A Constant Switching Frequency Of Direct Torque Control Of Brushless DC Motor

• Main Author: Ahmad Tarmizi, Yusnida
• Format: Thesis
• Language: English; English
• Published: 2019
• Subjects: TK Electrical engineering. Electronics Nuclear engineering
• Online Access: http://eprints.utem.edu.my/id/eprint/24686/; https://plh.utem.edu.my/cgi-bin/koha/opac-detail.pl?biblionumber=116932

Direct torque control (DTC) for DC motor have extensively used in many applications because it provides the simple control structure, faster torque dynamic control and longer lifespan. However, the used of hysteresis comparator in DTC structure have provides two major drawbacks namely, larger torque ripple and variable switching frequency. These problems occur due to low sampling time which creates delay actions in minimization of torque error with appropriate voltage vectors and inappropriate voltage selection of voltage vectors which leads to larger torque ripple in DTC scheme and cause the torque error cannot restrict within the hysteresis bandwidth. Therefore, this thesis presents the optimal DTC switching strategy to reduce torque ripple and gain the constant switching frequency for BLDC motor. Next, to analyze and compare the switching frequency and torque control performance produced by other strategy schemes such as torque hysteresis control (THC), direct torque control (DTC) and constant switching frequency (CSF). The minor modification is made without changing the original structure of DTC scheme. The hysteresis controller is replaced with torque controller and look-up table is added where the selection of voltage vector is occurred. The most suitable voltage vector for different speed range can be defined as the vector that produces minimum torque slopes. The torque ripple and switching frequency can be reduced when the torque slope is minimized. Next, to obtain the constant switching frequency, PI controller and high injection frequency are proposed. The proper proportional integral (PI) controller are determine by analyzing or insuring that the absolute torque shape does not exceed the absolute carrier slope. The results of improvements are obtained and were verified via simulation and experiment, as well as comparison with the conventional DTC and others schemes. The results obtained clearly show that the torque ripple is reduced and constant switching frequency is achieved.