Deep Dive Into Kia’s Innovative Dual-Wye-and-Delta EV Motor Configurations

Munro Live engineer explains how Kia managed to combine both electric motor configurations into one motor – and to switch between those modes on the fly.

Dan Carney, Senior Editor

September 17, 2024

4 Min Read
The Kia EV9's motor has six power connectors, providing two complete sets of connectors for the 3-phase motor.
The Kia EV9's motor has six power connectors, providing two complete sets of connectors for the 3-phase motor.Munro Live via YouTube

At a Glance

  • "Wye" electric motor configuration is good for producing torque, with high efficiency at low speeds
  • "Delta" configuration is good for high power, with high efficiency at high speeds
  • Kia's inverter and motor design can switch seamlessly between modes

Grab a seat, class, it is time for a lecture from Dr. Paul Turnbull on the fundamentals of EV motor design and Kia’s groundbreaking solution to switching between so-called Wye and Delta configurations for those motors to optimize performance to match driving conditions.

Though he earned his PhD in Mechanical Engineering from the University of Michigan, Turnbull still proudly wears his undergraduate alma mater Michigan State “Spartans” tee shirt. The veteran of Visteon, Ford, and General Motors was in charge of electric machine design and validation at those companies.

Now he’s lead electric machine engineer for the industry technical analysis group Munro Live, where he’s dissected the electric motor used in the Kia EV9 battery-electric family-hauler SUV for a Munro Live YouTube video.

“There is some really innovative electric machine development going on,” Turnbull observes. He points out that the Hyundai Group has already innovated with the motors in its earlier E-GMP-platform products such as the Hyundai Ioniq 5.

That car, he reminds us, employs four connectors in its 3-phase electric motor rather than the usual three because that lets the car use its electric motor as a transformer to boost voltage from 400-volt charging stations to match its 800-volt battery pack.

Related:Kia EV9 Targets the Family EV Sweet Spot

“They’re using the inductance of the motor as a part of the boost converter in their charging system,” he said. This avoids the need for an additional dedicated power inverter in the car to let it use the far-more-common 400-volt chargers.

Nifty. But the EV9 goes further, with six connectors in its otherwise similar motor. “What they’ve done is they have both the beginning and the end of each of the three phases connected to the inverter,” Turnbull said. “That gives them full access to the winding configuration of the motor.”

Why do that? Because there are two possible configurations for the windings, the Y-shaped “Wye” configuration and the triangular “Delta” configuration. Each has its pros and cons and ordinarily engineers have to pick one and work around its weaknesses.

210324_PP_Vitesco_Technologies_800Volt_HMMC_1.jpg

For the EV9, Kia lets the car switch between configurations as needed, so the motor runs in the optimum configuration for the conditions, maximizing power and efficiency.

Using both rather than either/or isn’t a new idea. It is just that while the concept has been around for decades, it has been impractical for use in vehicles until now. “Wye/Delta switches have existed in industry for a long time,” Turnbull noted.

“But typically, you have to turn off the machine, lock it out, and then flip the switch, and then turn the machine back on in order to get an effective switch from Wye to Delta,” he said. “When you switch from Wye to Delta, the personality of the motor completely changes.”

Related:Hyundai Will Ride the E-GMP Platform to 11 New EV Models by 2030

The “Y” or star-shaped configuration routes all power coming into the motor to a central point. This provides excellent low-speed torque, which is perfect for stop-and-go city driving.

The Delta configuration, on the other hand, routes power end-to-end between the three input points for the 3-phase motor. “This allows two different parallel paths for the current, so you end up with lower resistance on the winding and you get much higher power from the motor, about 1.7 times the power,” lectured Dr. Turnbull in his de facto online EV Motor 101 class.

Wye_Delta_diagram.png

“With the Kia EV9, they’re able to optimize for city efficiency in the Wye connection and then, on the fly, this inverter is able to switch – with power running – to change it to a high-power configuration with high efficiency at highway speed.”

“Absolutely brilliant,” Turnbull crowed. “In the past, it has never been practical. Because in order to do it, you have to have, in the inverter, two completely separate sets of switches, and the switches are the most expensive part of the inverter.” But as production volumes of EV components rise, part costs are finally falling. “The volume of electric machines has gotten to the point now that EVs are more popular, where the cost of two sets of switches are no longer prohibitive,” he said.

Related:2023 Hyundai Ioniq 6 Delivers EV Value

Also, Kia can cost-justify the extra set of switches because the company is using them to provide the boost-circuit functionality seen in the Ioniq 5. “With all that functionality built in, it more than pays for the extra set of switches in the inverter,” Turnbull stated. “It’s the first that we’ve seen in the industry, groundbreaking innovation that Kia has put on the road for us.”

“It is something that I think a lot of the other automakers are going to now be looking at as an innovation they might try to incorporate as well,” he concluded. Class dismissed.

About the Author

Dan Carney

Senior Editor, Design News

Dan’s coverage of the auto industry over three decades has taken him to the racetracks, automotive engineering centers, vehicle simulators, wind tunnels, and crash-test labs of the world.

A member of the North American Car, Truck, and Utility of the Year jury, Dan also contributes car reviews to Popular Science magazine, serves on the International Engine of the Year jury, and has judged the collegiate Formula SAE competition.

Dan is a winner of the International Motor Press Association's Ken Purdy Award for automotive writing, as well as the National Motorsports Press Association's award for magazine writing and the Washington Automotive Press Association's Golden Quill award.

He has held a Sports Car Club of America racing license since 1991, is an SCCA National race winner, two-time SCCA Runoffs competitor in Formula F, and an Old Dominion Region Driver of the Year award winner. Co-drove a Ford Focus 1.0-liter EcoBoost to 16 Federation Internationale de l’Automobile-accredited world speed records over distances from just under 1km to over 4,104km at the CERAM test circuit in Mortefontaine, France.

He was also a longtime contributor to the Society of Automotive Engineers' Automotive Engineering International magazine.

He specializes in analyzing technical developments, particularly in the areas of motorsports, efficiency, and safety.

He has been published in The New York Times, NBC News, Motor Trend, Popular Mechanics, The Washington Post, Hagerty, AutoTrader.com, Maxim, RaceCar Engineering, AutoWeek, Virginia Living, and others.

Dan has authored books on the Honda S2000 and Dodge Viper sports cars and contributed automotive content to the consumer finance book, Fight For Your Money.

He is a member and past president of the Washington Automotive Press Association and is a member of the Society of Automotive Engineers

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