Sensorless field oriented control of AC induction motor using PI, PD & PID controllers

Abstract

This dissertation focuses on the effective utilization and feasibility of fieldoriented control of AC induction motor using PI, PD and PID controller without any physical sensors. The speed, torque and position in this scheme are estimated, analyzed and simulated with the help of motor control block-set in MATLAB/Simulink for a (10HP, squirrel cage induction motor). Separately excited dc motors due to their simplicity has been used extensively in numerous applications for high performance application. Induction motors have been used to replace separately excited dc motor because they are rugged, cheaper, lighter, lesser maintenance and has lower moment of inertia. With the FOC vector approach, the control of the induction motor behaves similar to that of a separately excited dc motor. The torque and flux components in the d-q rotating reference frame can be independently controlled with the help of unit vectors. Based on how the field angle is used to determine the unit vector, the vector control scheme is classified into two, direct vector control using the measured field angle and indirect vector control using the evaluated field angle. The direct vector control is efficient but is also complex and reduces the reliability of the system especially for high-speed drives. The indirect vector-controlled induction motor drives primarily involve the decoupling of the stator current into the torque and flux producing component but it still faces the challenge that the motor parameters variate with temperature resulting in estimation error of speed in steady state and transient state. To overcome this drawback, flux observers are utilized to have better parameter variation effects and also speed accuracy. The dynamic performance of PI, PD and PID control techniques has been presented without speed sensors which improves the mechanical robustness, design space and reducing the overall cost.