Torque ripple reduction in a PMSM driven by direct torque control

Permanent magnet synchronous motors (PMSM) are extensively used in high-performance industrial applications. The electromagnetic torque in a PMSM is proportional to the angle between the stator and rotor flux linkages. Therefore, high dynamic response can be achieved by means of direct torque control (DTC). The main advantage of DTC is its structure simplicity, since no coordinate transformations and no PWM generation are needed. However, high torque ripple is produced when making use of full voltage vectors in classical DTC. The paper presents an improved PMSM DTC scheme by using an active-null vector modulation strategy based on an rms torque-ripple equation minimization. The proposed strategy improves the performances of DTC by combining low torque ripple characteristics in steady state with the faster torque dynamics. Theoretical development and simulation results by the classical and improved DTC are presented and compared to support the research.