SiC MOSFETs Replacing Si IGBTs in EV Inverters

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The year 2023 began with two major design wins for silicon carbide (SiC) semiconductors in traction inverters for electric vehicles (EVs). A traction inverter—located between the high-voltage battery and the electric motor in an EV—converts DC power derived from batteries to AC power used in EV motors.

First, on Jan. 4, 2023, onsemi announced that its SiC modules will power the traction inverter of Kia’s EV6 GT model, enabling high-efficiency power conversion from 800 V of the DC battery to the AC drive for the rear axle. It’s worth mentioning that in December 2022, STMicroelectronics announced that its SiC modules had been incorporated into Hyundai’s Electric-Global Module Platform (E-GMP), shared by Kia’s EV6 and several other models.

Figure 1: The traction inverter in Kia’s EV6 GT is based on SiC modules. (Source: onsemi)

Next, on Jan. 10, 2023, Rohm Semiconductor, which began mass production of SiC MOSFETs in 2010, announced that its SiC MOSFETs and gate-driver ICs will power EV inverters developed by Hitachi Astemo, an automotive parts supplier in Japan. Gate-driver ICs, an essential component in EV inverters, provide an interface between the inverter-control microcontroller (MCU) and the SiC MOSFETs that deliver power to the inverter. Gate-driver ICs receive control signals from the MCU in the low-voltage domain and transfer these signals to rapidly turn power devices on and off in the high-voltage domain.

SiC semiconductors are gaining mass adoption in EV systems like DC/DC converters, traction inverters and on-board chargers (OBCs). This article will explain how SiC semiconductors and modules are reinvigorating traction inverters, a fundamental building block in vehicle electrification. According to Research and Markets, the worldwide traction-inverter industry is expected to reach $39 billion by 2028.

Silicon carbide in inverters for 800-V systems

While doubling the voltage from the typical 400-V battery brings substantial benefits to EVs, performance suffers at higher voltages for EV inverters relying on silicon (Si) MOSFETS and IGBTs. As a result, automotive designers are replacing conventional Si power devices with SiC, a wide-bandgap semiconductor that allows faster switching and can operate at higher temperatures. The SiC devices are smaller and can handle higher operating voltages compared with their Si counterparts.

Take the case of automotive solution supplier Delphi Technologies, which employed SiC MOSFETs from Wolfspeed in EV inverters when it moved to 800-V battery systems. That allowed Delphi to develop inverters that are 40% lighter and 30% more compact than competitor inverter technologies.

The 800-V inverter employs SiC MOSFETs from Wolfspeed.
Figure 2: The 800-V inverter employs SiC MOSFETs from Wolfspeed. (Source: Delphi Technologies)

The SiC power switch is at the heart of Delphi’s inverter design, facilitating a higher level of integration with double-sided cooling. That significantly reduces the thermal resistance between the SiC components and the cooling-system design. It’s an important aspect in high-power applications like EVs, where heat rejection of the power module is critical.

The cooling system’s efficient interface with SiC MOSFETs leads to a lighter and smaller power system at a lower cost compared with Si-based inverters. As a result, in EV inverters, Si IGBT–based power switches are increasingly being replaced by SiC MOSFETs, which deliver up to 70% reduction in switching losses, leading to improved performance and lower costs in electrified propulsion systems.

Besides greater switching efficiency and increased junction-temperature capabilities, SiC MOSFETs deliver improved short-circuit withstand time and lower on-resistance. That further reduces power consumption compared with Si IGBTs. Rohm claims that its fourth-generation SiC MOSFETs reduce power consumption by 6% compared with IGBTs in the main inverter, as calculated by the international standard WLTC fuel-efficiency test.

From Si IGBTs to SiC MOSFETs

In traction inverters, a vital building block in EV designs, switching devices like IGBTs initially managed power as inverters converted DC power to AC power for EV motors. Over the years, engineers realized that inverters play a critical role in EV performance and driving range. Here, power-efficient components could extract more energy from the battery at a higher efficiency and thus extend the cruising range and reduce the size of the on-board battery.

SiC MOSFETs have become a technology of choice in EV traction inverters.
Figure 3: SiC MOSFETs have become a technology of choice in EV traction inverters. (Source: Rohm Semiconductor)

Next, while EV driving range and battery size and weight have been a crucial issue all along, when EVs moved from 400-V to 800-V battery systems, automotive engineers began looking for components that could efficiently handle higher operating voltages and temperatures. That’s when SiC MOSFETs became the technology of choice for EV building blocks like traction inverters.

According to Delphi Technologies CEO Richard F. Dauch, the SiC-based inverter enables electrical systems of up to 800 V to significantly extend EV range and halve charging times compared with 400-V systems. “Doubling the voltage from 400 V brings a substantial range of benefits, both for the vehicle user and manufacturer,” he said.

Simon Keeton, executive VP and GM of Power Solutions Group at onsemi, elaborated on the benefits of SiC-based power-traction solutions. “The high-density SiC devices minimize parasitics and thermal resistance,” he said. “That leads to reduced power losses associated with DC to AC conversion along with the reduced size and weight of the traction inverter.”

According to industry research firm IHS Markit, up to 45% of global vehicle production will be electrified by 2025, with about 46 million EVs to be sold annually. These figures are estimated to rise to up to 57% by 2030, with about 62 million EV sales annually.

That ambitious road to vehicle electrification requires high-voltage power devices first and foremost. Here, SiC semiconductors have been recognized as a technology of choice due to their faster switching speed and support for higher voltages and temperatures.

With the global push for vehicle electrification, this makes SiC a technology to watch in 2023 and beyond.

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