Analysis and compensation of current measurement error in vector-controlled AC motor drives

Recently, as the higher performance of torque control is required, current measurement error inherent in all kinds of AC drives becomes significant. In this paper, the effects of current measurement error, classified as offset error and scaling error, are analyzed. It is demonstrated that the offset error causes the torque of a motor to oscillate at the stator electrical frequency and that the scaling error causes the torque of a motor to oscillate at twice the stator electrical frequency. These torque ripples deteriorate the performance of speed control, because they act as disturbance loads. In order to obtain precise torque control and eliminate speed ripples, a compensation method is proposed. The simulation and experimental results show that the analysis is correct and the compensation method improves the performance of torque control by eliminating torque ripples effectively.