Analysis of Start-Up Response in a Digitally Controlled Boost Converter With Constant Power Load and Mitigation of Inrush Current Problems

In this paper, the start-up response of a digitally controlled dc-dc boost converter with a constant power load is studied. A mathematical expression of the system response during start-up is derived using a nonlinear averaged model. The time-domain response of the system during start-up when the converter is operating under current limitation mode is derived by analytically integrating the mathematical equations describing the dynamic behavior. Numerical simulations from a detailed switched model validate the theoretical results and a good agreement is obtained. A boost converter prototype is built to validate the theoretical finding and the numerical simulations. It is observed that even when the analysis and the simulation predict zero inrush current, the experimental circuit still exhibits an unsuitable initial current peak and an unacceptable transient response during start-up. This phenomenon is mainly attributed to the presence of an unavoidable delay due to the computation time required by the digital control platform. The resulting inrush current is more pronounced in the presence of nonlinear load such as a CPL and saturable inductor. Some solutions are proposed to mitigate the inrush current problems. Simulations results taking into account the delay and experimental measurements demonstrate the validity of the proposed solutions.