Direct Torque Control (DTC) of Induction Motor

Direct Torque Control strategy has been implemented for controlling the speed of a 2.2 kW Induction motor at various load torque demands.

A 50 Hz, 4 pole , 2.2 kW Induction Motor has been modelled in direct-quadrature (dq) frame.The rated torque of the machine is 14 N-m. And rated current is 4.4 Amps ( r.m.s ),at full load . At full load , the machine has a rated speed of 1440 r.p.m. The machine speed is controlled in closed loop by direct torque control strategy. The running voltage and current feedbacks are taken , converted into stationary Alfa-Beta frame and from there the electromagnetic torque , stator flux and sector of the rotating flux is calculated . The speed of the machine is fed back to compare it with reference speed. The PI controller is tuned appropriately to produce the reference torque which is then compared with the electromagnetic torque. The stator flux is monitored by a two level hysteresis controller to keep it at 1.1 Wb throughout the machine operation. Similarly, a three level torque controller also monitors the electromagnetic torque as per load demand. The status of torque and stator flux , along with the sector information , enables the proper selection of voltage space vectors . The corresponding switching states of the voltage space vectors enables the voltage source inverter ( VSI) to control the input voltage of the induction motor.
In this way , the speed is tracked and the load demand is catered. The current is found to be sinusoidal and within rated current limits throughout simulation.