Beat Phenomenon Feature Extraction Based Harmonic Decoupling for Electrolytic Capacitorless Motor Drives

There exists the harmonics coupling between dq-axis current in the beat envelope of permanent magnet synchronous motor (PMSM) drives with small direct-current link (dc-link) capacitors, which cause the performance reduction of traditional method, which only suppressing current harmonics in single axis, during the flux weakening (FW) region. To solve the beat phenomenon of harmonic coupling, this article proposes an impedance reshaping strategy based on the signal feature extraction of the beat envelope, which can eliminate the coupling of beat amplitude from dq-axis harmonics. On this basis, the beat suppression method with the closed loop of beat amplitude improves the adaptability to the motor speed and torque. The feature signal of the beat amplitude is extracted with the mean values and the harmonics of the motor currents in dq-axes, which is used to reshape the impedance relationship between the beat amplitude and rectifier side. Hence, the beat amplitude in motor current can be directly suppressed under dq-axis current harmonics coupling and operating condition variation. Experimental results show that the strategy can suppress the beat phenomenon of the motor current effectively.