Research On Sliding Mode Control Methods For DC-DC Converters

With the rapid development of power electronics technique,in the field of modern industry,switching power supply plays a more and more important role.The performance requirements of switching power supply are getting higher and higher.DC-DC converter serves as a typical switching power supply,and has been widely used in the industry.It is of great throretical and practical value to study control algorithm with good dynamic and static characteristics for DC-DC converter.Among many nonlinear control methods,sliding mode control for DC-DC converter has the advantages of good dynamic response and strong robustness.In this paper,advanced sliding mode control strategies are designed for typical buck converter and buck-boost converter.The research contents of this paper are as follows:Firstly,the working principles of buck converter and buck-boost converter are introduced respectively in this paper.The states of converter systems are described by Kirchhoff's voltage and current law,and then the mathematical models of the two converters are established by using the state space averaging methods.Secondly,for the output voltage control problem of the buck converter system,a current sensorless sliding mode control method,which can convergence in a finite time,is proposed based on the state space model of buck converter.In the case where inductor current information of buck converter can not be directly obtained,a finite-time state observer is designed to estimate the value of inductor current.Then,the estimation of inductor current is introduced in the controller design,and a current sensorless sliding mode controller is designed by using homogeneous sliding mode theory.The error of practical output voltage and the desired value is taken as the sliding manifold directly.The finite time stability analysis of the closed system is given in this paper.The simulations and experimental results are given to illustrate the effiveness and feasibility of the current sensorless control method for buck converter.Thirdly,for the output voltage control problem of buck-boost converter in load variations,a sliding mode controller based on disturbance observer is designed.In order to estimate the disturbance,a nonlinear disturbance observer is designed based on the mathematical model of buck-boost converter.Then,A sliding mode controller is designed by using the conventional sliding mode control theory and introducing the estimation of disturbances into the design of the controller.The inductor current of the converter is driven to reach the desired value asymptotically,then the output voltage reaches the desired value asymptotically.Simulations are carried out to validate the control performance of the composite controller.Finally,to further improve the control performance of the buck-boost converter system,a finite-time disturbance observer based nonsingular terminal sliding mode control method is designed.The exact feedback linearization model is obtained by nonlinear coordinate transformation based on the original mathematical model of buck-boost converter.A finite-time disturbance observer is designed to estimate the disturbance from load variations.Then,a nonsingular terminal sliding mode controller is designed for the exact feedback linearization model of the buck-boost converter,which achieves the goal of driving the output voltage of buck-boost converter to the desired value in a finite time.The effectiveness of the proposed method is validated by simulation results.