Harmonic Energy Regulation for Grid Current Quality Improvement in Electrolytic Capacitorless PMSM Drives

When the grid impedance changes, the performance of active damping strategies for electrolytic capacitorless permanent magnet synchronous motor (PMSM) drives may decay. A novel harmonic energy regulation strategy for grid currents is proposed to improve the robustness to the grid impedance. The quality of grid currents can be improved when the dc-link capacitors and the motor inductance serve as the main harmonic energy storage elements. Based on this concept, the harmonics in the dc-link voltage are extracted to reconstruct the sampled dc-link voltage in space vector pulsewidth modulation (SVPWM) for harmonic energy regulation. Specifically, the phase and amplitude processing units are applied to regulate the harmonics in the motor current and dc-link voltage based on system model to achieve the theoretical harmonic energy exchange state. By comparing the stability criterion of the cascaded system with the active damping strategy, the proposed method shows better robustness to the grid impedance. Finally, experiments are carried out on a platform of 5.5-kW electrolytic capacitorless PMSM drive to verify the effectiveness of the proposed control strategy.