Implementation of Twelve-Sector based Direct Torque Control for Induction motor

Direct torque control (DTC) is an advanced control technique, in which the torque produced by the motor is directly controlled by controlling the inverter switching states. Each switching state represents a voltage vector. DTC have the following features, it does not requires current controllers, elimination of rotor position sensors, fast torque response, lesser parameter dependence, and it does not requires any axes transformation. Due to the above said attractive features, DTC gains more popularity in industrial motor control. In basic DTC the circular locus is divided into 6 sectors and a total of 8 voltage vectors obtained from two level inverter used, these vectors cannot always generate exact stator voltage and produce more torque ripples. In this proposed work, the basic 6 sector DTC scheme is modified with 12 sector and conventional two level inverter is replaced by three level neutral point clamped inverter to get different voltage vectors to a maximum of 27 and they are classified into large, medium, small and zero voltage vectors. New optimum switching table is proposed for different voltage vector combinations and the response of the proposed DTC scheme is analysed with the basic DTC scheme which shows considerable torque ripple minimisation. The simulation is performed in MATLAB / SIMULINK environment.