Simulation of direct torque control of induction machine using three-level cascaded H-bridge multilevel inverter

Mohamad Rasyidi, Nazir Ali (2014) Simulation of direct torque control of induction machine using three-level cascaded H-bridge multilevel inverter. Project Report. Universiti Teknikal Malaysia Melaka, Melaka, Malaysia. (Submitted)

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Abstract

Direct torque control (DTC) is a method based on vector control that attracts many researchers since it been introduced in 1986. Mostly this method has significant implementation on the induction machine compared to other machine. This is because the simple structure and less parameter required in order performing this mechanism. However, this method has several disadvantages when applying with the two-level inverter such as less selection of effective voltage vector and high switching frequency. This is because the possible number of voltage vector that can be selected is only six. Thus, this problem leads to the losses during the operation of induction machine and increase the torque ripple. Therefore, this research project is to replace the conventional two-level inverter with the cascaded H-Bridge multilevel inverter (CHMI). One of the aims of this project is to formulate an optimal voltage vector selection according to the speed operation for direct torque control of induction machines. Besides that, this project aims to verify the proposed selection of voltage vectors which improve efficiency and reduce torque ripple. In order to achieve the objective, a comprehensive study done by emphasizing on current technical papers to develop the simulation model. First and the foremost, is to construct the induction machine model based on it mathematical equation. By having crystal clear of understanding of the CHMI topology, the next step is to formulate the look-up table. This look-up table consist of three important parameters that are flux magnitudes which control by two-level hysteresis comparator, torque magnitude which control by seven-level hysteresis comparator and the sectors definition of the stator flux plane. In addition, verification of efficiency is done by construct the switching calculation algorithm. The finding highlighted significant improvement of efficiency especially during low speed that is reduction of 61.4% compared to the conventional inverter. The zoom images manage to prove that the torque have reduce significantly compared to conventional.

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