A Simple Feedforward Approach to Stabilize VSI-Fed Induction Motor With Filter in RFOC

Abstract

LC filters are used in between a pulsewidth modulated three-phase voltage source inverter and a squirrel cage induction motor (SQIM) to reduce the losses in the motor and the high dv/dt at the motor terminals by feeding the motor with three-phase sinusoidal voltages. However, it affects the rotor-flux oriented control (RFOC) of the SQIM drive because of the sustained resonant frequency oscillations. It also destabilizes the drive at some operating points if proper control action is not taken. This article proposes a simple feedforward (FF) technique where the FF terms are subtracted from the d- and q-axis stator-current references to damp out the resonant frequency oscillations. Additional sensors and controllers are not required except the sensors and controllers used in RFOC of SQIM without filter. It does not depend on the tedious calculation of damping gain like in any active damping method. The stability of the drive has been analyzed and verified through simulation as well as experimental results at different test conditions. It ensures good steady-state and dynamic performances of the SQIM with filter. There is no need to change the parameters of four proportional-integral controllers previously designed for the RFOC of SQIM without filter.