New reliable start up DTC technique for induction motor drive

Direct torque control (DTC) is a control technique which can control flux and torque directly, using the inverter switching state. This control provides the indirect control of stator current and voltages in the motor, which can show its high dynamic performance. However, there is a disadvantage of over-current due to the required flux estimation in the induction motor drive at the start-up time. This issue sometimes could destroy the switching power of the inverter. Hence, predefined torque reference could have solved the issues if system torque reference is known. Alternatively, adequate torque is applied to start the DTC in safe mode. Therefore, the main gap is to find the appropriate reference torque and flux value to run the motor at the initial stage. Required reference torque and flux can solve the initial high current problem. This paper is reviewed the DTC start-up problems with mathematical analysis and presents a new simple start-up scheme without changing any switching table or DTC algorithm. The performance of the proposed method has been confirmed by experiment validation with a three-phase induction motor.