A Novel Direct Torque Control with or without Duty Ratio Optimization for Induction Motors

This paper proposes a novel direct torque control with or without duty ratio optimization for induction motors (IM). A proportional-integral (PI) torque controller is utilized to control the rotational angle of stator flux vector during one control period. Then a reference voltage vector (VV) can be derived, which is not synthesized by space vector modulator (SVM). By locating the reference VV in the complex plane, a candidate VV can be determined. For cases with restrictively limited switching frequency, the candidate VV can be directly imposed on motor terminals while producing large torque and current ripples. To improve the drive performance, an easy duty ratio optimization algorithm is introduced to mitigate the torque and current ripples. The simulation results verify the feasibility of the proposed strategy.