Increasing EV Powertrain Efficiency

The efficiency of the EV’s powertrain—the electric motor, transmission, and battery—directly affects the vehicle’s overall efficiency. When efficiency is improved, less energy stored in the battery is lost upon acceleration, improving range.

Power Electronics Onboard

Vehicle power electronics process and control electrical energy flow in hybrid and plug-in electric vehicles. They also control the speed of the motor and the torque produced.

Power is generated by the engine and transmitted to the driveshaft. The powertrain includes other internal parts and components of the engine, differentials, axles, emissions control, exhaust, engine cooling system, etc. At the heart of a battery-electric vehicle is the drive system and three main power electronic components on board: an inverter, a DC-DC converter, and an onboard charger (OBC).

  • The inverter converts DC power from the vehicle’s battery to AC power to drive the electric motor. The high-power devices are standalone or integrated with the electric motor into an electric drive unit (EDU).
  • A DC-DC converter steps down or decreases voltage from a high-voltage battery of 400-800 V to low voltages needed by low-power devices (3-7 kW).Several companies are currently developing 800-volt systems, and components are available for these systems, including power semiconductors. Such peripheral components as capacitors will need to be rated for high voltages.
  • An onboard charger (OBC) takes AC power from the electrical grid and converts it to DC for storage on the vehicle’s battery and is typically rated at 3-23 kW.

Enabling Technology

The transition to silicon carbide (SiC) MOSFETs and high voltage systems above 800V has been increasing for automotive power electronics since 2021. Most major auto manufacturers have announced both 800V platforms based on silicon carbide MOSFETs.

Wide bandgap (WBG) switching devices, including SiC MOSFETs and GaN HEMTs, will continue to drive 800V platform adoption and deliver greater efficiency. Until recently, most microchips in power electronics devices were made of ultra-pure silicon. SiC provides for better electrical conductivity and enables higher switching frequencies. It also allows power electronics applications to operate at much higher temperatures. The top benefits of the switch from Si to SiC semiconductors are longer ranges and faster EV recharging.

Other enablers include new double-sided cooling designs, copper wire bonds, and lead frames that have recently emerged.

Efficiency and Performance

Greater EV efficiency translates to longer range and lower operating costs based on reduced maintenance and scalability. Intelligent systems and software for powertrain thermal management, braking, and steering systems add even greater efficiency and safety.

We can see efficiency and performance also increase as the number of parts declines. For example, electric cars don’t use multi-speed transmissions because the electric car’s engine is an electric motor. While internal combustion engines require as many as a dozen gears, EV transmissions use a single gear. Electric motors deliver power instantly, rather than by building up torque through revving in an internal combustion engine. Although the original Tesla Roadster featured two-speed gearboxes, the gearbox was upgraded to a single gear after production.

Power electronics increase EV performance by handling higher currents and voltage levels. They handle and process all the energy stored in an EV’s battery for such functions as spinning motors used for vehicle propulsion to power air conditioning and entertainment.

Efficient power electronics improve EV range by minimizing losses in power conversion and increasing performance by handling higher currents and voltage levels that provide more power to electric motors.

Power electronics are fundamental to EVs. At the heart of these devices are semiconductors that are integral to any electrified powertrain, supplying and controlling the current and voltage throughout the drive system.

Challenges Remain

The cost and size of power electronics must be reduced while efficiencies and lifetimes remain high. Many components with individual functionality must fit close together, minimizing their size and weight in an EV. Power electronic components in proximity generate heat that affects each other. Finally, capacitors are large, and reducing their size with today’s dielectric materials and production processes is challenging.

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