Fixed-Time Sliding-Mode Disturbance Observer-Based Finite-Time Backstepping Control for Current Source Rectifier

It is challenging for current source rectifier (CSR) to assure the satisfactory tracking performance, robustness, and immunity ability simultaneously in the face of various uncertainties and disturbances. Aiming at this problem, this article proposes a composite control strategy that combines the fixed-time sliding mode disturbance observer (SMDO) with continuous finite-time backstepping control (FTBC) based on the recursive design concept. In contrast to the conventional infinite time asymptotic convergence, the FTBC ensures the close-loop system to reach a steady state in a finite time. To guarantee the rapidity and robustness of the proposed strategy, the fixed-time SMDO with the convergence time independent of the initial state of the system is designed to accurately estimates the matched and mismatched disturbances at a fixed time, and thus correct them in the control law for accurate current tracking. Meanwhile, the finite-time differentiator (FTD) is designed to obtain the desired differential signal, avoiding repeated derivative issue of the traditional backstepping control (BSC). Then, the stability of three-phase CSR closed-loop system is proved based on the finite-time Lyapunov stability theoretically. Finally, the comprehensive test results verify that the proposed strategy outperforms the comparative baseline controllers with a better static-dynamic performance and superior immunity and robustness which cover load disturbances, tracking reference step change, and parameter uncertainties.