The ever increasing progress of high-voltage high-power fully controlled semiconductor technology continues to have a significant impact on the development of advanced power electronic apparatus used to support optimized operations and efficient management of electrical grids, which, in many cases, are fully or partially deregulated networks. Developments advance both the HVDC power transmission and the flexible ac transmission system technologies. In this paper, an overview of the recent advances in the area of voltage-source converter (VSC) HVdc technology is provided. Selected key multilevel converter topologies are presented. Control and modeling methods are discussed. A list of VSC-based HVdc installations worldwide is included. It is confirmed that the continuous development of power electronics presents cost-effective opportunities for the utilities to exploit, and HVdc remains a key technology. In particular, VSC-HVdc can address not only conventional network issues such as bulk power transmission, asynchronous network interconnections, back-to-back ac system linking, and voltage/stability support to mention a few, but also niche markets such as the integration of large-scale renewable energy sources with the grid and most recently large onshore/offshore wind farms.

VSC-Based HVDC Power Transmission Systems: An Overview

(1990). ENERGY FUNCTION ANALYSIS FOR POWER SYSTEM STABILITY. Electric Machines & Power Systems: Vol. 18, No. 2, pp. 209-210.

Energy function analysis for power system stability

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

In this paper, the principle of modularity is used to derive the different multilevel voltage and current source converter topologies. The paper is primarily focused on high-power applications and specifically on high-voltage dc systems. The derived converter cells are treated as building blocks and are contributing to the modularity of the system. By combining the different building blocks, i.e., the converter cells, a variety of voltage and current source modular multilevel converter topologies are derived and thoroughly discussed. Furthermore, by applying the modularity principle at the system level, various types of high-power converters are introduced. The modularity of the multilevel converters is studied in depth, and the challenges as well as the opportunities for high-power applications are illustrated.

Modular Multilevel Converters for HVDC Applications: Review on Converter Cells and Functionalities

This paper describes a new power system stabilizer (PSS) design for damping power system oscillations focusing on interarea modes. The input to the PSS consists of two signals. The first signal is mainly to damp the local mode in the area where PSS is located using the generator rotor speed as an input signal. The second is an additional global signal for damping interarea modes. Two global signals are suggested; the tie-line active power and speed difference signals. The choice of PSS location, input signals and tuning is based on modal analysis and frequency response information. These two signals can also be used to enhance damping of interarea modes using SVC located in the middle of the transmission circuit connecting the two oscillating groups. The effectiveness and robustness of the new design are tested on a 19-generator system having characteristics and structure similar to the Western North American grid.

Damping controller design for power system oscillations using global signals

This paper presents a Bibliography of HVDC transmission technology from August, 2005 to present. It provides a listing of various journal and conference papers in this area.

Bibliography of HVDC Transmission: 2005-2006 IEEE Working Group Report

This paper presents a novel control of PV solar farm as a STATCOM (PV-STATCOM) coordinated with Power System Stabilizers (PSSs) for damping of electromechanical oscillations in a power system. A two-area power system with a 150 MW PV solar plant connected at the midpoint of the tie line is simulated in PSCAD/EMTDC software. During contingencies, the capacity of the PV inverter remaining after real power generation is utilized for dynamic reactive power exchange to accomplish power oscillation damping. The advantage of master-slave feature in PSCAD/EMTDC software is utilized for performing the optimization and controller coordination. It is demonstrated that a coordinated control of PV-STATCOM and PSS can effectively enhance the damping of power oscillations, leading to higher power transfers in lines. This novel control of PV solar farms will result in a more optimal utilization of the expensive PV system asset for grid stabilization and enhancement of power transmission capability.

Coordinated control of PV solar system as STATCOM (PV-STATCOM) and Power System Stabilizers for power oscillation damping

Subsynchronous resonance (SSR) is a potential problem in power systems having series compensated transmission lines. Flexible AC transmission systems (FACTS) controllers are widely applied to mitigate subsynchronous oscillations (SSO). With the advent of wide area measurement (WAM) technology, it is possible to measure the states of a large interconnected power system with synchronized phasor measurement units (PMU). In this paper the concept of using remote signals acquired through PMU has been proposed to damp SSR. An auxiliary subsynchronous damping controller (SSDC) for a static VAr compensator (SVC) using the remote generator speed as the stabilizing signal has been designed to damp subsynchronous oscillations. The IEEE first benchmark model is used to show the effectiveness of the controller. Extensive simulation results in EMTDC/PSCAD show that an SVC already installed in a transmission system with the primary objective of improving power transfer capability can also damp SSR with the auxiliary controller using remote generator speed. Finally, the effect of signal transmission delay is discussed.

Mitigation of subsynchronous resonance by SVC using PMU-acquired remote generator speed

In this paper, a STATCOM with voltage controller is proposed to mitigate the potential of SSR in a series compensated IG based wind farm. Detailed eigenvalue analysis is performed to demonstrate that Induction Generator effect SSR is successfully alleviated by STATCOM. The results are validated through electromagnetic transient simulation with PSCAD/EMTDC. The impacts of symmetrical fault at different locations and collector cables are investigated and the effectiveness of the proposed STATCOM controller is illustrated. It is shown that a three phase fault close to the wind farm may cause severe oscillations in the PCC voltage, electromagnetic torque and shaft torque of the wind turbine generator. To examine this situation, an equivalent circuit analysis is presented, which predicts the threshold resonant speeds within which the wind turbine becomes unstable. The study is extended to other commercially available induction generators, which also shows the potential for SSR even at realistic levels of series compensation levels, and the capability of the proposed STATCOM controller to obviate its occurrence.

SSR alleviation by STATCOM in induction generator based wind farm connected to series compensated line

Large-scale integration of wind turbine generators (WTGs) may have significant impacts on power system operation with respect to bus voltages, system frequency, etc. Voltage control and reactive power compensation in a weak distribution network for integration of wind power represents the main concern of this paper. Without reactive power compensation, the integration of wind power in a network may potentially cause voltage collapse in the system and under-voltage tripping of wind power generators. This paper shows that while static compensation (Fixed Capacitor Bank) is unable to prevent voltage collapse, dynamic reactive power compensation using Static Var Compensator (SVC) at the a point of interconnection of wind farm is successful in maintaining acceptable voltage level. Moreover, this paper shows that by using a fuzzy controller instead of a PI controller, the performance of SVC is improved. MATLAB/Simulink based simulation is utilized to demonstrate the application of SVC in wind farm integration and the enhancement in performance achieved with a fuzzy controller as compared to a Proportional Integral controller for voltage regulation during fault scenarios.

Rajiv K. Varma

Papers

Bibliography of HVDC Transmission: 2005-2006 IEEE Working Group Report

Coordinated control of PV solar system as STATCOM (PV-STATCOM) and Power System Stabilizers for power oscillation damping

Mitigation of subsynchronous resonance by SVC using PMU-acquired remote generator speed

SSR alleviation by STATCOM in induction generator based wind farm connected to series compensated line

Application of Static Var Compensator (SVC) with fuzzy controller for grid integration of wind farm