Discrete-Time Sliding Mode Control For DC-DC Buck Converter

DC-DC converters are widely being used in various electronics applications such as cellular phones, personal computers, office equipment, power supplies, chargers, dc drives and telecommunication equipment. For DC-DC converters it is really a challenging task to design such control technique that should be robust to parametric variations, improve the efficiency of converter, lessen the effects of external disturbances, and minimize the effects of electromagnetic interference. Different converters are used to convert the DC voltages to different levels. Boost converter is used to obtain a high DC voltage as compared to input voltage and buck converter is used to obtain a low DC voltage as compared to the input source voltage. This thesis presents the work on buck converter in which a robust sliding mode controller is designed for the buck converter and also tested for input voltage variations and perturbation in parameters.The sliding mode control is a nonlinear control technique that is used to stabilize a dynamical system. The control law designed by this technique is not a continuous function of time. The main objective of this method is to force the trajectories of the system under consideration to this sliding manifold and keep it there for the time being. The challenge is to define a surface so that the trajectories can reach the surface in finite time and stays there. In this thesis three sliding mode control(SMC) techniques are proposed for DC-DC buck converter. In first, the continuous time sliding mode controller is designed based on continuous time system. In second, the continuous time controller is designed based on continuous time system that is discretized by using emulation design method. The third approach is to attain the approximate discrete time equivalent system model for continuous time system and then design a discrete time controller directly for the approximate discrete time equivalent system. For obtaining approximate discrete time model Euler forward difference method is used.Although sliding mode control is robust to parameters uncertainties and external disturbances, but continuous sliding mode control suffers from chattering phenomenon that can be eliminated with the help of saturation function instead of using signum function but the robustness is compromised. Discrete time sliding mode control algorithm is designed to meet the required robustness and also to eliminate the chattering phenomenon. To implement these techniques for buck converter MATLAB/Simulink are used. At the end, results based on MATLAB simulations are compared and discussed for all three techniques.