Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 192 (2017) 421 – 426
TRANSCOM 2017: International scientific conference on sustainable, modern and safe transport
Application of MRAS algorithm to replace the speed sensor in induction motor drive system Pavel Karlovskýa*, Jiří Lettla a
Department of Electric Drives and Traction, Czech Technical University in Prague, Faculty of Electrical Engineering, Technická 2, 166 27 Prague, Czech Republic
Abstract Sophisticated control of induction motor drive requires knowledge of the rotor angular velocity. In order to obtain the speed information an optical sensor is usually utilized. However, it is not always advantageous because of the whole drive robustness decrease caused by the speed sensor inclusion. The paper presents some simulation and measurement results in case of the MRAS (Model Reference Adaptive System) method employing in attempt to eliminate the induction motor drive speed sensor. The operation principle is explained and a mathematical model of the drive system is created. The MRAS method influence on the drive behaviour is examined in simulation environment and experimentally. Finally, the experimental results and comparison of the drive behaviour with and without the speed sensor are discussed. © Authors. Published by Elsevier Ltd. This ©2017 2017The The Authors. Published by Elsevier Ltd.is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of TRANSCOM 2017: International scientific conference on Peer-review responsibility the scientific committee of TRANSCOM 2017: International scientific conference on sustainable, sustainable,under modern and safe of transport. modern and safe transport Keywords: MRAS; sensorless speed determination; induction motor drive
1. Introduction Induction motor is thanks to its simplicity, robustness, and low price the most widely used motor in many applications of the electric drive area. On the other hand, it has some disadvantages, too. One of them is the necessity
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1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of TRANSCOM 2017: International scientific conference on sustainable, modern and safe transport
doi:10.1016/j.proeng.2017.06.073
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Pavel Karlovský and Jiří Lettl / Procedia Engineering 192 (2017) 421 – 426
of the sophisticated control algorithm that is much more complex in comparison to other type of motors. These algorithms often require information about the rotor angular speed. Traditional way of this information obtaining is the speed sensor using. It is very accurate but suffers from a lot of undesired effects like the whole drive robustness reducing or the drive price increasing. For these reasons, it is advantageous to eliminate the sensor and obtain the speed information in another way. Many methods such as open-loop calculation, MRAS, observers or Kalman filters have been developed recently. Every of them can be implemented in numerous ways and every method suffers from some disadvantages [1] – [3]. The most important problems are operation near zero speed working point and the necessary knowledge of many parameters of the motor with very high accuracy. The paper shows one possible implementation of the MRAS method [4] – [9]. The specific drive with induction motor is controlled by the direct torque control (DTC) method with speed control loop. The speed is as usually measured by tachogenerator and the MRAS algorithm should be utilized to replace the tachogenerator in the drive system. The paper focuses on the difference between the estimated and measured speed value in some dynamic states such as drive speed reversing. Nomenclature us is ψr ψr T Rs Ls σ Lr Lm ωr e Kp Ki
Stator voltage vector Stator current vector Rotor magnetic flux vector Stator magnetic flux vector Torque Resistance of stator winding Inductance of stator winding Leakage coefficient Inductance of rotor winding Mutual inductance between stator and rotor Angular speed of the rotor Control deviation Proportional gain of PI controller Integrational gain of PI controller
2. Utilized MRAS method The MRAS method can be generally used to calculate almost every parameter or variable of the motor. In this case the method was used to estimate the angular speed of the rotor. The working principle consists in the calculation of the rotor flux vector by two models. The first model is called reference model. It is based on the induction motor U-I model and calculates the rotor flux using the voltage applied on the motor and the stator currents. The output of this model is considered to be correct and therefore its name is “reference model”. The equation for its output is expressed by Eq. 1.
d
