Study On Sliding Mode Control Strategy Of DC/DC Buck Converter

With the development of power electronic technology,power electronic converter has been widely used in all walks of life,and its working environment is gradually diversified and complicated.The output performance of traditional analog power supply will be greatly affected by the dramatic change of temperature,so the digital power supply which can provide stable loop gain begins to flourish.Switching power supply is a typical nonlinear system.Sliding mode variable structure control,as a nonlinear control theory of modern control,has the advantages of fast response,no sensitivity to parameter change and disturbance,no need for online system identification,simple physical implementation,and so on.It is the main control method of power electronic converter at present.With more and more stringent requirements on the performance of digital power supply,the output accuracy and robustness of traditional sliding mode converter need to be improved.In order to design a high robust and high precision sliding mode controller suitable for high performance power supply,the sliding mode control strategy of Buck converter,a common switching power supply,is further studied in this paper.The main work completed is as follows:Firstly,the functions of each component of Buck converter and its working process under different working modes are described.By analyzing the continuous working mode of the current of Buck converter,the mathematical model of the state space of Buck converter is established by using the state space average method,and the open-loop transfer function is obtained.Its characteristics in time domain and frequency domain are analyzed and verified,which lays a foundation for the subsequent control of Buck converter.Secondly,according to the nonlinear characteristics of Buck converter,the control method of sliding mode variable structure is used to analyze the traditional sliding mode control strategy and integral sliding mode control strategy.In order to completely eliminate the static difference of output voltage of Buck converter under the aforementioned control strategy,an approach law optimization strategy is proposed based on the approach law control.Mathematical analysis shows that this strategy can make the controller have stronger integration effect,but at the same time there are some problems of coupling of control parameters and difficult setting.Further,aiming at the problem of parameter coupling existing in the optimal approach law sliding mode control method,the improved particle swarm optimization algorithm is used to adjust the controller parameters.The simulation results show that the optimal approach law sliding mode control strategy can realize the voltage errorless output control of Buck converter,which significantly improves the robustness of the control system,but also leads to the problem of voltage buffeting and long regulation time.In order to improve chattering and shorten voltage regulation time,a fuzzy terminal sliding mode controller is designed by combining fuzzy control and terminal sliding mode control.The controller adaptively adjusts the switching gain of sliding mode variable structure controller using fuzzy logic theory,which can significantly reduce system buffeting and enhance system robustness.In addition,the attractor in the terminal sliding mode can guarantee the convergence speed of the system and enhance the dynamic performance of the control system.The simulation results show that the steady-state and dynamic performance of Buck converter is improved compared with the optimal approach law sliding mode control method.Finally,the experimental platform of Buck converter is constructed,and the control algorithm is verified and compared by start-up experiment,steady-state experiment and variable load experiment of the converter.The experimental results show that the output voltage static difference exists in the Buck converter under the general sliding mode control strategy and integral sliding mode control strategy.The Buck converter under the optimal approach law sliding mode control strategy can output the specified voltage stably and show good dynamic response,but it has some shortcomings such as large voltage buffeting and long adjustment time.The fast terminal fuzzy sliding mode controller has the best performance of Buck converter,which realizes the high precision and robust control of Buck converter.