SiC Power Devices: The Key to Success in the EV BusinessEnhancing power efficiency improves performance
while reducing electricity costs

The technical evolution of electric vehicles (EVs) is rapidly progressing. Recently, it has become possible to increase the battery voltage and capacity to extend the cruising range while reducing charging times. Going forward, further improving the conversion efficiency of power systems in EVs is expected to yield significant benefits in terms of sustainability.

The electric vehicle landscape offers a range of options, including Battery Electric Vehicles (BEVs), Hybrid Electric Vehicles (HEVs), Plug-in Hybrid Electric Vehicles (PHEVs), and series hybrid electric vehicles. At the heart of these lies a sophisticated electric propulsion system, comprised of an onboard charger (OBC), battery, inverter (DC-AC inverter), DC-DC converter, and motor.

While the core components of power systems remain consistent, the functions and circuit configurations will vary depending on the type of electric vehicle. For instance, BEVs need to enable fast bidirectional charging, requiring an advanced onboard charger (OBC) compatible with Vehicle to Grid (V2G) technology. To achieve this, a popular circuit topology combines a bidirectional totem-pole Power Factor Correction (PFC) circuit with bidirectional CLLC resonant DC-DC converter. The output of this onboard charger is then used to supply power to auxiliary isolated DC-DC converters, batteries, boost DC-DC converters for inverters, and the main traction inverter.

SiC Devices Dramatically Reduce Power Loss

Success in the electric vehicle business hinges on an important factor – improving the conversion efficiency of the onboard power supply circuits. This often-overlooked aspect significantly impacts driving performance, directly affecting cruising range and charging rates (electricity expenses). Increasing conversion efficiency extends the distance an EV can travel on a single charge while lowering costs, providing a powerful incentive for customers considering the switch to electric vehicles.

So how can conversion efficiency be improved? The key lies in the semiconductor switches that comprise the power circuit. Adopting high-performance switches capable of operating at high frequencies and handling high power loads can significantly boost conversion efficiency. As such, SiC power devices (SiC MOSFETs) have been garnering attention. SiC MOSFETs operate at higher frequencies, offer higher voltage tolerance, and provide better conversion efficiency over existing Si power devices like IGBTs.

Utilizing the latest SiC MOSFETs makes it possible to boost the efficiency of power systems in electric vehicles. Semiconductor manufacturer ROHM provides a detailed explanation on increasing efficiency in an application note on its 4th Gen SiC MOSFETs. These breakthrough devices further refine the trench gate structure introduced in the previous generation. The most notable improvement is a considerable reduction in ON resistance, by approx. 40%, without compromising short-circuit withstand capability. This effect is substantial, as the losses generated during power conversion are significantly lower. For example, when applied to a 5kW output inverter circuit, overall power was decreased by approximately 36% over conventional IGBTs.

The Effects in Traction Inverters is Also Significant

The power conversion system in electric vehicles is a complex network of components, consisting of an onboard charger (OBC), auxiliary isolated DC-DC converter, boost DC-DC converter, and traction inverter. Among these, the traction inverter plays a pivotal role, converting the DC power stored in the high voltage battery into AC power to drive the motor.

ROHM simulated the power consumption of traction inverters using the WLTC (World Harmonized Light Vehicle Test Cycle) fuel economy test method for passenger cars. The figure above compares the power consumption of a C-segment electric vehicle inverter when using 4th Gen SiC MOSFETs vs conventional IGBTs. It was found that replacing conventional IGBTs with 4th Gen SiC MOSFETs reduced electricity costs by 10% in urban mode and 6% across all driving modes (urban, suburban, and highway).

Improving OBC Efficiency with SiC MOSFETs

Like the traction inverter, the onboard charger (OBC) is a critical component of an electric vehicle’s power system. The OBC uses AC power supplied from the utility grid to charge the batteries. A key innovation is the adoption of bidirectional totem-pole PFC (Power Factor Correction) circuits that enable remarkably high conversion efficiency across the entire AC-DC converter system. For example, experiments with ROHM’s 4th Gen SiC MOSFETs have demonstrated conversion efficiencies of around 98% at half-load (1.5kW) and 97.6% at full-load (3kW) output power.

Adopting SiC MOSFETs into critical electric vehicle components like traction inverters and onboard chargers translates to significant gains in conversion efficiency, prompting many electric vehicle companies to focus on these next-generation devices.　

One such company is Vitesco Technologies, a world leader in the development and manufacture of cutting-edge powertrain technologies. To strategically secure the supply of SiC power devices that can enhance power efficiency, Vitesco Technologies has entered into a long-term partnership agreement with ROHM.

Another company focusing on SiC power devices is Semikron Danfoss, a global technology leader in power electronics. Semikron Danfoss has collaborated with ROHM for over a decade, centered on the development of power modules incorporating SiC power devices. Recently, Semikron Danfoss has strengthened its lineup of power modules for low-power applications by adopting ROHM’s newly released RGA series of 1200V IGBTs. This move represents an ongoing commitment by both companies to serve the needs of motor drive manufacturers worldwide.

These partnerships are likely to further accelerate the adoption of SiC power devices in the future. ROHM expects SiC power devices to improve conversion efficiency not only in electric vehicles, but also a wide range of other applications worldwide.