International Journal of Computer Applications in Engineering Sciences [VOL VI, ISSUE III, SEPTEMBER 2016] [ISSN: 2231-4946] 20 | Page Estimation of Rotor Resistance in Sensorless Field Oriented Controlled InductionMotor Drive Kunal B. Vashi 1 , Amit N. Patel 2 , Tejas H. Panchal 2 , Vinod Patel 3 1, 2 Department of Electrical Engineering, Institute of Technology, Nirma University, Ahmedabad 3 AMTECH Electronics(India) Ltd., Gandhinagar 1 knl.vashi@gmail.com 2 amit.patel@nirmauni.ac.in 2 tejas.panchal@nirmauni.ac.in 3 vinodp@amtechelectronics.com Abstract- In a sensorless vector control of induction motor drive the motor parameters have a strong influence on the performance of the drive. Variation of a rotor resistance impares performance of the drive system. It is very essential to estimate correct value of rotor resistance to ensure expected performace of drive system. No-load test, locked rotor test anddc test are the conventional methods for the parameter estimation.In real time system, no load test and locked rotor test have many limitations. The concepts of no-load test andlocked test can be modified under Field Oriented Control(FOC) of induction motor drive. An advanced locked rotor test is presented in this paper for the accurate estimation of rotor resistance without any additional hardware requirement.The presented method has been simulated for three different standared rating three phase inductionmotors, i.e. 10 hp, 100hp and420hp. Keywords - Field orientedcontrol(FOC), rotor resistance estimation, advanced locked rotor test I. INTRODUCTION Induction motors are the most widely used electrical motors in industrial as well as domestic applications. Superior control of induction motor must be necessary forbettrerperformance[1].Vector control is the most popular ac machine control method in high performance drive applications because it imparts control characteristics similar to a separately excited dc motor. Nowadays, sensorless vector control is increasingly becoming popular in induction motor drive. Performance of vector controlled induction motor drive strongly depends on the accurate estimation of motor parameters. The required parameters are stator resistance(R s ), rotor resistance(R r ), stator leakage inductance(L ls ),rotor leakage inductance(L lr ) andmagnetizing inductance(L m ). Over the past decades, many parameter estimation methods have been studied and analyzed in detail. Conventionally, these parameters are estimated by no load test, lockedrotor test and dc test.But in many industrial applications, it is very difficult to perform these tests because the machine is usually coupled to the mechanical load. Also, it is impossible to lockthe rotor in real time applications. The estimated rotor resistance from locked rotor test at rated frequency is inaccurate on account of skin effect [2].Among all parameters (R s ,L ls ,R r ,L r ,L m ), rotor resistance has a strong influence on the estimation of speed of sensorless vector controlled induction motor drive.An algorithm for the rotor resistance (R r ) estimation under the speed transient state without signal injection with only the stator current measurement is proposed in [3]. Though most of the vector control drives are based on the slip frequency type vector control technique (or indirect control)which is strongly influenced by the rotor resistance variation asR r is used for the speed estimation. It is known that the simultaneous estimation of the rotor speed and R r is very critical. It is difficult to estimate them simultaneously under the steady state conditionin the slip frequency type vector control[3].To overcome the above problem, there are several algorithms for the R r estimation in the sensorlessspeed control technique [4], [6]. This paper presents advanced locked rotor test to estimate the correct value of rotor resistance. II. SENSORLESS FOC OF INDUCTION MOTOR A. Model of induction machine The dynamic D-Q model of induction machineshown in Fig. 1 is the per phase equivalent circuit for the d s -q s equivalent circuits with counter emf[4].