Impact of inductance variation on the operation of a synchronous reluctance motor connected to a weak grid

Abstract

Changes in inductance profiles of motors from originally designed values are observed due to manufacturing defects and different measurement techniques adopted. This introduces changes in the magnitude of voltage dip that could be tolerated by a synchronous reluctance motor operating at a particular speed and torque while being connected to a weak grid. Since the voltage dip margin is dependent on the inductance of the motor, it changes as per the variations in inductance. This paper proposes a novel methodology to analyse the variations in the voltage dip margin as per the discrepancies in inductances when the motor drive is expected to deliver a particular speed and torque. A control strategy is also proposed to mitigate the ill-effects of the voltage dip by changing the operating point of the motor. Mathematical expressions are derived showing the voltage dip margin for different degrees of variations in the inductances. It is observed that with reduction in the inductance value, the voltage dip margin increases with increased current, where the current still remains within the maximum current limit of the motor, while the motor is forced to deliver the same speed and torque. The proposed mathematical derivations are validated through simulations and experiments.