A comparative study of speed control methods for induction motor fed by three level inverter

Now-a-days Variable Frequency Drives (VFDs) became popular due to the advantage of energy saving. Earlier, DC motors were used in variable speed applications which require good dynamic response, even though they have problems related to commutation. With the advancement in power electronics, dynamic response is no more a problem with induction motor. This paper demonstrates three speed control methods for induction motor. One of the three methods discussed here is scalar control in which speed control is done by varying the voltage and frequency keeping their ratio constant, the second method is Indirect Field oriented control (IFOC) in which rotor flux orientation is used, and the last method is Direct Torque Control (DTC) in which speed control is done by computing torque and stator flux directly from motor parameters. In all these speed control methods Space Vector Pulse Width Modulation (SVPWM) technique is used for three level inverter. Three level inverters are preferred to reduce the voltage stress on switches in medium voltage drive applications.