High-efficiency, low-torque ripple control of a permanent magnet synchronous motor based on current tracking vector of electromotive force

Since ordinary magnetic field poles of a PM (permanent magnet) motor generate higher harmonic flux, sinusoidal current will cause torque ripple. This is usually removed by short pitch winding, skew slot method, and so on. These methods have a drawback in terms of lower efficiency. Recently, new current control methods have been proposed to realize zero-torque ripple and high-efficiency drive at the same time. However, because the optimized reference current waveform obtained by these methods includes zero phase component, normal three-phase full bridge inverter and d–q coordinate control method cannot be used. This paper proposes a new current control method that can achieve zero-torque ripple and maximum efficiency by using a normal three-phase inverter. The three-phase optimum current can be derived by satisfying the following conditions: (1) the direction of the current resultant vector always agrees with that of the electromotive force resultant vector, and (2) the scalar product of the two vectors is held constant. By means of modifying the coordinate transformation angle, this method can also make it possible to compensate torque pulsation error with maximum efficiency using general d–q coordinate control method. The proposed method has been verified by experiments. © 2001 Scripta Technica, Electr Eng Jpn, 136(1): 57–64, 2001