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

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

In this paper, a low-voltage (LV) DC microgrid protection system design is proposed. The LV DC microgrid is used to interconnect distributed resources and sensitive electronic loads. When designing an LV DC microgrid protection system, knowledge from existing DC power systems can be used. However, in most cases, these systems use grid-connected rectifiers with current-limiting capability during DC faults. In contrast, an LV DC microgrid must be connected to an AC grid through converters with bidirectional power flow and, therefore, a different protection-system design is needed. In this paper, the operating principles and technical data of LV DC protection devices, both available and in the research stage, are presented. Furthermore, different fault-detection and grounding methods are discussed. The influence of the selected protection devices and grounding method on an LV DC microgrid is studied through simulations. The results show that it is possible to use available devices to protect such a system. Problems may arise with high-impedance ground faults which can be difficult to detect.

Protection of Low-Voltage DC Microgrids

This paper empirically investigates the factors driving the adoption of energy-efficiency measures by small and medium-sized enterprises (SMEs). Our analyses are based on cross-sectional data from SMEs which participated in a German energy audit program between 2008 and 2010. In general, our findings appear robust to alternative model specifications and are consistent with the theoretical and still scarce empirical literature on barriers to energy efficiency in SMEs. More specifically, high investment costs, which are captured by subjective and objective proxies, appear to impede the adoption of energy-efficient measures, even if these measures are deemed profitable. Similarly, we find that lack of capital slows the adoption of energy-efficient measures, primarily for larger investments. Hence, investment subsidies or soft loans (for larger invest-ments) may help accelerating the diffusion of energy-efficiency measures in SMEs. Other barriers were not found to be statistically significant. Finally, our findings provide evidence that the quality of energy audits affects the adoption of energy-efficiency measures. Hence, effective regulation should involve quality standards for energy au-dits, templates for audit reports or mandatory monitoring of energy audits.

Adoption of energy-efficiency measures in SMEs - An empirical analysis based on energy audit data

This paper presents a novel concept of utilizing a photovoltaic (PV) solar farm inverter as STATCOM, called PV-STATCOM, for improving stable power transfer limits of the interconnected transmission system. The entire inverter rating of the PV solar farm, which remains dormant during nighttime, is utilized with voltage and damping controls to enhance stable power transmission limits. During daytime, the inverter capacity left after real power production is used to accomplish the aforementioned objective. Transient stability studies are conducted on a realistic single machine infinite bus power system having a midpoint located PV-STATCOM using EMTDC/PSCAD simulation software. The PV-STATCOM improves the stable transmission limits substantially in the night and in the day even while generating large amounts of real power. Power transfer increases are also demonstrated in the same power system for: 1) two solar farms operating as PV-STATCOMs and 2) a solar farm as PV-STATCOM and an inverter-based wind farm with similar STATCOM controls. This novel utilization of a PV solar farm asset can thus improve power transmission limits which would have otherwise required expensive additional equipment, such as series/shunt capacitors or separate flexible ac transmission system controllers.

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New Control of PV Solar Farm as STATCOM (PV-STATCOM) for Increasing Grid Power Transmission Limits During Night and Day

This paper presents the Bibliography of Flexible AC Transmission System (FACTS) applications for grid integration of wind power systems and PV solar power systems during the period 1995 to 2010. It provides a listing of various journal and conference papers in this area.

Bibliography of FACTS applications for grid integration of wind and PV solar power systems: 1995–2010 IEEE working group report

This paper reports experimental validation of a Static Synchronous Compensation (STATCOM) by controller hardware-in-the-loop (CHIL) testing with a real-time digital simulator (RTDS). The controller is designed and developed for a 10 MVA STATCOM for voltage regulation at the PCC of a 50 MW wind farm connected to a 69kV utility grid. Emitter Turn-off (ETO) thyristors are switching devices in the multilevel inverter. The STATCOM controller was developed for a cascade multilevel inverter and has been validated on a laboratory test-bench. The CHIL testing of the controller is done with detailed scaled model of the 50 MW wind farm and 69kV utility system. The experimental results from the RTDS for both steady state and dynamic changes in the STATCOM output validate the STATCOM controller design and performance.

Controller hardware-in-the-loop validation for a 10 MVA ETO-based STATCOM for wind farm application

Although not the first HVDC transmission scheme, the Pacific HVDC Intertie (PDCI) has been the subject of keen interest from the HVDC community from its earliest days. The initial configuration has been repeatedly altered over a period of more than 30 years as a result of various upgrades and in response to two major earthquakes, a fire, and environmental concerns. Once a museum of HVDC technology development, the PDCI now contains the most modern equipment available. The owners of the southern converter station at Sylmar, California, have completely rebuilt the station, replacing nearly all of the converter equipment with modern high-power converters. At the northern end of the Intertie, at the Celilo converter station in The Dalles, Oregon, the changes have been more modest. This article traces the story of the creation of the PDCI and the subsequent changes that have taken the capacity from 1,440 MW in 1970 to 3,100 MW today

Pacific HVDC intertie

The western United States and Canada, bounded roughly by the Continental Divide and the Pacific Ocean and Mexico, form a large interconnected power system overseen by the Western Electric Coordinating Council (WECC). This interconnected system of approximately 210,000 MW has five high-voltage dc (HVdc) transmission systems dating from 1970 to 2014. Two new HVdc transmission schemes have been completed recently in Alberta, and several HVdc lines are being planned for the southwest to move power to southern California. There are also eight back-to-back converters that tie the western system to the eastern interconnection and to Texas. Other power electronic installations include a number of large transmission scale static var converters (SVCs) and two thyristor controlled series capacitors (TCSCs). These installations date from 1970, when the Vancouver Island HVdc transmission was installed.

When It's Time to Upgrade: HVdc and FACTS Renovation in the Western Power System

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.

Wayne H. Litzenberger

Papers

Bibliography of FACTS applications for grid integration of wind and PV solar power systems: 1995–2010 IEEE working group report

Controller hardware-in-the-loop validation for a 10 MVA ETO-based STATCOM for wind farm application

Pacific HVDC intertie

When It's Time to Upgrade: HVdc and FACTS Renovation in the Western Power System

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