For Flexible AC Transmission Systems Research Articles

WAMS-based Hierarchical Active Power Differential Signal Algorithm for Backup Protection of a FACTS Compensated Transmission Network

This paper proposes a hierarchical active power differential signal-based generalized backup protection algorithm using Wide Area Measurement System (WAMS) data for Flexible AC Transmission System (FACTS)-compensated transmission networks. The proposed algorithm can be used for backup protection of transmission systems with any shunt and series-type FACTS devices. The increased number of FACT compensators affects the reliable operation of primary and backup protection of the transmission lines. Both shunt and series compensated lines cause malfunctioning of existing backup protection schemes. The proposed algorithm utilizes the sequence components of bus voltages and active power differential signals of lines to identify the faulty line. The algorithm is validated on a modified 9-bus system under MATLAB/SIMULINK platform. It is observed that the algorithm is suitable for identifying a faulty line in transmission systems containing both uncompensated and compensated lines with series or shunt-type FACTS controllers. This algorithm has the advantage that it uses a generalized backup protection logic and can be used for the accurate identification of a faulty line irrespective of the type of compensation devices.

Coordinated Design of Type-2 Fuzzy Lead–Lag-Structured SSSCs and PSSs for Power System Stability Improvement

This work suggests a type-2 fuzzy lead–lag (T2FLL) controller structure for flexible AC transmission system (FACTS)-based damping controllers and power system stabilizers (PSSs) for power system stability improvement. The values of the suggested controller are optimized by a hybrid adaptive differential evolution and pattern search algorithm (hADE-PS) method. Initially, a single-machine infinite-bus (SMIB) system with lead–lag (LL)-structured FACTS and PSS controllers is considered, and the dominance of the hADE-PS method is established over the original differential evolution (DE), genetic algorithm (GA), and particle swarm optimization (PSO). The supremacy of T2FLL over the lead–lag (LL) controller is established under different large and small disturbance conditions, as well as varied loading conditions and fault positions. Lastly, the effectiveness of T2FLL is evaluated in a multimachine power system (MMPS). It is demonstrated that the suggested T2FLL offers better performance than the LL controller under various large and small disturbance conditions by providing significantly more damping to all modes of oscillations.

Reactive Power Compensation and Power Factor Correction by using Static VAR Compensator (SVC)

In this paper, a reactive power compensation system using static VAR compensator is presented. To confine on system stability and reliability, the reactive power compensation is the fundamental way forflexible AC transmission systems (FACTS). The variations of reactive power have an effect on thegenerating units, lines, circuit breakers, transformers, relays, and isolators. It can also cause effective voltage sags and increase losses. In the proposed system, the lead time between voltage pulse and curren pulse is measured and fed to the interrupt pins of the microcontroller where the program takes over to bring the shunt capacitors to the circuit to get the reactive power compensated. Back-to-back SCRs interfaced through optical isolation from the microcontroller are used in parallel for controlling the capacitor.

Robust wide‐area damping controller design for inter‐area oscillations with signals' delay

A new wide‐area damping control strategy is investigated for flexible AC transmission systems (FACTS) device using wide‐area measurement system (WAMS) signals. The purpose is to design a dynamic output wide‐area damping controller (WADC) for improving the stability of interconnected power systems. The time‐varying delay of wide‐area signal is incorporated into the design process, which can effectively reduce the delay effect on the damping performance. First, a discrete‐time plant model with time‐varying delay is established for power systems; then by using the proposed improved free‐weighting matrices (IFWMs) approach and a convex optimization algorithm, a new and less conservative delay‐dependent stability criterion, expressed in the terms of linear matrix inequalities (LMIs), is obtained without ignoring any useful terms on the difference of a Lyapunov function. Detailed case studies on a 4‐machine two‐area benchmark test system and 16‐machine five‐area NETS‐NYPS interconnected system show that the designed WADC can not only maintain effective damping performance under the condition of time‐varying delay but also get the maximum wide‐area time delay. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Enhancement and Design Considerations Distributed FACTS for Mitigation of Power Quality problem

This paper introduces the concept of a distributed static series compensator (DSSC) for Flexible AC transmission systems (FACTS) devices can control power flow in the transmission system to improve asset utilization, relieve congestion, and limit loop flows. High costs and reliability concerns have restricted their use in these applications. The concept of distributed FACTS (D-FACTS) is introduced as a way to remove these barriers. A new device, the distributed static series compensator (DSSC), attaches directly to existing HV or EHV conductors and so does not require HV insulation. It can be manufactured at low cost from conventional industrial-grade components. The DSSC modules are distributed, a few per conductor mile, to achieve the desired power flow control functionality by effectively changing the line reactance. Experimental results from a prototype module are presented, along with examples of the benefits deriving from a system of DSSC devices. Index Terms: Distributed FACTS, Flexible AC Transmission Systems (FACTS), interconnected power systems, MATLAB Simulink and programming, Power flow control.

Wide-Area Damping Controller of FACTS Devices for Inter-Area Oscillations Considering Communication Time Delays

The usage of remote signals obtained from a wide-area measurement system (WAMS) introduces time delays to a wide-area damping controller (WADC), which would degrade system damping and even cause system instability. The time-delay margin is defined as the maximum time delay under which a closed-loop system can remain stable. In this paper, the delay margin is introduced as an additional performance index for the synthesis of classical WADCs for flexible ac transmission systems (FACTS) devices to damp inter-area oscillations. The proposed approach includes three parts: a geometric measure approach for selecting feedback remote signals, a residue method for designing phase-compensation parameters, and a Lyapunov stability criterion and linear matrix inequalities (LMI) for calculating the delay margin and determining the gain of the WADC based on a tradeoff between damping performance and delay margin. Three case studies are undertaken based on a four-machine two-area power system for demonstrating the design principle of the proposed approach, a New England ten-machine 39-bus power system and a 16-machine 68-bus power system for verifying the feasibility on larger and more complex power systems. The simulation results verify the effectiveness of the proposed approach on providing a balance between the delay margin and the damping performance.

FACTS Devices Allocation With Control Coordination Considering Congestion Relief and Voltage Stability

This paper presents an optimal allocation method for flexible ac transmission system (FACTS) devices for market-based power systems considering congestion relief and voltage stability. The purpose of the FACTS devices installation is to provide benefit for all entities accomplished by both minimizing annual device investment cost and maximizing annual benefit defined as difference between expected security cost (ESC) with and without FACTS devices installation. Different from previous approaches, the proposed method accurately evaluates the annual cost and benefits obtainable by FACTS devices installation by formulating a large-scale optimization problem that contains power flow analyses for a large number of system states representing annual power system operations. In addition, dynamic state transitions caused by specified contingencies are also simulated in the optimization problem to evaluate the effect of FACTS control actions as well as the other coordinated controls. The expected cost consists of operating cost under normal and contingency states along with their related probabilities to occur. Maximizing social welfare is the objective for normal state while minimizing compensations for generations re-scheduling and load shedding as well as maximizing social welfare are the objectives in case of contingency. Although installation cost of FACTS devices is required, they are useful as cost free means, which can reduce effectively the annual costs for generations re-scheduling and load shedding.

An Eigenstructure-Based Performance Index and Its Application to Control Design for Damping Inter-Area Oscillations in Power Systems

An eigenstructure-based performance index is proposed in this paper to measure the dynamic performance of the system as well as control efforts. Calculation of this index is based on eigenstructure of the closed loop system and the design parameters; it does not rely on control structures. Therefore, this index can be applied for solving structurally constrained control problems. A tuning scheme based on this index is proposed for coordinating power system stabilizers (PSSs) and supplementary damping controllers (SDCs) for flexible AC transmission systems (FACTS) devices to damp inter-area oscillations of systems and to optimize their control efforts under multiple operating conditions. Both PSSs and SDCs utilize control structures as a low order single-input-single-output phase lead-lag compensator. Wide-area signals are employed to upgrade their effectiveness in damping inter-area oscillations. Time delays caused by usage of wide-area signals are also considered in the tuning scheme. Results of simulation on a four-machine two-area system and the New England and New York interconnected system show that the proposed index is effective in measuring dynamic performance of the system and the coordinatedly tuned PSSs and SDCs based on this index can robustly damp inter-area oscillations of systems with optimized control efforts.

Robust FACTS Controller Design Employing Modern Heuristic Optimization Techniques

Recently, Genetic Algorithms (GA) and Differential Evolution (DE) algorithm technique have attracted considerable attention among various modern heuristic optimization techniques. Since the two approaches are supposed to find a solution to a given objective function but employ different strategies and computational effort, it is appropriate to compare their performance. This paper presents the application and performance comparison of DE and GA optimization techniques, for flexible ac transmission system (FACTS)-based controller design. The design objective is to enhance the power system stability. The design problem of the FACTS-based controller is formulated as an optimization problem and both the PSO and GA optimization techniques are employed to search for optimal controller parameters. The performance of both optimization techniques has been compared. Further, the optimized controllers are tested on a weekly connected power system subjected to different disturbances, and their performance is compared with the conventional power system stabilizer (CPSS). The eigenvalue analysis and non-linear simulation results are presented and compared to show the effectiveness of both the techniques in designing a FACTS-based controller, to enhance power system stability.

Comparison of particle swarm optimization and genetic algorithm for FACTS-based controller design

Recently, genetic algorithms (GA) and particle swarm optimization (PSO) technique have attracted considerable attention among various modern heuristic optimization techniques. The GA has been popular in academia and the industry mainly because of its intuitiveness, ease of implementation, and the ability to effectively solve highly non-linear, mixed integer optimization problems that are typical of complex engineering systems. PSO technique is a relatively recent heuristic search method whose mechanics are inspired by the swarming or collaborative behavior of biological populations. Since the two approaches are supposed to find a solution to a given objective function but employ different strategies and computational effort, it is appropriate to compare their performance. This paper presents the application and performance comparison of PSO and GA optimization techniques, for flexible ac transmission system (FACTS)-based controller design. The design objective is to enhance the power system stability. The design problem of the FACTS-based controller is formulated as an optimization problem and both PSO and GA optimization techniques are employed to search for optimal controller parameters. The performance of both optimization techniques in terms of computational effort, computational time and convergence rate is compared. Further, the optimized controllers are tested on a weakly connected power system subjected to different disturbances over a wide range of loading conditions and parameter variations and their performance is compared with the conventional power system stabilizer (CPSS). The eigenvalue analysis and non-linear simulation results are presented and compared to show the effectiveness of both the techniques in designing a FACTS-based controller, to enhance power system stability.

Power Oscillation Damping Using FACTS Devices: Modal Controllability, Observability in Local Signals, and Location of Transfer Function Zeros

Modal controllability, observability, and transfer function zeros play an important role in the selection of candidate locations and feedback signals for flexible ac transmission systems (FACTS)-based power swing damping controllers. This paper investigates location of zeros of the transfer function corresponding to FACTS devices and certain local feedback signals. Signals synthesized from locally measured signals are derived that can give good pole-zero separation. It is also shown that relative modal controllability of FACTS controllers at various locations can be directly inferred from relative modal observability in certain signals at those locations. These signals are identified for various FACTS devices. Case studies using detailed model are used to validate the results.

Radiated Emissions From FACTS Equipment Operational Within Substations—Part III

Transient electromagnetic (EM) emissions are generated when thyristor or gate turn-off thyristor (GTO) valves are being switched on and off within substations installed with static var compensators (SVCs) and static synchronous compensators (STATCOMs). These emissions may cause malfunction of, or damage to, electronic equipment positioned nearby without appropriate protection. Four SVC-based substations and one STATCOM-based substation were selected for electromagnetic-interference (EMI) measurement, analysis, and evaluation. A comparison was made between the radiated EMI features from each. The analyzed results were correlated to the present electromagnetic-compatibility standards, and recommendations of changes for immunity tests were presented specifically for flexible ac transmission system (FACTS)-based radiated EMI. Preliminary analysis was also given to the causes of FACTS-based EMI, which indicated that valve switching behavior and the stray parameters of FACTS equipment layout were the main contributors to high-frequency-radiated interference.

Switching Modules for the Extraction/Injection of Power (Without Ground or Phase Reference) From a Bundled HV Line

A new class of devices is proposed for flexible ac transmission systems (FACTS) for high-voltage (HV) powerlines with bundled conductors. These new FACTS devices are based on switching modules (SMs), which are mounted on insulated portions of the transmission towers in close proximity to the line conductors. These SMs are composed of electromechanical and power-electronic switches and could be coupled to some other passive components. Such SMs can be used for connecting/disconnecting one or more subconductors of a phase bundle of the powerline at numerous line segments in the network. Power flow is managed in the line segment by changing the series impedance of the line segment with the SM. Furthermore, the SM could also be used for the extraction/injection of active/reactive power from a segment of the HV line. Power-flow management in an electrical power transmission network could be achieved by using serial SMs distributed throughout the transmission lines of the network. The system and method could eventually be used for modifying, in a steady state or dynamic manner, the power flow through an electric powerline. The passive components coupled with the SM improve the range of impedance modulation. A whole range of applications of the SMs could be developed.

Damping of multimodal power system oscillations by FACTS devices using non-linear Takagi-Sugeno fuzzy controller

The paper presents a non-linear Takagi-Sugeno fuzzy controller for flexible AC transmission system (FACTS) devices in a multi-machine power system. This controller uses a numerical consequent rule base, which can be either linear or non-linear producing control gain variations over a very wide range. This controller is expected to be more robust and effective in damping electromechanical oscillations of the power system compared to the conventional PI controller. Digital simulations of a multi-machine power system, with series connected FACTS devices like UPFC, TCSC and TCPST, etc. subjected to a wide variety of transient disturbances validate the efficiency of the new approach in damping multimodal oscillations.

Allocation of the UPFC to enhance the damping of power oscillations

On the basis of the linearized Phillips–Heffron model of a power system, we approach the problem of select the best input control signal of the Unified Power Flow Controller (UPFC) in order to enhance the damping of power oscillations. A technique is proposed to select the best location for Flexible AC Transmission System (FACTS) devices and the best input control signal, in order to get the major impact on the damping of the electromechanical modes of concern. Nonlinear simulations on a multimachine power system are carried out verifying the goodness of the technique.

An Innovative Load Equivalent Approach to Incorporate FACTS Devices in Active Power OPF

In this paper, a new load-equivalent model for flexible AC transmission system (FACTS) device embedded in power system is proposed for power flow (PF) and optimal active power flow (OPF) calculation. The FACTS devices and the control objectives may be represented by specified-value loads or voltage-dependent loads. The power flow of the power system embedded with FACTS devices can then be solved with slight modification of the conventional power flow program to include the effects of the introduced equivalent loads. The derivation of the model and its application are illustrated in the paper to show the applicability of the method.

Adaptive relay setting for flexible AC transmission systems (FACTS)

The paper presents an apparent impedance calculation procedure for distance relaying of transmission lines involving FACTS devices, particularly the UPFC (unified power flow controller). The presence of UPFC significantly affects the trip boundaries which are also adversely affected by fault resistance combined with remote end infeed. Depending on the UPFC location, the trip boundary is influenced by the fault location, prefault condition, the arc fault resistance and the parameters of the UPFC itself (series voltage magnitude and phase angle). The adaptive nature of this protection scheme necessitates the use of a neural network for generation of trip boundaries.

AEP unified power flow controller performance

The installation of the world's first unified power flow controller (UPFC) has been completed and a series of commissioning tests were conducted at the Inez Substation of American Electric Power (AEP) in eastern Kentucky. The project is a collaborative effort between AEP, the Westinghouse Electric Corporation, and the Electric Power Research Institute (EPRI). Comprising two /spl plusmn/160 MVA voltage-sourced GTO-thyristor-based inverters, this installation is the first large-scale practical demonstration of the UPFC concept, and its completion is a significant milestone in the progress of power electronics technology for flexible AC transmission system (FACTS). This paper briefly reviews the main features of the Inez installation and discusses the operation of the equipment. A collection of measured performance characteristics is presented to illustrate the unique capabilities of the UPFC. These dynamic measurements were made in the course of commissioning, and they graphically illustrate the ability of the UPFC to independently control the real and reactive power on a transmission line, while also regulating the local bus voltage. The results include a demonstration of the series inverter at Inez, operating in stand-alone mode. This test constitutes the first practical large-scale demonstration of the static synchronous series compensator (SSSC) concept.

Load Flow Calculation for Flexible AC Transmission Systems

In this paper, a comprehensive mathematical model of load flow for Flexible AC Transmission Systems (FACTS) with Unified Power Flow Controller (UPFC) is presented basing on the analysis of basic principle and operation states for UPFC. The model can use fast P-Q decoupled load flow method. Examples of test system show that the proposed model and method have good convergence. An effective tool is provided by the load flow computer program to analyze the load flow and calculate initial value of dynamic state for FACTS with UPFC.

Proposed terms and definitions for flexible AC transmission system (FACTS)

Proposed terms and definitions for flexible AC transmission system (FACTS)