On Sliding Mode Control For Basic DC-DC Converter Based On Fractional Theory

DC-DC converter is an electric device which can convert direct voltage of the system input to reference voltage value fast and effectively. Owing to the advantages of high energy utilization rate and less electronic elements, DC-DC converter has been widely applied in multiple areas such as office automation, home appliances, and space vehicles, etc. Because it’s a kind of time-varying and nonlinear system, the control is nonlinear and discontinuous. And the DC-DC converter control system has disadvantages of slow dynamic response and poor anti-interference ability. In order to improve the rapidity and robustness of the output response, this thesis designs sliding mode controllers based on fractional-order sliding mode surface. The main research contents are as follows:In the first part, integer-order models for Buck converter and Boost converter are established according to state space average method. But DC-DC converter system is actually a fractional-order system based on the fact that inductance and capacitance are not integer-order but fractional-order. Therefore, the fractional-order models are built by using basic operator of fractional-order calculus and state space average method. In the meantime, for the sake of facilitating the design of controller, further processing is put out by using feedback linearization method for Boost converter. What’s more, the correctness and necessity of fractional model of DC-DC converter are proved through theoretical proof and simulation.In the second part, a sliding mode controller is proposed for DC-DC converter with ripple disturbance in power supply and parameter perturbation, compared with the traditional sliding mode controller, which accelerates the response speed of the system and enhances the robustness of the system. In addition, the system states fall on the sliding mode surface at the initial moment by adding a linear term. The global robust control is realized while ensuring the rapidity. The effectiveness of the controller proposed is verified by the simulation results.In the third part, an adaptive sliding mode controller is designed for DC-DC converter with ripple disturbance in power supply and parameter perturbation. Using the adaptive law solves the problem that the upper bound of uncertainty and interference is unknown through online estimation of unknown upper bound, which not only keeps the advantages of fast response and the robustness of the system, but also reduces the high frequency chattering of controller. The effectiveness of the controller proposed is verified by the simulation results.At last, conclusions are presented and future research directions are discussed.