To reach the EV Everywhere Grand Challenge goal, the Vehicle Technologies Office (VTO) is supporting research to lower the cost and improve the performance of power electronics.
Vehicle power electronics primarily process and control the flow of electrical energy in electric drive vehicles, including plug-in electric vehicles. They also control the speed of the motor, and the torque it produces. Finally, power electronics convert and distribute electrical power to other vehicle systems such as heating and ventilation, lighting, and infotainment. Power electronics components include inverters, DC/DC converters, and chargers (for plug-in electric vehicles).
An inverter is needed in an electric drive system to convert the DC energy from a battery to AC power to drive the motor. An inverter also acts as a motor controller and as a filter to isolate the battery from potential damage from stray currents.
VTO's research and development in power electronics focuses on improving inverters. Researchers are working to reduce inverter volume by a third, reduce part count by integrating functionality, and reduce cost. Today's vehicle power electronics utilize silicon-based semiconductors. However, wide band gap (WBG) semiconductors are more efficient and can withstand higher temperatures than silicon components. As such, they offer a significant opportunity to meet 2022 program targets. The two most commonly used WBG materials are silicon carbide (SiC) and gallium nitride (GaN). The ability to operate at higher temperatures can decrease system costs by reducing thermal management requirements.
Achieving the 2022 targets for power electronics will require advances in several areas, including device packaging, innovative power module designs, high-temperature capacitors, and new inverter designs. Device packaging and innovative power module designs can eliminate existing interface layers and provide cooling at or very near the heat sources. Improved capacitors can reduce inverter cost and volume, and enable higher temperature operation. New inverter designs can reduce part counts and enable modular, scalable components.
DC/DC converters are used to increase (boost) or decrease (buck) battery voltages (typically 200 V to 450 V) to accommodate the voltage needs of motors and other vehicle systems. If the vehicle electric motor design requires higher voltage, such as an internal permanent magnet motor, it will require a boost DC/DC converter. If a component requires lower voltage, such as most vehicle systems (lighting, infotainment), it will require a buck DC/DC converter that reduces the voltage to the 12V to 42V level.
Onboard vehicle chargers convert AC energy from the electrical grid to DC energy required to recharge batteries. Battery chargers for plug-in electric vehicles are currently based on proven, traditional, high-frequency charger circuits and can be located either on the vehicle or off board, as part of a DC fast charger. Additionally, researchers are investigating on-board concepts that integrate the charging function into the existing power electronics and utilize the inductance of the electric motor for recharging. As with other power electronics, chargers must have a small physical footprint, be lightweight, and offer high efficiency and high reliability at low cost.
VTO Power Electronics R&D
The Power Electronics and Electrical Power Systems Research Center at Oak Ridge National Laboratory is leading research in wide bandgap integration, device packaging, and innovative power module designs. Researchers at the National Renewable Energy Laboratory are focused on improving the reliability of power electronics. Industry co-funded research is ongoing in the areas of advanced inverters (including WBG devices) and high temperature, low-cost capacitors.