Research On Sliding Mode Control For DC-DC Buck Converter

DC-DC converter is one kind of time-varying nonlinear circuit. And it’s modeling, controller design and performance analysis has been the hot issues in the field of power electronics. Among many nonlinear control strategy, the sliding mode control is fast in transient characteristics and good in robustness, therefore its controller algorithm design has important theoretical significance and practical application value. In this thesis, we make the buck converter as the research object which is one of DC-DC converter to design the strategy of sliding mode control (SMC).The main research work the paper is as follows:firstly, we established a mathematical model of buck converter; secondly, we explore the controller design and parameter selection of buck converter by traditional sliding mode control and analyze system performance under its control action; thirdly, in order to solve the drawback in traditional sliding mode control, we investigate two performance-oriented sliding mode control algorithm including terminal sliding mode control and adaptive sliding mode control; finally, we set up FPGA experimental platform to verify traditional sliding mode control algorithm. The main contents of this paper are as follows,(1) To describes the working principle of buck converter and analysis buck circuit when switch is turned on and off and then we establish the mathematical model of buck converter by Kirchhoffs Laws. We tried to build buck model in different way.(2) Based on introduction of traditional SMC algorithm, this thesis analyzes the application of the SMC algorithm in buck converter. The buck converter model has been established and the sliding surface and controller parameters are designed using variable structure control theory. Finally, we analyze the convergence of the algorithm.(3) In traditional SMC algorithm, the convergence of the closed-loop system is slowly and meanwhile, there exists the discrepancy between constant parameter and actual values of load resistor. Terminal sliding mode control and adaptive sliding mode control are introduced to solve those problems, respectively. Terminal sliding mode control makes the output errors convergence to zero in finite (fixed) time by modifying the sliding surface design. Adaptive sliding mode control achieves the optimal parameters of the sliding surface by real-time monitoring resistive current and output voltage.(4) Finally, the experimental platform was set up to verify the feasibility and effectiveness of the SMC on buck circuit. The components of the platform include NI 9683and NI sbRIO-9606, buck evaluation board and the SMC algorithm implemented by LabView environment. We also realized PID control algorithm, by way of contrast, to verify feasibility and advantage of the sliding mode control algorithms.The simulation and experiment validates the performance of buck converter by SMC and shows its advantage and two performance-oriented control algorithms also has satisfying control performance. It is an approach to performance optimization and increasing of design efficiency of DC-DC converter.