ONLINE ROTOR RESISTANCE ESTIMATION FOR EFFICIENT SPEED CONTROL OF IVCIM DRIVE

Abstract

Speed control of drives are necessary in order to achieve variable speed, variable frequency operation. Earlier dc motor was mostly used for variable speed operation and ac motors for fixed speed because control of ac motor is complex than dc. Also ac motor as in this case induction motor is highly inductive and non-linear so speed control of induction motor is difficult. But by the invention of vector control method, it can be controlled like a separately excited dc motor. Also it is less bulky comparative to dc motor, can be used in dusty environment and under water also. So it has replaced dc motor at various industries. Indirect vector control is used mainly in industries because of its simplicity, less number of sensors are required than direct vector control. Scalar control method is easy to implement but it has inherent coupling effect which makes the performance sluggish and also good dynamic performance cannot be achieved. As in indirect vector control, both flux and torque currents are controlled separately so if torque control is required, it only affects torque and flux control is necessary only flux can be controlled. But as motor has resistance also which is temperature dependent so under running condition, motor’s resistance can vary up to 100% which will result in coupling between torque and flux. So correct estimation of rotor-resistance is required to maintain the quality of indirect vector control.