New Inverter Device Could Improve Fuel-Efficiency, Range of Hybrid and Electric Vehicles

The new inverter, made using silicon carbide components, improves electric vehicle efficiency and range. (Credit: Iqbal Husain)

A new kind of inverter device that is smaller, lighter, and much more efficient has been developed by North Carolina State University researchers. This inverter device is expected to enhance the range and fuel-efficiency of electric and hybrid vehicles.

While functioning, hybrid, and electric vehicles rely on inverters to make sure that sufficient electricity is transferred from the battery to the motor. Conventional inverters rely on components made out of semiconductor material silicon.

The inverter was developed using off-the-shelf components that are made up of wide-band gap semiconductor material silicon carbide (SiC). This research was conducted by a team of researchers at the Future Renewable Electric Energy Distribution and Management (FREEDM) Systems Center at NC State, and has obtained promising results.

Our silicon carbide prototype inverter can transfer 99 percent of energy to the motor, which is about two percent higher than the best silicon-based inverters under normal conditions. Equally important, the silicon carbide inverters can be smaller and lighter than their silicon counterparts, further improving the range of electric vehicles, and new advances we’ve made in inverter components should allow us to make the inverters even smaller still.

Iqbal Husain, Professor, North Carolina State University

As “range anxiety” is one of the important factors that limit the public approval of electric vehicles, range becomes a vital criteria to be considered. The main concern expressed by people is that, they might get stuck in between their journey or they will not be able to travel very long distances.

The recently developed SiC-based inverter has the capability to transmit 12.1 kW/L of power, which is near the U.S. Department of Energy’s goal of developing inverters that has the ability of transmitting 13.4 kW/L by 2020. Drawing a comparison, an electric vehicle developed in 2010 was able to deliver just 4.1 kW/L.

“Conventional, silicon-based inverters have likely improved since 2010, but they’re still nowhere near 12.1 kW/L,” Husain says.

Engineers can develop inverters and their components such as inductors and capacitors, to be lighter and smaller, mainly because of the new SiC materials’ power density.

But, frankly, we are pretty sure that we can improve further on the energy density that we’ve shown with this prototype.

Iqbal Husain, Professor, North Carolina State University

This is mainly due to the off-the-shelf SiC components that were used to build the new inverter prototype. Also, FREEDM researchers have lately built new, ultra-high density SiC power components that are expected to reach closer to DOE’s 13.4 kW/L goal when it is integrated into next generation inverters.

Compared to older versions, the new power component is able to dissipate heat more effectively. This property creates potential for the development of air-cooled inverters without the requirement of heavy and bulky liquid cooling systems.

We predict that we’ll be able to make an air-cooled inverter up to 35 kW using the new module, for use in motorcycles, hybrid vehicles and scooters, and it will boost energy density even when used with liquid cooling systems in more powerful vehicles.

Iqbal Husain, Professor, North Carolina State University

The SiC inverter prototype that is currently being used was modeled to reach up to 55 kW, the kind of power seen in a hybrid vehicle. At present, the researchers are involved in the process of boosting the power up to 100 kW, similar to the kind of power seen in a fully electric vehicle, using off-the-shelf parts. Additionally, the team is also aiming to develop inverters that utilize the new, ultra-high density SiC power component that was designed on-site.

A paper describing the work involved in construction of the new inverter, titled “Design Methodology for a Planarized High Power Density EV/HEV Traction Drive using SiC Power Modules,” will be presented at the IEEE Energy Conversion Congress and Exposition (ECCE), scheduled to happen from September 18th to 22nd in Milwaukee. Dhrubo Rahman, a PhD student at NC State is the lead author of the paper. The co-authors of the paper are Wensong Yu and Douglas Hopkins, research professors in NC State’s Department of Electrical and Computer Engineering; Adam Morgan, Yang Xu and Rui Gao, who are Ph.D. students at NC State; and Husain.

At ECCE, a paper presenting the research works involved in the development of new, ultra-high density SiC power component, “Development of an Ultra-high Density Power Chip on Bus Module,” will be presented. Yang Xu is the lead author of the paper. Yu, Husain, Hopkins, and Harvey West, a research professor in NC State’s Edward P. Fitts Department of Industrial and Systems Engineering are the co-authors of this paper.

This research work received funds from the DOE’s Office of Energy Efficiency and Renewable Energy under award number DE-EE0006521. The PowerAmerica Institute, a public-private research initiative housed at NC State extended support to the research work. The development and implementation of new renewable electric-energy technologies will be facilitated by FREEDM, a National Science Foundation Engineering Research Center.

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