Grid-Side Current Harmonic Suppression and Power Factor Improvement Using q - Axis Damping Current Injection for PMSM Drives Without Electrolytic Capacitor

The dc-link film capacitor with low capacitance in permanent magnet synchronous motor (PMSM) drives without an electrolytic capacitor will not only reduce the system stability but also generate LC resonance with the grid-side filter inductor, which is the important reason for high grid-side harmonic current and low power factor. In this article, a grid-side current harmonic suppression strategy using q -axis damping current injection is proposed to address these issues of PMSM drives without an electrolytic capacitor. The analysis of the transfer function based on the simplified circuit of the drive shows the instability and LC resonance of the system. The feedforward modification method based on the difference between the quasi-dc-link voltage and the dc-link voltage is applied to improve the system performance. Meanwhile, the specific implementation of the proposed method by injecting damping current into the q -axis is introduced. In addition, a phase disturbance angle is introduced in the proposed control strategy to adjust the phase of quasi-dc-link voltage. By properly adjusting the phase disturbance angle, the conduction angle of the single-phase uncontrolled rectifier bridge can be effectively expanded, and the grid-side power factor can be further improved. Experiments on a PMSM drive with the low capacitance of a dc-link film capacitor are carried out to verify the effectiveness of the proposed method.