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Within substations installed with flexible ac transmission systems, the magnetic flux leakage (MFL) generated by air core reactors in static var compensator (SVC) can be very high. To reduce the influence of the high magnetic field, an optimal suppression method is selected based on fuzzy comprehensive evaluation. First, a series of onsite measurements are performed around the reactors in the SVC. From the measurement results, the low-voltage cables, dc system, grounding grid, and magnetic flux density around the air core reactors are seriously affected by the MFL generated by the air core reactors with currents of a few kiloamperes. Then, according to the actual parameters of the air core reactors, a three-dimensional simulation model is constructed using the finite-element method (FEM) to calculate the magnetic flux density and some parameters related to the magnetic field. Moreover, four different suppression methods are proposed to suppress the MFL influence. Due to the multiple aspects affected by MFL, it is always difficult to make a quantitative comparison for the suppression methods based on previous research. For this reason, a fuzzy comprehensive evaluation method based on a linear evaluation model is proposed to quantitatively compare the suppression methods by using the suppression effect value δ. In a comparison of different suppression methods, the aluminum plate shielding with proper parameters has prove to be an optimal method for achieving a comprehensive suppression effect. The modeling and evaluation methods presented in this article are both valuable to solve the complex MFL influence problem in different SVC-based substations. [ABSTRACT FROM AUTHOR]

Development of appropriate load flow model of Flexible AC Transmission System (FACTS) devices is an important issue for proper planning, control, and protection of power system. Holomorphic Embedding Load-Flow Method (HELM) is a novel technique for solving load flow nonlinear equations which overcomes the numerical problems faced by traditional iterative techniques. In order to evaluate the effects of FACTS devices in load flow problem by HELM technique, it is necessary to develop HELM modeling of these devices. This paper presents HELM modeling of Thyristor-based FACTS controllers, i.e., Static Var Compensator (SVC), Thyristor Controlled Switched Capacitor (TCSC), Thyristor Controlled Voltage Regulator (TCVR), and Thyristor Controlled Phase Angle Regulator (TCPAR). In this modeling, white germ solution is investigated along with recursive formula and controlling FACTS devices operation bounds. [ABSTRACT FROM PUBLISHER]

Based on cascaded ac–ac converter with controllable phase and amplitude (ACCPA), a novel π model ACCPA was proposed for power flow control, whose output voltage phase and amplitude can be regulated, respectively, and simultaneously with respect to the input voltage. Single-phase π model ACCPA comprises a buck-type ac unit, a third harmonic trap and a boost-type ac converter. Compared with single-phase cascaded ACCPA, it has a more simplified structure by dispensing with the LC output filter of the buck-type ac converter, and can adopt the same two-stage duty-cycle modulation. The buck-type ac unit regulates the phase of output voltage and the boost-type ac converter does the amplitude. By utilizing impedance compensation with capacitance in single-phase π model ACCPA, it is effective to counteract or reduce the lag effect which is put on fundamental voltage by line impedance of third harmonic trap and inductance. Three-phase π model ACCPA comprises three buck-type ac units and a three-phase boost-type ac converter, it not only dispenses with three LC output filters, but also does three third harmonic traps, so it has simple structure. Experimental results verified the feasibility of π model ACCPA and the correctness of its theory. [ABSTRACT FROM PUBLISHER]

This paper presents a model based on a Optimal Reactive Power Flow (ORPF) to allocation of Static VAr Compensator (SVC) in the power transmission network. The SVC was modeled as a variable susceptance and inserted into Ybus matrix. For discretization of the devices to be allocated in the system were used binary variables associated to SVC susceptance. A multiobjective function formed by two parts, active power losses and voltage deviation, was used in the ORPF formulation. In each one of parts was associated a parameter that allows to give more or less weight to each part. Due to the problem characteristics, Mixed Integer Nonlinear Programming (MINLP), was used a Branch & Bound (B&B) algorithm associated with the ORPF. The model was tested in the IEEE 118 bus system. The results show that the modeling and the technique of solution used are appropriate for SVCs allocation and powersystem analysis [ABSTRACT FROM PUBLISHER]

Voltage-sourced converter (VSC)-based static synchronous compensators (STATCOMs) are used for voltage regulation in transmission and distribution systems. Unlike PWM-controlled STATCOMs, angle-controlled STATCOMs are switched at line frequency to limit the system losses. In recent years, angle-controlled STATCOMs have been deployed by utilities for the purpose of transmission system voltage regulation, voltage stability improvement, and increasing operational functionality. Despite the superior feature on voltage waveform quality and efficiency, the practical angle-controlled STATCOMs suffer from the over-current (and trips) and possible saturation of the interfacing transformers caused by negative sequence current during unbalanced conditions and faults in the utility. This paper specifically proposes a control structure to improve the angle-controlled STATCOMs performance under unbalanced conditions and faults. The main improvement is a substantial decrease in the negative sequence current and dc-link voltage oscillations under power system faults by the proposed control. This eliminates the need to redesign the STACOM power components to operate under fault current and dc-link voltage oscillations. The proposed control structure is designed based on adding appropriate oscillations to the conventional angle-controller output that is the control angle by which the VSC voltage vector leads/lags the line voltage vector. Since this control structure uses two angles for controlling the VSC output voltage, it is called dual angle control (DAC). PSCAD/EMTDC and experimental results verify the validity of the proposed control structure under unbalanced system conditions and faults. The experiments were conducted on a transient network analyzer, a unique hardware-based flexible ac transmission system simulator which was designed to study system faults and transients for a 2 × 100 MVA STATCOM field installation. [ABSTRACT FROM AUTHOR]

A robust coordination approach for the controller design of multiple high-voltage direct-current (HVDC) and flexible ac transmission systems (FACTS) wide-area controls (WACs) is presented in this paper and has the aim of stabilizing multiple interarea oscillation modes in large-scale power systems. The suitable wide-area control signals, which are given to HVDC and FACTS wide-area controllers, respectively, are chosen from a large number of candidate items. Then, a sequential robust design approach is planned for the wide-area controller coordination of HVDC and FACTS devices. This approach is based on the robust control theory and is formulated as a standard problem of multiobjective mixed H2/H\infty output-feedback control with regional pole placement constraints. The linear matrix inequality (LMI) theory is applied to solve such a robust control problem. A case study on the 16-machine 5-area system, which is modified with one HVDC interconnected transmission, one shunt-FACTS device (SVC), and one series-FACTS device (TCSC), is performed to validate the robust performance in terms of multiple oscillations damping under various operating conditions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

This paper presents two approaches for multiobjective simultaneous coordinated tuning of damping controllers, a modified artificial immune network (MAINet) algorithm and a multiobjective immune algorithm (MOIA). The weighted-sum approach is used to handle the multiobjective optimization problem in the MAINet, while the Pareto-optimization approach is used in the MOIA. To investigate the ability of the proposed algorithms in designing the damping controllers, one small and one large power systems are considered. Two power-system stabilizers (PSSs) are designed for the small power system, while one PSS for a generator and one supplementary controller for a static var compensator (SVC) are designed for the large power system. The simulation studies show that the controllers designed by MOIA perform better than those by MAINet in damping the power-system low-frequency oscillations. [ABSTRACT FROM PUBLISHER]

Motivated by the development of power semiconductor technologies, flexible ac transmission systems (FACTS) devices and their penetration in the field of electrical power systems, an educational challenge in complementing theoretical knowledge with practical experience is recognized. In this paper, the design and implementation of a lab-scale hardware and software setup is presented. Three small-scale devices, including a static VAr compensator (SVC) unit, a transmission line model, and a substation, are developed. The SVC unit is validated by obtaining its operating characteristic. The lab setup is presented as a platform to carry out different experiments related to the SVC operation. Safety considerations in the design are discussed. Steady-state and dynamic analysis are presented showing the consistency between theory and practice. The potential use of small SVC units on low-voltage distributed generation schemes is discussed. [ABSTRACT FROM AUTHOR]

Flexible ac transmission system (FACTS) devices or their subderivative custom power devices are efficient and often used and recommended power-electronics-based devices for mitigation of voltage sags in electrical power system. With FACTS devices installed, the overall system (and individual bus) sag performance could significantly change depending on the type of the device used. In order to assess this change in sag performance in realistic large power systems, the classical (essentially static) fault calculation procedure should be amended to incorporate the effects of these devices on bus voltages. This paper presents a new approach of quasistatic sag analysis using a system impedance (Z bus ) matrix that incorporates FACTS devices. Three types of FACTS devices which are most often used in practical applications are considered in this study: static compensator, static var compensator, and the dynamic voltage restorer. The case studies based on the 295-bus generic distribution system are used to illustrate the modeling method and the effectiveness of these devices in sag mitigation. [ABSTRACT FROM PUBLISHER]

This paper presents an approach to optimally select and allocate flexible ac transmission (FACTS) devices in a distribution network in order to minimize the number of voltage sags at network buses. The method proposed is based on the optimization of a preselected objective function using simple and niching genetic algorithms (GA). The objective of the optimization is to achieve the improvement in overall system sag performance of the network. Using proposed GA-based optimization, the location, the type and the rating of six (in total) FACTS devices are optimized simultaneously. Three types of FACTS devices are implemented in this study, namely, static var compensator, static compensator, and dynamic voltage restorer. The performance of the proposed algorithm is tested and illustrated on 295-bus generic distribution system. [ABSTRACT FROM PUBLISHER]

STATCOM is a FACTS controller that is used in power systems to regulate the line voltage, enhance the power transmission capacity and extend the transient stability margin. STATCOM is conventionally realized by a voltage-source converter; however, being a current injection device, its performance can be improved when realized by a current-source converter (CSC) that can generate a controllable current directly at its output terminals. In this paper, a STATCOM based on the current-source converter topology is proposed. The nonlinear model of the current-source converter, which is the source of the difficulties in the controller design, has been modified to a linear model through a novel modeling technique. The proposed modeling technique is not based on the linearization of a set of nonlinear equations around an operating point. Instead, the power balance equation and a nonlinear input transformation are used to derive a linear model independent of the operating point. This model acts as the basis for the design of a decoupled state-feedback controller. The proposed STATCOM has been simulated using the PSCAD/EMTDC package. The simulation results show that a CSC-based STATCOM can result in excellent current and voltage waveforms as well as very short response time while operating at a low switching frequency. This makes the proposed scheme suitable for high power applications. [ABSTRACT FROM PUBLISHER]

This article discusses the implementation of an operational monitoring and fault diagnosis system (OMFDS) for a ±20 MVAr voltage-sourced STATCOM based on gate-turn-off thyristor (GTO). It well fulfills the purpose of real-time supervision, intelligent alarm handling, post-fault system analysis and gratifying man-machine interaction. The proposed system, with minor modification if needed, can also be applicable to other FACTS controllers or other power electronic devices [ABSTRACT FROM PUBLISHER]

This overview of the FACTS program sponsored by EPRI identifies the significant challenges and the adopted technology-based solutions that have been developed. FACTS technology has been successfully demonstrated and continues to be implemented at transmission locations in the United States. A STATCOM, UPFC, and convertible static compensator are discussed. The installed FACTS controllers have provided new possibilities and unprecedented flexibility aiming at maximizing the utilization of transmission assets efficiently and reliably. As the development and implementation of FACTS controllers evolve, there will be a need for an overall controller "hierarchical" logic to optimize transmission system operations [ABSTRACT FROM PUBLISHER]

A novel method for the analysis of the effectiveness of an SVC and a STATCOM of the same kVAr rating for first-swing stability enhancement is presented and the concept is demonstrated with a numerical example. The analysis shows that the STATCOM is superior to the SVC for first-swing stability enhancement [ABSTRACT FROM PUBLISHER]

This letter offers a state space representation of a voltage sourced inverter that forms the building block of modern flexible AC transmission systems (FACTS), such as STATCOM, SSSC, and UPFC. The representation includes consideration of the output phase, firing angle, and the conduction period. This model is used to devise a control algorithm of the DC link voltage and the output voltage. The concepts are demonstrated with a case study using PSCAD and MATLAB. [ABSTRACT FROM PUBLISHER]