Online Virtual Impedance Optimization-Based Grid Current Harmonics Suppression Strategy for Electrolytic Capacitorless PMSM Drives

Active damping strategies in electrolytic capacitorless permanent magnet synchronous motor (PMSM) drives are prone to failure under wide variations of grid impedance. Thus, a robust grid current harmonics suppression strategy based on online virtual impedance optimization is proposed. First, evaluation metrics are constructed to quantify the quality of grid currents and the system stability. An entropy-weighted technique for order of preference by similarity to ideal solution is employed to obtain an optimal impedance reshaping factor (IRF) subject to stability constraints. To derive the model parameters of the transfer function between the IRF and the DC-link voltage, an online gradient descent algorithm is presented incorporating real-time motor operating conditions. Based on the parameters and discrete vector synthesis, the IRF satisfying preset amplitude and phase constraints is obtained and utilized to reconstruct the DC-link voltage reference for space vector pulsewidth modulation. The proposed strategy can improve the resonance suppression capability under wide variations of grid impedance and motor operating conditions. Finally, the proposed strategy is verified on a platform of electrolytic capacitorless PMSM drive.