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Integrating a Silicon Carbide Cascode in a Vehicle Motor Drive

Company Name: United Silicon Carbide, Inc.
Program Office: Vehicles
Location: Monmouth Junction, NJ
Email: Jonathan Dodge, Project Manager & Principal Investigator;
Award Amount: $169,231
Project Term: 12 months
Project Status: Active
Participating Lab(s): Oak Ridge National Laboratory


Fundamental improvements to battery structure and design are critical for making these technologies more cost-competitive. Currently, power electronics for electric vehicle (EV) and industrial applications experience poor light load efficiency and their physical size must be limited. Silicon (Si) insulated gate bipolar transistors (IGBTs) have been used extensively in motor drives, but the devices suffer from high switch-off power loss and consequently, low switching frequency and large power converter volume. The diode voltage drop inherent in Si IGBTs also degrades light load efficiency.

A new device - the silicon carbide (SiC) metal oxide semiconductor field effect transistor (MOSFET) - offers a solution to switch-off power loss and light load efficiency problems, but has two critical drawbacks. First, it requires a gate drive voltage range that mandates the use of multiple isolated power supplies, which are costly. Second, the poor performance of the Si MOSFET’s reverse conduction necessitates the addition of bypass diodes, which adds cost and volume to the power converter. To overcome these challenges, the SiC cascode provides the combination of low conduction loss, low switching loss, high performance reverse conduction, and simple gate drive needed for these applications.

This project will allow United Silicon Carbide to partner with Oak Ridge National Laboratory to address a general lack of understanding about the function and utilization of SiC cascode devices in the industry, particularly with regard to controlling switching speed. Successful implementation of a working motor drive can accelerate acceptance of the SiC cascode, as a significant component for EV and industrial applications.


The SiC cascode combines the best features of a wide bandgap device and a Si MOSFET while eliminating the undesirable characteristics of each. Specifically, the advantages include low conduction and switching loss combined with a high-voltage rating, normally-off, low-cost gate control, and very high performance reverse conduction. These characteristics make the SiC cascode attractive for hard-switched bridge applications such as an EV motor drive. An additional benefit of the SiC cascode is extremely low output capacitance, which enables operation of resonant-mode power converters at much higher voltages or switching frequency. These combined features allow one device type to cover all types of circuit applications, reducing cost through economy of scale and simplified logistics.


Achieving power density at low cost can broaden the use of electric drives in vehicles. Substantial cost savings from the simplified gate drive and elimination of bypass diodes can give EV motor drive and power converter manufacturers a competitive technical advantage.

Electric vehicles already significantly reduce greenhouse gas emissions compared to their internal combustion engine counterparts. Making batteries more efficient will enhance these benefits, as will increasing market share for electric vehicles.

Developing alternative fuels — including electricity — for transportation can dramatically reduce oil demand, making the United States less exposed to disruptions in global oil supplies.

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