Study On Sliding Mode Control Method Of Buck Converter

The role of switching converter is to complete all kinds of power conversion,and its application is more and more widely.The control part is very important in the whole system.When the main circuit topology is the same,a successful controller can make the converter achieve better steady-state and transient performance.The conventional linear PWM controller is based on the small signal model,which depends on the model and transfer function very much,and is sensitive to parameter changes and disturbances.The controlled converter can only work in the optimal state under specific conditions,and can not obtain satisfactory performance when the input voltage or load changes greatly.Switching converter is a time-varying nonlinear system in essence.Sliding mode control is a variable structure control method,which is very suitable for switching converter.Sliding mode control has excellent large signal processing ability,and it shows strong stability and robustness when the input voltage and load change in a wide range,and it does not depend on the model and transfer function.Using sliding mode control,the switching converter can achieve better regulation performance and dynamic performance in a larger operating range.In this paper,taking buck converter as the research object,a sliding mode controller based on hysteresis modulation is designed and simulated in Matlab/Simulink.It can be found that the control effect of hysteresis modulation sliding mode controller is obviously better than that of PID controller.When the input voltage and load have large disturbance,the system shows good robustness,but the switching frequency has changed significantly.In order to achieve the fixed switching frequency,based on the equivalent control principle,the hysteresis modulation is converted to pulse width modulation,and the constant frequency PWM integral sliding mode(ISM)controller is designed to solve the problem of switching frequency change.But the output voltage of PWM integral sliding mode control converter has steady-state error,and the steady-state error increases with the decrease of switching frequency.In this paper,three methods are used to eliminate the steady-state error of PWM ism control converter.Increasing the reference voltage level can improve the steadystate error,but it can not completely eliminate the steady-state error,especially when the switching frequency is low.The PWM integral sliding mode controller based on exponential reaching law can eliminate the steady-state error,but this method increases the complexity of the controller.Using PWM double integral sliding mode(DISM)controller,the steady-state error of the converter can be eliminated when the switching frequency is high or low.Even when the switching frequency is low,it can achieve nearly perfect regulation ability and has good dynamic characteristics.The design complexity of double integral sliding mode controller is similar to integral sliding mode controller.So the PWM double integral sliding mode controller is the best among the three methods.