Performance Analysis of a DTC Based 4S3P VSI- Fed High Performance Induction Motor Drive

Abstract

More than two decades ago, Direct Torque Control (DTC) was introduced to give fast, effective and efficient dynamic response. DTC can be considered as an alternative to the field-oriented control (FOC) technique. In fact, a DTC scheme accomplishes the closed-loop control of the stator flux magnitude and the electromagnetic torque of the motor without the intermediary of any current loop or shaft sensor. To this end, the DTC scheme senses the stator currents and the dc-link voltage and processes them, together with the states of the inverter switches, to estimate the actual values of the controlled variables. Many attempts have been carried out in the literature since the DTC was introduced in 1986, aiming to improve the performance of DTC of induction motor drives. Two of the major issues which are normally addressed in DTC drives are the variation of the switching frequency of the inverter used in the DTC drives with (i) operating conditions and (ii) the high torque ripple for using torque hysteresis comparator. To improve the performance of DTC, researchers consider different analytical approaches. The author proposed a constant switching frequency torque controller to replace the conventional hysteresis based controller. The hardware of a DTC scheme is reduced by using only one sensor of current and by inserting it in the inverter dc link. Nowadays, researchers are working not only for better performance of the drives but also trying to reduce the cost of the drives. Conventional six switch three phase (6S3P) inverters have been widely used for AC motor drives for the last few decades. But the reduction of the number of power transistor switches from six to four reduces the cost of the inverter, decreases the switching losses and complexity of the control algorithms instead of generating six PWM signals. A cost effective four switch three phase (4S3P) inverter with almost similar performance is proposed for IM drives. The authors show a performance comparison of the 4S3P inverter fed drive with 6S3P inverter fed drive in terms of speed response and total harmonic distortion of the stator current. But overshoot and undershoot can not be eliminated in the speed response of the drive system. The proposed fuzzy logic controller based control scheme for 4S3P inverter has been fed in the interior permanent magnet synchronous motor (IPMSM) drive. Vector control of induction motor using 4S3P inverter for high performance industrial drive systems is presented in this paper. The 4S3P inverter fed IM drive is found quite acceptable considering its performance, cost reduction and other advantages. The proposed low cost control scheme is suitable for industry applications.