Seond-order Sliding-mode Controlled Synchronous Of Fixed-frequency BUCK DC-DC Converter

In daily life,more and more electronic devices are used.The DC power system is also widely used as a source of life for electronic devices.With the development of science and technology,the demand for DC-DC converters and the performance and parameters of DC-DC converters are increasing.The development trend of DC converter is smaller size,higher conversion efficiency and higher power density,as a type of DC-DC converters,have also been greatly developed.This paper introduces the current situation of DC-DC BUCK converters at home and abroad,and compares the control algorithms of existing DC-DC BUCK converters.Current converter control algorithms have the disadvantages of high requirements on the system model,weak parameter robustness and robustness to external disturbances,low control accuracy,low efficiency,and large switching losses.Therefore,the paper will design a second-order sliding mode controller which can be used for the DC-DC converter without overshooting fast tracking reference voltage and having strong robustness to parameter uncertainty and load disturbance.In order to facilitate the design of filter circuit and solve the problem of frequency change of sliding mode control,this paper proposes a fixed-frequency sliding mode control method to realize the fixed frequency control of DC-DC BUCK converter.Thesis research and design work is as follows:(1)The working principle of the DC-DC BUCK converter is analyzed,and the mathematical model of the converter is established using the Kirchhoff voltage law.In the phase plane,the trajectory of the circuit power switch in the two states of off and on,and the optimal switching point of the switch in the voltage tracking process are analyzed.(2)Analyze the mathematical relationship between the DC-DC BUCK converter frequency and the second-order sliding mode control hysteresis parameters,and design the PI controller.By controlling the hysteresis parameters,the converter's switching frequency can be adjusted.Through simulation,the control algorithm is verified.The converter can reach the reference value quickly and without overshoot at a fixed switching frequency,which effectively improves the dynamic performance and robustness of the system.(3)DC-DC BUCK converter hardware experiment platform was designed,including the design of main circuit,sampling circuit,driving circuit and controller circuit.With FPGA as the core control,the control algorithm was written using VHDL language.The experimental results verify the superiority of the proposed fixed frequency sliding mode control algorithm.In summary,the fixed-frequency second-order sliding mode control algorithm proposed in this paper can achieve fast and stable control of DC-DC BUCK converters at a fixed switching frequency.Compared with the existing algorithms,the proposed control algorithm can achieve fast and no overshoot control at any initial position of the output voltage without detecting the current or requiring an integrator.Therefore,the proposed second-order sliding mode control algorithm can effectively track the output voltage at a fixed frequency,which improves the DC-DC BUCK converter's fast response and robustness to load disturbances.