IEEE Power & Energy Society

Guest Editorial

DC Technologies

Solutions to Electric Power System Advancements

At the turn of the 20th century, as those of us who have studied our power industry’s history know, a fierce battle was fought over how electricity would be generated, delivered, and utilized: alternating current (ac) or direct current (dc). The pioneers who founded and invented the technologies and businesses of our industry well over 100 years ago, George Westinghouse, Nikolai Tesla, Thomas Edison, and others, waged at that time what become famously known as the “War of the Currents.” Of course, back then and for all the right reasons, the approaches advocated by Westinghouse and Tesla for ac ultimately won out over Edison’s push for dc. This was primarily due to ac’s ability to transmit electricity more effectively over long distances; this allowed the implementation of large centralized power plants and eventually the right form of supply to Tesla’s polyphase ac motor that helped to launch the electrical revolution and forever change the way the world would work.

Ever since, and certainly up through the turn of the 21st century, the electric power industry has been established and expanded across the globe predominately using ac technologies and networks. Throughout this time, electricity has become the life blood of modern society. There is no single resource commodity like electricity, one that we depend on heavily in our daily lives for our businesses, schools, hospitals, factories, homes, and personal pursuits.

The downside to this dependence is that when power disruptions or blackouts occur, they have a crippling effect on nearly everything that we do. Yet, over 100 years later, from the time when ac was proven superior over dc, we still rely on electric power equipment, networks, and grids that were built primarily during the middle decades of the 20th century, in most developed nations, on the premise of ac technologies.

So what has changed since then? Why are we seeing more dc technologies and infrastructure beginning to penetrate power systems? And how do we deal with these changes and evolutions from the perspective of existing infrastructure, alongside the need to expand and modernize grids in many developing parts of the world?

The answers are multifaceted, but we can certainly start with the advent of semiconductor technology and the first developments of power electronics converter systems for electric power applications in the early 1970s, which introduced, for the first time, the advantages of transmitting power over long distances with dc. The timing of power electronics technology development is very interesting from this historical perspective. The United States and many parts of Europe saw the greatest development and expansions of their power grids during 1930–1970, when the vast majority of infrastructure was put in place as part of pre- and post-World War II federal programs. And, as we know all too well, from the mid-1970s to the turn of the 21st century, we experienced a continued decrease in grid investment and expansion. Indeed, even today, Westinghouse and Edison would still be very familiar and comfortable in a typical power plant or utility transmission or distribution substation.

Thus, as we developed the means through power electronics to convert ac to dc and vice-versa in the 1970s and thereby discovered the merits of dc technologies—then primarily for long-distance high voltage transmission—it was almost too late to implement dc as a large-scale strategic solution to power grid design and operation. Most early-era dc systems were developed for very-long-distance transmission linking economic resources from remote locations to more densely populated load centers and were typically several hundred miles or more in length. This still holds true today for many high-voltage dc (HVdc) applications.

However, we’re beginning to witness dc solutions well beyond high-voltage transmission and at all levels of the grid, including new converter capabilities for renewable energy integration and storage, data center supply, and vehicle charging, as well as submarine and dc cable systems, to name just a few. So, perhaps it isn’t too late after all for dc to play a larger role, and the timing may actually be more aligned with our needs today than it was 100 years ago, or even just 40 or 50 years ago.

Back to the Future

Consider some “revisionist history” that I always posit to my students at the University of Pittsburgh. If Tesla had the thyristor at his fingertips back in the late 1800s, imagine the inventions and uses he would have developed for it that we haven’t even thought of yet and how different our power networks would look today! By revisiting those early, incredible days of electric generation and delivery, today’s engineers have an opportunity to become modern-day Teslas and Westinghouses, but with Edison’s original vision.

It begs the question that many today are asking in earnest: Was Edison ahead of his time? Perhaps, but much more has changed since the late 1800s and early 1900s, and even since the 1970s through the 1990s. Leading the transformation has been the emerging application of dc at both the end-use level of power networks and the energy resource level. These changes are bringing the necessity and promise of dc technologies to the forefront of the industry as we move further into the 21st century. It is time that we re-evaluate the legacy 120-V ac supply for most end-use devices as well as the legacy of ac approaches to power delivery and even the interconnection of energy generation. It is time to challenge these foundations with new methods that provide innovation, greater efficiency, and opportunity for a new era of business and technology development throughout the entire power sector.

If we review the trends in electrical energy usage at the load level, more is based upon the premise of dc. Look around your home or office or manufacturing facility, and you will find a tremendous amount of energy conversion from ac to dc taking place. So much of what we use and operate electrically in typical commercial facilities and residences (consumer and business electronics, lighting, data servers, appliances, and so on) all operate as constant-power loads on low-voltage dc (LVdc) power input. Even in our factories we see the significant role of variable frequency drives, representing more power electronics.

Today, nearly 30% of all power generated will pass through a power electronics converter before it is utilized, and that percentage is predicted to increase to 80% within the next 10–15 years. This represents staggering growth in the converter technology market. Much of this conversion is to service LVdc loads but also to integrate new types of dc-based resources, especially solar energy generation from residential to utility-scale systems. Also from the load perspective, add to everything mentioned thus far thestrong prospect of a greatly expanded electric vehicle market (batteries) in the near future and the expected promise of utility-scale energy storage applications (more batteries). Many of these systems operate essentially on dc power or produce a form of dc power. Yet we continue to supply such loads through a predominately ac system, which brings about inefficiencies and high losses through various levels of power conversions throughout the delivery chain!

Thus, as these evolutions in electricity generation and use continue to develop, it is time that we begin to look at how to more effectively match supply with demand and also at how we deliver that supply to meet demand technologically. A new age of dc technologies is rapidly emerging, and a strong case can be made for more strategic applications of dc throughout all levels of the grid. One area where this is already happening is in the data center industry, where recent examples show complete dc facilities designed and implemented to supply large computer server facilities and the vast majority of the center’s auxiliary loads, such as lighting and controls.

A Push for Greater Efficiencies

So much of what we depend on today for our electrical energy reliability is more efficient power electronics conversion technologies. Our ability to increase efficiencies, reduce loss and footprint, and improve the economics of power conversion technologies is paramount for the future of power systems operation and control. Power electronics will not only play a key role in all of the ac-to-dc (and vice-versa) conversion but also as a new era of dc-to-dc transformation devices are required. Likely, a form of hybrid ac/dc systems will initially emerge that will be highly dependent on new power technologies, advances in semiconductor and control methodologies, and changes in operational approaches.

These advances will not only benefit new dc systems but will also help to improve existing ac networks, such as through more advanced FACTS technologies that have been implemented in recent years at an unparalleled rate around the globe for improved system operation and performance. All of this represents unprecedented but inevitable changes in how we begin to plan and expand new electrical infrastructure.

In this dc-themed issue of IEEE Power & Energy Magazine, we explore the trends in dc technologies, applications, and developments across the entire grid, from renewable energy integration, to long-distance high voltage transmission, to end-use supply, as well as recent medium voltage dc (MVdc) developments for distribution system applications, while also addressing issues of standards, protection, safety, and equipment for wider use of dc technologies. Starting with a very good review of the state-of-the-art of HVdc technologies and new developments by Ram Adapa of EPRI, we continue with an article from Peter Lundberg and coworkers at ABB Grid Systems that addresses dc converters and cable technologies for off-shore renewable energy integration; a piece coauthored by Rajat Majumder and colleagues at Siemens Energy along with Wayne Galli of Clean Line Energy on new power transmission applications for HVdc; and a treatment of LVdc efficiency and reliability for sustainable data center applications by Guy AlLee of Intel Labs and Bill Tschudi of Lawrence Berkeley National Laboratory.

These articles are followed by an overview of dc at the building level including microgrids and a discussion on standards by Brian Patterson of the E-Merge Alliance and Armstrong World Industries. The issue concludes with an overview of some efforts by my own research group here at the University of Pittsburgh’s Swanson School of Engineering on MVdc concepts and developments. We round out the issue with an excellent “In My View” opinion appropriately titled “DC Versus AC” by Peter Fairly, well-known environmental journalist, energy editor of IEEE Spectrum, and contributing editor ofTechnology Review.

The continued growth of dc systems at both the load and the resource levels is inevitable. It is time that, as an industry, we begin to more strategically explore the merits of dc over ac throughout the system and explore the merits of hybrid ac/dc infrastructure and operations. Westinghouse and Edison would be proud to see us making these advances in our ever-changing electrical world. Certainly a shift toward dc would make Edison happy. In fact, some folks have begun to comment on this dc evolution as more of a “revolution” that vindicates Edison!

Perhaps this is true, but you may ask, What would Westinghouse think? Since I’m from Pittsburgh, I feel somewhat beholden to Westinghouse and his approach. Yet I also believe that Westinghouse was a businessman first and would definitely see the value proposition today of the emergence and growth toward dc advances. In fact, he would probably be setting up new manufacturing facilities, buying dc technology patents, and hiring the best and brightest minds in the business—our modern-day Teslas—to capture this new business opportunity! So, while this issue cannot cover all aspects of what is taking place today along with all of the historical developments in dc technologies, it does provide a good overarching treatment of dc developments that we hope will encourage continued discussion, debate, and eventually more development and deployment of dc solutions and power electronics technologies that are coming along with this evolutionary paradigm shift in the power industry.

I hope you enjoy reading this issue of IEEE Power & Energy Magazine as much as I have enjoyed serving as guest editor. It has been a true pleasure and a tremendous amount of fun to work with Mel Olken, Peter Fairley, and the authors of the informative articles contained herein.

In This Issue

Feature Articles

Departments & Columns

Upcoming Issue Themes

  • November/December 2017
    Renewable Integration
  • January/February 2018
    Societal Views of the Value of Electricity
  • March/April 2018
    Controlling the Unpredictable Grid