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Recently, Direct Torque Control (DTC) of AC motors is considered a significant method to attain torque control behavior compared to DC motors. However, it still suffers from some drawbacks such as the large torque and current ripples. Choice of hysteresis band amplitude is one of the initial difficulties involved in the technique since it determines ripple frequencies and amplitude error of control variables. This paper presents a comprehensive analysis of hysteresis band variations in DTC on the dynamic performance of induction motor (IM) drives. In this concern, effects of flux and torque hysteresis bands on switching frequency, torque and flux ripples as well as current distortion are explored. A simulation model is implemented by Matlab/Simulink. An experimental system of DTC for IM drives using DSP-DS1102 is built and tested. Experimental results are captured to prove the simulation results. The results show that the proposed DTC exhibits a good performance with minimum torque ripples and low current distortion under small hysteresis band amplitudes. However, small hysteresis band amplitudes produce high switching frequencies which cause high switching losses and high computation burden. To guarantee a high dynamic performance DTC of IM drives, a fuzzy logic controller (FLC) instead of a PI speed controller is designed. [ABSTRACT FROM AUTHOR]

The torque ripple produced in a switched reluctance motor (SRM) can be seen as one its major drawbacks. It occurs mainly due to the sequential switching of the motor phases and changes in the length of the air gap. The torque sharing functions (TSFs) are the more effective and favorable techniques developed to reduce the torque ripple in SRMs. However, the time responses of instantaneous torque for incoming and outgoing phases during commutation period (CP) are different. In addition, with increasing motor speed the CP decreases and the torque response of the outgoing phase oversteps it. In this paper, a modified torque sharing function based on the change of the overlap angle during the commutation process depending on the motor speed is presented. In the designed control algorithm of the TSFs, the motor speed is has become an input besides the rotor position and the torque command. The commutation time is precisely adjusted enough for the commutating process. The proposed method gives good results in a wide speed range. To deduce the magnetic characteristics of the SRM, finite element analysis (FEA) is applied and a look-up table model is derived. The effectiveness and robustness of the proposed control technique are exhibited in the simulation results. [ABSTRACT FROM AUTHOR]

This paper suggests a robust control approach for induction motor (IM) drives. The novel approach incorporates the two-degrees-of-freedom (2DOF) control scheme principle and the variable structure control (VSC) method. This highly modifies the capability of VSC scheme to suppress the influences of load torque disturbances and parameters uncertainty. Lyapunov stability concept is applied to guarantee the stability and to design the gains of VSC. A complete IM drive with the proposed 2DOF VSC scheme is assessed by simulations. The experimental system setup is executed practically by digital signal processor to apply the proposed controller. The results are provided under various working conditions to justify the efficacy of the suggested 2DOF VSC scheme. The 2DOF VSC approach and previous works are evaluated together under the variation of torque and speed reference. The results proved that the new 2DOF VSC scheme has significant dynamic performance with high suppression of disturbances and parameters mismatch in comparison to 1DOF and 2DOF control schemes. [ABSTRACT FROM AUTHOR]

Operation at low frequencies of sensorless drives using machine model-based estimation methods is a challenging issue. This paper proposes an adaptive flux observer (AFO) method of speed estimation for sensorless Induction Motor (IM) drives. The observer feedback gains are designed to guarantee accurate speed estimation, especially at low frequencies in the regenerating mode operation. A complete sensorless IM drive with the proposed AFO is executed in the laboratory. Extensive experimental results under different operating conditions are provided to prove the effectiveness of the proposed AFO, particularly under low stator frequencies in both motoring and regenerating modes of operation. [ABSTRACT FROM AUTHOR]