PROJECT 3

Title: A 12 Sector-Based Switching Scheme for Abnormal Grid-Connected Ultra-Sparse Z-Source Matrix Converter Based DTC of IM Drive

Abstract: This research presents a direct torque control (DTC) switching scheme based on ultra-sparse Z-source matrix converter (USZSMC) using 12-side polygonal space vector for variable speed control of an induction motor (IM). The conventional DTC scheme based direct matrix converter (DMC) is limited by 60°sectors of both flux and voltage vectors which introduce high torque ripple. The proposed method utilizes twelve 30°sectors of both flux and voltage vectors to increase the degrees of freedom for selection of proper vectors and reduce the torque ripple. The proposed switching scheme for MC based DTC of IM drive select the appropriate switching vectors for control of torque with small variations of the stator flux within the hysteresis band. This improves the degrees of freedom in selecting the vector algorithm and the torque ripple as well. Furthermore, during the large torque demand, the probabilities of transgressing reference vector limits, which are enclosed by 12-side polygonal space vector, are reduced. The sensitivity of DMC into the abnormal input voltage from a side and limitation of maximum voltage transfer ratio (86.6%) from other side are the most important drawbacks for conventional prototype of DMC. This study illustrates an USZSMC under abnormal input voltage which could properly reduce the total harmonic distortion (THD) of output current equal to 1.10% by applying compensation method in Particle Swarm Optimization (PSO) PI controller. Although, the Z-source network is cause of intensification of low order harmonics in input and output current; the proposed method optimizes the shoot-through timing in order to abate the distortion spectrum and increase the performance. The eliminating of abnormality rate less than 0.15% for output current, 0.32% for output voltage and accumulated phase synchronization are the advantages of aforementioned system where the restriction of maximum tolerated abnormality for input voltage is 40%. Extensive simulation and experimental results are presented to verify the effectiveness of the 12-sector space vector switching scheme for DTC control of IM fed by USZMC.