Abstract: This paper researches behavior of rotor field oriented (RFO) and direct torque controlled (DTC) drives in speed controlled application in voltage sags circumstances. Problems in application will be able to appear, especially in work cases with speed and torque close to rated, even in a case when typical voltage tolerance curves show no drive trips. To overcome appeared drop in speed it was posed a field weakening algorithm during voltage sag. Analytic calculation and numerical simulation were presented in detail in this work. Knowing delay in RFO flux response and prompt DTC flux recall, methods for dynamic performance improving were advised.
Keywords: Adjustable speed drives, power quality, voltage sag, drop in speed, direct torque control, flux vector control.