Energy conversion and storage components are notoriously large. The size of power supplies, battery chargers, battery packs, etc. are marginally smaller than what they were ten or twenty years ago. Why?
Last month the world celebrated the 50th anniversary of an article written by Gordon Moore. The observations he made based on the size reduction of integrated circuit components are enshrined as the famous “Moore’s Law”. Although not a law in the strictest sense, the roadmap it provided to the electronics industry has been a powerful prophecy. Comparatively, energy systems have developed at a snail’s pace. Why have we not observed the same rapid pace of development that we have become accustomed to in the world of integrated circuits?
The obvious answer is that physical scaling does not help. Power transistors are processing packets of energy, not data. Making a smaller power transistor would only be helpful if the properties of transistors improved. Generally, this is not the case. Smaller power transistors have lower voltage ratings and/or current ratings, thereby reducing their power processing capabilities.
The real impediment is passive components: inductors, capacitors, and transformers. Again, these components do not improve by simply making them physically smaller. Inductors and capacitors are usually used in dc-dc, ac-dc, and dc-ac converters as energy buffers. Operating a power converter at a higher switching frequency can reduce the cycle-by-cycle energy storage requirement enabling the use of smaller passive components. This only works to a certain extent: increasing switching frequency also increases switching related power loss which is released as heat. Higher frequency operation not only reduces energy conversion efficiency but also makes thermal dissipation more challenging. Typical energy converters today operate in the low frequency (LF) or medium frequency (MF) range (30kHz to 300kHz or 300kHz to 3MHz, respectively) depending on their power level.
What does the future hold?
While I am too diffident to make bold claims on what the future will hold, there are noteworthy trends in the field of energy conversion. One popular trend is wide bandgap devices, specifically, gallium nitride (GaN) and silicon carbide (SiC). Their improved device characteristics enable power converters to switch at higher frequencies with less switching power loss. There is also the possibility of higher temperature operation. Some believe that wide bandgap devices will trigger a major shift in power conversion much like the introduction of power MOSFETs and IGBTs opened the door to innovation and displaced BJTs years ago.
One catalyst for the implementation of wide bandgap devices is the Little Box Challenge. The IEEE Power Electronics Society and Google have teamed up to offer $1 million to the team that can build a kW scale inverter in the size of a small laptop. Many of the wide bandgap device manufacturers are listed on the Little Box Challenge website and offer support to contestants. It will be exciting to see who makes it to the finals and what the grand prize winner will be able to achieve when the results are announced in January 2016.
It will take more than just better devices to improve the density of power converters. There are developments in magnetic materials and structures, converter topologies, control schemes, packaging, and integration that are just as important. Startups like FINSix and Zolt are trying to leverage some of these new technologies to introduce significantly smaller laptop/phone chargers. Since neither of these companies have released any products yet it is hard to ascertain exactly what they are doing, but based on the information available so far they appear to be using new converter topologies, devices, and control schemes.
What remains to be seen is how useful smaller power converters are. There are certainly benefits in terms of space and weight savings, which are particularly valuable in transportation systems. Less physical material may reduce bill of materials cost as well. Higher efficiency leads to less energy consumption and longer battery life. However, do higher density energy systems enable new applications or open up new fields? These benefits would distinguish the evolutionary advances from the truly revolutionary.
The internet as we know it today would not have been possible were it not for improvements in integrated circuits such as those noted by Gordon Moore. What do you think the broad impacts of smaller power converters could be? Please share you comments below.
Pradeep Shenoy is a systems engineer at Texas Instruments. His focus area is energy conversion and system design. He received a B.S. degree in electrical engineering from the Illinois Institute of Technology, Chicago, and M.S. and Ph.D. degrees in electrical engineering from the University of Illinois, Urbana-Champaign.
He received the Illinois International Graduate Achievement Award in 2010 and was a finalist for the Lemelson-MIT Illinois Student Prize for Innovation in 2012. He serves as the Young Professionals Chair and as an Administrative Committee Member for the IEEE Power Electronics Society.