IJSRD - International Journal for Scientific Research & Development| Vol. 2, Issue 08, 2014 | ISSN (online): 2321-0613 All rights reserved by www.ijsrd.com 236 Speed Control Technique for Induction Motor - A Review Chandni A. Parmar 1 Prof. Ami T. Patel 2 1 M.E student 2 Assistant Professor 1,2 Department of Electrical Engineering 1,2 MGITER, Navsari Abstract— In this paper, various types of speed control methods for the single phase induction motor are described. Speed can be controlled to control the frequency or slip can be controlled to control the torque. Then flux and torque are also function of frequency and voltage. Various methods are used to control the flux and voltage. This paper is focused on sliding mode control technique for induction motor. Keywords: induction motor, sliding mode control, speed control, non linear control I. INTRODUCTION Induction motors are widely used in many residential, industrial, commercial, and utility applications.[1] The control and estimation of ac drives in general are considerably more complex than those of DC drives and this complexity increase substantially if high performances are demanded. The main reasons for this complexity are the need of variable frequency, machine parameter variation, the complex dynamics of ac machines and the difficulties of processing feedback signals in the presence of harmonics. Above all these problems are reduce by using different control techniques of induction motor drives including scalar control, vector (field oriented control), and direct torque control. [2] However, in AC machine drives, have major drawbacks that are the sensitivity to the system parameters variations and bad rejection of external disturbances. To surmount these drawbacks and improve the induction motor control technique like adaptive (sliding mode) control. [2] Sliding mode control techniques are used in a wide number of applications to control of switching power converters, electrical machines, robotics, and other machinery. [3] II. VARIOUS SPEED CONTROL TECHNIQUES Various speed control techniques are mainly classified in the following categories: A. Scalar Control (V/f Control) In this type of control, the motor is fed with variable frequency signals generated by the PWM control from an inverter. Here, the V/f ratio is maintained constant in order to get constant torque over the entire operating range. Since only magnitudes of the input variables – frequency and voltage – are controlled, this is known as “scalar control”. Generally, the drives with such a control are without any feedback devices (open-loop control). Hence, a control of this type offers low cost and is an easy to implement solution. In such controls, very little knowledge of the motor is required for frequency control. Thus, this control is widely used. [5] B. Vector Control This control is also known as the “field oriented control”, “flux oriented control” or “indirect torque control”. In general, there exists three possibilities for such selection and hence, three different vector controls. They are: (1) Stator flux oriented control (2) Rotor flux oriented control (3) Magnetizing flux oriented control As the torque producing component in this type of control is controlled only after transformation is done and is not the main input reference, such control is known as “indirect torque control”. [4] The most challenging and ultimately, the limiting feature of the field orientation, is the method whereby the flux angle is measured or estimated. Depending on the method of measurement, the vector control is divided into two subcategories: direct and indirect vector control. In direct vector control, the flux measurement is done by using the flux sensing coils or the Hall devices. This adds to additional hardware cost and in addition, measurement is not highly accurate. Therefore, this method is not a very good control technique. The more common method is indirect vector control. In this method, the flux angle is not measured directly, but is estimated from the equivalent circuit model and from measurements of rotor speed, the stator current & the voltage. [5] Fig. 1: Direct Vector Control. Fig 2: Indirect Vector Control. C. Direct Torque Control (DTC) This model is based on the mathematical expressions of basic motor theory. This model requires information about the various motor parameters, like stator resistance, mutual inductance, saturation co efficiency; etc