Traction inverters: the intersection of automotive innovation and performance

Step on the pedal of a modern electric vehicle (EV) and you’re rewarded with quick, smooth acceleration. Should you be satisfied? Absolutely not.

And you don’t have to be, because higher performance and longer driving range are coming to EVs. Because of the way EVs turn stored energy into propulsion, many of these improvements happen at the electrical level rather than at the traction motors level. Recent advancements in traction inverter technology have made it a particularly fruitful area for growth. The traction inverter manages the flow of energy from the high-voltage battery pack to the motor, turning the wheels and propelling the vehicle. Most EV headlines focus on innovations in battery systems, often overlooking the multi-kilowatt traction inverter.

But advances in traction inverters, enabled by our company’s microcontrollers with real-time control capabilities and isolated gate drivers, are pushing expectations of EV performance even further. Better switching leads directly to improvements in reliability, performance, weight and power density – not to mention paving the way for lighter, faster motors. 

The result: Next-generation EVs will be even more fun to drive.

“Innovation in power electronics is actually overtaking the constraints on the mechanical side,” said Xun Gong, a systems manager for HEV/EV traction inverters at our company. “We’re getting close to the mechanical limits." 

Setting a new bar for efficiency

By some measures, EVs are already extremely efficient. EVs experience just one-quarter the energy waste of a typical gas-fueled engine.^[1] But there’s still plenty of room for improvement. Better components under the hood mean more years of reliable, trouble-free driving. When microcontrollers can assume more duties, the amount of circuitry and enclosures can be reduced, shrinking the size and weight of the overall electronics systems in the car.

Our company has designed industrial controllers and power integrated circuits (ICs) for high-voltage motors used in grueling industrial settings and able to withstand adverse conditions for decades, and that experience informs how we help customers solve EV design challenges. Vehicles are expected to perform reliably in bitterly cold temperatures, in torrential rainstorms and on blazingly hot days. 

“We have learned a lot from working with our industrial customers and their motor drives, and our products have been designed for high-voltage systems since the beginning," said Audrey Dearien, an applications manager for isolated gate drivers at our company. “We’re making traction inverters better by building upon our previous innovations."

Why silicon carbide matters

One of the most significant changes pushing EVs to greater real-world performance is a transition from insulated gate bipolar transistors (IGBT) to silicon carbide (SiC) technology for the high-voltage switches used in a traction inverter. Because SiC transistors are more efficient – turning more stored battery input into usable motor output – than IGBTs, they are a natural upgrade. They are also smaller than IGBTs and run cooler, further reducing weight, size and energy waste in the drive system.

But moving to SiC switching creates other challenges. A SiC switch is more susceptible to damage from short circuits than IGBT technology. The EV needs the right driver technology to accompany the move to SiC. 

“Our gate driver quickly detects a short and turns that switch off in less than one-millionth of a second to protect it from damage," Audrey said.

SiC transistors switch very fast, which is part of their efficiency advantage. This high switching speed also creates the potential for high levels of electrical noise that could activate a motor in error. Our gate drivers control this risk with safety features that reduce the impact of noise in the drive system. 

“In the past with slower switching transistors, the switching losses could only go so low,” Audrey said. “But with silicon carbide, you’re given a very fast switch that must be controlled efficiently. If you don’t have efficient switching, you’re not going to get the full advantages of SiC."

Supporting higher EV power density

Traction inverter upgrades are just one part of a bigger quest by the EV industry. One major goal is to improve power density in high-power electronic systems. That improvement will enable more energy out of smaller boards, which will reduce the size and weight of power conversion systems, motors and other drive components, including the traction inverter. 

“When power density is improved, the car can be lighter so you can accelerate even faster,” Xun said. “Or you gain more space in the car, so there is more room for seating." 

Integrating powertrain systems is one way to improve power density. Advances in analog and embedded processing technologies enable carmakers to combine individual systems such as the on-board charger, DC/DC converters and traction inverter into a single, compact mechanical enclosure under a single domain controller. By integrating the powertrain, carmakers can cut design costs in half while increasing efficiency and improving reliability and power density. That, in turn, creates a better experience for drivers, including lower costs of purchase or ownership, longer vehicle life, and better on-road performance.

The next generation of traction inverters improves EV efficiency and performance by delivering:

Efficiency levels that are 800-volt ready. Most of today’s EVs run on a 400-volt battery pack, but the industry is shifting to 800 volts. An 800-volt motor can run at twice the revolutions per minute, but can have a higher risk for energy loss and waste. Our high-performance microcontrollers (MCUs) and fast gate drivers are ready for the challenge, with fast current loop control that can adjust the motor switching algorithm every one-millionth of a second. 

“As power levels in a system go up, the losses from any inefficiency become more pronounced," said Mike Pienovi, product line manager for Sitara™ MCUs at our company. “To take advantage of this new potential, you need to have microcontrollers with low-latency, high-precision sensing and control to support the higher switching frequencies and maximize efficiency."

Road-ready safety. Our proprietary isolation techniques can help the car and its high-voltage battery to operate safely on the road. Additionally, our automotive microcontrollers and other components for traction inverters and motor control are functional-safety compliant and can help system designers meet all safety integrity levels up to ASIL D, which represents the strictest test of automotive safety.

Improved reliability. Our products and system designs can help extend the life of traction inverters and other key EV components through reinforced capacitive isolation, failure detection and state-of-health monitoring, including heat and voltage monitoring. These diagnostics and component health checks provide early warning and workaround options, helping carmakers reduce failure-in-time rates for key components.

When they arrive, the next generation of light, ultra-fast motors may grab most of the headlines. But informed EV drivers will understand that much of their performance and reliability is made possible by traction inverter advancements.

^{References:
[1] https://www.fueleconomy.gov/feg/atv-ev.shtml}