The Research On Sliding Mode Controller For BUCK Converter

With the rapid development of power electronics technology,the improvement potential for the efficiency,size and weight of power supply have attracted more and more attention.The switched mode power supply has the advantages of high efficiency,fast response and robustness to parameter degradation.On the other hand,with the development of integrated circuit,the volume of the digital controller tends to miniaturization and it can be implemmented on FPGA.For the above reasons,the switched mode power supply controlled by digital mode has attracted much attention in the past ten years.BUCK circuit is the research object in this paper,and an effective PID control algorithm and sliding mode variable structure control algorithm are designed.The main research work of the paper is as follows:firstly,the mathematical model is established according to the BUCK circuit;secondly,researching on the controller design and parameters of BUCK converter controlled by traditional PID control algorithm and sliding mode variable structure control algorithm respectively,and analyzing the system performance;thirdly,the current observer is designed according to the topology of BUCK circuit;fourthly,high precision hybrid Delay-Line digital pulse width modulator is designed on the foundation of PID control and the sliding mode variable structure control respectively;fifth,an AD circuit board and a BUCK circuit board are designed using Altium Designer software;finally,the traditional PID control algorithm and sliding mode variable structure control algorithm of BUCK converter are compared and verified based on theFPGA platform.The main contents of this paper are as follows:(1)To introduce the research background and significance,and put forward the research methods.The feasibility of this project is illustrated from two aspects:the research methods and the research steps.(2)To introduces the basic working principle of BUCK circuit,and analyze the two different states of BUCK circuit:open switch and closed switch,then we establish the state space model and state small signal model of the system using Kirchhoff's voltage and current laws.(3)After introducing the PID control algorithm,the PID control algorithm is applied to the BUCK circuit controller.According to the mathematical model,the controller parameters are calculated using PID control theory.(4)After introducing the sliding mode variable structure control algorithm,the sliding mode variable structure control algorithm is applied to the BUCK circuit.According to the mathematical model,the sliding mode variable structure control theory is used to calculate the parameters of the controller.(5)A Delay-Line type high resolution digital pulse width modulator(DPWM)is implemented.An 11 bit DPWM resolution is realized using a fast count comparator and the delay unit with the working frequency of the FPGA board is 128 MHz,and the working frequency of the switch in the BUCK circuit is under the condition of 1 MHz.The 11 bit DPWM is implemented,and the minimum delay of a single is 0.488ns.(6)The design principles of AD circuit board and BUCK circuit board are introduced.The experimental platform is built by the FPGA board Xilinx XUP Virtex II Pro,AD circuit board and BUCK circuit board.The control algorithm is realized by VHDL language to verify the feasibility of the sliding mode variable structure control algorithm.At the same time,the PID control algorithm is compared to verify the superiority of sliding mode variable structure control algorithm.Both the simulation and experimental results demonstrate the advantages of the sliding mode variable structure control,which is helpful to improve the performance and efficiency of the switched mode power supply.