Effects of unsymmetrical voltage sags on adjustable speed drives torque ripple

This paper researches unsymmetrical voltage sag influence on torque ripple in scalar controlled (VHz), rotor field oriented (RFO) and direct torque controlled (DTC) drives. Electric drives performance degradation during voltage sag mainly depends by used control algorithm. The simulation results of the study suggest that C type sag is the most critical and can cause drive fault. The performance of adjustable speed drives with all three types control methods experimentally tested under sag condition. Furthermore, sag induced vibration measured and achieved results are compared.