Since ordinary magnetic field poles of PM (permanent magnet) motor generate higher harmonic flux, sinusoidal current will cause torque ripple. They are usually removed by short pitch winding, skew slot method and so on. These methods show 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 can not be used.
This paper proposes a new current control method that can achieve the zero torque ripple and maximum efficiency by using a normal three-phase inverter. The three-phase optimum current can be derived by satisfying both conditions: (1) the direction of the current resultant vector always agrees with that of the electromotive force resultant vector, and (2) 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.
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