In this paper, an adaptive load torque observer based on backstepping control is designed, which achieves accurate load estimation where the load is unknown. Based on this, in order to reduce the loss of the motor at low load, a smooth switching strategy of rotor flux based on speed error is designed. According to the real-time speed error of the induction motor, the smooth switching strategy achieves dynamic flux switching. Firstly, when the uncertain load occurs for the first time in the recursive design, the adaptive law of the load is designed, and a novel adaptive load torque observer is obtained, which accurately estimates the uncertain load torque in real time. Secondly, the relationship between the loss and the rotor flux is established by analyzing the loss model of induction motor, and the optimal rotor flux is obtained. The smooth switching control strategy based on speed error is designed to realize the efficiency optimization of induction motor. Finally, the control strategy proposed in this paper is experimentally verified on the LINKS-RT platform. The results show that the proposed control strategy has excellent load disturbance attenuation performance and reduces the energy loss.

In this study, combining backstepping sliding mode (BSM) and disturbance observer‐based control (DOBC), a state feedback controller is designed to regulate the speed of induction motor (IM). First, a feedforward compensation method is proposed based on the rotor flux observer and BSM control to counteract the mismatched lumped disturbances. Then, a disturbance observer is established to estimate the overall effect of possible modelling inaccuracy, load disturbance and motor parameters variation in the IM model. Compared with the conventional vector controller, the proposed controller solves the problems of modelling imprecise, unknown load injection and parameter variation, and realises the speed tracking of IM with good performance. Finally, experiments are presented to verify the effectiveness and practicability of the proposed control strategy.