Fixed Switching Frequency Digital Sliding-Mode Control of DC-DC Power Supplies Loaded by Constant Power Loads with Inrush Current Limitation Capability

This paper proposes a digital sliding-mode controller for a DC-DC boost converter under constant power-loading conditions. The controller has been designed in two steps: the first step is to reach the sliding-mode regime while ensuring inrush current limiting; and the second one is to move the system to the desired operating point. By imposing sliding-mode regime, the equivalent control and the discrete-time large-signal dynamic model of this system are derived. The analysis shows that unlike with a resistive load, the boost converter under a fixed-frequency digital sliding-mode current control with external voltage loop open and loaded by a constant power load, is unstable. Furthermore, as with a resistive load, the system presents a right-half plane zero in the control-to-output transfer function. After that, an outer controller is designed in the z-domain for system stabilization and output voltage regulation. The results show that the system exhibits good performance in startup in terms of inrush current limiting and in transient response due to load and input voltage disturbances. Numerical simulations from a detailed switched model are in good agreement with the theoretical predictions. An experimental prototype is implemented to verify the mathematical analysis and the numerical simulation, which results in a perfect agreement in small-signal and steady-state behavior but also in a small discrepancy in the current limitation due a small propagation delay. Some efficient solutions have been proposed to mitigate the inrush current in the experimental results.