Browsing by Author "Dawit, Mezgebu"

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    Space Vector Based Fuzzy Controlled DTC (Direct Torque Control) Of Three Phase Induction Motor Drive
    (Addis Ababa University, 2018-12) Dawit, Mezgebu; Mengesha, Mamo (PhD)
    Induction motors have a wide range of applications due to their well-known advantages, like low costs and robust performances. Among many kinds of modern control strategies for controlling an induction motor, a DTC has gained a huge importance due to its excellent control strategies for torque control. However a conventional DTC of three phase induction motor drive has high ripples in electromagnetic torque, stator flux linkage, stator currents and speed response. In this thesis, a space vector based Fuzzy logic duty ratio controller is designed to reduce the ripples. In DTC three phase induction motor drive supplied by a voltage source inverter, it is possible to control the stator flux linkage and electromagnetic torque by the selection of the voltage space vector in the inverter. The switching states produce the switching status according to the output of torque and flux comparator and sector judgment. The output of the voltage source inverter is given to the induction motor which is modeled in stationary D and Q axis reference frame. A Fuzzy logic based duty ratio minimizes the ripples by varying the DC link voltage of a voltage source inverter which is limited by the conventional DTC. A comparison is made between a conventional DTC and Fuzzy logic duty ratio based DTC of three phase induction motor drive using MATLAB/Simulink. The use of Fuzzy logic duty ratio controller reduces the ripples by 2.2% and the settling time of the step speed response is 4.122 milliseconds that is better response by 2.713 milliseconds than the conventional DTC. The use of fuzzy logic duty ratio controller also reduces the speed fluctuations at step speed response and at different speed levels when the load torque is applied compared to conventional DTC . The comparison of simulation results are valid by evaluating the performances of the simulation results.