Scalar V/f and I-f control of AC motor drives: An overview

While field oriented control (FOC) and direct torque and flux control (DTFC) have been established as mature technologies for high performance a.c. motor variable speed drives, scalar (V/f and I-f) control is sufficient for general sensorless, lower cost, a.c. motor drives in applications such as pumps, compressors, ventilators, which constitute the majority in terms of installed power. The present paper presents an overview about recent progress of scalar control of a.c. motors in terms of speed control and precision range, response to faster load torque perturbations and energy savings within limited control complexity (lower cost) and without speed close loop control.