This study presents the operation of a synchronous reluctance motor drive under a sustained voltage dip condition while being connected to a weak grid. In the presence of an input voltage dip, motor may not be able to produce sufficient torque and maintain its original speed. A new technique is proposed in this study to maintain the desired reference torque and speed during a sustained voltage dip. The proposed technique is realised by evaluating mathematically the motor's allowable voltage dip margin corresponding to an operating point pertaining to a particular torque and speed in the current locus diagram of the motor. With prior knowledge of the voltage dip margin for every operating point in the current locus diagram, it would be possible to retain the same reference torque and speed by moving to a new operating point, which can be with lesser or greater i d as compared to the initial operating point, in case a voltage dip greater than the tolerable margin occurs. To start with, voltage dip margin has been derived theoretically and the operation of the motor is investigated by deliberately introducing a voltage dip. The proposed methodology has been verified through simulations and experiments in this study.

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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.

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