Induction Motor Drive Variable Speed and Torque Control Using DC Link

This paper presents a new control strategy for threephase induction motor which overcome the limitation limitation (i. e. sluggish/slow response) of volts per hertz controlled industrial drives and provide independent speed& torque control loops and the current regulation. Induction motors are the most frequently used machines in different electrical drives. About 80 % of all industrial loads utilize induction motors for various applications which require speed control for its implementation. Speed control of an induction motor requires position feedback information from an encoder, or a hall sensor to a controller unit. These feedback signals, which often pickup noise due to electromagnetic interference, can change the performance of the motor control system. In this project the feedback signals like current and speed are not taken directly from the motor side, instead it is estimated from the current and voltage measured from the dc link. The phase voltages and line currents are reconstructed from the measured dc link current and voltage. An algorithm is used to reconstruct the voltage and current. The inputs to this algorithm are the reconstructed waveforms of stator currents and voltages obtained from the dc link and not measured directly on stator side which avoid the noise. It also reduces the use of mechanical sensor as the rotor speed is not measured directly. The proposed drive thus requires only one sensor in the dc link to implement the close-loop speed and torque control of a three-phase induction motor which is simulated using MATLAB/ Simulink software.