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In this study, a non-linear digital control of a boost converter based on a sliding discrete-time approximation is presented. The control strategy follows a classical cascade regulation scheme with the inner loop consisting in a nonlinear current-control based on discrete-time sliding mode, and the outer one being composed of a simple discretetime proportional-integral (PI) controller for output voltage regulation. An analytical expression of the current control law is developed using a simplified discrete-time small-signal model of the boost converter. The discrete-time PI compensator is designed from a discrete-time small-signal parametric model of the inner loop obtained by linearisation around the desired equilibrium point. The proposed method is initially based on the notion of discretetime sliding motion to eventually derive a pulse width modulation (PWM) controlled system. Thus, the reported approach can be categorised not only as a direct digital design technique for voltage regulation but also as a competitive method to design sliding-mode-based PWM controllers. Simulated and experimental results in a boost converter operating in continuous conduction mode verify the theoretical predictions.

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A discrete-time sliding mode approach allowing direct digital design of a pulse width modulation (PWM) control of a synchronous buck converter is presented in this study. Without the need of a compensating ramp, a non-linear difference equation representing the output voltage dynamic behaviour is employed to demonstrate the global stability of the internal control loop of the inductor current. Discrete-time small-signal model is derived from the linearisation of the ideal sliding-mode equations, which facilitates the design of the output voltage controller. This model exhibits a zero whose value depends on the operating point coordinates and explains the duty cycle delay associated to digitally PWM controlled converters. The validity of the transfer function is demonstrated through simulation by comparing its frequency behaviour with that obtained from the more accurate switched model of the converter. Experimental results for start-up, load and line perturbations, current and voltage reference variations in a 25 W prototype switching at 100 kHz are in good agreement with the theoretical predictions.

In this work, a Loss-Free Resistor based on a semibridgeless rectifier is proposed for power factor correction applications. This particular bridgeless rectifier type is composed of two different boost cells which operate complementarily during each half-line cycle. In case of two unbalanced inductors, many control techniques can produce different inductor current ripples during each half-line cycle that can result in the addition of a DC component to the line current. This work demonstrates that the application of sliding-mode control by means of hysteretic controllers results in a 1st order stable system that can mitigate these harmful consequences due to its capability to ensure the symmetry of the line input current waveform for both positive and negative half-line cycles. Thus, the system does not absorb any DC component from the grid and it is also capable to reduce dramatically the amplitude of the 3rd harmonic. The theoretical predictions have been validated by means of PSIM simulations and experimentally on a prototype of 1 kW which has been controlled using only one sliding control surface.Index Terms -AC-DC power conversion, loss-free resistor, sliding-mode control, power factor correction, semi-bridgeless boost rectifier. P