Novel fast terminal sliding mode controller with current constraint for permanent-magnet synchronous motor

Under the noncascade structure, the balance between q-axis current constraint and dynamic performance in permanent-magnet synchronous motor system has become a critical problem. On the one hand, large transient current is required to provide high torque to achieve fast dynamic performance. On the other hand, current constraint becomes a state constraint problem, instead of governing q-axis reference current in the cascade structure directly. Aiming at this issue, a novel fast terminal sliding mode control (FTSMC)-based controller with current constraint is developed in this paper. The novelty of this scheme is related to the proposed penalty function based on interior point method, which is established in control action directly. Unlike ordinary solutions, the suggested solution combined with sliding mode variable can achieve current constraint of q-axis without scarifying dynamic performance. Furthermore, by adopting the FTSMC-type surface and new reaching law, the proposed implementation guarantees high performance with significant reduction of chattering phenomenon and has fast convergence characteristics. Then, the stability proof of the whole closed-loop system by employing the Lyapunov method is given in detail. Finally, series of simulations are provided to evaluate the performance of the presented FTSMC-type controller, in terms of current constraint, dynamic performance, and chattering reduction.