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

Photovoltaic (PV) solar farms are typically dormant at nighttime with their entire expensive assets unused. This paper presents the first in Canada (and perhaps first in the world) utility demonstration of a novel nighttime and daytime technology of utilizing PV solar farm as a dynamic reactive power compensator (STATCOM), and named PV-STATCOM. The field demonstration was performed on a 10 kW PV solar farm installed in the utility network of Bluewater Power Distribution Corporation, in Sarnia, Ontario. It is demonstrated that the solar farm autonomously transforms into a STATCOM and ensures continuous stable operation of a critical induction motor during large disturbances which would otherwise destabilize the motor. The PV-STATCOM is thus shown to be a new FACTS device STATCOM which provides a 24/7 dynamic voltage control functionality as a STATCOM but is about 50 times less costly than an actual equivalent sized STATCOM. The PV-STATCOM is further demonstrated to be a new smart inverter which operates much faster than a conventional smart inverter and also during nighttime, which present-day smart inverters do not. Shutdown of critical induction motors used in industries such as petrochemicals, process control, mining, automotive, medicines, etc. can result in significant financial loss to the industries. This novel functionality of critical motor stabilization by solar farms as PV-STATCOM can potentially open a substantial new revenue earning opportunity for solar farms in addition to generation of active power. This paper presents the first stage results of field demonstration of PV-STATCOM technology on 13th Dec. 2016, in an ongoing project.

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First in Canada, Night and Day Field Demonstration of a New Photovoltaic Solar-Based Flexible AC Transmission System (FACTS) Device PV-STATCOM for Stabilizing Critical Induction Motor

This paper presents a novel day-and-night control of large PV solar farm as STATCOM, termed PV-STATCOM, for FIDVR alleviation. The proposed control involves dynamic modulation of both reactive and real power during day, and of reactive power during night. The active and reactive power output of solar farm are based on the sensitivity of solar plant voltage to active and reactive power injections. Enhanced voltage control up to utility Transient Overvoltage Limit is utilized. Eigenvalue analysis is done to study the sensitivity of proposed controller performance to various power system and PV plant parameters. Extensive PSCAD simulation studies of FIDVR are performed in a realistic power transmission system with large-scale PV plant and comprehensive IM loads. It is shown that the proposed PV-STATCOM control: (i) mitigates FIDVR even if solar farm is located more than 100 km from motor loads, (ii) is more effective than reactive power support required by German Grid Code, (iii) is equally effective as a STATCOM connected locally at motor loads, and (iv) stabilizes motors at night which is beyond Grid Code requirements. The PV-STATCOM potentially provides significant cost savings to utilities and new revenue stream for solar plants in providing 24/7 FIDVR mitigation service.

Mitigation of Fault Induced Delayed Voltage Recovery (FIDVR) by PV-STATCOM

This paper describes a fundamental study into modeling the effects of frequency variation on network and shunt impedances in long term power system stability simulations. The focus is on extreme post-fault situations where significant generation-load mismatch causes wide excursions in power system frequency. A novel application of singular perturbations is presented. This method is compared with the "constant reactance" technique, the "variable reactance" method in which the network reactances are varied with system frequency, and a method in which the network transients are fully simulated. Stability simulations for an interconnected two-area power system employing the different modeling techniques show that a two time scale analysis using the singular perturbation method is a feasible technique for accurate prediction of long term post fault system behaviour.

Modeling effects of system frequency variation in long-term stability studies

This paper presents a comprehensive testing, validation and installation plan for a new technology which utilizes PV solar farm as a STATCOM both during nighttime and daytime. This technology is termed PV-STATCOM. It will be utilized in the night for power factor correction and voltage control at the terminals of an induction motor operating at poor power factor. During daytime, the same objectives will be accomplished together with production of real power from solar insolation, by utilizing the inverter capacity remaining after real power generation. The local distribution company London Hydro is implementing this new technology, for the first time in Canada, on a 10 kW solar system to be installed on the rooftop of their headquarters building in Spring 2012. The proposed new control on PV solar system will help increase the utilization of the PV solar system, improve overall electrical system performance and provide a potential of additional revenue earning for solar system for providing the above services, both during night and day.

Novel application of a PV solar plant as STATCOM (PV-STATCOM) during night and day in a distribution utility network: Part 2

Systems, methods, and devices relating to the provision of system control support in the form of reactive power support or voltage control support to power transmission or distribution networks using inverter based power generation facilities that are coupled to the power transmission or distribution networks. An inverter based power generation facility, such as a photovoltaic based solar farm or a wind farm, can task all or a portion of its inverter capacity to provide reactive power support or voltage control support to the power transmission or distribution network. This invention applies to the operation of PV solar systems anytime during the day (even during peak power generation times) and other inverter based DGs during the entire 24-hour period. The power generation facility disconnects at least one of its power generation modules from the power transmission or distribution network and makes available required inverter capacity for providing system control support.

Rajiv K. Varma

Papers

First in Canada, Night and Day Field Demonstration of a New Photovoltaic Solar-Based Flexible AC Transmission System (FACTS) Device PV-STATCOM for Stabilizing Critical Induction Motor

Mitigation of Fault Induced Delayed Voltage Recovery (FIDVR) by PV-STATCOM

Modeling effects of system frequency variation in long-term stability studies

Novel application of a PV solar plant as STATCOM (PV-STATCOM) during night and day in a distribution utility network: Part 2

Enhanced utilization of real power generating capacity of distributed generator (dg) inverters as statcom