression of interconnected multi‐source power systems

Alleviating dynamic oscillations of the tie-line power exchange and area frequencies in affected interconnected power systems caused by loading condition changes is the prominent responsibility of automatic generation control (AGC). To compensate such the load-changes and also suppress these oscillations, the application of the flexible AC transmission systems (FACTS) can be assigned as one of the practical and effective approaches. In this study, the static synchronous series compensator (SSSC) which is one the series FACTS families is engaged to enhance the overall dynamic performance of multi-area multi-source interconnected power system. Likewise, accomplished endeavours in this regard are led to exude the hierarchical adaptive neuro fuzzy inference system controller–SSSC (HANFISC–SSSC) to suppress both prominent issues in multi-area interconnected power systems i.e.: the low frequency oscillations and the tie-line power exchange deviations. Hereof also, implementation of multi-objective optimisation technique is not avoidable. Due to high efficiency of multi objective particle swarm optimisation (MOPSO) to unravel the non-linear objectives, it has been used to solve the optimisation problem. To verify the high performance of suggested HANFISC–SSSC, two different multi-area interconnected power systems i.e.: two-area hydro–thermal–diesel and three-area hydro–thermal power systems have been considered for this study. In the interim, the capability of HANFISC–SSSC has been perfectly and precisely evaluated and compared with conventional SSSC by incidence of the step load perturbation in all areas of both the test power systems. To sum up, the simulations results obtained from both the power systems have transparently corroborated high performance of HANFISC–SSSC compared with conventional SSSC.

ATC enhancement by incorporating FACTS devices for deregulating scenario in present power market

The cost based monopolistic power market rules are new fangled by the word deregulation. Trepidations in its conceptualisation and integrated operation in the impending scenario are transmission pricing, congestion management and Available Transfer Capability (ATC). Of this intriguing technical challenge, ATC is the one that needs to be interrogated and dogged to make open access a feasible obsession for private entity participation which is deregulation’s intention. This research work aims at calculating ATC using non iterative, simple, Power Transfer Distribution Factors (PTDF) based methodology, enhancing them using Flexible AC Transmission system (FACTS) devices like Static compensator (STATCOM) and Unified Power Flow Controller (UPFC). A proven alternative to overcome extravagance by erecting new transmission facility is incorporation of FACTS devices in the existing structure that indulge in reactive power compensation. These FACTS devices are modelled using the power flow equations and is placed optimally based on the slope of sensitivity factors. The optimal settings of FACTS devices is obtained by a soft computing technique labelled as Particle Swarm Optimisation (PSO) to enhance the ATC for the assumed bilateral and multilateral power contracts. The voltage and angle of shunt and series FACTS devices are randomly generated as the population of PSO on sample 6 bus and standard IEEE 30 bus systems.

SSR Damping in Fixed-Speed Wind Farms Using Series FACTS Controllers

Subsynchronous resonance (SSR) damping in fixed-speed wind turbine generator systems (FSWTGS) by using two series flexible ac transmission system (FACTS) devices, the thyristor-controlled series capacitor (TCSC), and gate-controlled series capacitor (GCSC) are studied in this paper. The former is a commercially available series FACTS device, and the latter is the second generation of series FACTS devices using gate turnoff (GTO) or other gate-commuted switches. The GCSC is characterized by a fixed capacitor in parallel with a pair of antiparallel gate-commuted switches enabling rapid control of series impedance of a transmission line. It is shown that the SSR damping with a GCSC is limited to changing the resonance frequency, in comparison with a fixed capacitor, which may not be adequate to damp out the SSR. Therefore, a supplementary SSR damping controller (SSRDC) is designed for the GCSC. Moreover, it is proven that the GCSC equipped with a well-designed SSRDC can effectively damp the SSR in FSWTGS. In order to verify the effectiveness of the GCSC in SSR damping, its performance is compared with the TCSC, which is an existing series FACTS device. In addition, time-frequency analysis (TFA) is employed in order to evaluate and compare the SSR time-varying frequency characteristics of the GCSC and TCSC. The IEEE first benchmark model on SSR is adapted with an integrated FSWTGS to perform studies, and extensive simulations are carried out using PSCAD/EMTDC to validate the result.

Power flow controlling using SSSC based on matrix converter via SA-PSO algorithm

Abstract: The static synchronous series compensator (SSSC) is one of the series flexible AC transmission system (FACTS) devices that can be used in power flow control and reactive compensation in transmission lines. In this paper, a new configuration of SSSC based on a matrix converter is presented. The proposed SSSC has some advantages such as elimination of the DC link, bidirectional power flow control capability, fast dynamic response, and simple control system. By presenting a switching algorithm for the AC-AC matrix converter, an almost sinusoidal series compensation voltage is injected to the transmission line with low total harmonic distortion. In this paper, a modified particle swarm optimization (PSO) algorithm is used to obtain the optimal parameters of a power flow controller. The modified PSO algorithm is simulated annealing-PSO. Application of the proposed SSSC in different operating points is simulated by MATLAB/Simulink software. Simulation results verify that the designed control system enables the proposed SSSC topology with independent control of active and reactive power flow in transmission lines. Presented simulation results confirm the validity and effectiveness of the suggested SSSC in power flow controlling system.

Performance comparison of TCSC with TCPS and SSSC controllers in AGC of realistic interconnected multi-source power system

Abstract The primary goals of employing series flexible ac transmission system (FACTS) in automatic generation control (AGC) studies of interconnected power systems are mitigating area frequency and tie-line power oscillations. This paper compares dynamic performance of thyristor controlled series capacitor (TCSC) as damping controller with thyristor controlled phase shifter (TCPS) and static synchronous series compensator (SSSC) which are series FACTS damping controllers. Commonly used lead-lag controllers are used in structure of damping controllers. The effect of TCSC in tie-line power exchange is modeled mathematically based on the Taylor series expansion for small-signal load disturbance. The performance of the proposed TCSC controller in coordination with integral AGC is compared with cases of TCPS–AGC and SSSC–AGC. An improved particle swarm optimization (IPSO) algorithm and integral of time multiplied squared error (ITSE) performance index are used to design the damping controllers. A two-area power system having generations from reheat thermal, hydro, and gas units in each area is evaluated regarding nonlinearity effects of generation rate constraint (GRC) and governor dead band (GDB). The simulations results in MATLAB/SIMULINK environment show that the proposed TCSC–AGC yields superior performance than others in damping of area frequencies and tie-line oscillations. Furthermore, sensitivity analyses are performed to show greater robustness of TCSC–AGC.

Coordinated design of PSS and TCSC to mitigate interarea oscillations

Abstract Thyristor controlled series compensator (TCSC) as a promising series flexible AC transmission system (FACTS) device is generally used for controlling the real power flow in transmission lines. It can increase the system stability as the complementary functionality by minimizing the power oscillations. The effectiveness of TCSC in its primary and supplementary applications depends on the selection of its optimal location and defining a proper input signal. In this paper, a new method based on the active power sensitivity approach is applied to find the optimal location of TCSC. In addition, Hankel singular values (HSVs) and right half plane-zeros (RHP-zeros) analyses have been proposed to find the most appropriate stabilizing input signal for the supplementary functionality of TCSC to damp out the interarea modes of oscillation. Finally, the optimal design of power oscillation damper (POD) and simultaneous coordinated design of power system stabilizer (PSS) and POD are implemented separately in a large-scale power system. The tuning problem of POD-TCSC parameters as well as the coordinated POD-TCSC & PSS are converted to a multi-objective optimization problem and solved using particle swarm optimization (PSO) algorithm. The performance of the proposed method has been validated through eigenvalue analysis and nonlinear time domain simulation in a 16-machine 68-bus test system. The simulation results show a satisfactory robust performance with an excellent capability in damping of local and interarea power oscillations.

Optimal Location of Thyristor-Controlled Series Compensation and Static VAR Compensator to Enhance Steady-state Performance of Power System with Wind Penetration

Wind generation connection to power system affects steady-state and transient stability. Furthermore, this effect increases with the increase of wind penetration in generation capacity. In this article, optimal location of flexible AC transmission system devices is carried out to solve the steady-state problems of wind penetration using a genetic algorithm. Case study is carried out on modified IEEE 39-bus system with wind penetration increases by 50%; the system suffers from outage of one generator with load decrease in one of system buses by 15%. The system suffers from minimum voltage reduction, total loss increase, and violation of power and power angle limits. Series and shunt flexible AC transmission system devices are used in this article. Results showed that series flexible AC transmission system devices in certain range are able to solve these problems associated with wind penetration in power systems with acceptable cost saving.

Fuzzy wavelet plus a quantum neural network as a design base for power system stability enhancement

In this study, we introduce an indirect adaptive fuzzy wavelet neural controller (IAFWNC) as a power system stabilizer to damp inter-area modes of oscillations in a multi-machine power system. Quantum computing is an efficient method for improving the computational efficiency of neural networks, so we developed an identifier based on a quantum neural network (QNN) to train the IAFWNC in the proposed scheme. All of the controller parameters are tuned online based on the Lyapunov stability theory to guarantee the closed-loop stability. A two-machine, two-area power system equipped with a static synchronous series compensator as a series flexible ac transmission system was used to demonstrate the effectiveness of the proposed controller. The simulation and experimental results demonstrated that the proposed IAFWNC scheme can achieve favorable control performance.

A Comparative Study of Ground Fault Analysis for a Practical Case of a Transmission Line Equipped with Different Series FACTS Devices

Due to the rising power demand and increasing population worldwide, electrical power networks have been extensively growing and striving to satisfy the escalating loads. This necessitates the need for using Flexible AC Transmission System (FACTS) devices which have become indispensable during normal and abnormal operating conditions. This paper investigates the impact of using series FACTS devices, namely Thyristor Controlled Series Capacitor (TCSC), GTO Controlled Series Capacitor (GCSC) and Thyristor Controlled Series Reactor (TCSR), on the impedance and power flow of a practical 400 kV transmission line in the Algerian power network. It also investigates the effect of varying the fault resistance on short-circuit calculations in the case of a phase to ground fault that occurs at the end of the compensated line. Analytical formulas of the employed FACTS devices, the system model under fault and short-circuit calculations are deduced and presented in the paper. Simulations results obtained using MATLAB are demonstrated for the compensated line and without compensation. These simulations are compared to show the effect of using these devices for the studied cases.It is concluded that GCSC provides better performance in the active and reactive power flow of the line under normal operating conditions and in reducing the fault current during abnormal operating conditions when the fault resistance increases. On the other hand, TCSR shows a better performance in maintaining higher voltages under fault with the increase of fault resistance.

Analysis of sub‐synchronous resonance in doubly‐fed induction generator‐based wind farms interfaced with gate – controlled series capacitor

This paper first presents a step-by-step tutorial on modal analysis of a doubly-fed induction generator (DFIG)-based series compensated wind farm. The model of the system includes a wind turbine aerodynamics, a sixth-order order induction generator, a second-order two-mass shaft system, a fourth-order order series compensated transmission line, an eighth-order rotor-side converter (RSC) and grid-side converter (GSC) controllers, and a first-order DC-link model. Then, using modal analysis and time-domain simulations, it is shown that a fixed-series compensated DFIG is highly unstable due to the sub-synchronous resonance (SSR) mode. In order to damp the SSR mode, the wind farm is interfaced with the gate-controlled series capacitor (GCSC) - which is a new series flexible AC transmission system (FACTS) device. A SSR damping controller (SSRDC) is designed for the GCSC using residue-based analysis and root locus diagrams, and an effective input control signal (ICS) to the SSRDC is identified in order to simultaneously increase damping of both the SSR and super-synchronous (SupSR) modes. The IEEE first benchmark model on SSR is adapted with an integrated DFIG-based wind farm to perform studies. Matlab/Simulink is used as a tool for designing process, and PSCAD/EMTDC is used for time-domain simulations.

The Application Research of HVDC & FACTS to Suppress the Power System Low-Frequency Oscillation

With the widely application use of UHV（ultra- high- voltage） transmission，increased the system low frequency oscillations，and flexible application of high-voltage direct current transmission (HVDC) and flexible ac transmission system (FACTS) can improve the system damping oscillation inhibition. This paper Based on the research results in recent years, classify& summarize HVDC and FACTS devices the theoretical basis and the main application places, and according to the way of access system of parallel, series and parallel hybrid FACTS devices stable controller design and optimization are summarized and classified.

Low voltage ride-through enhancement of fixed-speed wind farms using series FACTS controllers

This paper studies the application and control of three series flexible AC transmission system (FACTS) devices namely, the gate-controlled series capacitor (GCSC), the thyristor controlled series capacitor (TCSC), and series braking resistor (SBR), in order to enhance the low voltage ride-through (LVRT) in fixed-speed wind turbine generator systems (FSWTGS). Modeling and simulations are carried out in order to investigate and compare the performance of these devices, considering (1) successful reclosing of circuit breakers (CBs), (2) unsuccessful reclosing of CBs, and (3) connection of a dynamic load to the point of common coupling (PCC). Simulation results exhibit significantly enhanced transient stability of FSWTGS due to the employment of the GCSC. Furthermore, the GCSC is competitive with the TCSC and the SBR, and it requires less power rating to stabilize the wind generator system. Therefore, the proposed GCSC can be considered an effective tool to improve the LVRT of FSWTGS.