1. Introduction. 1.1 Background. 1.2 Electrical Transmission Networks. 1.3 Conventional Control Mechanisms. 1.4 Flexible ac Transmission Systems (FACTS). 1.5 Emerging Transmission Networks. 2. Reactor--Power Control in Electrical Power Transmission Systems. 2.1 Reacrive Power. 2.2 Uncompensated Transmission Lines. 2.3 Passive Compensation. 2.4 Summary. 3. Principles of Conventional Reactive--Power Compensators. 3.1 Introduction. 3.2 Synchronous Condensers. 3.3 The Saturated Reactor (SR). 3.4 The Thyristor--Controlled Reactor (TCR). 3.5 The Thyristor--Controlled Transformer (TCT). 3.6 The Fixed Capacitor--Thyristor--Controlled Reactor (FC--TCR). 3.7 The Mechanically Switched Capacitor--Thristor--Controlled Reactor (MSC--TCR). 3.8 The Thyristor--Switched capacitor and Reactor. 3.9 The Thyristor--Switched capacitor--Thyristor--Controlled Reactor (TSC--TCR). 3.10 A Comparison of Different SVCs. 3.11 Summary. 4. SVC Control Components and Models. 4.1 Introduction 4.2 Measurement Systems. 4.3 The Voltage Regulator. 4.4 Gate--Pulse Generation. 4.5 The Synchronizing System. 4.6 Additional Control and Protection Functions. 4.7 Modeling of SVC for Power--System Studies. 4.8 Summary. 5. Conceepts of SVC Voltage Control. 5.1 Introduction 5.2 Voltage Control. 5.3 Effect of Network Resonances on the Controller Response. 5.4 The 2nd Harmonic Interaction Between the SVC and ac Network. 5.5 Application of the SVC to Series--Compensated ac Systems. 5.6 3rd Harmonic Distortion. 5.7 Voltage--Controlled Design Studies. 5.8 Summary. 6. Applications. 6.1 Introduction. 6.2 Increase in Steady--State Power--Transfer Capacity. 6.3 Enhancement of Transient Stability. 6.4 Augmentation of Power--System Damping. 6.5 SVC Mitigation of Subsychronous Resonance (SSR). 6.6 Prevention of Voltage Instability. 6.7 Improvement of HVDC Link Performance. 6.8 Summary. 7. The Thyristor--Controlled SeriesCapacitor (TCSC). 7.1 Series Compensation. 7.2 The TCSC Controller. 7.3 Operation of the TCSC. 7.4 The TSSC. 7.5 Analysis of the TCSC. 7.6 Capability Characteristics. 7.7 Harmonic Performance. 7.8 Losses. 7.9 Response of the TCSC. 7.10 Modeling of the TCSC. 7.11 Summary. 8. TCSC Applications. 8.1 Introduction. 8.2 Open--Loop Control. 8.3 Closed--Loop Control. 8.4 Improvement of the System--Stability Limit. 8.5 Enhancement of System Damping. 8.6 Subsynchronous Resonanace (SSR) Mitigation. 8.7 Voltage--Collapse Prevention. 8.8 TCSC Installations. 8.9 Summary. 9. Coordination of FACTS Controllers. 9.1 Introduction 9.2 Controller Interactions. 9.3 SVC--SVC Interaction. 9.4 SVC--HVDC Interaction. 9.5 SVC--TCSC Interaction. 9.6 TCSC--TCSC Interaction. 9.7 Performance Criteria for Damping--Controller Design. 9.8 Coordination of Multiple Controllers Using Linear--Control Techniques. 9.9 Coordination of Multiple Controllers using Nonlinear--Control Techniques. 9.10 Summary. 10. Emerging FACTS Controllers. 10.1 Introduction. 10.2 The STATCOM. 10.3 THE SSSC. 10.4 The UPFC. 10.5 Comparative Evaluation of Different FACTS Controllers. 10.6 Future Direction of FACTS Technology. 10.7 Summary. Appendix A. Design of an SVC Voltage Regulator. A.1 Study System. A.2 Method of System Gain. A.3 Elgen Value Analysis. A.4 Simulator Studies. A.5 A Comparison of Physical Simulator results With Analytical and Digital Simulator Results Using Linearized Models. Appendix B. Transient--Stability Enhancement in a Midpoint SVC--Compensated SMIB System. Appendix C. Approximate Multimodal decomposition Method for the Design of FACTS Controllers. C.1 Introduction. C.2 Modal Analysis of the ith Swing Mode, C.3 Implications of Different Transfer Functions. C.4 Design of the Damping Controller. Appendix D. FACTS Terms and Definitions. Index.

Thyristor-Based Facts Controllers for Electrical Transmission Systems

This paper describes the theory and the modelling technique of a flexible alternating current transmission systems (FACTS) device, namely, static synchronnous series compensator (SSSC) using an Electromagnetic Transient Program (EMTP) simulation package. The SSSC, a solid-state voltage source inverter coupled with a transformer, is connected in series with a transmission line. An SSSC injects an almost sinusoidal voltage, of variable magnitude, in series with a transmission line. This injected voltage is almost in quadrature with the line current, thereby emulating an inductive or a capacitive reactance in series with the transmission line. The emulated variable reactance, inserted by the injected voltage source, influences the electric power flow in the transmission line.

SSSC-static synchronous series compensator: theory, modeling, and application

The scientific principle of “mechanical springs” was described by the British physicist Robert Hooke in the 1660's. Since then, there has not been any further development of the Hooke's law in the electric regime. In this paper, this technological gap is filled by the development of “electric springs.” The scientific principle, the operating modes, the limitations, and the practical realization of the electric springs are reported. It is discovered that such novel concept has huge potential in stabilizing future power systems with substantial penetration of intermittent renewable energy sources. This concept has been successfully demonstrated in a practical power system setup fed by an ac power source with a fluctuating wind energy source. The electric spring is found to be effective in regulating the mains voltage despite the fluctuation caused by the intermittent nature of wind power. Electric appliances with the electric springs embedded can be turned into a new generation of smart loads, which have their power demand following the power generation profile. It is envisaged that electric springs, when distributed over the power grid, will offer a new form of power system stability solution that is independent of information and communication technology.

Electric Springs—A New Smart Grid Technology

Fast acting static synchronous compensator (STATCOM), a representative of FACTS family, is a promising technology being extensively used as the state-of-the-art dynamic shunt compensator for reactive power control in transmission and distribution system. Over the last couple of decades, researchers and engineers have made path-breaking research on this technology and by virtue of which, many STATCOM controllers based on the self-commutating solid-state voltage-source converter (VSC) have been developed and commercially put in operation to control system dynamics under stressed conditions. Because of its many attributes, STATCOM has emerged as a qualitatively superior controller relative to the line commutating static VAR compensator (SVC). This controller is called with different terminologies as STATic COMpensator advanced static VAR compensator, advanced static VAR generator or static VAR generator, STATic CONdenser, synchronous solid-state VAR compensator, VSC-based SVC or self-commutated SVC or static synchronous compensator (SSC or S2C). The development of STATCOM controller employing various solid-state converter topologies, magnetics configurations, control algorithms, switching techniques and so on, has been well reported in literature with its versatile applications in power system. A review on the state-of-the-art STATCOM technology and further research potential are presented classifying more than 300 research publications.

Static synchronous compensators (STATCOM): a review

The interline power flow controller (IPFC) proposed is a new concept for the compensation and effective power flow management of multi-line transmission systems. In its general form, the IPFC employs a number of inverters with a common DC link, each to provide series compensation for a selected line of the transmission system. Because of the common DC link, any inverter within the IPFC is able to transfer real power to any other and thereby facilitate real power transfer among the lines of the transmission system. Since each inverter is also able to provide reactive compensation, the IPFC is able to carry out an overall real and reactive power compensation of the total transmission system. This capability makes it possible to equalize both real and reactive power flow between the lines, transfer power from overloaded to underloaded lines, compensate against reactive voltage drops and the corresponding reactive line power, and to increase the effectiveness of the compensating system against dynamic disturbances. The paper explains the basic theory and operating characteristics of the IPFC with phasor diagrams, P-Q plots and simulated waveforms.

The interline power flow controller concept: a new approach to power flow management in transmission systems

This paper describes an active approach to series line compensation, in which a synchronous voltage source, implemented by a gate turn-off thyristor (GTO) based voltage-sourced inverter, is used to provide controllable series compensation. This compensator, called static synchronous series compensator (SSSC), can provide controllable compensating voltage over an identical capacitive and inductive range, independently of the magnitude of the line current. It is immune to classical network resonances. In addition to series reactive compensation, with an external DC power supply it can also compensate the voltage drop across the resistive component of the line impedance. The compensation of the real part of the impedance can maintain high X/R ratio even if the line has a very high degree of series compensation. Concurrent and coordinated modulation of reactive and real compensation can greatly increase power oscillation damping. The paper discusses the basic operating and performance characteristics of the SSSC, and compares them to those characterizing the more conventional compensators based on thyristor-switched or controlled series capacitors. It also presents some of the results of TNA simulations carried out with an SSSC hardware model.

Static Synchronous Series Compensator: A Solid-State Approach to the Series Compensation of Transmission Lines

This paper describes the theory and the modeling technique of a flexible alternating current transmission systems (FACTS) device, namely, unified power flow controller (UPFC) using an Electromagnetic Transients Program (EMTP) simulation package. The UPFC, in this paper, consists of two solid-state voltage source inverters which are connected through a common DC link capacitor. Each inverter is coupled with a transformer at its output. The first voltage source inverter, known as a static synchronous compensator (STATCOM), injects an almost sinusoidal current, of variable magnitude, at the point of connection. The second voltage source inverter, known as a static synchronous series compensator (SSSC) injects an almost sinusoidal voltage, of variable magnitude, in series with the transmission line. This injected voltage can be at any angle with respect to the line current. The exchanged real power at the terminals of one inverter with the line flows to the terminals of the other inverter through the common DC link capacitor. In addition, each inverter can exchange reactive power at its terminals independently. The functionalities of the models have been verified.

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

This paper compares the field results of voltage-sourced converter (VSC)-based flexible alternating current transmission system (FACTS) controllers, such as static synchronous compensator (STATCOM), static synchronous series compensator (SSSC), and unified power flow controller (UPFC) with that obtained from the computer models of the FACTS controllers using an Electro Magnetic Transients Program (EMTP) simulation package. The operational results of the actual equipment include the control of the line voltage and the control of the real and reactive power flow in the line. The correlation of the results establishes the validity of the models. The protection scheme of the FACTS controllers during faults and contingencies is also described. The simulation results can be used to accurately predict the behavior of an actual controller.

K.K. Sen

Papers

Static Synchronous Series Compensator: A Solid-State Approach to the Series Compensation of Transmission Lines

SSSC-static synchronous series compensator: theory, modeling, and application

The interline power flow controller concept: a new approach to power flow management in transmission systems

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

Comparison of field results and digital simulation results of voltage-sourced converter-based FACTS controllers