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Owing to simple implementation and excellent performance, the conventional stator flux observer based on active flux concept is considered as a competitive scheme for direct torque control system of a permanent magnet synchronous motor. However, it is constructed by a large number of motor parameters, which may vary with the operating points. This leads to weak robustness. To improve its performance, a stator flux observer with phase self-tuning is proposed as an improved version in this article. First, relationship between the stator flux observed values obtained by current and voltage models and observed error of rotor position angle is analyzed. Then, according to the aforementioned analysis, a phase self-tuning link constructed by a proportional-integral regulator is proposed to ensure that the observed coordinate system converges to the actual one even under motor parameters vary conditions. Consequently, the robustness and accuracy of the stator flux observer can be improved. Finally, the stability of the proposed phase self-tuning link is analyzed. Experimental comparison between the conventional stator flux observer based on active flux concept and the proposed improved stator flux observer has been done, and the results verify the feasibility and effectiveness of the proposed stator flux observer. [ABSTRACT FROM AUTHOR]

Direct torque control (DTC) has become a widely acceptable alternative to field-oriented control in permanent magnet synchronous motor (PMSM) drives. Deadbeat direct torque and flux control (DB-DTFC) is a significant improvement over the classical DTC. However, there are some aspects that can be improved, such as insufficiently small electromagnetic torque ripple, unsmooth dynamic response, heavy computation burden, and relatively weak robustness to motor parameters variation. To improve the operation performance, an advanced DB-DTFC strategy is proposed in this article. First, the algorithm model based on stator flux oriented coordinate system is deduced. On this basis, the basic principle of proposed DB-DTFC is presented. Second, a novel graphical analysis method is proposed to help illustrate the proposed strategy. Third, a general solution method is proposed to solve the reference stator voltage, which is a key variable for the DB-DTFC. Finally, the stability of system is analyzed. Theoretical and experimental comparisons between the proposed DB-DTFC and the conventional DB-DTFC are done. The results show that the performance in the aspects of electromagnetic torque and stator current ripples reduction, dynamic response, computation burden, and robustness to motor parameters variation are all improved in the proposed DB-DTFC. [ABSTRACT FROM AUTHOR]

This article introduces the classical direct torque control (DTC) to a three-phase open-end winding permanent magnet synchronous motor with common dc bus for the first time. The electromagnetic torque and the stator flux are controlled at the same time. However, the zero-sequence current is not suppressed, and the ripples of the electromagnetic torque and stator flux are large. To improve the operation performance of this drive system, a DTC based on a duty ratio modulation (DRM-DTC) is proposed. First, a deadbeat zero-sequence current controller is proposed in the DRM-DTC to suppress the zero-sequence current. Second, another strategy, which is based on a graphical analysis method and a simple deadbeat direct torque and flux controller, is proposed to optimize the duty ratio of the active voltage vector. Thus, the electromagnetic torque and stator flux ripples can be reduced. Finally, an optimized pulsewidth modulation implementation strategy is proposed in the DRM-DTC to further reduce the switching frequency of inverters. The classical DTC and the proposed DRM-DTC are compared through simulation and experiment, and the results verify the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]