Fixed-Time Sliding Mode Control For DC/DC Converters

With the continuous development of social science and technology,sustainable energy sources such as wind energy,fuel cells and solar energy are becoming more and more popular in people's lives.However,such energy sources have a wide range of variations in output voltage or output power,and traditional linear control strategies based on small-signal models are difficult to achieve fast transient response and good stability in such a complex environment.Therefore,in order to overcome the shortcomings of the linear control method,many nonlinear control strategies are applied to the switching power supply.Among many nonlinear control strategies,the sliding mode control method has the advantages of strong robustness,high stability,and simple implementation.The switching converter itself is variable structure,so applying sliding mode control to switching power supply is a method.In this paper,the basic topology of DC/DC switching converter,Buck converter,is used as the control algorithm to design a fixed-time sliding mode controller.The main work of this paper includes:At present,there are many finite time control algorithms applied to Buck converters.However,the upper bound of the convergence time of the output voltage error of the system under the control of the finite time control algorithm will change with the initial value of the system variable.This method has certain limitations.Therefore,this paper designs a fixed-time sliding mode controller,which can make the output voltage error convergence time upper bound only related to the control parameters,and improve the convergence speed and steady state accuracy of the system.The design of the fixed-time sliding mode controller depends on the model parameters of the system,and the system parameters such as inductance,resistance and capacitance in the switching converter may be affected by environmental factors such as temperature.The parameter values are subject to change and are not easily measured accurately.Therefore,in this paper,a non-singular fixed-time sliding mode controller is designed for the Buck converter system with parameter perturbation to avoid the singular value phenomenon in the terminal sliding mode control.At the same time,the adaptive update law is designed to estimate the upper bound of the system disturbance,compensate the system disturbance and improve the stability of the system.In order to further reduce the dependence of the controller on the system parameters,an adaptive updating law is designed to estimate all unknown parameters of the system.Based on this,a fixed-time adaptive controller is designed to realize that the output voltage error can converge from any initial position to the equilibrium point in a fixed time even if the system parameters are unknown,and the upper bound of the convergence time is only determined by the control parameters,thereby further improve the versatility of the controller.Meanwhile,when the system parameters change,the controller has stronger robustness.Finally,a fixed-time control and PI control experiment are compared using a DSP-based Buck-type DC/DC converter experimental platform.Compared with PI control,the fixed time control proposed in this paper has faster dynamic response speed and stronger resistance to load changes.