Novel Switching Table for Direct Torque Controlled Permanent Magnet Synchronous Motors to Reduce Torque Ripple

Abstract

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.

A New Predictive Direct Torque Control Method for Improving Both Steady-State and Transient-State Operations of the PMSM

“…WITH RECENT SIMILAR METHODS After investigating the recent studies presented about the ripple reduction in DTC method, it is observed that the methods proposed in [9] and [37] have a good performance in both the steady-state and transient-state; hence, these two methods are selected to be compared with the predictive method proposed in this paper. In this section the comparison is done from the analytical point of view while in sections IV and V the comparison is done by using simulations and experimental tests.…”

“…Based on (8), because the values of the ⃗⃗ ⃗ , ⃗⃗⃗⃗⃗ and ⃗⃗⃗⃗⃗ can be obtained in every control cycle, by proper control of the ⃗⃗⃗⃗ one can control the motor torque towards a desirable value. If it is assumed that: 1) duration of one control period is equal to , 2) a non-zero voltage vector ( ⃗⃗⃗⃗ ) is applied to the motor with a time duration of , and 3) a zero voltage vector is applied to the motor in the rest of the control period, then, based on (8), the result of these voltage vectors on the torque is calculated by (9) and (10), respectively: | ⃗⃗⃗⃗⃗ || ⃗⃗⃗⃗ | ⃗⃗⃗⃗⃗ ⃗⃗⃗⃗⃗…”

“…In some of these approaches, a new hardware is incorporated to reduce the torque ripple [9]- [12]. For example, in [9], a three-level Neutral Point Clamped (NPC) inverter is used instead of the conventional two-level inverter and four new switching tables are proposed to reduce the torque ripple among which the third method has the lowest ripple and the first method has the fastest dynamic response.…”

“…For example, in [9], a three-level Neutral Point Clamped (NPC) inverter is used instead of the conventional two-level inverter and four new switching tables are proposed to reduce the torque ripple among which the third method has the lowest ripple and the first method has the fastest dynamic response. However, the third method cannot rotate the motor at speeds higher than 70% of the rated speed and the first method has a high torque ripple.…”

Selection of Voltage Vectors in Three-Level Five-Phase Direct Torque Control for Performance Improvement

“…The first is the high torque and flux ripples, whereas the second is the variable switching frequency of the devices. Several methods have been proposed to overcome these problems by using modified DTC techniques [2]- [9].…”