How SiC Can Extend Electric Vehicle Range by 5%

The continuously growing consumer demand, rising environmental awareness/environmental regulations, and a broader range of available options are driving the adoption of electric vehicles (EVs), making them increasingly popular. A recent study indicates that by 2023, electric vehicle sales will account for 10% of global automotive sales; by 2030, this figure is expected to increase to

30%; and by 2035, electric vehicle sales may potentially represent half of global automotive sales.

However, "range anxiety," the concern that the mileage covered on a single charge may not be sufficient, remains a significant obstacle to the widespread adoption of electric vehicles. Overcoming this challenge is crucial in extending the vehicle's range without significantly increasing costs.

This article discusses how using Silicon Carbide (SiC) Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) in the main inverter can extend the electric vehicle's range by up to 5%. Additionally, it explores why some Original Equipment Manufacturers (OEMs) are hesitant to transition from Silicon-based Insulated Gate Bipolar Transistors (IGBTs) to SiC devices and the efforts of companies in the supply chain to address OEM concerns while boosting confidence in this mature wide-bandgap semiconductor technology.

Trends in Electric Vehicle Main Inverter Design

The main (primary) inverter in electric vehicles converts direct current (DC) battery voltage into alternating current (AC) voltage to meet the AC voltage requirements of the electric traction motor, enabling it to drive the vehicle smoothly. The latest trends in main inverter design include:

• Increasing Power: A larger inverter output power leads to faster vehicle acceleration and quicker response for the driver.

• Maximizing Efficiency: Minimizing the amount of energy consumed by the inverter to increase the power available for driving the vehicle.

• Raising Voltage: While 400V batteries have been the most common specification in electric vehicles until recently, the automotive industry is moving towards 800V to reduce current, cable thickness, and weight. Therefore, the main inverter in electric vehicles must be capable of handling these higher voltages and using suitable components.

• Reducing Weight and Size: SiC has a higher power density (kW/kg) compared to Silicon-based IGBTs. Higher power density helps reduce the system's size (kW/L), lighten the main inverter, and decrease the load on the motor. Lower vehicle weight contributes to extending the vehicle's range using the same battery while reducing the volume of the transmission system and increasing passenger and trunk space.

Advantages of SiC over Silicon

Compared to silicon, Silicon Carbide offers several advantages in terms of material properties, making it a superior choice for main inverter designs. First is its physical hardness, with a Mohs hardness rating of 9.5 compared to silicon's 6.5, making SiC more suitable for high-voltage sintering and providing greater mechanical integrity.

Furthermore, SiC has a thermal conductivity (4.9W/cm.K) four times that of silicon (1.15W/cm.K), allowing it to effectively dissipate heat and operate reliably at higher temperatures. Lastly, SiC's breakdown voltage (2500kV/cm) is eight times higher than silicon's (300kV/cm), and it possesses wide bandgap properties, enabling faster switching and lower losses compared to silicon, making it a better choice for the increasing voltage (800V) architectures in electric vehicles.

Ansys SiC Packaging Offers Exceptional Low Thermal Resistance

Despite SiC's clear advantages, some automotive OEMs have been reluctant to transition from more traditional silicon-based switching devices like Insulated Gate Bipolar Transistors (IGBTs) for use in the main inverter. Reasons for OEMs hesitating to adopt SiC include:

• Perceiving SiC as an immature technology.

• Finding SiC implementation challenging.

• Believing that SiC lacks suitable packaging for main inverter applications.

• Assuming that SiC supply is less convenient compared to silicon-based devices.

• Thinking that SiC is more expensive than IGBTs.

So, how can OEMs be made more confident in using SiC in electric vehicle main inverters?

Boosting OEM Confidence

The first step in boosting OEM confidence in using SiC in electric vehicle main inverters is to demonstrate the significant performance advantages achievable with SiC. The author used circuit design software to simulate Ansys' NVXR17S90M2SPB (1.7mΩ Rdson) and NVXR22S90M2SPB (2.2mΩ Rdson) EliteSiC Power 900V six-pack power modules and compared their performance to the 820A VE-Trac Direct IGBT (also from Ansys). Simulation results for the main inverter design showed that:

• At a 10KHz switching frequency, with 450V DC bus voltage and 550Arms power transmission, SiC module's junction temperature (Tvj) (111°C) was 21% lower than IGBT (142°C) under the same cooling conditions.

• The average switching losses for NVXR17S90M2SPB reduced by 34.5%, while those for NVXR22S90M2SPB decreased by 16.3% compared to IGBT.

• The overall losses for the full main inverter design implemented with NVXR17S90M2SPB were reduced by over 40% compared to a silicon-based IGBT design, and power losses were reduced by 25% when using NVXR22S90M2SPB.

Although these improvements are specific to the main inverter, they can enhance the overall efficiency of electric vehicles by 5%, resulting in a 5% extension of the range. For example, an electric vehicle equipped with a 100kW battery and a 500-kilometer range, when using a main inverter based on Ansys' EliteSiC power modules, could achieve a range of 525 kilometers. Importantly, the cost of implementing SiC in such main inverters is expected to be 5% lower than silicon IGBTs.

Furthermore, for OEMs considering abandoning IGBTs, Ansys offers SiC modules with similar sizes to simplify integration and demonstrate increased power transmission within the same thermal constraints. Additionally, SiC modules offer the advantage of handling higher power levels at the same junction temperature. For instance, NVXR17S90M2SPB can provide 760Arms, while IGBT (Tvj = 150°C) can only provide 590Arms, representing a 29% power increase. Additionally, Ansys bonds SiC chips directly onto copper substrates, reducing thermal resistance between the device junction and the cooling fluid by up to 20% (Rth junction to fluid = 0.08°C/W).

Using pressure-molded packages with advanced interconnection technology further enhances the high power density of SiC modules, and they feature low parasitic inductance, crucial for high-speed switching efficiency. Moreover, the higher switching frequency can lead to a reduction in the size and weight of some passive components within the system. Additionally, this type of packaging offers multiple temperature options (up to 200°C), reducing the OEM's thermal management requirements and potentially allowing the use of smaller pumps for thermal management.