Development of soft computing controllers for direct torque controlled induction motor drive

Abstract

The induction motor drives are used in Industry predominantly. Due to their ease of maintenance, ruggedness and cost effectiveness, the induction motors have replaced the DC motors from industries. On the other hand, the control system issues have bothered the benefits of the induction motors for high performance. Most of the low performance drives use scalar control concept. In scalar control, only the magnitude of stator voltage and frequency are altered to maintain the constant stator flux. The spatial position of the stator flux is not taken into consideration. Vector control is used for its ability to control the induction motor like a DC motor in induction motor drives. Later, Direct Torque Controlled induction motor (DTC-IM) drives were introduced. The stator currents are the control quantities in vector controlled induction motor drives. In Direct Torque Controlled drive, the control quantities are stator flux linkages. The decoupled control of the torque and stator flux in Direct Torque Control is attained by the radial and tangential components of the stator flux linkage. The direct-axis stator flux controls the flux and the quadrature-axis stator flux controls the torque. The high performance vector control drives in industries are replaced by Direct Torque Controlled drives. The Direct Torque Control is of simple control newlinestructure with less machine parameter dependence. In a voltage source inverter supplied Direct Torque Control of induction motor drive, the stator flux linkage and electromagnetic torque of induction motor can be controlled by selecting the suitable inverter switching signals from a look-up table. The objective of the selection of inverter switching signals is to control the flux and torque errors by corresponding torque and flux hysteresis bands. The stator flux angle and the hysteresis comparators outputs are the inputs to the look-up table. newlineIn Direct Torque Control, the reference flux is estimated based on the speed of induction motor using a reference flux estimator. newline newline