Sliding mode speed and load torque observer for core and copper loss minimization control of the induction motor drive

The paper studies the problem of efficiency improvement control of the induction motor drive based on copper and core loss minimization. The main idea is to operate the machine at a certain flux level that places the combined losses at a minimum level, thus improving the efficiency. A sliding mode observer (SMO) is developed to estimate the quantities needed for control implementation: magnetizing currents, speed, and load torque. The SMO uses feedback terms that are constructed using the estimated fluxes in the stationary reference frame. The paper develops a Voltage Model Observer for flux estimation that is specific to the IM model with core loss and involves a small approximation. Estimation of the magnetizing currents allows to set the appropriate flux level in the motor - the scheme proposed controls the speed and flux magnitude of the IM while minimizing the total copper and iron losses.