Variable Rate Reaching Law Control For Buck Converters

At present,China has entered a new stage of ecological civilization construction,more and more families are using electricity generated from clean energy such as wind,tidal and solar energy.For this kind of power converter,the traditional control method is mainly based on its small signal model used by linear control,such as PID control.It can be only used in the occasions where the output voltage don't need to be accurate,so it has limitations.DC-DC convert is a kind of variable structure system with switching characteristics,which is more suitable for nonlinear control.Its relay control characteristic is very suitable for power electronic converter systems.It has good robustness to the circuit system with parameter perturbation and external disturbances.It can meet the requirements of different circuit topologies and different working conditions with a wide range of voltage output.In this dissertation,the influence of sliding mode control algorithm on its performance is studied for the buck topology of DC-DC converters.The main work includes:The output voltage of Buck converter system under terminal sliding-mode control algorithm can converge in finite time,howerver the upper bound of convergence time can not be guaranteed.And the convergence speed may not be faster than general sliding-mode control.In this dissertation,the global terminal sliding mode control method is proposed to ensure the voltage error of the Buck converter system converges in finite time.In order to obtain better control performance,a controller based on a variable rate reaching law is designed,such that the system state has a fast convergence rate whenever it is far away from the sliding mode or closed to the sliding mode,which improves the dynamic performance of the system and make the system have better stability.In order to improve the robustness of the controller,considering the input voltage fluctuation,the output load mutation and circuit parameters perturbation in the system,an novel observer(Unknown System Dynamics Estimator,USDE)is designed to estimate system dynamic uncertainty and unknown disturbances in the converter.On this basis,a sliding mode controller based on the variable rate reaching law is designed to make the output voltage error converge to the equilibrium point in a finite time.And the disturbance rejection ability of the system has been improved.Finally,the experimental platform of Buck converter is built with DSP28335 chip as the control microprocess,and the control algorithm in this dissertation is programmed on CCS5.0 software compiler for experimental verification.Through the experimental comparison,it is verified that the dynamic response speed of the Buck converter under the proposed control method is faster and the disturbance rejection ability is stronger.