Discrete Space Vector Modulation Applied on a PMSM Motor

The 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). However, because the rotor flux linkage is fixed on the rotor of PMSM, 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 a simplified space vector modulation technique, which addresses the problem by introducing a higher number of predefined voltage space vectors. The voltage vectors are tabulated in more precise switch tables which also take the emf induced in the stator windings into account. While still using switch tables to maintain the simplicity of the classical DTC scheme, the torque ripple results significantly decreased. Theoretical development and simulation results from the classical and improved DTC are presented and compared to support the research. Results show that the torque, flux linkage and stator current ripple are significantly decreased with the improved DTC