Speed sensor less direct torque controlled induction motor drive with constant switching frequency operation

A sensor less space vector pulse width modulated (SV-PWM) direct torque controlled (DTC) induction motor drive, having reduced torque ripple even at low operating speeds and maintaining constant switching frequency has been studied and implemented. It utilizes MRAS based closed loop speed estimation and symmetrical switching scheme for the semiconductor devices. In the scheme presented in this paper a combination of high- pass and low-pass filter is used to avoid DC drift, problem of saturation and to enhance the response of speed estimation. Detailed simulation studies are carried out to verify the efficacy of the system. The viability of the scheme is confirmed by performing detailed experimental studies.