Hybrid AC and DC Distribution Design Would Lower Costs and Improve Reliability

February 02, 2019 by Scott McMahan

A new distribution system developed by researchers at the University of Waterloo would reduce electricity prices by more than five percent while also improving service reliability, according to their findings. The design includes the integration of the two kinds of electric current that power homes, industries, and electric vehicles; ac and dc.

Researchers found enhanced efficiencies with a system design that delivers both kinds of current to customers instead of the ac-only distribution systems now used throughout the world. Their strategy minimizes conversions from one kind of current to the other and makes it easier to integrate growing green technologies.

"Minimizing power conversion requirements creates a simpler system with greater efficiency and less loss," said Haytham Ahmed, a postdoctoral fellow who led the research with electrical engineering colleagues at Waterloo. "As you reduce the number of converters, you also reduce the chances of service interruptions due to breakdowns."

Number of AC-DC Conversions Minimized in Design

Existing power networks carry ac because the utilization of power transformers are needed to increase voltage for increased long-distance transmission efficiency and reduced voltage for distribution purposes. As a result, the distribution systems that then deliver electricity from local substations to end users also carry ac.

For this reason, common electronic devices such as computers, televisions, and smartphones, which all use dc power, must include ac-dc converters. This also means converters are required to charge dc-powered electric vehicles and feed electricity into the grid from green electricity-generating sources such as solar panels and fuel cells, which produce dc. So, instead of needing ac-dc conversion for each dc-using electronic device, their proposed system would use just one ac-dc converter for a residential or commercial area.

Computer Modeling Evaluated Cost/Reliability Tradeoff

The new ac and dc hybrid system, which is the result of advanced computer modeling and optimization, introduces ac-dc converters at strategic points in the distribution system itself, instead of only at endpoints where customers access it.

According to these complex models, a comparison of the ac and dc hybrid distribution system to an ac-only system estimated savings of more than five percent due to lower energy losses and lower infrastructure costs. The sophisticated modeling of the system evaluated the tradeoff between the two objectives to obtain both the lowest cost with the highest reliability.

The researchers point out that if electronic devices and electric vehicles no longer needed converters, they would also be cheaper to make, and consume less electricity.

"When you feel heat coming off the charger for your laptop, that is lost energy," said Ahmed. "We can eliminate those losses so we consume less power."

They found that the planned ac and dc hybrid system could achieve improvements in both the electricity distribution costs and reliability. The system design is expected to have the most significant potential for adoption in new residential and commercial areas, or when existing systems are expanded with additional substations.

For the research, Ahmed collaborated with Magdy Salama, a professor of electrical and computer engineering, and Ayman Eltantawy, a former postdoctoral fellow at Waterloo.

The latest in a series of papers on their research, A reliability-based stochastic planning framework for ac-dc hybrid smart distribution systems, appears in the International Journal of Electrical Power and Energy Systems.