General-purpose ripple-based fast-scale instability prediction in switching power regulators

This paper extends the validity of a ripple-based index able to predict the frontier of fast-scale instability bifurcation in switching power converters, for the whole design-space and for different conduction modes. Hitherto a first validation of the index, based on the approximated ripple level in the PWM modulator, was carried out for a basic proportional voltage feedback PWM buck converter and for L, C, fs, Kp parameters. This article has carried out a complete design-space analysis and has found the stability boundary dependence on converter parameters. Besides, the circuit-based approach has been validated through a comparison between the proposed index and the classical analytical methods based in the linearization of the discrete-time nonlinear map. The paper also proposes improved ripple approximations, by obtaining the exact analytic ripple expression for a buck converter derived from Laplace transform. The index is also validated for a buck converter operating in DCM, through time domain simulations and bifurcation diagrams.