Abstract: In order to reduce voltage overshoot of DC/DC converter and suppress chattering，a sliding mode

control method based on improved variable speed reaching law was proposed. The improved variable speed reaching law inherited the advantages of variable speed reaching law and adjusted approach speed with system state variables.By introducing exponential term，the optimization of the speed change reaching law was insufficient，and the voltage overshoot was reduced. The improved variable speed reaching law control method was applied to Buck converter third-order sliding mode controller，and the controller parameters were further screened. The simulation and experimental results show that，compared with the variable speed reaching law，the improved variable speed reaching law control method can reduce the Buck converter voltage overshoot and improve the system dynamic performance.

      Key words: DC/DC converter ；improved variable speed reaching law ；third-order sliding mode controller ；

overshoot