High-Performance Suppression of PMSM Current Sideband Clusters Induced by Mechanical Speed Modulation and Frequency Offset

Improper harmonic suppression in permanent magnet synchronous motor (PMSM) drives can not only fail to attenuate the targeted harmonics but also introduce additional spectral components, forming sideband clusters that exacerbate harmonic distortion through a feedback loop. This paper presents a rigorous theoretical analysis of this phenomenon, identifying mechanical speed modulation and residual frequency offsets as the two dominant mechanisms responsible for generating primary frequencies. The interaction of these frequencies within the drive system leads to the formation of the observed side-band clusters. To address this issue, an adaptive suppression scheme is proposed, which jointly estimates complex harmonic amplitudes and residual frequency offsets by minimizing a designed optimization problem. The estimator employs a variable projection formulation with regularized whitening to stabilize amplitude identification and a normalized-gradient frequency update augmented by a smooth repulsion term to prevent spurious convergence to the nominal frequency. Experimental results on a PMSM testbench validate the method’s effectiveness in significantly attenuating the targeted harmonics and their associated sideband clusters under both steady-state and dynamic operating conditions.