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Harmonic injection method is widely used in the suppression of current harmonic and torque ripple in field-oriented control (FOC) permanent magnet synchronous motor (PMSM) servo system. However, under some working conditions of FOC PMSM, the harmonic injection method fails to suppress the current harmonics and causes oscillation. To analyze the cause of oscillation, the transfer mechanism of injected voltage harmonic is analyzed in this article, and the relation between injected voltage harmonic and current harmonic is derived. The theoretical analysis results show that the relation between harmonics will change with motor speed and parameters of FOC PMSM. When the relation between harmonics is reversed, the existing harmonic injection method will fail and cause harmonic oscillation. To solve this problem, a simple improvement of the harmonic injection method is proposed in this article based on the proposed close-loop model. The correctness of the mathematical derivation and the effectiveness of the proposed method is evaluated by experiment and simulation. [ABSTRACT FROM AUTHOR]

The current, torque, and speed harmonics caused by deadtime effect in voltage source inverter (VSI)-fed permanent magnet synchronous motor (PMSM) usually lead to undesired torque ripple and extra electrical loss, etc. In this article, a mathematical model is proposed to predict the deadtime-related harmonics in VSI-fed field-oriented control PMSM, and a deadtime-related harmonic minimization method is proposed based on proportional-integral (PI) controllers tuning and under the premise of keeping the same control strategy. The expressions of current, torque, and speed harmonics caused by deadtime effects are obtained based on the complex amplitude expression of the voltage error harmonic and the derivation of the closed-loop transfer function from the deadtime-related voltage error to the d–q axis current. Based on the derived expressions, optimization objective functions are built to search the optimal PI parameters for minimizing deadtime-related harmonics and reducing the torque ripple. The optimization constraint functions can be adjusted for transient performance requirements, so the transient performance can keep good even if the deadtime-related harmonics are minimized with the optimal PI parameters. Both simulation analysis and experimental data verify the correctness of the analytical prediction and the validity of the deadtime-related harmonic minimization method. [ABSTRACT FROM AUTHOR]