A Novel Method to Minimize Torque Ripple, Mechanical Vibration, and Noise in a Direct Torque Controlled Permanent Magnet Synchronous Motor Drive

Abstract

The Direct Torque Control (DTC) technique of the Permanent Magnet Synchronous Motor (PMSM) receives increasing attention due to its simplicity and robust dynamic response compared with other control techniques. The classical switching table based DTC presents large flux, torque ripples, and more mechanical vibrations in the motor. Several studies have been reported in the literature on classical DTC. However, only limited studies exist that actually discuss or evaluate the classical DTC. This paper proposes a simple DTC method/switching table for PMSM, to reduce flux and torque ripples as well as mechanical vibrations and noise. In this paper, two DTC schemes are proposed. The six sector and twelve sector methodology is considered in DTC Scheme I and DTC Scheme II, respectively. In both DTC schemes, a simple modification is made in the classical DTC structure by eliminating the two-level inverter available in the classical DTC and replacing it with a three-level Neutral Point Clamped (NPC) inverter. To further improve the performance of the proposed DTC Scheme I, the available 27 voltage vectors are allowed to form different groups of voltage vectors such as Large-Zero (LZ), Medium-Zero (MZ), and Small-Zero (SZ), whereas in DTC Scheme II, all the voltage vectors are considered to form a switching table. Based on these groups, a new switching table is proposed. The proposed DTC schemes are comparatively investigated with the classical DTC and existing literatures from the aspects of theory analysis and computer simulations. It can be observed that the proposed techniques can significantly reduce the flux, torque ripples, mechanical vibrations, and noise and improve the quality of current waveform compared with traditional and existing methods.