Novel hybrid sliding-mode controller for direct torque control induction motor drives

Classic direct torque control (DTC) is well known to produce fast dynamic response and robust control. However, notable torque and stator flux ripples occur in steady-state operation. A novel hybrid sliding-mode controller for direct torque and stator flux control (DTC) of an induction motor is presented. The newly developed hybrid sliding-mode control law consists of proportional-integral (PI) control at steady state, sliding-mode control at transient state, and a simple adaptive switching mechanism between steady state and transient state, to achieve satisfied performance under steady and transient conditions. A modified model of an induction motor, in which the stator currents and the stator fluxes act as state variables, is founded. Proportional-integral sliding-surfaces are proposed. And the parameters of sliding-mode variable structure controller are designed by Lyapunov's stability theory. The proposed control scheme not only preserves the transient merits and robustness of the sliding-mode controller, but also improves the steady-state behavior by PI controller. Comparative results of simulations with the proposed control scheme, versus classic DTC, are conducted.