Analysis of Torque Ripple Caused by Current Signal Injection on the Maximum Torque Control Frame for Sensorless Control

This paper presents an analysis of torque ripple caused by current signal injections for sensorless controls at low speed. The torque ripple caused by the injections of signal currents can be represented by a cross product of a virtual flux and a differential current vector. By using the current components parallel to the direction of the virtual flux, signal injection method without torque ripple has been proposed. However, since estimated positions are used to define the directions of the virtual flux, a position estimation error causes torque ripple in sensorless controls. In this paper, the fluctuation of the torque ripple approximately is derived as a sine function of the angle between d-axis and f-axis. And it is evaluated by experiments, that this analysis is useful to decide criteria for the position estimation error of sensorless controls.