Document Type : Original Research Paper

Authors

• Seyed Reza Mousavi-aghdam
• Milad Purhasan

Department of Electrical Engineering, University of Mohaghegh Ardabili

Abstract

Objectives: The objective of this study is to achieve fast finite-time control of DC-DC buck converters by designing a robust-adaptive terminal sliding-mode controller utilizing a fractional-order control strategy combined with a state-disturbance observer. The work begins by considering that all dynamic parameters of the converter circuit, such as resistance, capacitance, and inductance, are completely unknown due to significant uncertainties.
Methods: To formulate the stabilizing fractional-order sliding mode controller, the fractional-order sliding surface is initially presented. Given the absence of knowledge about the converter's dynamic parameters, an adaptive fractional-order finite-time sliding mode controller is developed to ensure the finite-time stability of the system and to achieve rapid convergence of the converter voltage to the prescribed reference value in the presence of parameters uncertainties and external disturbances. To estimate unknown varying parameters in the converter, an adaptive law is additionally designed. Furthermore, a high-speed observer is incorporated to estimate both external disturbances and the state variables affecting the system. An analysis is also presented to find the maximum allowable sampling time based on the controller parameters.
Results: The closed-loop system stability is validated through the application of the extended Lyapunov method. Importantly, the proposed method ensures that the output voltage of the converter reaches its desired value within a finite time taking external disturbances into account as well as operating with unknown parameters, and also, without direct feedback from voltage or current measurements. Ultimately, simulation results along with some enhanced robustness analysis are presented to demonstrate the effectiveness of the proposed control approach.
Conclusion: The innovative controller based on fractional-order sliding mode control in a sensor less DC-DC buck converters is considered. The goal is to converge the output voltage to the desired value in finite time considering that all of the converter dynamic parameters are unknown and system is exposed to external disturbances. Chattering is reduced using a new technique and the maximum allowable sampling time is also obtained. The results validate the suitability of the proposed technique especially in overcoming against uncertainties and disturbances without requiring voltage/current measurements.

Keywords

• Fractional-Order Control
• DC-DC bulk Converter
• Robust-Adaptive Control
• Sliding Mode Control
• State-Disturbance Observer

Main Subjects

• Power Electronics