Nonsingular Fast Terminal Sliding Mode Control for a Bearingless Induction Motor

In order to solve the problem of the speed response and system buffeting for a bearingless induction motor (BIM), which is subjected to various interferences and uncertainties, as well as the worse convergence performance of linear sliding mode and the singularity of terminal sliding mode, a nonsingular fast terminal sliding mode control strategy is proposed. Taking the power function of system state variables into consideration, the sliding mode hyperplane is designed as a combination of linear and nonsingular terminal sliding modes, which make the approaching speed correlate with the state variables of the system. Meanwhile, the differential sliding surface is constructed, and it is based on the rotational speed and radial displacement error of the BIM. Therefore, current signal and radial force are derived by the synthesis of the equations of electromagnetic torque, motion, and levitation force motion. Compared with the conventional strategies, the convergence speed of system state variables can be accelerated during the whole process, which contributes to operate without chattering and achieve high servo precisions. The theoretical simulation and experimental results indicate that the presented strategy can not only quickly track the given value of speed and radial displacement simultaneously, but also enhance the operation quality and robustness of the system. In addition, the rotor is capable of quickly reaching the steady position and achieving stable suspension.