The Sliding Mode Control Technique For Buck-kind Converters

The sliding mode control (SMC) technique as a nonlinear control approach has been widely used in power electronic systems and realizes its advantages of good dynamic response, high robustness, wide-range signal stability and simple control implementation etc. But its disadvantages of big steady-state error and variable frequency restrict its application range.In this paper, the detailed analysis and design of sliding mode control technique for buck-kind converters is presented. N-order sliding mode control strategy for bi-directional Buck converter is proposed with Lie derivative method and the design procedure of first, second and third order sliding mode controller are given in detail. The sliding action is described by phase trajectory vividly. To simplify the analysis of third-order SMC with which the steady-state error problem solved, three-dimension trajectory transforms into the two one through mapping method. The problems of constant disturbance, hysterisis error and time delay, especially the ESR problem, are also researched for the implementation in practical system. The new system model and approved SMC approach are given through the analysis of ESR effect after which a more precise design method is presented. Besides, the fixed frequency methods of PWM-SMC and RTW-SMC are researched from second-order to third-order, from which some conclusions contained the theoretic sliding surface of PWM-SMC, infeasibility of second-order PWM-SMC, the limitation of second-order RTW-SMC and the merit of third-order RTW-SMC are proposed. Further more, the SMC technique for isolation converters is reached. The feasibility of SMC applied in dual transistor forward is educed through the comparison of HM-SMC, RTW-SMC and PWM-SMC. The system model is rebuild in DCM and its effects for SMC system is pointed.Finally, simulation and experimental results are included to validate the theoretical analysis and proposed methods.