Research On Fractional Order Sliding Mode Control Of Buck-Boost Converter

Buck-Boost converter is a kind of DC/DC voltage converter,which has the advantages of fewer electronic devices,simple structure,low cost and high energy utilization.The Buck-Boost converter has become the main equipment for power conversion and control,widely used in data communication,robotics,military aerospace and other fields.As a typical time-varying and non-linear system,Buck-Boost converter is also non-linear and discontinuous in its control mode,and is sensitive to the changes in system parameter and load.When the load changes significantly,Buck-Boost converter has the disadvantages of slow dynamic response and the distortion of output voltage waveform.As an important branch of calculus,fractional-order calculus can provide a more accurate model for practical systems due to its unique heritability and memory.Therefore,in order to improve the output characteristics of Buck-Boost converter,a fractional-order sliding mode controller is designed for the Buck-Boost converter based on fractional-order calculus theory.The main research contents are as follows:Firstly,according to the actual system of Buck-Boost converter,the fractional order state space average model is established by using the state space average method and the fractional-order model of inductance and capacitance.Based on this model,the inductance current and output voltage ripple of Buck-Boost converter are analyzed,and compared with the integer-order state space average model,which verifies the correctness and necessity of building fractional-order mathematical model.Secondly,in order to facilitate the design of the controller,the fractional-order nonlinear model of Buck-Boost converter is further transformed,and the fractional order feedback linearization method is used to transform it into the fractional-order linear model.Based on the fractional-order linear model,the fractional-order sliding mode controller and fractional-order terminal sliding mode controller are designed,and the response speed and robustness of the output voltage and inductance current under the conditions of system start-up response,output voltage change,load resistance change,input voltage change and inductance value change are verified by simulation experiments.The simulation results show that the fractional-order sliding mode controller and fractional-order terminal sliding mode controller can speeds up the response speed and enhance the robustness of the system compared with the integer order sliding mode controller.Thirdly,by comparing the approximation effects of different discretization methods of fractional-order differential operators,Tustin+CFE is chosen to discretize fractional-order sliding mode controller,which is convenient for software programming.The detection,sampling and PWM driving of Buck-Boost converter are analyzed and the software flow chart is designed.Finally,in the actual Buck-Boost converter,the control effect of fractional-order sliding mode controller is tested to verify its good output characteristics and robustness.Finally,the paper summarizes the research work,and put forward the direction for further study.