Programme MERIT to bridge the power electronics ‘medium-voltage gap’ in the US
Prasad Kandula builds a medium-voltage solid state circuit breaker as part of ORNL’s project to develop medium-voltage power. Credit: Carlos Jones/ORNL, US Dept. of Energy
The US Department of Energy’s Oak Ridge National Laboratory (ORNL) has announced the Medium Voltage Resource Integration Technology programme (MERIT) which aims to bridge the medium-voltage gap in power electronics.
According to ORNL, current power electronics tend to operate at either end of the spectrum – personal EV charging or storing energy from a commercial solar panel, for example, requires low voltage, while high voltage is used for utility-scale projects like wind and solar farms or interconnecting power distribution and transmission systems.
However, there is a power electronics gap between 1,500 and 50,000 volts — the “medium-voltage” range — which is critical to larger-scale renewable energy projects, larger equipment such as wind turbines and larger electric vehicles like trains and vertical-takeoff aircraft.
Through MERIT, ORNL scientists are looking for a medium to fill this gap, which they say will help the US achieve clean energy goals and expand capacity in an overburdened power grid without erecting thousands of miles of new transmission lines.
ORNL will be guiding the MERIT programme, which teams four national labs and five universities to develop devices that operate efficiently in that middle range.
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“There are many applications that can fit here, but the technology for that middle space hasn’t been proven to be reliable or cost-effective,” said Prasad Kandula, leader of ORNL’s Grid Systems Hardware group, in a release.
Additionally, according to Kandula, medium-voltage power electronics have become more affordable and making the switch could reduce the size, weight and volume of a system.
“Power conversion using medium-voltage power electronics is expected to be more efficient, in addition to packing more power into a smaller space.”
Benefits to grid reliability
Most of the North American electric grid uses alternating current (AC), while renewable energy generation and electric cars require direct current (DC).
Power electronics are used to switch between these flows and to link separate systems. Expanding these capabilities to medium voltages would open new options for electric reliability.
For example, medium-voltage power electronics could be used to feed electricity from a region with extra supply to a neighbouring system struggling to meet demand.
This could prevent rolling blackouts, price spikes and activation of polluting backup power plants.
In another scenario, medium-voltage power electronics could help convert key portions of the distribution grid from AC to DC, because DC is more efficient at carrying power long distances. This would essentially increase the amount of delivery capacity using the same power lines.
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According to Kandula, medium-voltage power electronics could also enable complete DC operation for projects such as a microgrid with its own solar power and batteries.
“Initially a DC ecosystem would most likely be used at isolated systems like a campus,” Kandula said. “The next level might be a distribution feeder of a few miles, like a solar farm at the edge of the grid.”
A DC-only system requires less power conversion equipment and eliminates energy losses that occur during the conversion process. It could make clean energy more efficient and economical, especially as big solar and wind farms are increasingly built far from population centres where electricity demand is concentrated.
Reliability building blocks
ORNL researchers have been developing a menu of medium-voltage building blocks, such as converter modules, specialized magnetics, and protection mechanisms that isolate electrical problems.
This effort builds on the experience and capabilities in ORNL’s Grid Research Integration and Development Center, or GRID-C, where researchers can simulate different architectures, build a converter and test it up to 13,000 volts.
“With MERIT, we’ll develop building blocks of varying types to increase reliability, then stack multiple blocks to reach higher voltages,” Kandula said. The ability to plug a variety of modules into a larger architecture will make it easier to explore new power applications, from recharging long-haul electric trucks to producing green hydrogen for the steel industry.
Additionally, for MERIT, ORNL will expand existing relationships with utilities to identify medium-voltage needs.
“The end goal for us is to pick a use case, work with a partner, build a full system, install it, show it operational in the field and show the financial implications,” Kandula said.
Other MERIT research partners include National Renewable Energy Laboratory, Sandia National Laboratories, Pacific Northwest National Laboratory, University of Arkansas, Virginia Polytechnic Institute and State University and Florida State University.
The MERIT project is funded under DOE’s Grid Modernization Initiative through the Grid Modernization Laboratory Consortium.
