Discrete-time variable structure control for switching converters

The design of discrete-time variable structure control (VSC) with discrete sliding mode for switching converters is presented in this paper, discrete time quasi sliding mode control systems are considered, the reaching law satisfied conditions of the definition are proposed and applied to the design of appropriate control strategies which drive the state of the controlled system to a band around the sliding hyperplane. The reaching law used the equivalent form of Lyapunov-type of continuous reaching condition Vdot < 0 where V = S²/2, to get the discrete version. The paper gives a technique for the design of the switching function, this is done through the design of the desired ideal quasi-sliding mode, the reaching law is used to develop the control law for the discrete VSC system under the nominal condition, and too the analysis of the width of quasi-sliding mode band. The design technique is illustrated by a simulated switching buck and boost converter. The analysis of behavior is realized by modifying the control parameters, the parameter in the reaching law are modified for optimal control, and this results are comparing with the continuous sliding mode control. A sampled data model of switched mode converter applicable for the low frequency range is used; the assumption made is that the sampling rate is sufficiently high as dictated by the sampling theorem. The basic DC-DC switched converter is assumed to operate in continuous conduction mode with fixed switching rate and variable duty ratio.