High Performance Direct Torque Control of Induction Motor using Space Vector Modulation

This paper describes sinusoidal pulse width modulation of the voltage impressed to the stator of an induction motor for direct control of torque and stator flux. Instantaneous voltage vectors applied by an inverter have redundancy characteristics which provide some flexibility for selecting the inverter switching modes. By using this switching freedom, control is achieved according to the following properties; high speed torque control, regulation of the primary flux, minimization of the inverter switching frequency. This utilizes a constant hysteresis band for both developed torque and stator flux and indirectly maintains the switched stator voltage waveforms averaged over a switching period to sinusoidal as in SPWM technique. It improves the dynamic performance of the machine compared to the conventional speed control of induction motor drives. A simulation programme has been developed to verify the results. The inverter duty cycle can then be calculated using the space vector PWM technique. The proposed method is very promising for rapid torque control which is quite different from FOC (field orientation control)