Tutorial and Workshop

Tutorial 1: Practical experience from DC microgrids in buildings

Abstract and Outline

This tutorial will discuss challenges and practical experiences acquired from more than 2000 DC micogrid installations in buildings ranging from private villas to large commercial buildings. The DC microgrids include components such as solar cells, batteries, HVAC systems, LED lighting, water heaters and EV chargers. All DC microgrids are actively regulated using DC/DC and AC/DC converters with hierarchical control strategies including droop control. The majority of DC grids are built using a bipolar +/-380 VDC system voltage.
The tutorial will start by illustrating some representative projects including the design and control strategies employed. This is followed by a discussion about considerations when interfacing various DC devices in terms of voltage levels, inrush currents, EMC characteristics and efficiency. Combining LVDC with USB-C to enable efficient use of DC all the way to small office appliances. One section will be devoted the DC grid codes that just like their AC counterpart are necassry to ensure interoperability and stability in DC microgrids when using devices from different suppliers. Finally there will be a discussion about how to accelerate taking DC microgrids and DC applications from the research labs to everyday applications.

This tutorial will be a smörgåsbord of hands-on examples, experience and discussions about planning, building and operating DC microgrids in buildings.

– Description of a selection of representative projects
– Hierarchical control strategies
– Interfacing commercially available DC devices to DC grids
– USB-C for powering office appliances ”Last meter DC”
– EMC considerations in DC microgrids
– Short circuit protection
– DC grid codes
– Bridging the knowledge gap for an AC world
– Getting DC from research labs to everyday applications

Lead instructor:    Björn Jernström

Björn has a Master of Science degree in Electrical Engineering from the Royal Institute of Technology in Stockholm and speciailized in high voltage engineering and plasma physics. He has founded three successful startups in the electric power industry and are now working full time as CTO with Ferroamp. A company he founded in 2010 based on a phase balancing technology that enables savings on grid fees and faster EV charging. A concept that has now evolved into a modular system based on DC microgrids. Björn is the inventor behind four different patents related to the technology. Prior to starting Ferroamp he has worked as project manager for a thin film CIGS pilot plant, R&D manager for optical media replication equipment and also within different companies related to electric measurement technology. Björn is a member of the standardization comittes TC8 and TC64 as well as IEC SyC LVDC.

Tutorial 2: DC Circuit Breakers: Current Status, Technology Comparison, and Challenges

Abstract and Outline

DC circuit breakers (DCCBs) must be provided for LVDC (<1kV), MVDC (<40kV), and HVDC (100’s kV) power systems.  A wide range of DCCB technologies have been investigated for different applications. Presently, solid-state circuit breakers (SSCBs) can quickly interrupt a DC fault current within tens of microseconds but suffer from high conduction losses and weight and cost penalties associated with the cooling and semiconductor components, especially for high power applications. The most distinct advantage of semiconductor switches is their capability of switching current during fault interruption while the most distinct disadvantage is their nonnegligible on-resistance when conducting current. Unfortunately, they are used in SSCBs in the worst way possible—continuously dissipating power except during infrequent fault interruption.  Numerous hybrid circuit breaker (HCB) schemes have been proposed to offer an on-state resistance 2-3 orders of magnitude lower than that of SSCBs. All the HCBs are of parallel type, in which an electronic path is in parallel with a main mechanical switch. The fault current in the mechanical switch is initially commutated to the electronic path to create artificial current zero crossings in various forms to aid the opening of the mechanical switch. The electronic path will then be interrupted with varistors (MOV) clamping the transient voltage surge and absorbing the residual electromagnetic energy. However, these HCB solutions offer only a moderate fault response time of several milliseconds. This may be too slow to limit the fast-rising fault current in low-impedance DC power networks. The most distinct disadvantage of all the HCBs is the relatively long opening time of the mechanical switch to achieve a sufficiently wide gap for sustaining the DC voltage, during which the fault current continues to rise through the electronic path.

This tutorial will provide a review and performance comparison on the state of the art DCCB solutions in a systematic way. It will cover a few case studies in detail, including a 380VDC SSCB for DC data center applications, 6kV MVDC HCB based on a transient commutation current injection concept, and a cost-effective 600VDC electronically assisted HCB for PV applications. The talk will also hightlight the fundamental challengesfaced by these DCCB technologies and shed some light on future research directions.

– Overview on DCCB technologies
– HCBs
– Other current limiter or interrupter technologies (e.g., SFCL)
– Major challenges and future trends

Lead instructor:    John Shen

Dr. John Shen is Grainger Chair Professor of Electrical and Power Engineering at Illinois Institute of Technology. He has more than 30 years of industrial, academic, and entrepreneurial experience in power electronics and power semiconductor devices with over 300 publications and 19 issued U.S. patents in these areas. He has been involved in DC circuit breaker research since 2013, and is an inventor of several patents and an author of 25 publications on the subject. He serves as PI of an ARPA-E CIRCUITS project on low-voltage solid-state circuit breakers and co-PI on an ARPA-E BREAKERS project on MVDC hybrid circuit breakers. He is a Fellow of IEEE and the U.S. National Academy of Inventors.

Workshop 1: DC Microgrid Design and Controller Testing Using the PLECS Toolchain

Presenter: Lino Capponi, PLEXIM

Lino Capponi received the B.S. degree in electrical energy systems in 2016 and the M.S. degree in electrical engineering from HES-SO Valais-Wallis, Sion, Switzerland, in 2019. Since 2019, he has been with Plexim as an Application Engineer, working on the software PLECS for fast simulation of power electronic systems. His current research interest include real-time HIL simulation of power converter and automatic code-generation tools for embedded targets.

Workshop 2: The Grid of Grids – A hybrid multi-tiered bi-direction microgrid network based on DC coupling

Presenter: Brian T. Patterson, EMerge Alliance

The seminar discusses the main technologies that enable this non-synchronous approach to networked microgrids including its fundamental reliance on distributed energy resources, DC technology and distributed intelligence.  The presentation features one of the first multi-tier dc networks in North America, located at Kirtland AFB in Albuquerque NM and operated by Emera Technologies.