Non-linear adaptive state feedback speed control of a voltage-fed induction motor with varying parameter

An adaptive non-linear state feedback speed control algorithm for a voltage-fed induction motor is proposed in which the control of torque and flux are decoupled. The inputs to the control algorithm are the reference speed, the reference flux, the measured stator currents, the measured rotor speed, the estimated rotor flux and the estimates of the rotor resistance, stator resistance and load torque, which may vary during operation; the outputs are the reference stator voltages. Accurate knowledge of the flux is very important in maintaining high performance, high efficiency operation and although the estimated rotor flux using rotor model is insensitive to stator resistance variation it does depend on rotor resistance. A Model Reference Adaptive System (MRAS) rotor resistance estimator has also been designed and is stable in motoring, braking and generating operating modes and insensitive to stator resistance variation. The stator resistance and load torque are also estimated. The simultaneous operation of the estimators constitutes a decoupled cascade structure control system. This simplifies the design of the estimators for stable operation in the various operating modes. The continuous, adaptive updating of the varying machine parameters and load torque ensures accurate flux estimation and high performance operation. Simulation and experimental results are presented to verify the stability and performance of the proposed drive in motoring, braking and generating modes of operations.