New Audi A2 e-tron Achieves 12.8 kWh/100 km WLTP Consumption With SiC Inverter

Audi says the new A2 e-tron is its most efficient model ever, with the 140 kW version rated at 12.8 kWh/100 km in the WLTP cycle when fitted with the optional efficiency package.

A key part of that is a newly developed silicon carbide (SiC) pulse inverter that reaches efficiencies of more than 97%, working alongside improvements to the electric motor and transmission.

Silicon carbide electronics help reduce energy losses

The A2 e-tron uses a permanent-magnet synchronous motor at the rear, positioned parallel to the axle and operating at a 400-volt level. The Volkswagen Group’s APP350 drive delivers up to 350 Nm of torque and was optimized for the Modular Electric Drive Matrix (MEB).

The pulse inverter now uses silicon carbide MOSFETs instead of the silicon-based bipolar transistors that have been standard until now, cutting switching losses, according to Audi.

New software adjusts the inverter’s switching frequency to the operating point, since a lower switching frequency means fewer losses. Audi says this pays off most in city traffic and on rural roads at medium speed and load, and the power electronics can also supply full power at low states of charge.

The inverter also helps with acoustics by superimposing high-frequency harmonic components on the motor current to compensate for disruptive noises, depending on the operating point.

Motor and transmission updates improve efficiency and comfort

Compared with the MEB predecessor drive, the APP310, the rotor thickness was reduced by more than 30%, which lowers iron losses. The rotor segments are now arranged in a staggered pattern rather than linearly to improve drive acoustics.

The stator winding has also moved from a star to a delta layout, and with fewer parallel branches, the motor runs more efficiently.

The A2 e-tron uses the APP350 in three performance levels. The 125 kW and 140 kW versions use a 10.21:1 gear ratio, and the 170 kW version uses 11.53:1, keeping motor speeds low.

A very low-viscosity transmission oil and optimized oil routing significantly reduce churning losses in the gear set. Audi says the result is low consumption, long range and pleasant acoustics.

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