Speed and torque estimation of variable frequency drives with effective values of stator currents

Abstract

We introduce a new method for torque and speed estimation of induction motors under voltage/frequency (V/f) open-loop control. In contrast to existing approaches that need the phase current, the proposed algorithm only requires the effective value (root mean square) of the stator current and the synchronous frequency, which are usually available from variable frequency inverter (VFI) at no additional cost. Our approach is particularly useful for inverter-fed motor-pumps in which the load varies slowly. We demonstrate the proposed algorithm is able to estimate the pump torque, speed, differential pressure and flow rate in a hydraulic process with a progressive cavity pump.