The Direct Torque Control (DTC) technique for Permanent Magnet Synchronous Motors (PMSM) is receiving increased attention due to its simplicity and robust dynamic response when compared with other control techniques. The classical switching table based DTC results in large flux and torque ripples in the motors. Several studies have been reported in the literature on classical DTC. However, there are only limited studies that actually discuss or evaluate the classical DTC. This paper proposes, novel switching table / DTC methods for PMSMs to reduce torque ripples. 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 to the classical DTC structure. The two level inverter available in the classical DTC is eliminated by 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), where as in DTC scheme II, all of the voltage vectors are considered to form a switching table. Based on these groups, a novel switching table is proposed. The proposed DTC schemes are comparatively investigated with the classical DTC and existing literatures through theory analysis and computer simulations. The superiority of the proposed DTC method is also confirmed by experimental results. It can be observed that the proposed techniques can significantly reduces the torque ripples and improves the quality of current waveform when compared with traditional and existing methods.

The direct torque control (DTC) technique of a permanent magnet synchronous motor (PMSM) has received 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, the studies that actually discuss or evaluate the classical DTC are limited. This paper proposes, an alternative DTC method/switching table for PMSM, to reduce flux and torque ripples as well as mechanical vibrations. This is achieved by a simple modification 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 inverter. To further improve the performance of the proposed DTC, the available 27 voltage vectors are allowed to form different groups of voltage vectors such as Large - Zero, Medium - Zero and Small - Zero. Based on these groups, a new switching table is proposed. The proposed DTC is compared with the classical DTC and existing literature from the aspects of theory analysis and computer simulations. It can be observed that the proposed technique can significantly reduce the flux, torque ripples, and mechanical vibrations and improves the quality of current waveform compared with traditional and existing methods.

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Model predictive control widely advocates in the better performance control technique for permanent magnet synchronous motor drives for its exceptional flexibility of incorporating nonlinear parameters. However, the higher ripples in torque and harmonics in stator current are the major criticisms in this method. Enlightened by the idea of including nonlinear constraints in the cost function, this article proposes a novel cost function with reduced ripples in torque, stator flux, and current harmonics. The improvised cost function uses torque tracking, maximum torque per ampere, minimization of switching losses, and system constraints. This approach attains effectiveness in the minimization of the ripples in torque, stator flux, and stator current harmonics and also reduces the acoustic noise of the system. The claims of the proposed work are supported by the quantitative comparison of the simulated response with the standard model predictive torque control that uses errors in the stator flux and electromagnetic torque in its cost function. The compared simulation results prove the effectiveness of the proposed control technique.