2 Architectures and Trends

The architecture of a traction inverter varies with vehicle type. Plug-in hybrid electric vehicles (PHEVs) and battery electric vehicles (BEVs) have a three-phase voltage source inverter topology, with power levels in the 100- to 500-kW range. The battery pack can either directly connect to the inverter DC input or a DC/DC boost converter can be used to step up the battery voltage and supply the inverter with a controlled DC voltage.

The two-level inverter is the most common power converter used in electrified vehicles and in the industry, with the power range of tens of kilowatts up to hundreds of kilowatts. Usually, the switching frequency is in the range of 5 kHz to 30 kHz, Currently, three-level inverters are becoming more popular because the inverters offer higher power capability (beyond 300 kW), higher efficiency, and lower harmonic distortion and allow the use of a smaller electromagnetic interference (EMI) filter. Among many topologies, neutral point clamped and T-type neutral point clamped (TNPC) are the most competitive designs. #FIG_GCM_5CZ_N5B illustrates an example of a three-level TNPC inverter.

A second trend is a dual-motor architecture. As early as in 2012, Tesla introduced the Model S, a rear-wheel drive, full-size luxury sedan with a range of up to 426 km with the 85-kWh battery pack. In 2014, Tesla announced an all-wheel drive version of the Model S with an electric motor on both the front and rear axles. Since then, dual inverters have been implemented by various OEMs such as the Chevy Volt PHEV, Toyota Prius HEV, and Cadillac CT6 PHEV.

A third trend improving system integration is the implementation of e-axles, which combine the power electronics, electric motor, and transmission in a compact system housing. E-axles improve motor performance because this design can achieve higher torque and top speed, for example 20-k RPM. Better cooling and a coil winding structure improve power density and motor efficiency.

Other trends in traction inverter features include:

• Increasing power levels and Automotive Safety Integrity Levels (ASILs) (100 kW to 500 kW, ASIL C to
  ASIL D)
• Shifting towards 800-V technology with increased switching transient voltages
• Easily adjusting the gate-drive strength to reduce overshoot, optimize efficiency, and reduce EMI
• Employing an inductive position-sensing technology instead of a resolver to reduce costs
• Integrating active discharge into a Gate driver integrated circuit (IC) to reduce costs and save space