Observer-based sliding-mode control of a DC/DC buck converter for railway systems

DC/DC power converters are critical parts of railway applications because they are required in on-board, off-board, and communication systems. Traditionally sliding-mode control is only insensitive to the matched disturbances, and the system performance is reduced when mismatched disturbances appear. This study develops a non-linear disturbance observer (NDO)-based adaptive non-singular fast terminal sliding-mode control strategy for DC/DC buck converter with mismatched disturbances. The proposed strategy exhibits the following three attractive features. Firstly, the observer can estimate the matched and mismatched disturbances in finite time. Next, by taking the estimations of the disturbances into account, a sliding-mode variable is designed, the system reach the sliding-mode surface in finite time, and the output voltage tracking error converges to zero in finite time. Then, the convergence rates of the sliding-mode variable and output voltage tracking error are faster compared with those of the NDO-based non-singular terminal sliding-mode (NTSM) controller. Finally, with the adaptive law, the control gain is adjusted to an appropriate value with respect to disturbances, and the chattering of the control signal is reduced. Experimental results show that comparing with the NDO-based NTSM controller, the proposed method exhibits better steady-state performance and dynamic performance including robustness and disturbance rejection ability.