Audi A2 e-tron debuts upgraded APP350 drive with SiC inverter for greater efficiency

Audi reports that the electric drive in its new A2 e-tron compact EV, the Volkswagen Group’s APP350 drive unit, has been upgraded to reduce energy consumption and improve acoustic comfort.

Audi says the A2 e-tron is the most efficient Audi ever. The 140 kW version with the optional efficiency package has a preliminary combined WLTP consumption of 12.8 kWh/100 km.

The APP350 is a permanent-magnet synchronous motor positioned parallel to the rear axle. It operates at 400 V and delivers up to 350 Nm of torque. The A2 e-tron uses it in three performance levels: 125, 140 and 170 kW.

Instead of the silicon-based bipolar transistors used previously, the new pulse inverter uses silicon carbide (SiC) MOSFETs. Audi says these reduce switching losses and enable efficiencies of more than 97%.

A new software function uses the higher switching speed of the SiC MOSFETs to adjust the switching frequency to the operating point, since a lower switching frequency means fewer losses. The adaptive strategy is designed to make the most of lower switching frequencies in city traffic and on rural roads, at medium speed and load. For acoustic comfort, the inverter also superimposes high-frequency harmonic components on the motor current to compensate for noise.

The rotor laminations are more than 30% thinner than in the predecessor MEB drive, the APP310, to reduce iron losses. The rotor segments are staggered instead of arranged linearly, which Audi says almost eliminates dominant tonal components when pulling away from a standstill. Switching the stator winding from a star to a delta configuration and reducing the number of parallel branches are designed to increase efficiency under partial load.

The transmission uses a 10.21:1 gear ratio in the 125 kW and 140 kW versions and 11.53:1 in the 170 kW version. Each ratio is chosen so the motor operates in the most efficient ranges of its characteristic map. Fine machining produces smooth tooth flanks that reduce friction losses and allow the use of a low-viscosity transmission oil. The low-viscosity oil and revised oil routing are designed to reduce churning losses in the gear set.

Source: Audi