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International Journal of Pure and Applied Mathematics Volume 116 No. 11 2017, 171-179 ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version) url: http://www.ijpam.eu doi: 10.12732/ijpam.v116i11.18 Special Issue ijpam.eu FUZZY LOGIC BASED DIRECT TORQUE CONTROL OF THREE PHASE INDUCTION MOTOR 1Premalatha K and 2Thirumoorthi P 1,2 Department of Electrical and Electronics Engineering, Kumaraguru College of Technology, Coimbatore - 49 kppremalatha@gmail.com Abstract This paper presents the comparison between three different Direct Torque Control (DTC) strategies for the speed control of Induction Motor (IM): (i) DTC strategy with Hysteresis controllers (ii) DTC-Space Vector Modulation (SVM) with Proportional Integral (PI) controller and (iii) DTC-SVM with Fuzzy Logic controller (FLC). Dynamic behavior as well as steady state behavior of all the three methods is analyzed using MATLAB/SIMULINK. Simulation results show that, the FLC based DTC-SVM gives excellent dynamic and steady state performances. Also DTC SVM gives low torque ripples and maintains the switching frequency constant. Keywords: Direct Torque Control, Space Vector Modulation, Fuzzy Logic Controller, Induction Motor, Torque Ripple Minimization. 1. Introduction Squirrel cage induction motors are used in almost 75% of industrial applications, the popularity of the induction machine is due to its advantages like rugged construction, economical, less maintenance and self-protection against short circuit. Control strategies have indispensable role in high performance of induction motor applications. Predominantly, scalar control and vector control methods are used. Scalar control is simple and easy for implementation. But, the dynamic performance of the IM depends on the machine parameters [1]. DTC has simple calculation and no coordinate transformations. It requires only stator resistance for flux and torque calculation, which diminishes the machine parameter dependency [5, 6]. But conventional DTC 171 International Journal of Pure and Applied Mathematics Special Issue has some drawbacks; switching frequency of inverter varies with error band and large torque and flux ripples [7].Torque and flux ripples can be reduced by using Multi level inverter (MLI) or DTC-SVM inverter. In this paper three control strategies based on DTC, that can be used for the control of induction motor are described. Comparison between conventional DTC, PI controller based DTC- SVM and Fuzzy controller based DTC-SVM are presented. The fuzzy controller based DTC-SVM gives better result compared to the other methods. 2. Design of PI controller Proportional (Kp) and Integral (Ki) are the two main parameters used for the calculation of change in angle. Proportional constant depends on the present error and Integral time constant depends on the past error. The process can be controlled using weighted sum of these two parameters. The transfer function of PI controller is synthesize as ( ) (26) Figure 1. PI controller based system model PI controller based DTC system can be modelled as shown in fig.1. The performance of PI controller depends on the parameters of Kc and i. 172 International Journal of Pure and Applied Mathematics Special Issue 3. Design of Fuzzy Logic Controller Design of PI controller is quite complicated since it requires accurate mathematical model of the system and also has slower and poor transient responses such as overshoots during dynamic change in torque, oscillation in speed, high settling time and high torque ripple [10-13]. But FLC requires the knowledge of mapping between the inputs and output and it overcomes the drawbacks of PI controller. The Input of FLC is torque error and change in error. Each input and output consists of seven fuzzy sets. Linearized membership corresponding to inputs and output are shown in fig.6. Mamdani

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