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(s alpha), phi(s beta)) and stator currents (i(s alpha), i(s beta)) as state variables. In this model the motor iron losses is modeled by a shunt rotor speed dependent core resistance (R-o) 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-o*) and the actual values of these signals (phi(s,) T-o) 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-fine search methods are adopted. Finally some simulation results are presented to show the capability and validity of the proposed control scheme.