Sliding Mode Control Of Synchronous Rectification Buck Converter

More and more attention has been paid to the conversion and use efficiency of electrical energy.Consequently,synchronous rectifier Buck converters are widely used in the products,such as microprocessors,mobile electronic devices,communication equipment and et al.This kind of products usually works under the condition of low voltage and large current,and the load current varies in a wide range.In this case,linear control based on small-signal model is difficult to meet the requirement of load to power performance.Small signal and large signal are taken into account by sliding mode control(SMC),thus,SMC is perfect for switching converter and paid more attention to.SMC of synchronous rectification Buck(SR-Buck)converter is researched.Parasitic parameter such as on-resistance of switch and series equivalent resistance(ESR)is considered.Firstly,characteristic of SR-Buck converter is analyzed based on Kirchhoff's law,and state space model is built.“Switching line” is used to obtain the relationship between the location of switching line,the hysteresis width and switching frequency.It is proved that switching frequency can be controlled accurately by the switching line method,in MATLAB/Simulink.Secondly,digital second-order sliding mode differentiator(DSOSMD)is designed,based on super-twisting algorithm,to estimate state information of SR-Buck converter by measuring the output voltage.It is proved that DSOSMD works better than conventional sliding mode differentiator(CSMD),can estimate accurately,through simulation.Thirdly,hysteresis width is calculated by the switching line method,and conventional sliding mode controller and second-order sliding mode controller are designed.Simulation systems are built in MATLAB/Simulink.The switching frequency of sliding mode controllers are controlled accurately,and second-order sliding mode controller is more accurate and robust than conventional sliding mode controller.Moreover,the performance of second-order controller is analyzed.Finally,the PCB of 12-bits high speed AD circuit and 1.8V,11 A SR-Buck converter are designed.DSOSMD and second-order controller are realized with FPGA.Simulation and experimental results show that switching frequency is controlled effectively,second-order controller is very robust against load disturbance.