Design Of Digital Control System For Buck Converter Based On Sliding Mode Control

DC-DC Buck converter has been widely used in all walks of life of the national economy because of its small size and high power quality.Advanced control strategy is the key to ensure its good output performance.Compared with traditional control methods such as PI,sliding mode control(SMC)has become a new nonlinear control method with its robustness and excellent dynamic and static control characteristics,and its variable structure characteristics have excellent matching with the relay characteristics of the converter.From the practical point of view of SMC,this paper aims to study the design of digital control system of Buck converter.From the four aspects of discrete realization,disturbance problem,control algorithm and observer design,this paper deeply studies the influencing factors and influencing mechanism of each link restricting the system performance.The control algorithm of buck converter is usually designed in continuous domain,and implemented in discrete domain based on DSP,FPGA and other chips.How to transplant high-quality algorithm is the key first step to ensure its digital control system.In contrast,firstly,the design of SMC controller is given in the continuous domain,and the working region and the tuning principle of controller parameters are derived to ensure the stability of the system.Then,taking the application of Zero order holder(ZOH)as an example,the effect of discretization on SMC algorithm migration is studied,and the constraints of sampling time on controller parameters are revealed under the condition of system stability;The limit cycle phenomenon induced by discretization is studied from the mechanism,and the mathematical relationship between switching frequency and steady-state error is deduced quantitatively.The disturbance problem of Buck Converter digital control system is studied,and a unified SMC design method suitable for various disturbances is proposed.Considering the variation of input voltage and reference output voltage of Buck converter,the parameter uncertainty of load resistance,inductance and capacitance and external time-varying disturbance,the influence of various disturbances on controller design is analyzed,and the unified discrete model of Buck converter is derived.Different from the traditional method of controller design based on nominal model,the disturbance is directly included in the controller design process,a new method is derived,and the influence of disturbance on the control performance of Buck converter is revealed.The algorithm improvement of Buck Converter digital control system is studied,and a new SMC method which can be extended to any order converter is proposed.Firstly,the algorithm is designed in the continuous domain,and a new sliding surface and state variable are constructed.The corresponding control law is derived based on the sliding mode equivalent control principle and the Lyapunov stability theory.Then,the digital system implementation is studied,and the controller parameter tuning and performance quantitative analysis are studied by using the trajectory periodicity.The observer design of digital control system for Buck converter is studied to solve the problem of state differentiation in discrete domain.Taking Walcott-Zak sliding mode observer as an example,the problem of discretization and stability of observer under ZOH action is studied.Considering the existence of system disturbance,the relationship between observation error and nonlinear characteristics of discrete system is derived.