Spectral synthesis of switching distortion in automotive drive inverters
Conventional inverters rely on switching modulation to generate the alternating current (AC) output required by many loads, such as electric machines. Particularly in mass-produced electric vehicles (EV), inverters exclusively use pulse-width modulation (PWM) with fixed switching rates, resulting in strong though confined peaks in the output spectrum at the switching frequency, as well as its overtones. These peaks conflict with electromagnetic compatibility and interference (EMC/EMI) regulations due to their large spectral power concentration, and interfere with other electronic components such as - most obvious to the passengers - the entertainment electronics. We present a modulator for commercial EV inverters that shapes the spectral content of the unavoidable distortion of switching modulation according to given constraints such that load requirements, regulatory limits, and constraints provided by other automotive components can be balanced. We will further present how the modulator can, unlike in known methods, balance switching loss and distortion. A gallium nitride (GaN) inverter demonstrates the high potential for motor-drive applications. The spectral density of the switching harmonics in the experimental inverter could be reduced more than three-fold compared to conventional PWM.
