Robust Generalized PI sliding mode control for the induction motor

In this article, we propose a two stage control design scheme for simultaneous flux regulation and angular position reference trajectory tracking in induction motors. The first outer loop design stage uses a linear GPI observer based robust control, aimed at on-line load torque estimation, thus making possible its cancelation from the controller. The stator currents act as auxiliary control input variables, within a field oriented control scheme, which uses a nonlinear asymptotic flux reconstructor. The designed current signals are used then as reference trajectories for the second, inner loop, design stage, corresponding to a switched stator input voltage strategy based on an average Generalized Proportional Integral control design. This average design defines a discontinuous control input by means of a properly set sign function on the input tracking error. The second controller design stage, largely overcomes the effects of nonlinearities, including unknown motor parameters, present in the rotor voltages-to-rotor currents multi-variable dynamics.