Coordinated Suppression Strategy of Beat Envelope and Current Harmonics for Electrolytic Capacitorless Motor Drives

In the permanent magnet synchronous motor (PMSM) drives with small dc-link capacitors, conventional beatless methods cannot characterize the harmonic internal model, which causes the phase current harmonics to still exist. Besides, the coupling of the beat envelope and current harmonics further the application range of the conventional methods, like in flux-weakening (FW) region. This article proposes a coordinated astatic suppression strategy based on positive–negative sequence regulation, which can solve the beat envelope and the current harmonics at the same time. The feature signals of phase current harmonics are generated with the multiple synchronous rotating frame transformations (MSRFTs), and the positive and negative sequence components can be separated. The influence of the fluctuated position error is eliminated, and the amplitudes of different sequence harmonic can be extracted with the feature signals, which improves the adaptability to the current coupling and operating conditions. The compensation voltages generated from the inverse MSRFTs are used to reshape the impedance relationship between beat current and rectified voltage. The equivalent harmonic controller contains the internal model of the motor current, which can realize the coordinated suppression of the harmonics and the beat envelope without static error. The experimental results show that the strategy can suppress both the beat envelope and the phase current harmonics effectively.