Behavior of AC and DC drives during voltage sags with phase-angle jump and three-phase unbalance

Voltage sags can be characterized through a number of parameters. These include magnitude, phase-angle jump and three-phase unbalance. This paper presents a set of tests for adjustable-speed drives, applied to drive models. The include different types of three-phase unbalanced sags different phase-angle jumps. Simulations have been done using a MATLAB program based on simplified models that are described in this paper. The simulation results show an obvious relation between sag magnitude and motor behavior. It is also shown that different types of three-phase unbalanced sags give different drive behavior. The drives´ sensitivity to phase angle jumps is limited to certain combinations of firing angle and sag magnitude. The behavior improves with increasing negative phase angle jump.