The Decoupled Stator Flux and Torque Sliding-Mode Control of Induction Motor Drive Taking the Iron Losses into Account

This paper presents a novel decoupled sliding-mode (SM) stator flux and torque controller for three-phase induction motor drive which is supplied by a two level SVM voltage source inverter (VSI). The nonlinear controllers are developed in a stationary two axis ( alpha, beta ) IM reference frame with stator fluxes ( phi_salpha, phi_sbeta) and stator currents ( i_salpha, i_sbeta) as state variables. In this model the motor iron losses is modeled by a shunt rotor speed dependent core resistance (R_c) in IM two axis equivalent circuits. Using the proportional integral type SM switching surfaces, the Lyapunov based control efforts are designed so that the errors between stator flux (phi_s*) and motor reference torque ( T_e* ) and the actual values of these signals ( phi_s,T_e ) asymptotically converge to zero in spite of machine parameters mismatching and uncertainty. In this control strategy, since the control of stator flux and torque are decoupled hence, for a given motor load torque and a given motor speed, the drive system efficiency can be easily minimized by adjusting the magnitude of stator reference flux. To do so, both the model based and on-line search methods are adopted. Finally some simulation results are presented to show the capability and validity of the proposed control scheme.