1 Abstract—Two different speed estimation techniques for the doubly fed induction machines (DFIM) are reported here. One of the methods is based on reactive power and the other is based on the computation of flux. Model reference adaptive systems (MRAS) are formulated for speed estimation. The uniqueness of the reactive power based MRAS is that the instantaneous reactive power (IRP) is used in the reference model, whereas, steady state reactive power (SRP) is considered for the adjustable model. This type of estimator does not require calculation of the flux and hence reduces computational burden. Also, the scheme is independent of stator and rotor resistance variation. Simulation and experimental results are presented for the validation of the proposed algorithm. The flux based MRAS, independent of stator resistance variation, is also developed for the speed senseless operation of DFIM drive. It is noted that the available flux based MRAS are dependent on the change of stator resistance. Index Terms— Doubly-fed, Model Reference Adaptive System, MRAS, reactive power, induction motor, sensorless, vector control. I. INTRODUCTION NDUCTION motor control from stator and rotor side is gaining popularity due to the availability of wider speed controlling zone without flux weakening. The concept of doubly fed motors was first found in the Kramer and Scherbius drive, where the slip power is recovered through mechanical arrangement. The next generation research eliminates the mechanical assembly by means of power electronic system in the rotor side. In some configuration [1], stator side is directly connected to grid and rotor side is field oriented controlled. The main disadvantage of this type of configuration is that the drive is unable to operate in negative speed zone. An alternative arrangement is the injection of variable voltage and variable frequency (VVVF) from both the sides [2]. With this approach, the negative speed restriction can be overcome and the rotor speed variation may be extended from -2pu to +2 pu without flux weakening. Also, the zero speed operation is achieved by judicious choice of stator and rotor side frequencies, as Ȧ e =Ȧ s -Ȧ r . Here, Ȧ e is the electrical rotor speed; Ȧ s and Ȧ r are the stator and rotor side frequencies respectively. Such schemes are operated with or without speed sensor with varying performance. Mounting, signal transmission, hazardous environment and economy may restrict the use of speed sensor in many applications. So, speed estimation is more appreciated than the speed sensing in industry applications. Some speed estimation techniques for vector controlled doubly-fed induction motors are available in [1-2] and [4-6]. The MRAS based speed estimation technique for DFIM drive is comparatively new. Some literatures are available on flux based MRAS [5, 6]. However, no attention has been paid to the investigation of reactive power based MRAS for DFIM drive. It is worth noting that the existing flux based MRAS are sensitive to stator resistance variation. In this paper, a reactive power based MRAS is proposed for the estimation of speed for DFIM drive. For speed estimation, both instantaneous and steady state reactive powers are utilized. The scheme does not require flux estimation. I 3-Ф converter 3-Ф Inverter 3-Ф Inverter Fig. 1. Converter configuration of doubly fed SRIM drive Suman Maiti Chandan Chakraborty, Senior Member, IEEE Department of Electrical Engineering Department of Electrical Engineering Indian Institute of Technology-Kharagpur Indian Institute of Technology-Kharagpur INDIA INDIA e-mail: sumanmaiti@rediffmail.com e-mail: chakraborty @ieee.org MRAS-based Speed Estimation Techniques for Vector Controlled Double Inverter-fed Slip- ring Induction Motor Drive   k ,(((