KARPE S.R.* et al. ISSN: 2250–3676 [IJESAT] INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE & ADVANCED TECHNOLOGY Volume-2, Issue-4, 912 – 917 IJESAT | Jul-Aug 2012 Available online @ http://www.ijesat.org 912 FUZZY LOGIC BASED DIRECT TORQUE CONTROL OF INDUCTION MOTOR Mr. Karpe S.R., Mr.Dhote V.P. Assistant professor , Dept of Electrical Engg, S.B.Patil College of Engg, Indapur, M.S., India, karpe_suraj@yahoo.in Assistant Professor, Deptt. Of Electrical Engg, G.E.C.A. Aurangabad, M.S., India, vpdhote@gmail.com Abstract: This paper presents an improved Direct Torque Control (DTC) based on fuzzy logic technique. The major problem that is usually associated with DTC drive is the high torque ripple. To overcome this problem a torque hysteresis band with variable amplitude is proposed based on fuzzy logic. The fuzzy proposed controller is shown to be able to reducing the torque and flux ripples and to improve performance DTC especially at low speed. Keywords: Direct torque control, induction motor, fuzzy logic, torque ripple minimization -------------------------------------------------------------------------------***---------------------------------------------------------------------------- 1. INTRODUCTION DTC (Direct Torque Control) is characterized, as deduced from the name, by directly controlled torque and flux and indirectly controlled stator current and voltage. It is an alternative dynamic control for vector control. The big interest in DTC is caused by some advantages in comparison with the conventional vector-controlled drives, like: - The control is without using current loops. - The drive does not require coordinate transformation between the stationary frame and synchronous frame. - A pulse-width modulation (PWM) modulator is not required. Conventional DTC has also some disadvantages: - Possible problems during starting and low speed operation. - High requirements upon flux and torque estimation. - Variable switching frequency. These are disadvantages that we want to remove by using and implementing modern resources of artificial intelligence like neural networks, fuzzy logic, genetic algorithms etc. In the following, we will describe the application of fuzzy logic in DTC control. 2. DTC PRINCIPLES The DTC scheme is given in Fig. 1, the ε φ and ε τ signals are delivered to two hysteresis comparators. The corresponding digitized output variables: change of magnetic flux ∆φ, of mechanical torque ∆τ and the Stator flux position sector S N created a digital word, which selects the appropriate voltage vector from the switching table? The selection table generates pulses S a , S b , S c , to control the power switches in the inverter. Three-level torque and two level flux hysteresis controllers are used according to the outputs of the torque controller and the sector information of appropriate voltage vectors for both the inverters are selected from a switching table as it is shown in fig.1.Figure.2 shows the voltage vectors which are usually employed in DTC scheme when the stator flux vector is lying sector I. The selection of a voltage vector at each cycle period is made in order to maintain the torque and the stator flux within the limits of two hysteresis bands. This simple approach allows a quick torque response to be achieved, but the steady state performance is characterized by undesirable ripple in current, flux and torque. Torque and rotor speed values in the voltage selection algorithm. Table 1. DTC switching table 3. TORQUE RIPPLE ANALYSIS Since none of the inverter switching vectors is able to generate the exact stator voltage required to produce the desired changes in torque and flux, torque and flux ripples compose a real problem in DTC induction motor drive. According to the principle of operation of DTC, the torque presents a pulsation