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Under the traditional proportional integral differential (PID) controllers, it is usually not easy to obtain a satisfactory control performance for Buck converters subject to large disturbances. Aiming at this problem, a chatteringfree control method based on the second order sliding mode control was proposed to improve the robustness of the Buck converters. Firstly, the average statespace model of Buck converter was established and the design of the chatteringfree sliding mode controller was associated with controlling the output voltage of the Buck converter by selecting an appropriate sliding mode surface. The control design was accomplished by designing a discontinuous second order sliding mode controller where the derivative of the duty ratio was regarded as a virtual controller. The actual controller was the integration of the discontinuous secondorder sliding mode controller, and thus the chattering problem can be avoided. On this basis, taking a direct discretization on the proposed algorithm by using Euler method, the chatteringfree sliding mode controller can be implemented by the way of fixedfrequency PWM control technique based on a LabVIEW platform. Finally, the reliability and superiority of the chatteringfree sliding mode controller were verified by comparing PID controller through simulation and experimentation. It can be shown that: the system startup time can be shortened by nearly 50%; the variation range of system output voltage is significantly reduced under the conditions of load perturbation and input voltage change.