Comparing Methods to Mitigate the Effect of Grid Voltage Sag and Frequency Variation on the Operation of Variable Speed Drives

Abstract

In this paper, the effect of unsymmetrical grid voltage sag on the performance of a slip power recovery drive is studied, and two strategies to mitigate its effects are investigated. The first strategy consists of three phase parallel RL impedance connected to the rotor circuit. The second strategy consists of three phase LCL filter connected to the rotor circuit. A PI controller is tuned to test the drive at constant speed. Also, the effect of grid frequency drop on the drive performance is investigated with the same two protection strategies. The proposed systems are modeled with Matlab/Simulink and the simulation results are compared. The drive performance without any protection schemes are compared with its performance with the two proposed strategies. The compared results include the stator voltage and current, the rotor voltage and current, the DC link voltage and current, the electric torque, and the rotor speed.