The torque ripple produced in a switched reluctance motor (SRM) can be seen as one of 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.
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 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.
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