Adaptive random pulsewidth modulation scheme for locating and shaping the spectral content of induced vibration in electric power conversion, applied to a three-phase synchronous motor

Pulsewidth modulation schemes used in various electric power conversion applications can result in objectionable vibration and acoustic behavior resulting from electromagnetically induced mechanical response. The response will be more salient if the modulation carrier frequency coincides with a system mechanical resonance, especially if the carrier frequency is constant. Several random pulsewidth modulation (RPWM) techniques have been proposed over the last 20 years in order to reduce the prominence of the modulation over the 2 kHz to 5 kHz range. The area where these RPWM techniques are lacking arises when system response varies under different operating conditions, or when it is not known a priori. While effective at reducing objectionable content (either acoustic or electromagnetic) by spreading it over neighboring regions, they still do not address the robustness requirements of systems with varying responses. Additionally, the approach may actually increase the likelihood of coinciding with a system resonance, since the exciting frequency range is wider than in constant switching frequency techniques. The proposed approach builds upon existing RPWM strategies by using an adaptive algorithm to position and shape the RPWM modulation frequency distribution based on system vibration feedback. Gradient descent is employed to vary the center frequency and distribution range of the randomized carrier frequency in response to change in the objective metric based on the vibration feedback.