Harmonic Impedance Reshaping Based Flux-Weakening Control Strategy for Electrolytic Capacitorless PMSM Drives

In electrolytic capacitorless permanent magnet synchronous motor (PMSM) drives, the output voltage vector in the flux-weakening (FW) region exhibits significant fluctuation due to the periodic oscillations of DC-link voltage and reference voltage vector, leading to increased motor current harmonics. To suppress the current distortion, a harmonic impedance reshaping-based FW control strategy is proposed, which is effective only when the machine operates in the motor mode. By analyzing the impact of inherent periodic fluctuation on output voltage, the influence mechanism of reference voltage vector oscillation on motor current harmonics is revealed. Multiharmonic digital filters are employed to extract inherent frequency components from the reference modulation index, and a FW coefficient adjustment component is generated. In this way, the FW depth can be regulated in real-time, optimizing the trajectory of the output voltage vector and achieving effective suppression of motor current harmonics. The proposed method extracts harmonics from the reference modulation index, enabling feedforward-based decoupling of modulation output harmonics and suppression of motor current harmonics. Compared to feedback control methods, the proposed strategy directly controls the modulation command, avoiding complex angle observation and parameter dependency issues. This not only simplifies the control loop but also enhances the system's adaptability to varying operating conditions. Experimental results validate the effectiveness of the proposed method.