Analytical modeling of pulsating torques of induction motors caused by supply voltage unbalance

Voltage unbalance is frequently encountered in a low voltage AC power network to which many three-phase loads are connected. Pulsating torque of IMs caused by voltage unbalance is well known to electrical engineers, and it can easily be simulated by a computer program or measured from laboratory experimental setups. However, analytical models that clearly interpret the physical mechanism linking the pulsating torque and voltage unbalance are not found in literature. In this paper, we develop an analytical model of pulsating torque produced by an IM under voltage unbalance. The amplitude of the pulsating torque is explicitly expressed as a function of the voltage unbalance factor, i.e., the ratio of the negative- to positive-sequence voltage components. The illustrated examples are analyzed by the proposed analytical model, and validated by results obtained from simulation using the universal machine module of the EMTP.