Kia EV9: A quick look into the Dual Inverter Strategy with PSIM

NikosDimitrakopoulos · December 3

The Kia EV9 showcases an innovative approach to maximizing EV efficiency through its dual inverter and open-winding motor setup. While the core focus of this article is the system-level power electronics, let’s touch briefly on the motor.

With six winding-end connections, the design has sparked speculation about a star-delta approach. But why use a second inverter (6 active switches) for this? Adding to the intrigue, patent US20240039448A1, published in February 2024, outlines a unique approach that opens new possibilities.

The EV9 motor design may aim to increase efficiency by using more turns in the windings, reducing drive current and minimizing PWM losses—key for urban driving. However, this creates a trade-off: at higher speeds, back EMF rises rapidly, limiting power output. To solve this, Kia introduces a second inverter that effectively increases the available voltage in highway mode. This allows the EV9 to maintain high torque and power at higher speeds, overcoming the limitations of back EMF.

I’m simulating this system in PSIM, capturing the trade-offs between efficiency/cost and power across driving conditions. A single operating point takes seconds; an efficiency map minutes; and design space exploration with adaptive gate driving and cooling tests, just hours for thousands of points.

With HyperStudy, I’m generating multi-dimensional efficiency maps and visualizing the tradeoffs through Pareto plots and custom post-processing scripts. You can even import machine models from Flux for simulations tailored to your motor geometry/materials. More info on the PSIM-Flux connection here:

Flux-PSIM Coupling : Leverage the system simulation speed while working around your Motor Design

This analysis highlights the Kia EV9's innovative design and demonstrates the critical role of system-level optimization for e-drives. Altair provides the most complete suite of tools to investigate the trade-offs under a single, cost-efficient licensing umbrella!

I am attaching the simulation files in this article, and I totally recommend that you try this yourself.

Disclaimer: The results here are hypothetical and not actual data or designs by Kia. This is just my understanding of the situation and an effort to explore the reasoning behind the open-winding motor and dual-inverter setup.

Here is my analysis: